The pressure hydraulic valve (Fig. 1.1a) consists of a housing I, in which there is a spool 2, pressed at the end by a spring 4, the force of which is adjusted by a screw 5 and has inlet (P) and outlet cavities (A, T), auxiliary cavities (a, b), control channels (c, d, e, f, g, a) and damper hole (i).
In the lower normal position of the spool, 2 cavities (P) and (A, T) are disconnected if the pressure force of the working fluid on the lower end of the spool 2 in the cavity (a) does not exceed the force of the adjustable spring 4 and the pressure force of the working fluid on the upper end of the spool in the cavity (b). If it is exceeded, spool 2 moves upward and the inlet cavity (P) is connected through a groove on the spool with the outlet cavity (A, T).
This principle of operation of a pressure hydraulic valve in general case, however, depending on the control method, i.e. Depending on how the control channels are connected to the main lines or used independently, there can be four ways to connect a pressure hydraulic valve (Fig. 1.1 b,c,d,e), having different functional purposes.
Fig.1.1. General form(a) and execution diagram
(b - first, c - second, d - third, d - fourth) pressure hydraulic valve.
The pressure hydraulic valve of the first design (Fig. 1.1b) can be used as safety or overflow valve (connected in parallel), as well as valve pressure difference (connected in series). When the pressure hydraulic valve operates according to the first design, the working fluid is supplied to the cavity (P) and enters through the control channels (e, g, h) and the damper hole (i) into the auxiliary cavity (a), in which pressure is created on the lower end of the spool 2 The outlet cavity (T) of the safety and overflow valves is connected to the drain, and the cavity (A) of the pressure difference valves is connected to the hydraulic system.
When using a pressure hydraulic valve as a safety valve in a volumetric hydraulic drive with a variable pump, the flow of working fluid does not pass through it under normal conditions. The valve is activated only when the set pressure in the hydraulic system is exceeded for some reason, for example, permissible load on the cylinder, stop at the stop, etc. In this case, the pressure in the supply hydraulic line (P) increases, and consequently, the pressure in the cavity (a) on the lower end of the spool 2 increases. If the force from the pressure on the spool 9 of the cavity (a) exceeds the force of the adjustable spring, the spool moves up and the pressure line through cavities (P) and (T) it is connected to the drain line. Working fluid under pressure is passed into the tank and the pressure in the pressure line decreases. As a result, the pressure in the cavities (P) and (a) decreases, and provided that the force from the pressure on the lower end of the spool becomes lower than the spring force on the upper end, the spool will lower under the action of the spring and disconnect the cavity (P) from (T).
When using a pressure hydraulic valve as an overflow valve in systems with throttle control, excess working fluid constantly flows through it, i.e. he is constantly at work, because the throttle limits the flow of working fluid into the system. Using a hydraulic pressure valve, the required pressure is adjusted and maintained almost constant, regardless of changes in the load on the cylinder. This is achieved by the fact that spool 2, under the influence of force from pressure on the lower end, is in equilibrium in a position in which there is a throttling slot of a certain size through a groove on the spool from cavity (P) to cavity (T). If the set pressure is exceeded, the pressure on the lower end of the spool will increase, its balance will be disrupted and it will move upward, increasing the size of the throttling gap. At the same time, the flow of liquid to the drain increases, as a result of which the pressure decreases, i.e. is restored, and the spool is balanced. When the pressure decreases compared to the set value, the balance of the spool will also be disrupted, but the spool will move downward under the action of the spring, the dimensions of the throttling gap and the flow of liquid to the drain will decrease and the pressure will be restored.
When using a pressure hydraulic valve as a pressure difference valve, cavity (P) is connected to the pressure line, and cavity (A) is connected to some other hydraulic line in the system. Since cavity (a) of the lower end of the spool is connected to cavity (P), and cavity (b) of the upper end of the spool is connected to cavity (A), the pressure difference in the inlet and outlet flows will be determined by the force of the adjustable spring and will be maintained constant regardless of changes in pressure in the hydraulic system.
When using a pressure hydraulic valve, the second, third and fourth designs are used as a sequence valve. When the pressure hydraulic valve operates according to the second design (Fig. 1.1c), a plug is installed in channel (e), and control flow (x) is supplied through channel (h) under the lower end of the spool. The passage of the working fluid flow from the inlet cavity (P) to the outlet cavity (A, T) is ensured only when the corresponding pressure value is reached in the control line (x), determined by the setting of the adjustable spring and the pressure value in the outlet flow. In this case, the force on the lower end of the spool from the pressure in the control flow exceeds the spring force and the force from the pressure in the cavity (b) on the upper end, the spool rises and connects the cavities (P) and (A, T). This ensures that a constant pressure difference is maintained in the control (x) and discharge (A) flows.
When the pressure hydraulic valve operates according to the third design scheme (Fig. 1.1d), channel (e) is plugged with a plug, and cavity (b) above the upper spool valve is connected through channel (c) to the tank or control flow (y). The flow of working fluid from the inlet cavity (P) to the outlet cavity (A, T) is ensured when the specified pressure value is reached in the inlet cavity, determined by the spring setting and the pressure in the control line (y). In this case, the force from the pressure on the lower end of the spool exceeds the spring force and the force from the pressure of the control flow in cavity (b), the spool moves and connects cavities (P) and (A).
When the pressure hydraulic valve operates according to the fourth design scheme (Fig. 1.1 e), channels (d) and (e) are plugged, cavity (b) above the upper end of the spool is connected through channel (c) to the tank or control flow (y), and c cavity (a) under the lower end of the spool and channel (h) supply control flow (x). The passage of the working fluid flow is ensured in both directions when the control flow lines (x) and (y) reach a given pressure difference, determined by the spring setting. In this case, the force from the pressure in the cavity (a) of the control flow (x) exceeds the spring force and the force from the pressure in the cavity (b) of the control flow (y), the spool rises and the cavities (P) and (A) are connected.
TO category:
Pipe laying cranes
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Operating principle of the hydraulic system of attachments
General information. The hydraulic system of the attachment is designed to extend and retract the counterweight, as well as control the brakes and clutches. It consists of a hydraulic pump, hydraulic cylinders, hydraulic valves, hydraulic safety valves, hydraulic throttles, hydraulic tanks, instrumentation (pressure gauges), hydraulic lines, and a filter.
In the pipelayers under consideration, the circuits of the hydraulic system of the attached equipment, despite the use of standardized assembly units and elements, have some differences due to the difference in the principle of engaging the winch drum control clutches and the presence special devices load control.
Pipelayer T-3560M. From the tank (Fig. 85), the pump supplies working fluid along line a to the distributor. In the neutral position of the spool handles, the working fluid flows through the holes in the distributor body into the tank along a line. The distributor consists of three sections, two of which direct the flow of working fluid to the control cylinders for the lifting and lowering clutches and the boom control, and the third section serves the counterload control cylinder. If the handle (and the spool along with it) is raised or lowered, the working fluid from the distributor will flow through the throttles into the right or left cavities of the cylinder, respectively pushing out or pulling in the counterweight.
Rice. 85. Hydraulic diagram of the attachments of the T-3560L1 pipe layer:
1 - gear pump, 2 - safety valve, 3 - pressure gauge, 4 - three-spool distributor, 5 - counterweight control cylinder, b, 12, 13 - spool handles, 7 and 8 - control cylinders for the lifting and lowering clutches of the hook and boom, 9 - breaker, 10 - tank, 11 - chokes
When the handle is set to the neutral position (shown in the figure), the cylinder piston will be locked in the position in which it was when the handle was moved.
When the handle is raised (shown in the figure), the working fluid from the distributor enters the left cylinder, which turns on the load lifting clutch and turns off the brake - lifting the load begins. When this handle is returned to the neutral position, the working fluid from the cylinder is directed back into the tank along the line and the load-lifting clutch is disengaged and the brake brakes the drum. To lower the load, the handle is lowered, engaging the lowering clutch.
When the handle is raised, oil from the distributor enters the cylinder, which turns on the boom lift clutch and releases the brake.
Rice. 86. Hydraulic diagram of the TT-20I pipelayer attachment:
1 - control panel, 2 - sensor cylinder, 3 - automatic switching cylinder of the distributor, 4 7, 8, 10 - cylinders for controlling the clutches for lowering and raising the bunk and boom; 5, b, 12 - single-spool distributors, 9 - breaker, 11 - counterweight control cylinder, 13 - gear pump, 14 - tank, 15, 19 - direct-acting safety valves, 16 - filter, P - differential-acting safety valve, 18 – check valve, 20 – load device settings panel, 21 – throttle; 22 - load indicator
When the boom reaches a vertical position, the buffer device presses the breaker cam and the boom will stop lifting, since the oil will flow through the breaker from the cylinder on the winch into the tank via an additional drain line e. In this case, the clutch will turn off and the brake will be tightened. When the handle (shown in the picture) is lowered, the boom will lower.
Safety valve provides the pressure of the working fluid in the system necessary to control the winch and counterweight - about 7800 kPa and transfers fluid from the pump to the tank along line g when this pressure is exceeded in the distributor.
Pipelayer TG-201. The working fluid, pumped from the tank (Fig. 86) by the pump, flows through line a to the spool valve. When the spool is in the neutral position, the working fluid flows through the distributor simultaneously along lines b and c to the single-spool distributors, and also reaches the differential-action safety valve, which has remote unloading using line g. Along this line, as well as line d coming from the distributor, the liquid is drained into the tank with the distributors not turned on, passing through them sequentially.
When the distributor spool moves to the right or left, the working fluid under pressure enters the rod or piston cavity of the hydraulic cylinder, ensuring the movement or tilting of the counterweight. As soon as the counterweight reaches its extreme position, the pressure in the hydraulic system will increase to the value to which the direct-acting safety valve is set, and the valve will operate, beginning to transfer liquid into the tank along line e. The supply of liquid and its drainage will stop after the distributor is turned off.
To turn on the cargo drum of the winch, you need to move the distributor spool to the left or right. Line g of the remote unloading will be blocked in the distributor and the working fluid will flow to the clutch activation cylinders from line c. The pressure of the liquid when supplied to the cylinders will be limited by the setting value of the differential-action safety valve, which, if the set pressure is exceeded, will operate and connect line b with an additional drain line w, which has a filter.
The boom drum is turned on by moving the distributor spool. The working fluid will be supplied to the activation cylinders of the boom drum clutches, and to the activation cylinder of the boom lift clutch - through a distributor-breaker. When the boom approaches the vertical position, it will press on the spool of the distributor-interrupter, the supply of working fluid to the cylinder will stop and the boom will automatically stop.
The pressure (4500 kPa) to which the differential-acting safety valve is set is less than the pressure (9500 kPa) of the direct-acting safety valve, since the cylinder and counterweight interacting with the valve and distributor require more pressure than the cylinders interacting with the valve and distributors.
All distributors and valves of the pipelayer hydraulic system are concentrated in the driver’s cabin in the form of a single control panel, which also includes a load control device settings panel. This device includes a sensor cylinder that controls the load on the hook of the pipe layer, and a cylinder for automatically turning on the winch load drum control distributor, connected to the sensor cylinder.
Rice. 87. Hydraulic diagram of the attached equipment of the TO-1224G pipe layer:
1 - filter, 2 - breaker, 3 and 4 - friction clutch control cylinders, winch drive and counterweight, 5 and 6 - two- and three-position distributors, 7 - pressure gauge, 8 - safety valve, 9 - gear pump, 10 - tap, 11 - tank
An increase in the pipelayer load leads to an increase in pressure in the rod cavity of the sensor cylinder, the line to and the piston cavity of the automatic activation cylinder. Under the influence of this pressure, the cylinder rod moves to the right. If, when moving it, the left of the two stops attached to the rod reaches the distributor handle, the distributor will turn on and the supply of working fluid to the cylinder will begin, which will ensure the operation of the cargo drum to lower the pipeline. In this case it is used characteristic elastic state of the pipeline: with increasing upward deflection, the load from it increases, and with decreasing deflection, it decreases. As soon as the deflection of the pipeline as a result of the operation of the winch drum decreases, the pressure in the cylinders decreases to normal, the contact between the left stop of the cylinder rod and the distributor handle under the action of the cylinder spring will stop and the distributor will turn off and the winch drum will stop.
If the pressure in the sensor cylinder due to low external load falls below normal, then the cylinder spring and the right stop mounted on its rod will turn on the distributor for the lifting rotation of the winch cargo drum.
The load control panel includes a check valve, an adjustable direct acting relief valve, an adjustable throttle and a load indicator.
Pipelayer TO-1224G. The hydraulic system works as follows. When the pipelayer engine is running and the power take-off is switched on, the working fluid from the tank (Fig. 87) is supplied via line a by a pump to a three-position distributor. When the distributor spool is in the neutral position, the working fluid flows out of it through the distributor and goes to drain.
When the distributor spool is moved by the handle to one of the extreme positions, the working fluid begins to flow through lines e or e into one of the cylinder cavities, ensuring the movement or retraction of the counterweight. From the other cavity, the working fluid is displaced along opposite lines e or d, and then flows through the lines to be drained into the tank through a filter.
When the driver presses the handle of the two-position distributor, the free-flow circulation of the working fluid through it stops and the fluid flows through line w to the winch drive friction clutch control cylinder, ensuring that the drive is turned on. When the load boom rests on the buffer device of the upper frame and the distributor-breaker is activated, the supply of working fluid to the cylinder is interrupted, since the working fluid begins to flow from line g into the drain line g and then into the tank.
If the pressure in the hydraulic system increases excessively, the safety valve is activated and the working fluid flows through the line and enters the tank.
2015-11-15
Hydraulic drive(volumetric hydraulic drive) is a set of volumetric hydraulic machines, hydraulic equipment and other devices designed to transmit mechanical energy and convert motion through fluid. (T.M Bashta Hydraulics, hydraulic machines and hydraulic drives).
The hydraulic drive includes one or more hydraulic motors, fluid energy sources, control equipment and connecting lines.
The operation of the hydraulic drive is based on the principle
Let's consider the system.
In this system, the force created on piston 2 can be determined by the dependence:
It turns out that force depends on area ratio, the larger the area of the second piston, and the smaller area first, the greater the difference between the forces F1 and F2. Thanks to the hydraulic lever principle, you can get a lot of force with little effort.
Gaining in effort on a hydraulic lever, you will have to sacrifice movement, having moved the small piston by the amount l1, we obtain the movement of piston 2 by the amount l2:
Considering that the piston area S2 more area S1, we find that the displacement l2 is less than l1.
The hydraulic drive would not be so useful if the loss in movement could not be compensated, but this was done thanks to special hydraulic devices - .
A check valve is a device for blocking flow moving in one direction, and allowing the return flow to pass freely.
If in the example considered, install at the output of the chamber with piston 1 check valve, so that the liquid can leave the chamber, but cannot flow back. The second valve must be installed between the chamber with piston 1 and the additional tank with liquid, so that the liquid can enter the chamber with, and cannot flow from this chamber back into the tank.
The new system will look like this.
By applying a force F1 to the piston and moving it a distance l1, we obtain the movement of the piston with a force F2 at a distance l2. Then we move piston 1 to the initial distance; liquid will not be able to flow back from the chamber with piston 2 - the check valve will not allow it - piston 2 will remain in place. Liquid from the tank will flow into the chamber with piston one. Then, you need to again apply force F1 to piston 1 and move it to distance l1, as a result of which piston 2 will again move to distance l2 with force F2. And in relation to the initial position, in two cycles piston 2 will move a distance of 2*l2. By increasing the number of cycles, it is possible to obtain a larger displacement of piston 2.
It was the ability to increase movement by increasing the number of cycles that allowed the hydraulic lever to get ahead of the mechanical lever in terms of the possible force developed.
Drives where enormous forces are required are usually hydraulic.
The unit with the chamber and piston 1, as well as with check valves in hydraulics is called pump. Piston 2 with chamber - hydraulic motor, in this case - .
Distributor in hydraulic drive
What to do if in the system under consideration it is necessary to return piston 2 to its initial position? With the current configuration of the system, this is impossible. The liquid from under piston 2 cannot flow back - the check valve will not allow it, which means a device is needed that allows the liquid to be sent to the tank. You can use a simple tap.
But in hydraulics there is a special device for directing flows - distributor, allowing you to direct fluid flows according to the desired direction.
Let's get acquainted with the operation of the resulting hydraulic drive.
Devices in hydraulic drives
Modern hydraulic drives are complex systems consisting of many elements. The design of which is not simple. In the presented example there are no such devices, because they are generally intended to achieve required characteristics drive.
The most common hydraulic devices
- Safety valves
- Reducing valves
- Flow regulators
- Chokes
You can get information about hydraulic devices on our website in the - section. If you have any questions, ask them in the comments to this article.
Purpose of pressure and flow.
When studying the basics of hydraulics, the following terms were used: force, energy transfer, work and power. These terms are used to describe the relationship between pressure and flow. Pressure and flow are the two main parameters of every hydraulic system. Pressure and flow are interrelated but perform various jobs. Pressure compresses or applies force. The flow moves objects. The water gun is good example pressure and flow in application. Pulling the trigger creates pressure inside the water gun. Water under pressure flies out of the water pistol and thus knocks down the wooden soldier.
What is pressure?
Let's think about how and why pressure is created. The fluid (gas and liquid) tends to expand or resistance occurs when they are compressed. This is pressure. When you inflate a tire, you create pressure in the tire. You pump more and more air into the tire. When the tire is completely filled with air, pressure is applied to the tire walls. This kind of pressing is a type of pressure. Air is a type of gas and can be compressed. Compressed air presses against the tire walls with equal force at each point. The liquid is under pressure. The main difference is that gases can be compressed into bolas.
Equal force at every point
Pressure in compressed fluid
If you press on a compressed liquid, pressure will be created. Just like with a tire, the pressure is the same at every point in the barrel containing the liquid. If the pressure is too high, the barrel may break. The barrel will break in weak point, and not where the pressure is greater, because the pressure is the same at each point.
The liquid is almost incompressible
Compressed fluid is convenient for transmitting force through pipes, bends, up, down, because fluids are almost incompressible and energy transfer occurs immediately.
Many hydraulic systems use oil. This is because the oil is almost incompressible. At the same time, oil can be used as a lubricant.
Pascal's law: The pressure produced by external forces on the surface of a liquid or gas is transmitted in all directions without change.
Section 2
Relationship between pressure and force
According to Pascal's law, the relationship between pressure and force is expressed by the formulas:
F = P/S, where P is pressure, F is force, S is area
Hydraulic lever
The piston model shown in the figure below shows an example of balancing different weights through a hydraulic lever. Pascal discovered, as can be seen in this example, that the small weight of a small piston balances the large weight of a large piston, proving that the area of the piston is proportional to the weight. This discovery applies to compressible fluid. The reason this is possible is because a fluid always acts with equal force on an equal area.
The figure shows a 2 kg load and a 100 kg load. The area of one load weighing 2 kg is 1 cm?, the pressure is 2 kg/cm?. The area of another load weighing 100 kg is 50 cm?, the pressure is 2 kg/cm?. The two weights balance each other.
Mechanical lever
The same situation can be illustrated by the mechanical lever in the figure below.
A 1 kg cat sits 5 meters from the lever's center of gravity and balances a 5 kg cat 1 meter from the center of gravity, similar to the weight in the hydraulic lever example.
Hydraulic lever energy conversion
It is important to remember that a liquid acts with equal force over an equal area. This helps a lot when working.
There are two cylinders of the same size. When we push one piston with a force of 10 kg, the other piston is pushed out with a force of 10 kg because the area of each cylinder is the same. If the areas are different, the forces are also different.
For example, let's say that the large piston has an area of 50 cm?, and the small piston has an area of 1 cm?, with a force of 10 kg, the small piston experiences an impact of 10 kg/cm? on each part of the large valve according to Pascal's law, so the large piston receives a total force of 500 kg. We use pressure to transfer energy and do work.
There is an important point in the transformation of energy, namely, the relationship between force and distance. Remember, on a mechanical lever, light weight requires a long lever to achieve balance. In order to lift a 5 kg cat 10 cm, a 1 kg cat must move the lever down 50 cm.
Let's look at the hydraulic lever diagram again and think about the stroke of the small piston. A small piston stroke of 50 cm is required to transfer enough fluid to move the piston large cylinder by 1 cm.
Section 3
Flow creates movement
What is a flow?
When there is a difference in pressure at two points in a hydraulic system, the fluid tends to the point with the lowest pressure. This movement of fluid is called flow.
Here are some flow examples. The water in the city water supply creates pressure. When we turn the tap, water flows from the tap due to the pressure difference.
In a hydraulic system, flow is created by a pump. The pump creates a continuous flow.
Flow speed and magnitude
Flow velocity and magnitude are used to measure flow.
Speed shows the distance traveled in a certain period of time.
The flow rate shows how much liquid flows through a certain point in a this moment time.
Flow rate, lit./min.
Flow amount and speed
In a hydraulic cylinder, it is easy to consider the relationship between flow and velocity.
First, we have to think about the volume of the cylinder that we have to fill and then think about the stroke of the piston.
The figure shows cylinder A, 2 meters long and with a volume of 10 liters, and cylinder B, 1 meter long and with a volume of 10 liters. If you pump 10 liters of fluid per minute into each cylinder, a full stroke of both pistons lasts 1 minute. The piston in cylinder A moves twice as fast as cylinder B. This is because the piston has to travel twice as far in the same amount of time.
This means that a cylinder with a smaller diameter moves faster than a cylinder with large diameter at the same flow rate for both cylinders. If we increase the flow rate to 20 l/min, both chambers of the cylinder will fill twice as fast. The piston speed should double.
Thus, we have two ways to increase the speed of the cylinder. One by reducing the size of the cylinder and the other by increasing the flow rate.
The speed of the cylinder is thus proportional to the flow rate and inversely proportional to the area of the piston.
Pressure and force
Creating pressure
If you press on a stopper in a barrel filled with liquid, the stopper will be stopped by the liquid. When pressed, the liquid under pressure presses against the walls of the barrel. If you press too hard, the barrel may rupture.
Path of least resistance
If there is a barrel with water and a hole. When you press the top of the lid, water flows out of the hole. Water passing through the hole encounters no resistance.
When force is applied to a compressed fluid, the fluid seeks the path of least resistance.
Equipment malfunctions using oil pressure.
The above characteristics of hydraulic fluids are useful for hydraulic equipment, but are also the source of many malfunctions. For example, if there is a leak in the system, hydraulic fluid will flow out as it seeks the path of least resistance. Typical examples are leakage of loose connections and seals.
Natural pressure
We talked about pressure and flow, but often pressure exists without flow.
Gravity is a good example. If we have three interconnected reservoirs different levels As shown in the figure, gravity keeps the liquids in all tanks at the same level. This is another principle that we can use in a hydraulic system.
Liquid mass
The mass of the liquid also creates pressure. A diver who dives into the sea will say that he cannot dive too deep. If the diver goes too deep, the pressure will crush him. This pressure is created by the mass of water. Thus, we have a type of pressure that appears independently from the weight of water.
Pressure increases in proportion to depth and we can accurately measure pressure at depth. The picture shows a square column with water 10 meters high. It is known that one cubic meter of water weighs 1000 kg. If the height of the column increases to 10 meters, the weight of the column will increase to 10,000 kg. One is formed at the bottom square meter. In this way the weight is distributed over 10,000 square centimeters. If we divide 10,000 kg by 10,000 square centimeters, it turns out that the pressure at this depth is 1 kg per 1 square centimeter
Gravity value
Under the influence of gravity, oil flows from the tank to the pump. The oil is not sucked into the pump as many people think. The pump serves to supply oil. What is commonly understood as pump suction refers to the supply of oil to the pump by gravity.
Oil flows to the pump under the influence of gravity.
What causes pressure?
When pressure mixes with flow, we have hydraulic force. Where does pressure come from in the hydraulic system? Some is the result of gravity, but where does the rest of the pressure come from?
Most of the pressure comes from the impact of the load. In the picture below, the pump supplies oil continuously. Oil from the pump finds the path of least resistance and is directed through a hose to the slave cylinder. The weight of the load creates pressure, the magnitude of which depends on the weight.
Working Cylinder Hydraulic Force
(1) The law of inertia says that the property of a body to maintain its state of rest or rectilinear uniform motion until some external force takes it out of this state. This is one reason why the slave cylinder piston does not move
(2) Another reason why the piston does not move is that there is a load on it.
Flow
Earlier we said that the flow does work and moves objects. There is another key moment- How does flow rate relate to the operation of a hydraulic system?
The answer is that the flow rate is constant,
The increasing flow rate creates high speed
Many people think that increasing pressure increases speed, but this is not true. You cannot make the piston move faster by increasing the pressure. If you want to make the piston move faster, you must increase the flow rate.
Pressure in parallel connection
There are three different weights connected in parallel in one hydraulic system, as shown in the figure below. Oil, as usual, looks for the path of least resistance. This means that the lightest load will rise first because cylinder B will need the least amount of pressure. When the lightest load is lifted, the pressure will increase to lift the next heaviest load remaining. When cylinder A reaches the end of its stroke, the pressure will increase to lift the heaviest load. Cylinder C will be the last to rise.
(3) When the pump begins to push on the cylinder, the working piston and weight resist the flow of oil. Thus, the pressure increases. When this pressure overcomes the resistance of the piston, the piston begins to move.
(4) When the piston moves up, it lifts the load. Pressure and flow are used together to do work. This is hydraulic force in action.
When the safety valve closes, the speed does not increase
Here is one common mistake when troubleshooting a hydraulic system. When the cylinder speed drops, some mechanics go straight to the relief valve because they think that increasing the pressure will increase the operating speed. They try to reduce the safety valve settings, which is supposed to increase the maximum pressure in the system. Such changes do not lead to an increase in the speed of action. The safety valve serves to protect the hydraulic system from excessive pressure. Pressure settings should never be higher than the set pressure. Instead of increasing pressure settings, mechanics should look for other causes of system failure.
Conclusion
Now you have knowledge of the basic theory of hydraulics. You know that Pascal's Law says that the pressure produced by external forces on the surface of a liquid or gas is transmitted in all directions without changes.
You also learned that hydraulic fluid under pressure follows the path of least resistance. It's good when it works for us and bad when it causes a leak in the system. You've seen how we can use a small weight on one cylinder to move a large weight on another cylinder. In this case, the piston stroke of the small load is greater. You also gained a clear understanding of the relationship between pressure and force, flow rate and speed, and of course pressure and flow.
Hydraulic mechanisms
Hydraulic systems
Hydraulic systems are used to transfer mechanical energy from one place to another. This happens through the use of pressure energy. The hydraulic pump is driven by mechanical energy. Mechanical energy is converted into pressure energy and kinetic energy of the hydraulic fluid and then converted back into mechanical energy to do work.
Energy Conversion Value
The energy that is transferred to the hydraulic system is converted from the mechanical energy of the engine, which drives the hydraulic pump. The pump converts mechanical energy into fluid flow, converting mechanical energy into pressure energy and kinetic energy. The fluid flow is transmitted through the hydraulic system and directed to the cylinder and motor drives. The pressure energy and kinetic energy of the fluid causes the actuator to move. With this movement, another transformation into mechanical energy occurs.
How it works in a hydraulic excavator.
In hydraulic excavators, the primary mechanical energy from the engine drives a hydraulic pump. The pump directs the flow of oil into the hydraulic system. When the drive moves under the influence of oil pressure, it is again converted into mechanical energy. The excavator boom can be raised or lowered, the bucket moves, etc.
Hydraulics and operation
Three elements of work
When there is any work, then certain conditions are necessary to perform this work. You need to know how much force is needed. You need to decide how quickly the work needs to be done and you need to determine the direction of the work. These three operating conditions: force, speed and direction are used in hydraulic terms as shown below.
Hydraulic system components
Main Components
The hydraulic system consists of many parts. The main parts are the pump and the drive. The pump supplies oil by converting mechanical energy into pressure energy and kinetic energy. An actuator is part of a system that converts hydraulic energy back into mechanical energy to perform work. Parts other than the pump and drive are required to full work hydraulic system.
Tank: oil storage
Valves: control the direction and amount of flow or limit pressure
Pipe lines: connection of system parts
Let's look at two simple hydraulic systems.
Example 1, hydraulic jack
What you see in the picture is called a hydraulic jack. When you apply force to the lever, hand pump supplies oil to the cylinder. The pressure of this oil presses on the piston and lifts the load. The hydraulic jack is in many ways similar to the Pascal hydraulic lever. Added here hydraulic tank. A check valve is installed to keep oil in the tank and cylinder between strokes of the piston.
In the top picture, the pressure is held, the check valve is closed. When the pump handle is pulled up, the inlet check valve opens and oil flows from the tank into the pump chamber.
The bottom picture shows the open shut-off valve to connect the tank and cylinder, allowing oil to flow into the tank while the piston moves down.
Example 2, hydraulic cylinder operation
1. First, there is a hydraulic tank filled with oil and connected to a pump.
3. The pump is running and pumping oil. It is important to understand that the pump only moves volume. Volume sets the rate of hydraulic action. The pressure is created by the load and not created by the pump.
4. The hose from the pump is connected to the distribution valve. Oil flows from the pump to the valve. The operation of this valve is to direct flow either to the cylinder or into the tank.
5. The next step is the cylinder, which does the actual work. Two hoses from the control valve are connected to the cylinder.
6. Oil from the pump is directed to the lower cavity of the piston through the distribution valve. The load causes resistance to flow, which in turn creates pressure.
7. The system looks complete, but it is not. It is also very necessary important detail. We must know how to protect all components from damage in the event of a sudden overload or other incident. The pump continues to operate and supply oil to the system even if an incident occurs to the system.
If the pump supplies oil and there is no way for the oil to escape, the pressure increases until a part breaks. We install a safety valve to prevent this. Usually it is closed, but when the pressure reaches the set value, the safety valve opens and oil flows into the tank.
8. Tank, pump, control valve, cylinder, connection hoses and safety valve are the core of the hydraulic system. All these details are necessary.
Now we have a clear understanding of how the hydraulic system works.
Pump classification
What is a pump?
Just like your heart pumps blood throughout your body, a pump is the heart of a hydraulic system. A pump is the part of the system that pumps oil to do work. As we wrote earlier, a hydraulic pump converts mechanical energy into pressure energy and kinetic energy of the fluid.
What is a hydraulic pump?
Each pump creates a flow. Liquid moves from one place to another.
There are two types of displacement pumps.
Forced action pump
Non-forced pump
The water circle in the picture is not an example forced pump. The circle picks up the liquid and moves it.
Another forced action pump. It is called forced action, since the pump pumps liquid and prevents it from returning back. If the pump cannot do this, there will not be enough pressure in the system. Today, all hydraulic systems use high pressure and thus positive action pumps are required.
Types of hydraulic pumps
Today, many machines have one of three pumps:
- Gear pump
- Vane pump
- Piston pump
All pumps operate on a rotary piston type; the liquid is driven by the rotation of a part inside the pump.
Piston pumps are divided into two types:
Axial piston type
Radial piston type
Axial piston type pumps are so called because the pump pistons are positioned parallel to the pump axis.
Radial piston pumps are so called because the pistons are positioned perpendicular (radially) to the axis of the pump. Both types of pumps perform reciprocating motion. The pistons move back and forth and use rotary piston motion.
Displacement of hydraulic pump
Displacement means the volume of oil that the pump can pump or move in each cylinder. Hydraulic pumps are divided into two types:
Fixed working volume
Variable working volume
Fixed displacement pumps pump the same amount of oil each cycle. To change the volume of such a pump, it is necessary to change the pump speed.
Variable displacement pumps can change oil volume depending on the cycle. This can be done without changing the speed. Such pumps have internal mechanism, which regulates the output amount of oil. When the pressure in the system drops, the volume increases; when the pressure in the system increases, the volume decreases automatically.
Power
Fixed displacement pump Variable displacement pump
Design
Drive classification
What is a drive?
The drive is the part of the hydraulic system that produces power. The drive converts hydraulic energy into mechanical energy to do work. There are linear and rotary drives. The hydraulic cylinder is a linear drive. The force of the hydraulic cylinder is directed in a straight line. The hydraulic motor is a rotary drive. The output force is torque and rotary action.
Rotary drive
Linear actuator
Hydraulic cylinders
Hydraulic cylinders are like a lever. There are two types of cylinders.
Single acting cylinders.
Hydraulic fluid can only move to one end of the cylinder. The return of the piston to its original position is achieved by gravity.
Double acting cylinders.
Hydraulic fluid can move to both ends of the cylinder, so the piston can move in both directions.
In both types of cylinders, the piston moves in the cylinder in the direction in which the liquid pushes against the piston. Various types of seals are used in pistons to prevent leakage.
Single acting cylinder
Double acting cylinder
Hydraulic motor
Like a cylinder, a hydraulic motor is a drive, only a rotary drive.
The principle of operation of a hydraulic motor is exactly the opposite of the operation of a hydraulic pump. The pump pumps fluid and the hydraulic motor is powered by this fluid. As we wrote earlier, a hydraulic pump converts mechanical energy into pressure energy and kinetic energy of the fluid. The hydraulic motor converts hydraulic energy into mechanical energy.
With hydraulic drive, pumps and motors work together. The pumps are mechanically driven and force fluid into hydraulic motors.
The motors are driven by fluid from the pump and this movement in turn rotates the mechanical parts.
Types of hydraulic motors
There are three types of hydraulic motors and they all have internal moving parts that are driven by incoming flow, their name is:
- Gear motor
- Vane motor
- Piston motor
Displacement and torque
The operating time of the motor is called torque. This is the rotational force of the motor shaft. Torque is a measurement of force per unit length and does not include speed. The torque of the motor is determined by the maximum pressure and volume of fluid it can move during each cycle. The speed of the motor is determined by the amount of flow. Greater flow rate faster speed.
Torque is the force of rotation of the motor shaft
Torque equals force x distance
Valve classification
What types of valves are there?
Valves are controls in a hydraulic system. Valves regulate pressure, direction of flow, and amount of flow in a hydraulic system.
There are three types of valves:
In the figure below you can see how the valves work.
Pressure control valves
These valves are used to limit hydraulic system pressure, unload a pump, or adjust chain pressure. There are several types of pressure control valves, some of them are relief valves, pressure reducing valves and relief valves.
Pressure control valves
The pressure control valve is used for the following purposes:
System Pressure Limitations
Reducing pressure
Setting the Incoming Circuit Pressure
Unloading pump
A safety valve is sometimes called a safety valve because it reduces excessive pressure when it reaches an extreme level. The safety valve prevents system parts from being overloaded.
There are two types of safety valve:
Direct acting safety valve that simply open and close.
Pilot Line Safety Valve, which has a pilot line to control the main safety valve.
The direct acting safety valve is usually used in places where the flow volume is small and the operation is infrequently repeated. A pilot line relief valve is required in areas where a large volume of oil must be reduced.
Directional control valve
This valve controls the flow direction of the hydraulic system. A typical direction control valve is a directional control valve and spool valve.
Value control valve
This valve controls the oil flow rate of the hydraulic system. Control occurs by limiting the flow or diverting it. Several different types of magnitude control valve are the flow control valve and the flow division valve.
These valves are controlled in various ways: manually, hydraulically, electrically, pneumatically.
Directional Control Valves
This valve sets the oil flow as the governor controls traffic. These valves:
Check valve
Spool valve
Are used Various types direction control designs.
A check valve uses a poppet and a spring to direct flow in one direction. A spool valve uses a movable cylindrical spool. The spool moves back and forth, opening and closing passages for flow.
Check valve
The check valve is simple. It is called a single flow valve. This means that it is open to flow in one direction, but closed to oil flow in the opposite direction.
In the figure below you can see the operation of the check valve. This is a check valve that is designed for through flow in one line. The poppet valve opens when the inlet pressure is greater than the outlet pressure. When the valve is open, oil flows freely. The poppet valve closes when inlet pressure drops. The valve interrupts the flow in the reverse direction and stops the flow under the action of the outlet pressure.
Spool valve
A spool valve is a typical control valve that is used to control the operation of an actuator. What is commonly called a control valve is a spool valve. The spool valve directs the flow of oil to start, carry out and finish work.
When the spool moves from the neutral position to the right or left, some channels open and other channels close. In this way, oil is supplied to and from the drive. The spool flange tightly blocks the incoming and outgoing oil flows.
The spool is made of durable material and has a smooth, precise, strong surface. It's even plated with chrome to resist wear, rust and damage.
The spool valve in the picture shows three positions, neutral, left and right. We call it four-position because it has four possible directions, which are directed into both chambers of the cylinder, into the tank and into the pump.
When we move the spool to the left, the oil flow is directed from the pump into the left cylinder cavity and the flow from the right cylinder cavity is directed into the tank. As a result, the piston moves to the right.
If we move the spool to the right, the actions are exactly the opposite, and accordingly the piston moves to the right.
In the central position, neutral, the oil is directed into the tank. The channels in the wallpaper of the cylinder cavity are closed.
neutral
Value control valves
As we wrote earlier, the magnitude control valve works in one of two directions. It either blocks the flow or changes its direction.
Flow control valve used to control drive speed by measuring flow. Metering involves measuring or adjusting the flow rate to or from an actuator. A flow splitting valve regulates the volume of flow, but also splits flows between two or more circuits.
Flow split valve controls the amount of flow, but also splits the flow between two or more circuits.
Proportional flow divider
The purpose of this valve is to divide the flow from one source.
The flow divider in the figure below divides the flows in a ratio of 75-25 at the output. This is possible because input #1 is larger than input #2.
Hydraulic circuit
Earlier in the text, drawings were given to help understand the principles of operation of the hydraulic system and its components. We tried to show the design on various examples and used different types of designs.
The pictures we use are called graphic diagram.
Each part of the system and each line is represented by a graphic symbol.
Below are examples of graphical charts.
It is important to understand that the purpose of a graphical diagram is not to show the arrangement of parts. The graphic diagram is only used to show functions and connections.
Line classification
All components of the hydraulic system are connected by lines. Each line has its own name and performs its own function. Main lines:
Working lines: Pressure line, Suction line, Drain line
Non-working lines: Drain line, Pilot line
The operating line oil is involved in energy conversion. The suction line carries oil from the tank to the pump. The pressure line carries oil from the pump to the drive under pressure to do work, and the return line returns oil from the drive back to the tank.
Non-working lines are additional lines that are not used in the main functions of the system. The drain line is used to return excess oil or pilot line oil to the tank. The pilot line is used to control the working parts.
Advantages and disadvantages of the hydraulic system
We have learned the basic principles of how a hydraulic system works.
Before finishing, let's look at the advantages and disadvantages of the hydraulic system over other systems.
Advantages
1. Flexibility - a limited amount of liquid is a more flexible source of energy and has good properties energy transfer. Using high pressure hoses and hoses instead of mechanical parts eliminates many problems.
2. Strengthening - A small force can control a large force.
3. Smooth - The hydraulic system operates smoothly and quietly. Vibration is kept to a minimum.
4.Simplicity - There are few moving parts and few connections in the hydraulic system, and it is self-lubricating.
5. Compactness - The design of the components is very simple compared to mechanical devices. For example, a hydraulic motor is much smaller in size than an electric motor, which produces the same power.
6. Economy - Simplicity and compactness ensures the efficiency of the system with low power losses.
7. Safety - The safety valve protects the system from overloads.
Flaws
THE NEED FOR TIMELY MAINTENANCE - Hydraulic system components are precision parts and operate under high pressure. Timely maintenance is necessary to protect against rust, oil contamination, increased wear, so using and replacing the correct oil is a must.
A little more about hydraulics
Energy loss (pressure)
Another important point To understand the basics of hydraulics is the loss of energy (pressure) in a hydraulic system.
For example, some resistance to flow causes a decrease in flow pressure, resulting in a loss of energy.
Now let's look at some details.
Oil viscosity.
Oil has viscosity. The viscosity of the oil itself creates resistance to flow.
Resistance to flow due to friction.
As oil passes through the pipes, pressure decreases due to friction.
This decrease in pressure increases in the following cases:
1) When using a long pipe
2) Using a small diameter pipe
3) With a sharp increase in flow
4) For high viscosity
Decreased blood pressure for other reasons
In addition to reducing pressure due to friction, losses can occur due to changes in flow direction and changes in oil flow channels.
Oil leakage through throttle body
As we said earlier, pressure reduction occurs when oil flow is restricted.
A throttle is a type of restriction often installed in a hydraulic system to create a pressure difference in the system.
However, if we stop the flow behind the throttle, Pascal's law applies and the pressure equalizes on both sides.
Loss of energy
As you well know, there are many pipes, fittings (joints) and valves that go into a hydraulic system.
A certain amount of energy (pressure) is used just to move the oil from one place to another before the work is done.
Lost energy is converted into heat
Energy loss due to pressure reduction is converted into heat. An increase in oil flow, an increase in oil viscosity, an increase in the length of a pipe or hose, as well as similar changes, cause an increase in resistance and causes overheating.
To avoid this problem, use replacement parts identical to the original ones.
Pump efficiency
As we said earlier in the previous text, a hydraulic pump converts mechanical energy into hydraulic energy. The efficiency of the pump is checked by its performance and is one of the points when checking its performance. Pump efficiency refers to how well the pump does its job.
There are three approaches to determining pump efficiency.
FEEDING EFFICIENCY
TORQUE EFFICIENCY (MECHANICAL)
FULL EFFECTIVENESS
Torque efficiency
Torque efficiency is the ratio of the actual output torque of the pump to the input torque of the pump.
The actual output torque of the pump is always less than the input torque of the pump. Torque loss occurs due to friction of the moving parts of the pump.
Full efficiency
Total efficiency is the ratio of outgoing hydraulic power to incoming mechanical power pump
This is a measure of both feed efficiency and torque efficiency. In other words, total efficiency can be expressed as the output power divided by the input power. The output power is less than the input power due to losses in the pump due to friction and internal leakage.
In general, the efficiency of gear and piston pumps is 75 - 95%.
A piston pump is usually rated higher than a gear pump.
Feed efficiency
Flow efficiency is the ratio of the actual pump flow to the theoretical pump flow. In reality, the actual pump flow is less than the theoretical pump flow.
This is usually expressed as a percentage.
The difference is usually expressed by internal leakage in the pump due to holes in the working parts of the pump.
Some holes are made in all parts for lubrication.
Internal leakage occurs when pump parts manufactured with small tolerances wear out.
We consider increased internal leakage as a loss of efficiency.
Power required to operate the pump
For the reasons given earlier, the power required to operate the pump must be greater than the power output.
Here is an example of a 100 HP pump.
If the pump efficiency is 80%, then it is necessary to supply 125 hp.
Power required = power output/efficiency = 100/80
In other words, a 125 hp engine. required to operate a 100 hp pump. with an efficiency of 80%.
Pump fault
What reduces pump efficiency?
Dirty oil is the main cause of pump failure.
Solid particles of dirt, sand, etc. in oil are used in the pump as an abrasive material.
This causes intense wear on parts and increases internal leakage, thereby reducing pump efficiency.
Drainage channel
The channel that is used to drain the oil into the tank is called the drain channel.
Pump cavitation
When does cavitation occur?
Cavitation occurs when oil does not completely fill the intended filling space in the pump.
This creates air bubbles that are harmful to the pump.
Imagine that the pump inlet line is narrow, this causes a drop in incoming pressure.
When pressure is low, oil cannot flow into the pump as quickly as it can leave it.
The result is that air bubbles form in the incoming oil.
Air in oil
This reduction in pressure leads to the appearance of a certain amount of dissolved air in the oil and the air fills the cavities.
Air in the oil in the form of bubbles also fills the cavities.
When air-filled cavities that are formed at low pressure enter the high pressure area of the pump, they collapse.
This creates an explosive action that breaks up or dislodges small particles from the pump and causes excessive noise and vibration in the pump.
Consequences of the explosion
Destruction that occurs constantly causes an explosion.
The force of this explosion reaches 1000 kg/cm² and small metal particles are carried out of the pump. If the pump is operated under cavitation for a long period of time, it can be seriously damaged.
Hydraulic motor
The motor operates in reverse order compared to the pump.
The pump supplies oil, while the motor runs on this oil.
The motor converts hydraulic energy into mechanical energy to perform work.
Motor efficiency
Like a hydraulic pump, a motor's efficiency is determined by its performance.
Flow efficiency is one of the indicators when determining motor performance.
Internal leakage occurs due to holes in the working parts of the motor. Some holes are present in all parts for lubrication. An increase in leakage is associated with wear of parts with a small tolerance.
We consider increased internal leakage as a loss of efficiency.
Checking the motor operation
As we said earlier, the channel through which the oil enters the tank is called the drain channel.
This gives us one method to check the operation of the motor by comparing the actual amount of oil drained from the motor into the tank with the set amount. The greater the amount of oil drained into the tank, the greater the energy loss and, accordingly, the decrease in engine performance.
Hydraulic cylinder
Cylinder leak - external leak
Dirt and other material may enter when the cylinder rod is pulled out. Then, when the rod retracts, dirt gets into the cylinder and damages the seals.
The cylinder rod has a protective seal that prevents dirt from entering the cylinder when the rod is retracted. If a leak occurs from the cylinder rod, all rod seals must be replaced.
Cylinder leak - internal leak
A leak inside the cylinder can cause slow movement or stalling under load.
A piston leak can be caused by a faulty piston seal, ring, or a scratched surface inside the cylinder.
The latter can be caused by dirt and sand in the oil.
Slow motion
Air in the cylinder is the main cause of slow action, especially when installing a new cylinder. All air trapped in the cylinder must be vented.
Lowering the cylinder
If the cylinder deflates when stopped, check for internal leaks. Other causes of malfunction could be a faulty control valve or a broken safety valve.
Rough or rusty cylinder rod
An unprotected cylinder rod may be damaged by impact hard object. If the smooth surface of the stem is damaged, the stem seals may be destroyed.
Irregularities on the stem can be corrected special means.
Another problem is rust on the stem.
When storing the cylinder, retract the rod to protect it from rust.
Valves
The previous text has covered the basic knowledge of valves and their differences in operation.
There are a few technical terms associated with control valves that you need to learn.
Cracking pressure and full flow pressure
Cracking pressure is the pressure at which the safety valve opens.
Full flow pressure is the pressure at which the fullest flow passes through the relief valve.
Full flow pressure is slightly higher than cracking pressure. The safety valve adjustment is set to full flow pressure.
Cracking pressure and pressure regulation
In the previous text, we learned that there are two types of safety valves: direct acting safety valve and pilot line operated safety valve.
Let's look at the pressure adjustments of these valves.
A pilot line operated safety valve has a lower control pressure than a direct operated safety valve.
The figure shows a comparison of these two types of valves.
While the direct acting relief valve in the figure opens at half its full flow pressure, the pilot line operated relief valve is open at 90% of its full flow pressure.
Pressure adjustment
As we said earlier, full flow pressure is slightly higher than cracking pressure.
This is because the spring tension is adjusted to open the valves. This condition is called pressure regulation and is one of the disadvantages of a simple safety valve.
What's better?
A pilot line controlled safety valve is better for high pressure and high flow systems.
Because these valves do not open until full flow pressure is reached, effective protection systems - oil is stored in the system.
Although more slow work than a direct acting safety valve, a pilot line operated safety valve maintains more in the system constant pressure.
Pressure reducing valve
What it is?
Pressure reducing valve Used in a hydraulic motor circuit to create back pressure for control during operation and to stop the motor when the circuit is in neutral.
Pressure reducing valve for faucets
The pressure reducing valve is usually closed together with the pressure control valve with an internal check valve.
When the pump supplies oil to the winch motor for lowering, the motor operates by inertia under the influence of the gravity of the load, in other words, when the motor exceeds the permissible speed, the pressure reducing valve supplies back pressure, thus preventing free fall cargo
An internal check valve allows reverse flow to rotate the motor in the opposite direction to lift the load.
Pressure reducing valve for excavators.
The pressure reducing valve of the excavator provides a soft start and increased travel/turning speed, and also prevents motor cavitation.
The pressure in the pump pressure line is always higher than the pressure in the motor line.
An attempt to exceed the set motor speed by inertia causes a decrease in pressure in the pressure line and the valve immediately shuts off the motor line until the pressure line pressure is restored.
Maintenance valves
Support good condition valves
As you well know, valves are precision products and must take accurate readings of pressure, direction and volume of hydraulic oil.
Therefore, valves must be installed correctly and maintained in good condition.
Causes of valve failure
Contaminants such as dirt, lint, corrosion and sludge can cause malfunction and damage to valve components.
Such contamination causes the valve to stick, not open completely, or strip the mating surface until it begins to leak.
Such malfunctions are excluded by keeping the equipment clean.
Check points
When troubleshooting or repairing, check the following items.
Pressure distribution valve - Safety valve
Check the valve seat (valve seat and valve poppet) for leaks and galling.
Check to see if the plunger is stuck in the body.
Check the rubber rings.
Check if the throttle is clogged.
Flow control valve
- Check the spool and channels for irregularities and scratches.
- Check seals for leaks
- Check for uneven edges.
- Check for scratches on the spool.
The flow control valve spools are installed in the housing in the calculated locations.
This is done to ensure the smallest clearance between the body and spool to prevent internal leakage and maximize build quality. Therefore, install the spools in the appropriate holes.
February 10, 2016A hydraulic system is a device designed to convert small forces into large ones by using a fluid to transmit energy. There are many varieties of nodes operating according to this principle. The popularity of systems of this type is explained primarily high efficiency their operation, reliability and relative simplicity of design.
Scope of use
This type of system is widely used:
- In industry. Very often, hydraulics are an element of the design of metal-cutting machines, equipment intended for transporting products, loading/unloading them, etc.
- In the aerospace industry. Similar systems used in various types of controls and chassis.
- IN agriculture. It is through hydraulics that the attachments of tractors and bulldozers are usually controlled.
- In the field of cargo transportation. Cars often have a hydraulic braking system.
- In ship equipment. In this case, hydraulics are used in the steering and are included in the design of the turbines.
Operating principle
Any hydraulic system operates on the principle of a conventional fluid lever. Supplied inside such a unit working environment(in most cases, oil) creates the same pressure at all its points. This means that by applying a small force on a small area, you can withstand a significant load on a large one.
Next, we will consider the principle of operation of such a device using the example of such a unit as the hydraulic brake system of a car. The design of the latter is quite simple. Its circuit includes several cylinders (main brake, filled with liquid, and auxiliary). All these elements are connected to each other by tubes. When the driver presses the pedal, the piston in the master cylinder moves. As a result, the liquid begins to move through the tubes and enters the auxiliary cylinders located next to the wheels. After this, the braking is applied.
Design of industrial systems
The hydraulic brake of a car - the design, as you can see, is quite simple. Industrial machines and mechanisms use more complex liquid devices. Their design may be different (depending on the scope of application). However circuit diagram industrial hydraulic system is always the same. Typically it includes the following elements:
- Liquid reservoir with neck and fan.
- Coarse filter. This element is designed to remove various types of mechanical impurities from the liquid entering the system.
- Pump.
- Control system.
- Working cylinder.
- Two fine filters (on the supply and return lines).
- Distribution valve. This structural element is designed to direct fluid to the cylinder or back to the tank.
- Check and safety valves.
The hydraulic system of industrial equipment is also based on the fluid lever principle. Under the influence of gravity, the oil in such a system enters the pump. It is then directed to the control valve and then to the cylinder piston, creating pressure. The pump in such systems is not designed to suck in liquid, but only to move its volume. That is, the pressure is created not as a result of its work, but under the load from the piston. Below is a schematic diagram of the hydraulic system.
Advantages and disadvantages of hydraulic systems
The advantages of units operating on this principle include:
- The ability to move large-sized and weighted loads with maximum precision.
- Virtually unlimited speed range.
- Smooth operation.
- Reliability and long service life. All components of such equipment can be easily protected from overloads by installing simple pressure relief valves.
- Economical in operation and small in size.
In addition to the advantages, hydraulic industrial systems, of course, also have certain disadvantages. These include:
- Increased risk of fire during operation. Most fluids used in hydraulic systems are flammable.
- Sensitivity of equipment to contamination.
- The possibility of oil leaks, and therefore the need to eliminate them.
Hydraulic system calculation
When designing such devices, many different factors are taken into account. These include, for example, the kinematic coefficient of viscosity of the liquid, its density, the length of pipelines, rod diameters, etc.
The main goals of performing calculations for a device such as a hydraulic system are most often to determine:
- Pump characteristics.
- The stroke values of the rods.
- Working pressure.
- Hydraulic characteristics of lines, other elements and the entire system as a whole.
The hydraulic system is calculated using various types of arithmetic formulas. For example, pressure losses in pipelines are determined as follows:
- The estimated length of the highways is divided by their diameter.
- The product of the density of the liquid used and the square of the average flow rate is divided by two.
- Multiply the resulting values.
- Multiply the result by the travel loss coefficient.
The formula itself looks like this:
- ∆p i = λ x l i(p) : d x pV 2: 2.
In general, in this case, the calculation of losses in highways is carried out approximately according to the same principle as in such simple designs like hydraulic heating systems. Other formulas are used to determine pump characteristics, piston stroke, etc.
Types of hydraulic systems
All such devices are divided into two main groups: open and closed type. The schematic diagram of the hydraulic system we considered above belongs to the first type. Low and medium power devices usually have an open design. In more complex systems closed type, a hydraulic motor is used instead of a cylinder. The liquid enters it from the pump and then returns to the main line.
How the repair is carried out
Since the hydraulic system in machines and mechanisms plays a significant role, its maintenance is often entrusted to highly qualified specialists from companies engaged in this particular type of activity. Such companies usually provide a full range of services related to the repair of special equipment and hydraulics.
Of course, these companies have all the equipment necessary to carry out such work. Hydraulic system repairs are usually performed on site. Before carrying it out, in most cases, various kinds of diagnostic measures must be carried out. For this purpose, companies involved in hydraulic maintenance use special installations. Employees of such companies also usually bring the components necessary to fix problems with them.
Pneumatic systems
In addition to hydraulic ones, pneumatic devices can be used to drive components of various types of mechanisms. They work on approximately the same principle. However, in this case, the energy of compressed air, not water, is converted into mechanical energy. Both hydraulic and pneumatic systems cope with their task quite effectively.
The advantage of devices of the second type is, first of all, the absence of the need to return the working fluid back to the compressor. The advantage of hydraulic systems compared to pneumatic ones is that the environment in them does not overheat or overcool, and therefore, there is no need to include any additional components or parts in the circuit.