Hydraulics is the science of flowing and stationary fluid (liquid). It can be understand as the generation of force and motion by hydraulic fluid.

The word hydraulic comes from two Greek words “Hydor” which means water and “Aulos” which means pipe. Hydraulics definition may be as simple as it defines here but it has a very wide application.

Historical Development

Human already started the use of hydraulic in ancient time in the form of the water wheel at around 350 BCE. According to the author and historian Helaine Selin, there is evidence that ancient people from the Persian Empire were using the water wheel for millstones. The water wheels still are in use with today’s advanced technologies. Moreover, in 6 BCE human started irrigation system that played an important role for civilisation like Mesopotamia.

Development in hydraulics in the modern era

Blaise Pascal a French physician studied about the fluid hydrostatic nature and laid the foundation of industrial hydraulics in 1653. By using Pascal’s law British engineer Joseph Bramah invented hydraulic press in the year of 1795.

Later, William George Armstrong an English industrialist and engineer invented hydraulic accumulator in 1851. When hydraulic pressure was not available he used weighted accumulator for pressurised flow. Although he first used his accumulator in his hydraulic cranes, later it found in many applications.

In 1905 two American engineers Reynold Janney and Harvey D Williams first used mineral oil in the hydrostatic transmission in the axial piston design. In this way, the use of oil in the hydraulic system begins.

After oil hydraulic invented, The world of hydraulic grows very rapidly. We begin to use hydraulic in agriculture, construction like excavators, cranes etc, Industrial uses, in automobile, in aerospace and many more.

Now, because hydraulic are using every field, in order to classify the possibilities of uses we can divide it into two categories.

1. Industrial Hydraulics.
2. Mobile Hydraulics.

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In this article, you will learn about hydraulics flow control valve, basic jobs, the principle of working, construction and some type of hydraulic flow control valve.

Definition of a flow control valve

Definition: A hydraulic flow control valve is a hydraulic device which controls the flow rate by giving a definite amount of passage to the flow of hydraulic fluid. Basically, it controls the speed of actuators or complete operation in the hydraulic system. A hydraulics flow control valve has two main jobs.

1. Speed regulation
2. The equalisation of pressure fluctuation.

A hydraulics flow control valve is also called a flow restrictor valve because it restricts the flow and allows the fluid in the desired flow rate. For example,

In this hydraulic circuit, consider when we start the pump and position the direction control valve in position B what will happen? The cylinders piston extend rapidly. This rapid movement can cause jerking in the system and the function will not smooth. So, we need something which can control the rapid movement. Therefore, we use hydraulics flow control valve or simply a flow restrictor.

Figure 2 is the symbol for flow restrictor. Various kind of flow restrictors are available and according to that symbols also differs. Above figure represents a constant flow restrictor or flow control valve. Now, see the solution for the above-mentioned problem.

When you place a flow restrictor in the system it will reduce the cross-section of the pipe and allow less hydraulic oil flowing per unit time. Because of less quantity of hydraulic oil flowing per second to the actuator, the actuator moves slowly and you can control the speed.

Type of hydraulic flow control valve

1. onstant flow control valve
2. Adjustable flow control valve

Constant flow control valve

A constant flow control valve controls the flow rate but it will be fixed forever. We can not change the cross-sectional area and hence, we can not change the flow rate. In the above figure 3, The speed of the actuator will be fixed irrespective of load and if the load increased again operation will not smooth. So, as per changing a load the design also changes.

Adjustable flow control valve

An adjustable flow control valve is also controlling the flow rate of hydraulic fluid but we can change the cross-sectional area and hence, we can change the flow rate. If a load is increased then we can reduce the cross-sectional area and can change the speed of actuator and operation will be smoother. Figure 4 shows the symbol of a variable flow control valve.

Construction of Flow control valve

Flow control Valve can be designed in various ways but the basic designs are

1. Throttle type- It can be a constant or variable flow control.
2. Orifice type- it can only be a constant type.

In throttle type, there is an opening for flow rate limitation and it can be adjusted by a screw. But in orifice type, there is just an orifice which limits the flow rate and we can not change the size of an orifice.

Influence of pressure fluctuation on speed

With restrictor (flow control) valve either constant or variable type, minor pressure fluctuation can cause flow rate changes and speed of operation. For example,

Consider a rope winch driven by hydraulic power. The speed of winch is controlling by a variable flow restrictor. When a load is not changing or single user then speed will nearly constant but if additional users and also changing loads in the system can cause pressure fluctuations. when load increase in winch pressure will increase on the other hand addition of user (load in system) will decrease the pressure. So, pressure may change repeatedly in the system and also change the flow rate. The challenge is that the pressure in the system changes in an undefined way and not parallel. The motor will rotate with different speeds—and therefore the rope winch will too. But we do not want that. Ideally, a rope winch should always rotate at the same speed, rotational speed should remain constant even with pressure differences.

To achieve this, a pressure balance valve is added to a variable flow restrictor valve.

In this diagram, there will be some pressure drop due to flow restrictor when fluid is flowing. Let us consider the flow restrictor is preset at a particular pressure difference delta P( difference of pressure before and after restrictor valve). When the load at rope winch increase pressure will also increase after the flow restrictor and accordingly speed will effects.

Metering Throttle

See figure 8 and 9, the increased pressure above the restrictor valve called a metering throttle here, acts via the control line on the spring side of the pressure balance. The piston of the pressure balance extends toward the left and releases more flow volume. The pressure in front of the metering throttle increases, and the preset pressure difference here, delta p, is restored. The pressure fluctuation was thus balanced. And the outlet pressure of the metering throttle stays unchanged despite the pressure fluctuation. This is also called Pressure compensated flow control valve.

This is all about Flow control valve/flow regulator valve/flow restrictor valve or throttle valve. Hope you understood. Comment below if you have any queries.

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Most of us are very familiar with the pressure relief valve and pressure reducing valve. Both valves control the pressure in the hydraulic system. Since both are pressure controlling device still both are different from each other. Therefore, we will learn in this article how they differ with each other, where it can be used, and their construction. Also, we will see some special-purpose valves.

Pressure relief valve

Consider a simple hydraulic system without a relief valve for instance.

When the pump starts and does the work by lifting the load up to its maximum limit. But when it reaches its limit what will happen? The pump is still running and tries harder to push more oil in the system and ultimately pressure will increase tremendously and damage the weaker component. Therefore we need something which will limit the pressure in the system. This component is a pressure relief valve.

Pressure relief valve: A pressure relief valve is a hydraulic component that provides safety to the hydraulic system from excessive pressure. This is normally closed but when the pressure in the hydraulic system increase beyond the set limit of a pressure relief valve, it opens the path and allows hydraulic oil to flow into the tank. In this way, it releases the excessive pressure from the system and provides protection. As soon as pressure reduces in the system, the pressure relief valve comes in the initial position and closes the open path again.

As shown above, an arrow shows the closed path for hydraulic fluid and there is also spring tension which forces the relief valve to remain closed. But when the pressure in the hydraulic system is enough or more than relief valve spring tension, a pilot line will push the arrow against the spring tension and open the path. In this way, the pressure is relieved from the system and save the components.

Click to learn Industrial Hydraulic Symbols.

Construction of pressure relief valve

A pressure relief valve can be designed in many more ways but, here it is the most common type of pressure relief valve. It consists of two passages one is inlet port and the other is outlet port. Inlet port is connected with the pressurized hydraulic system while on the other hand outlet is connected with the tank.

As in above figure 4, you can see there is a valve seat which is normally closing the inlet and seat holder is forced against a spring. At the top, there is a screw which will set the spring tension or in other word set the pressure of the relief valve. Usually, the screw is protected with a cap so, the unauthorized person can not change the pressure setting and also it protects the screw from rusting.

Pressure Reducing Valve

Pressure reduction valves are used to limit the hydraulic pressure in a system. However, instead of reducing inlet pressure, they reduce the outlet pressure. It divides a hydraulic system into different sub-systems. For Example, If a hydraulic system there are numbers of operations, and each has its own capacity. As per every hydraulic component, there may be a different pressure requirement but with only one pump this cannot be achieved but with the use of pressure reducing valve it can easily achieve.

Pressure reducing valve is normally open valve and it allows the pressurized fluid to flow but when the pressure at the output of the valve is more than the valve pressure setting, a pilot pressure pushes the arrow down and the path will close. The valve will not allow pressurized fluid to flow in the system until the pressure drops lower than the valve pressure setting.

In the above example, there are two hydraulic actuators for clamp A and B which holds a workpiece. A pressure relief valve. A pressure reducing valve. And a direction control valve and positive displacement pump. The pressure relief valve setting is 300 bar. So, the maximum system pressure is 300 bar. When the direction control valve is in the first position both the clamp cylinders extend but in clamp A the pressure will be maximum as system pressure but in clamp B due to the pressure reducing valve setting, the pressure will be 200 bar. As soon as the pressure increases in the clamp B line the pressure reducing valve will close and not allow the pressurized fluid to flow. Hence, the pressure will limit at 200 bar.

For better understanding, you may read click here this article.

Construction of pressure reducing valve

A common pressure reducing valve consists of an inlet port (C), an outlet port (D), and a pilot line (E). There is a spool against the spring tension which opens and closes the path for pressurized fluid. As the pressure increase at the outlet port (D) beyond the spring tension (i.e. Pressure setting), pilot line (E) shift the spool against the spring and make the opening narrow. Due to the pressure difference between inlet and outlet this spool continuously maintains almost constant pressure.

FAQ about pressure relief valve and pressure reducing valve

1. What exactly happens if the pressure relief valve replaced by a reducing valve?

Answer: The function of a pressure relief valve is to limit the maximum pressure in a hydraulic system. It closes normally and opens only when the system pressure exceeds the setting of the pressure relief valve, by releasing pressurized oil to the lower pressure side or tank. Whereas on the other hand, the pressure reducing valve limits the pressure for the system to less than the maximum pressure. It opens normally and closes only when the system pressure at the output of the reducing valve exceeds its set pressure. But if we replace a pressure relief valve with a pressure reducing valve, the required pressure cannot be generated. Because there is no longer the necessary restriction to generate pressure and the flow will be directed to the tank due to their constructional difference. For more understanding Read hydraulic symbols.

Hope, you like this article and learned the basic of pressure relief valve and pressure reducing valve.

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In brief, the hydraulic direction control valve is a device to direct the flow of fluid in a hydraulic or pneumatic system. It makes the hydraulic system to work repetitive.

As shown in figure 1. the pump will make the fluid to flow and extend the piston and does work. But, after complete extension, we can not retract the piston which is not intended. Therefore, we need something which makes our system repetitive. This is Direction control valve or in short DCV.

In the above figure 2. a hydraulic direction control valve (DCV) is used. In the central position, the cylinder will stay in its place and valve will be called in 0 positions or in the rest position. However, if it changes the position from 0 to b cylinder rod will extend. Similarly, when direction control valve changes its position from b to a cylinder rod will retract. Thus Hydraulic direction control valve makes the system repetitive and useful and we can get benefited to continue work.

Graphical symbol

Although the graphical symbol of the direction control valve depends on the number of port and number of position, however, figure 3 shows a general idea of the symbols. Here the number of square boxes indicates the number of positions whereas arrows indicate the direction of flow through the valve. Similarly, Closed paths show close ports. A and B are the working ports. P is the port connecting with the pump while T is the port connecting to the tank. So, this is a 4/3 direction control valve with 4 ports and 3 positions.

Here are some symbols of various hydraulic direction control valve

2/2 Direction Control Valve

3/2 Direction Control Valve

3/3 Direction Control Valve

2/2 Direction Control Valve

4/3 Direction Control Valve

5/2 Direction Control Valve

5/3 Direction Control Valve

6/3 Direction Control Valve

Controlling the hydraulic direction control valve

The hydraulic direction control valve can be controlled in various ways. However here are some mentioned.

1. Mechanically controlled.
2. Electrically controlled.
3. Pneumatically controlled.
4. Hydraulically controlled.
5. Controlled by combination of any of above.

The direction control valve either can be directl controlled or can be pilot controlled.

Illustrated figure. 4 is the example of 4/3 spring centred lever operated direction control valve.

Illustrated figure. 5 is the example of 4/3 spring centred electrically operated direction control valve.

Illustrated figure. 6 is the example of 4/3 spring centred electro-pneumatic operated direction control valve.

Illustrated figure. 7 is the example of 4/3 spring centred electro-hydraulic operated direction control valve.

Illustrated figure. 8 is the example of 4/3 spring centred electro-pneumatic operated direction control valve.

Hydraulic direction control valve types

1. Spool type
2. rotary type

Spool type

Rotary type

Spooling Position of 4/3 hydraulic direction control valve

1. Open centre: In this 4/3 DCV all the ports are connecting with each other in centre position.

2. Close Center: In this 4/3 DCV all the ports are blocked in center position.

3. Float center: In this 4/3 DCV pressure port is block but working ports are connected with the tank in cente position.

4. Tandem Center: In this 4/3 DCV, pressure port and tank port are connected in center position but working ports are blocked.

So, this is the brief description of Hydraulic direction control valve. Hope you learned something.

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You have read in article Hydraulic basic principle-part I how hydraulic jack works. Now consider the following example

Pressure will build up when pumping the lever on a car jack. The load will lift. But what would happen here if you let go off the lever? The piston will come again to its initial position. But your requirement is to lift the load and hold it in lifted position. For this you need to maintain the built-up pressure.

The solution is non-return valve or check valve. It will allow the flow in only one direction but in opposite direction it will restrict the flow. In the above jack a flap valve is used as a non-return valve.

Similarly, in hydraulic system we use the check valve or non-return valve to maintain pressure and to allow the flow in only one direction.

Spring Loaded Check valve

Most of the check valve is coming with a spring. This check valve type is called spring loaded check valve. The function of a spring-loaded check valve is to open and allow flow in one direction only when pump-side pressure is more than the spring pressure.

Here in figure 5, it is a ball type check valve. However, there are various design of check valve. Some are poppet type, disc type and diaphragm type.

Pilot operated check valve

Function of pilot operated check valve or reversible check valve is quite interesting. As the check valve does not allow reverse flow but reversible check valve will allow only when there is a sufficient pressure in control line to open the ball. See figure 6.

In figure 6 when pump is on and direction control valve in position b then cylinder will extend against the load. The pump will built pressure. First check valve behaves like normal check valve but second check valve will restrict the return line flow from rod side. But the pressure line will control the pilot line and open the ball to allow return line flow to tank. Hence, a control pressure is required to allow flow in reverse direction.

Hope You enjoy this artical and learnt somthing. Keep reading and stay in touch with us.

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Hydraulic Accumulator

In a hydraulic system, energy can transfer by means of pressure. Sometimes though it is also necessary to store hydraulic energy for a short time. Thus we use a hydraulic accumulator. As we store energy by compressing spring or inflating balloon similarly we can store energy in the accumulator in the same manner. We use pressure for storing energy in both spring and balloon. Below is some paragraph you can find the hydraulic accumulator working principle.

A hydraulic accumulator is used to store hydraulic energy by using the back pressure of gas, spring or weight. Hence we can categorize the accumulator in the following.

1. Gas pre-charged accumulator
2. Spring-loaded accumulator.
3. weight load accumulator.

1. Gas pre-charged hydraulic accumulator working principle

A gas pre-charged accumulator is charged with a non-toxic, non-reactive gas such as nitrogen. When the system’s hydraulic pressure increases above the accumulator charging pressure the gas begins to compress. Hydraulic oil starts to flow in the accumulator container. The gas and oil separate by means of some membrane. That happens until the gas pressure matches the hydraulic pressure. Hydraulic kinetic energy is now stored in potential energy in gas pressure. When the pressure in the hydraulic circuit declines, the same thing happens in the hydraulic accumulator. The gas expands again. The stored energy now converts back into motion. It pushes the hydraulic fluid back into the circuit until the gas pressure has dropped to the value of the hydraulic pressure or original pre-charge pressure whichever is more. In fact, the charging-discharging accumulator is very fast and happens at the same time with system pressure.

Now, we will see how accumulator can help us in hydraulic system in more details.

Let’s see how hydraulic accumulator can help in a hydraulic system

Let us consider an example, a hydraulic press is tasked with compressing a workpiece. It needs a lot of force (know why) to do that, but only at a low speed. It means we need high pressure with a low flow rate pump. The recirculation after pressing means piston for retraction does not need much force, but it needs to go quickly, which means low pressure and high flow rate pump. To full fill both condition we need to adjust the pump which is pretty expensive.

But, the hydraulic accumulator gives the solution. We can use a pump having high pressure and a low flow rate with the addition of accumulator to the delivery of the pump.

As shown in figure 4 accumulator is installed between the pump and direction control valve. The pump’s flow rate is enough for pressing at low speed. The high pressure during pressing compresses the gas in the hydraulic accumulator and it charges itself with liquid. As soon as the retraction of piston starts due to less load restriction pressure will drop in the circuit. Therefore, the gas in the hydraulic accumulator expands pushes out the liquid and increases the flow rate. The press can, therefore, return faster than with just the pump’s flow rate.

Types of the pre-charged gas accumulator.

• Bladder type
• Diaphragm type
• Piston type

The use of these various accumulators depends on the pressure and volume required in the system. Bladder and diaphragm type accumulator is used for moderate pressure and less volume (0.5 to 500 liters). But its response time is quick. On the other hand, the piston-type accumulator is used for high pressure and large volume (more than 500 liters). But it has low response time because of piston large mass. Lastly, the pre-charged gas accumulator should mount in the specified position as per design for better results.

2. Spring-loaded hydraulic accumulator working principle

In the spring-loaded hydraulic accumulator, there is a spring along with container & movable piston. A spring-loaded accumulator can mount in any position. However, the spring force is not easy to adjust. These springs create the required pressure on the hydraulic piston to pump out fluid. The amount of pumping depends upon the compression rate of the spring. The main advantage of this type of hydraulic accumulators is that they are comparatively small in size, have a low weight and are easy to assemble in the hydraulic system and at the same time cost-effective. They can be used as mobile hydraulic accumulators due to their lightweight. Because of limitations on spring sizes, the use of this accumulator is impractical where a large volume of fluid is required.

3. Weight loaded hydraulic accumulator working principle

The weight loaded type was the first used but is much larger and heavier for its capacity than modern piston and bladder types. On the other hand, it is the only type of accumulator where the pressure is constant, whether the chamber is full or nearly empty (you can know here why). It is heavy & bulky, making the use limited. For example, it is used in heavy presses where constant pressure is required.

Example: Accumulator use for damping in the automobile.

For damping of undesirable pressure spikes and fluctuation, we can use an accumulator. For example, hydro-pneumatic shock absorber in vehicles as shown in figure 7. It basically consists of a hydraulic cylinder and a gas pre-charged accumulator. If bumps in the road push the wheel upwards, the pressure in the hydraulic fluid increases abruptly. It is pushed into the hydraulic accumulator and compresses the gas present there. As a result, the gas acts as a spring. The shock’s pressure and motion are absorbed and only transmitted to the vehicle in dampened form.

As the wheel’s pressure on the hydraulic fluid attenuates after the shock, the gas in the hydraulic accumulator expands again due to the attenuated backpressure and pushes the liquid back into the cylinder.

The above example is also applicable in damping in the hydraulic system. When the hydraulic direction control valve changes position rapidly then accumulator comes into play and absorbs the sudden pressure fluctuation.

Maintenance of Accumulator

Hydraulic pre-charged does not require much maintenance but gas pressure is to be regularly checked.

For example. In a piston-type accumulator, if the charging pressure is too high, the hydraulic fluid will be completely pushed out of the accumulator at minimum operating pressure. The piston strikes the hydraulic connection and can be damaged.

The opposite happens when there is too little charging pressure. The piston is pushed completely upward against the gas valve at maximum operating pressure, and can also be damaged.

Similarly, in bladder and diaphragm type the separating membrane can be damaged due to incorrect charging pressure.

On the other hand, due to incorrect gas-charged, the usable volume of hydraulic fluid needed for the system changed. These results alter the behavior of the system and can damage other hydraulic components.

The procedure of gas charging

• Firstly, the hydraulic system must not be pressurized
• The charging equipment should directly connect to the accumulator gas valve.
• There must an integrated gauge in the charging kit which will the show prevailing gas pressure of the accumulator.
• To charge, connect a commercially available gas cylinder to the equipment using a flexible hose.
• There should be two control valves for controlling the amount of gas in an accumulator. One will control the gas cylinder and one will control accumulator gas.
• After connecting the charging kit, the first thing is to open the check nut of the accumulator. Then open cylinder control valve little and open the accumulator gas control valve. After that check for leakage and then close completely.
• If there is no leakage the then completely open the cylinder gas control valve. And by accumulator gas control valve charge the accumulator with the required pressure. Then tight the check nut. Do not over tight and damage the check nut.
• Then First close the cylinder control valve and then remove the charging kit from the accumulator gas valve.

Safety regarding accumulator

1. Do not weld the accumulator. It may damage the accumulator and cause serious injury.
2. Do not drill for fastening with bolts.
3. Only secure the accumulator instructed by manual like secure with strap in instructed position.
4. Before maintenance release the accumulator pressure securely. It may store pressure energy even in stop condition and cause serious injury.

Hope you enjoyed this article. See you in next article. Till then bye bye.

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In this article we will learn about the hydraulic tank basic concept, its design, tasks, components, the importance of pressure ratio in a hydraulic tank, which component is responsible for which task & hydraulic tank types. So, be ready for an adventurous journey of knowledge.

Hydraulic fluid is the media that transfers force with the help of pressure & flow. Therefore, the amount of hydraulic fluid is very important in a hydraulic system and it depends on force multiplication and motion multiplication. For example,

We have read in How hydraulic works: Basic- Part-I that how simple hydraulic jack works and help to lift heavy load such as car’s wheels. For example, in figure 2 this amount of hydraulic oil is not sufficient for lifting tire enough to change. So, what we can do?

Here is some solution for that situation.

1. Either lengthen the stroke of the pump. Means increase the pump’s cylinder length.
2. Either reduce the area of the lifting cylinder.
3. Top up the hydraulic fluid and pump again.

By the first method, you can make available more hydraulic fluid to pump, however, it is not convenient because it makes the jack bulkier, bigger and heavier. So, it is not an applicable daily practice.

The second answer, reducing the area of lifting cylinder will reduce the consumption of hydraulic fluid and cause long-stroke, however, it is not convenient because now force multiplication is less and more force required.

The third solution is best and suitable. we can top up the fluid from a separate supply of fluid and pump again as much we need.

Introduction of the hydraulic tank in the system

In this diagram, we are seeing a hydraulic tank that provides fluid to the system whenever needed and directed back to the hydraulic tank when it is no longer needed. In this diagram, we also see two flap gate (check valve)
To lift the vehicle, the hydraulic fluid is pumped out of the hydraulic tank and into the lifting cylinder while these flap gates prevent the fluid to push back into the pump cylinder or to the tank. And for lowering the lifting cylinder there is another valve in a separate return line call the coke valve that needs to be open which will direct the fluid back to the tank.

But the hydraulic tank is not only for storing the hydraulic fluid. Now we will find a more significant purpose of a hydraulic tank.

Hydraulic tanks do not just hold hydraulic fluid; they often full fill other tasks, such as:

• Calming the hydraulic fluid.
• Gas purging.
• Cooling Hydraulic Fluid.
• Cleaning the hydraulic fluid.

Calming hydraulic oil is one of the most important tasks for a hydraulic tank. The liquid might flow very quickly back into the tank. That can cause the formation of foam and air inclusions. The pump should not suck them in. That is why the tank has to be constructed so that the flow calms down well.

Gas purging is also one of the hydraulic tank’s tasks. The hydraulic fluid can contain air, for instance in the form of tiny air bubbles. This air in the tank must be able to escape from the liquid as much possible.

While we performing any hydraulic operation, hydraulic fluid gets heat up due to friction and it may also heat up due to working in high-temperature environments such as processing of hot red metal. Therefore, the hydraulic fluid must be cool down somewhere in a hydraulic system and this task is being done in a hydraulic tank.

In the hydraulic system, there are plenty of moving parts. Due to these moving parts wear and tear occurs. Also, seals will damage. These all unwanted particles are carried by the hydraulic fluid as dirt. So, the filtering of hydraulic fluids becomes much more important. Without filtering, if hydraulic fluid is used it may cause some catastrophic damage.

Now, we will see the basic design and component of hydraulic tank.

Basic Design of hydraulic tank or reservoir.

Suction Line:

The suction line connects the hydraulic tank to the pump. After that hydraulic fluid goes to the circuit. Suction pipes generally have a larger diameter as compared to return lines. Suction pipes have a smaller length so as to facilitate lesser loss and cavitation.

Return Line:

After performing the necessary task hydraulic fluid comes back to the tank by return line through the return manifold and return filter. The return line end should not be too high from the bottom of the reservoir as the too high an outlet will cause turbulence to the output flow. Normally the return line ends are taper cut to facilitate the flow direction towards the wall side. This will help the fluid to travel a larger distance so that it gets more time to cool.

Access Plate:

the access plate is for cleaning the tank.

Suction Strainer:

The strainer is placed in the suction line of the pump. This provides filtered hydraulic fluid to the pump. It typically has some filtering screens (for particles of a particular size) that filters the contaminants before going to the pump. This is periodically replaced to ensure uninterrupted flow.

Baffle Plate: 

Baffle plates are normally the steel plates that are incorporated in the reservoir to divide the fluid into different chambers so that the fluid has to travel through other ways to get to the suction chamber from the return flow chamber. As a result, oil gets cool and contaminants set at the bottom of the chamber. It gives them time to hydraulic oil for suppressing, calming, and gas purging.

Breather:

This is the opening for equalization of air pressure when fluid level changes.  A filter for a breather protects the fluid from dirt. It is important to understand that too small a breather cap or choked filter will cause a vacuum in the oil tank and cause cavitations in the pumps. So, it needs extra care.

Oil level gauge:

In a hydraulic tank, an oil level gauge shows the level of oil. commonly there are two lines in gauge. one for a high level and one for a low level.

Filler cap:

The filler is for top-up the hydraulic oil.

Next, we will see Processes in the hydraulic tank and combine all tasks of a hydraulic tank.

Processes in the hydraulic tank

The return-line filter first cleans dust particles from the recycled hydraulic fluid. The liquid still has a strong current upon entering the re-circulation area. The calming baffle suppresses the flow’s motion and prevents it from spreading to the suction area. Any air bubbles that might be present rise to the surface of the liquid and escape into the tank. Excess air escapes from the tank to the outside via a breather (ventilation and exhaust). The liquid flows into the suction area through openings in the calming baffle’s floor area. The liquid dissipates heat to the outer air over the hydraulic tank’s entire surface, thereby cooling it.

Types of hydraulic tank or reservoir

For the proper function of a pump, the pump needs a continuous feed of fluid. And therefore, the pressure at the suction line must be great enough. When the tank is full, the pressure at the inlet will be great enough (liquid pressure + atmospheric pressure). That is why much fluid is available for suction but if the fluid is just above the inlet then the pressure will be less enough and cause less fluid available for suction which can create a cavity in the pump.

In this way, we can categories hydraulic into two types.

1. Atmospheric tank
2. Pressure tank.

Atmospheric Hydraulic Tank

Atmospheric Tank: Because of the atmospheric tank is open with the atmosphere via a breather so, pressure on the suction line depends only on the liquid level. Hence, we can not increase the pressure anymore. The total pressure will be the sum of pressure due to liquid level and atmospheric pressure

Pressurised Hydraulic Tank

Pressure tank: In a pressure tank firstly, pressurized air is fed from external to maintain the required pressure, and the second thing pressure regulator is added for regularising the pressure. As a result, if pressure exceeds the required pressure a spring-loaded check valve releases the pressure and if pressure is lowered below the atmospheric second check valve will allow atmospheric air into the tank.

We have completed all the basics of hydraulic tank and their types. Hope you learned something and will come soon for another interesting article. Till then bye-bye. Thank you.

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Pressure Multiplication

As we read in the previous article ‘How Hydraulic works: Basics Part-I‘ we knew how force is multiplying in hydraulic system. But its reverse is similarly correct. In other words we can multiply pressure according to our use i.e Pressure Multiplication.

Sometimes for industrial use we have to increase the pressure without increasing the force, like high pressure pump for fuel injection. Then we can use this method for increasing pressure with the help of low pressure.

We know that Pressure,

p = F/A

Let the force ‘F’ acts over an area ‘A1’ and then reduce the area by ‘A2’ it will increase the pressure or we can say we multiplication of pressure.

Let, p1 = 10 bar (Low pressure available)

Note: bar is the unit of pressure usually use in industrial application.

1 bar = 100000 N/m²

A1 = 100 cm²

A2 = 1 cm²

F1 = p1 X A1

F1 = 10 x 100 = 1000

Same force will act on area A2,

p2 = F/A2

p2 = 1000/1 = 1000 bar.

Hence, we multiplied the pressure 100 times with the available pressure. Similarly like we multiply the force.

Pressure multiplication in double acting cylinder.

Here is one of the reason for cylinder seal damage. As per the pressure multiplication theory you know even there is low pressure in larger area (piston end) pressure may be much higher in other end of the piston (rod end) due to less area available.

Now, suppose if system pressure for preventing the damage of cylinder seal is 250 bar. This mean maximum pressure should not increase 250 bar ever. But due to some reason your rod end is block and now hydraulic oil is not flowing from rod end. If you have set pressure relief valve on 250 bar and at your piston end you have maximum 250 bar then definitely due to pressure multiplication, the rod end pressure will much higher then 250 and ultimately damage the seal.

In conclusion, if we are using pressure multiplication according to our purpose then it is beneficial but however it has negative effects too. So, be care full and must consider this effects while setting maximum pressure of system.

This pressure multiplication is also known as Pressure Intensification.

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The post How Hydraulic works: Basics Part-II appeared first on Stuffworking.com.

Before going to understand Hydraulics one must have some knowledge of Physics. Because, it will help for better understanding of basic concepts, how hydraulic works and where to use it. Read this article and after that you will be able to understand some basic physics & basic hydraulics. So, have fun.

Some basic physics which we need for basic hydraulics are
Mass, Force, Pressure, Work, Energy, Pressure Ratio, Force multiplication.

Mass:- The amount of matter present in an object is call mass.

Force:- It is the push or pull which can change or tends to change the state of rest or uniform motion of a body, change the shape of the body or change the direction of the motion.

Pressure:- It is force applying perpendicular to a surface per unit area on a body.

Work:- Work is said to done if force is applied on an object and it gets some displacement in the direction of force.

Energy:- Energy is the ability of doing work.

Now suppose your vehicle’s tyre gets flat. what do you do? Of course the first thing you try to find a jack. If you found a hydraulic jack it would be more easier for you to lift the vehicle and change your flatted tyre.

Hydraulic Jack

In this simple Diagram you can see a small piston and a big piston. we apply a small force in small piston as in our hydraulic jack but it lift heavy load like car.

As we know pressure is equal to perpendicular force on a surface per unit area. i.e: P=F/A. means larger the area lesser the pressure or vice versa.

The post How Hydraulic works: Basic Part-I appeared first on Stuffworking.com.