pressure compensated hydraulic pump how it works for sale

Hydraulic pumps are an incredibly important component within hydraulic systems. IFP Automation offers a variety of pump and hydraulic system products that deliver exceptional functionality and durability. Our partner Parker’s extensive line of hydraulic pumps deliver ideal performance in even the most demanding industrial and mobile applications. In this post, we are going to spend time discussing pressure compensated and load sensing hydraulic pumps.

Do to the surface area of the servo piston and the pressure exerted on that area, a force is generated that pushes the swash plate of the pump to a lower degree of stroke angle.

The pump tries to maintain compensator setting pressure, and will provide whatever flow (up to it’s maximum flow rate) that is necessary to reach that pressure setting.

For more information on how you can make use of hydraulic pump technology in your applications, please contact us here to receive a personalized contact by an IFP Application Engineer:

IFP Automation supplies innovative technology and design solutions to the automation and mobile marketplaces.  Our firm is a technology supplier specializing in the design and supply of automation and motion control products to OEM, integrator, and end user customers. Companies partner with IFP because they like the depth of our product and application knowledge and our commitment to outstanding customer service.

A pressure compensator is a device built into some pumps for the purpose of automatically reducing (or stopping) pump flow if system pressure sensed on the pump outlet port, should rise above a pre-set desired maximum pressure (sometimes called the "firing" pressure). The compensator prevents the pump from being overloaded if an overload is placed on the hydraulic system.

A compensator is built into the pump at the factory and usually cannot be added in the field. Any pump built with variable displacement can be controlled with a compensator. These include several types of axial piston pumps and unbalanced (single lobe) vane pumps. Radial piston pumps can sometimes be built with variable displacement but do not lend themselves readily to this action. Most other positive displacement pumps including internal and external gear, balanced (double lobe) vane, gerotor, and screw types cannot be built with variable displacement.

Figure 1 is a schematic of a check valve axial piston pump, variable displacement, controlled with a pressure compensator. The pistons, usually 5, 7, or 9 in number, are stroking inside a piston block which is keyed to and is rotating with the shaft. The left ends of the pistons are attached through swivel joints, to piston shoes which bear against and slide around on the swash plate as the piston block rotates. The swash plate itself does not rotate; it is mounted on a pair of trunnions so it can swivel from neutral (vertical) position to a maximum tilt angle. The angle which the swash plate makes to the vertical causes the pistons to stroke, the length of stroke being proportional to the angle. Normally, at low system pressures, the swash plate remains at its maximum angle, held there by spring force, hydraulic pressure, or by the dynamics of pump construction, and pump flow remains at maximum. The compensator acts by hydraulic pressure obtained internally from the pump outlet port. When pump pressure rises high enough to over-come the adjustable spring behind the compensator piston, the "firing" pressure has been reached, and the compensator piston starts to pull the swash plate back toward neutral, reducing pump displacement and output flow. The spring in the compensator can be adjusted for the desired maximum or "firing" pressure.

Under working conditions, on a moderate system overload, the compensator piston reduces the swash plate angle just enough to prevent the system pressure from exceeding the "firing" pressure adjusted on the compensator. On severe overloads the compensator may swing the swash plate back to neutral (vertical) to reduce pump flow to zero.

Maximum Displacement Stops. Some pumps are available with internal stops to limit the tilt angle of the swash plate. These stops limit the maximum flow and limit the HP consumption of the pump. They may be fixed stops, factory installed and inaccessible from the outside, or they may be externally adjustable with a wrench.

Manual Control Lever. Some pressure compensated pumps, especially hydrostatic transmission pumps, are provided with an external control lever to enable the operator to vary the swash plate angle (and flow) from zero to maximum. On these pumps the pressure compensator is arranged to override the manual lever and to automatically reduce the swash plate angle if a system overload should occur even though the operator control lever is still shifted to maximum displacement position.

Basically the pressure compensator is designed to unload the pump when system pressure reaches the maximum design pressure. When the pump is unloaded in this way, there is little HP consumed and little heat generated even though pressure remains at the maximum level, because there is no flow from the pump.

Variable displacement pumps are usually more expensive than fixed displacement types, but are especially useful in systems where several branch circuits are to be supplied from one pump, and where full pressure may be required simultaneously in more than one branch, and where the pump must be unloaded when none of the branches is ill operation. If individual 4-way valves are used in each branch, each valve must have a closed center spool. The inlet ports on all 4-way valves must be connected in parallel across the pump line. However, if all branch circuits are operated from a bank valve of the parallel type, a pressure compensated variable displacement pump may not be necessary; a fixed displacement pump, gear, vane, or piston, may serve equally well because the bank valve will unload the pump when all valve handles are placed in neutral, but when two or more handles are simultaneously shifted, their branch circuits will automatically be placed in a parallel connection.

As in all hydraulic systems, more pump oil will flow to the branch with the lightest load. Bank valve handles can be modulated to equalize the flow to each branch. When individual 4-way valves are used in each branch, flow control valves may be installed in the branch circuits and adjusted to give the flow desired in each branch.

Figure 2 shows a multiple branch circuit in which a variable displacement pump is used to advantage. Individual 4-way valves, solenoid operated, are used for each branch, and they have closed center porting. Please refer to Design Data Sheet 54 for possible drift problems on a pressure manifold system. A pressure relief valve is usually required even with a pressure compensated pump due to the time interval required for the swash plate to reduce its tilt angle when a sudden overload occurs. The relief valve will help absorb part of the pressure spike generated during this brief interval. It should be adjusted to crack at about 500 PSI higher than the pressure adjustment of the compensator piston spring to prevent oil discharge across it during normal operation.

All hydrostatic transmission systems use a variable displacement pump with pressure compensator, and often combine the compensator with other controls such as the horsepower input limiter, load sensing, flow sensing, or constant flow control.

© 1990 by Womack Machine Supply Co. This company assumes no liability for errors in data nor in safe and/or satisfactory operation of equipment designed from this information.

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These pumps are designed for applications where light weight design, lower displacements, and multiple configuration capabolities are design requirements.

This Pressure Compensated Piston Pump is one of many pumps that the Hydraulic Megastore has to offer and they are all available for next day delivery.

There are typically three types of hydraulic pump constructions found in mobile hydraulic applications. These include gear, piston, and vane; however, there are also clutch pumps, dump pumps, and pumps for refuse vehicles such as dry valve pumps and Muncie Power Products’ Live PakTM.

The hydraulic pump is the component of the hydraulic system that takes mechanical energy and converts it into fluid energy in the form of oil flow. This mechanical energy is taken from what is called the prime mover (a turning force) such as the power take-off or directly from the truck engine.

With each hydraulic pump, the pump will be of either a uni-rotational or bi-rotational design. As its name implies, a uni-rotational pump is designed to operate in one direction of shaft rotation. On the other hand, a bi-rotational pump has the ability to operate in either direction.

For truck-mounted hydraulic systems, the most common design in use is the gear pump. This design is characterized as having fewer moving parts, being easy to service, more tolerant of contamination than other designs and relatively inexpensive. Gear pumps are fixed displacement, also called positive displacement, pumps. This means the same volume of flow is produced with each rotation of the pump’s shaft. Gear pumps are rated in terms of the pump’s maximum pressure rating, cubic inch displacement and maximum input speed limitation.

Generally, gear pumps are used in open center hydraulic systems. Gear pumps trap oil in the areas between the teeth of the pump’s two gears and the body of the pump, transport it around the circumference of the gear cavity and then force it through the outlet port as the gears mesh. Behind the brass alloy thrust plates, or wear plates, a small amount of pressurized oil pushes the plates tightly against the gear ends to improve pump efficiency.

A cylinder block containing pistons that move in and out is housed within a piston pump. It’s the movement of these pistons that draw oil from the supply port and then force it through the outlet. The angle of the swash plate, which the slipper end of the piston rides against, determines the length of the piston’s stroke. While the swash plate remains stationary, the cylinder block, encompassing the pistons, rotates with the pump’s input shaft. The pump displacement is then determined by the total volume of the pump’s cylinders. Fixed and variable displacement designs are both available.

With a fixed displacement piston pump, the swash plate is nonadjustable. Its proportional output flow to input shaft speed is like that of a gear pump and like a gear pump, the fixed displacement piston pump is used within open center hydraulic systems.

As previously mentioned, piston pumps are also used within applications like snow and ice control where it may be desirable to vary system flow without varying engine speed. This is where the variable displacement piston pump comes into play – when the hydraulic flow requirements will vary based on operating conditions. Unlike the fixed displacement design, the swash plate is not fixed and its angle can be adjusted by a pressure signal from the directional valve via a compensator.

Flow and Pressure Compensated Combined – These systems with flow and pressure compensation combined are often called a load-sensing system, which is common for snow and ice control vehicles.

Vane pumps were, at one time, commonly used on utility vehicles such as aerial buckets and ladders. Today, the vane pump is not commonly found on these mobile (truck-mounted) hydraulic systems as gear pumps are more widely accepted and available.

Within a vane pump, as the input shaft rotates it causes oil to be picked up between the vanes of the pump which is then transported to the pump’s outlet side. This is similar to how gear pumps work, but there is one set of vanes – versus a pair of gears – on a rotating cartridge in the pump housing. As the area between the vanes decreases on the outlet side and increases on the inlet side of the pump, oil is drawn in through the supply port and expelled through the outlet as the vane cartridge rotates due to the change in area.

Input shaft rotates, causing oil to be picked up between the vanes of the pump which is then transported to pump outlet side as area between vanes decreases on outlet side and increases on inlet side to draw oil through supply port and expel though outlet as vane cartridge rotates

A clutch pump is a small displacement gear pump equipped with a belt-driven, electromagnetic clutch, much like that found on a car’s air conditioner compressor. It is engaged when the operator turns on a switch inside the truck cab. Clutch pumps are frequently used where a transmission power take-off aperture is not provided or is not easily accessible. Common applications include aerial bucket trucks, wreckers and hay spikes. As a general rule clutch pumps cannot be used where pump output flows are in excess of 15 GPM as the engine drive belt is subject to slipping under higher loads.

What separates this pump from the traditional gear pump is its built-in pressure relief assembly and an integral three-position, three-way directional control valve. The dump pump is unsuited for continuous-duty applications because of its narrow, internal paths and the subsequent likelihood of excessive heat generation.

Dump pumps are often direct mounted to the power take-off; however, it is vital that the direct-coupled pumps be rigidly supported with an installer-supplied bracket to the transmission case with the pump’s weight at 70 lbs. With a dump pump, either a two- or three-line installation must be selected (two-line and three-line refer to the number of hoses used to plumb the pump); however, a dump pump can easily be converted from a two- to three-line installation. This is accomplished by inserting an inexpensive sleeve into the pump’s inlet port and uncapping the return port.

Many dump bodies can function adequately with a two-line installation if not left operating too long in neutral. When left operating in neutral for too long however, the most common dump pump failure occurs due to high temperatures. To prevent this failure, a three-line installation can be selected – which also provides additional benefits.

Pumps for refuse equipment include both dry valve and Live Pak pumps. Both conserve fuel while in the OFF mode, but have the ability to provide full flow when work is required. While both have designs based on that of standard gear pumps, the dry valve and Like Pak pumps incorporate additional, special valving.

Primarily used on refuse equipment, dry valve pumps are large displacement, front crankshaft-driven pumps. The dry valve pump encompasses a plunger-type valve in the pump inlet port. This special plunger-type valve restricts flow in the OFF mode and allows full flow in the ON mode. As a result, the horsepower draw is lowered, which saves fuel when the hydraulic system is not in use.

In the closed position, the dry valve allows just enough oil to pass through to maintain lubrication of the pump. This oil is then returned to the reservoir through a bleed valve and small return line. A bleed valve that is fully functioning is critical to the life of this type of pump, as pump failure induced by cavitation will result if the bleed valve becomes clogged by contaminates. Muncie Power Products also offer a butterfly-style dry valve, which eliminates the bleed valve requirement and allows for improved system efficiency.

It’s important to note that with the dry valve, wear plates and shaft seals differ from standard gear pumps. Trying to fit a standard gear pump to a dry valve likely will result in premature pump failure.

Encompasses plunger-type valve in the pump inlet port restricting flow in OFF mode, but allows full flow in ON mode lowering horsepower draw to save fuel when not in use

Wear plates and shaft seals differ from standard gear pumps – trying to fit standard gear pump to dry valve likely will result in premature pump failure

Live Pak pumps are also primarily used on refuse equipment and are engine crankshaft driven; however, the inlet on a Live Pak pump is not outfitted with a shut-off valve. With a Live Pak pump, the outlet incorporates a flow limiting valve. This is called a Live Pak valve. The valve acts as an unloading valve in OFF mode and a flow limiting valve in the ON mode. As a result, the hydraulic system speed is limited to keep within safe operating parameters.

Outlet incorporates flow limiting valve called Live Pak valve – acts as an unloading valve in OFF mode and flow limiting valve in ON mode restricting hydraulic system speed to keep within safe operating parameters

Pressure compensated hydraulic systems are becoming more popular due to their high efficiencies. These systems run great when properly applied but there are things you should know before you run a pressure compensated system.

Heat and contamination are the two leading causes of failure in a hydraulic system; if both aren’t properly maintained then your system will inevitably fail. For now, let’s focus on the heat. Heat can be a hard culprit to chase down when starting a prototype system. Two major factors of heat generation in a pressure compensated system are relief valve heat and standby heat.

When first starting up a pressure compensated hydraulic system, you have to always set the pressures on the pump’s compensator and the main system relief valve. Doing this properly is the key to avoiding heat generation. The compensator must always be set at a lower pressure than your system relief valve. If the system relief is lower or equal to the compensator setting, you will have constant flow over the main relief, which will then produce a ton of heat until the system fails. It is a safe practice to set your system relief valve 300 PSI above what your compensator is set at. This will ensure no flow is going over the relief during normal working conditions but will still protect your systems from any pressure spikes.

A cause of heat that is rarely considered – and to some, completely unknown – is the standby heat. The benefit of a pressure compensated pump is that it will destroke once the pressure builds to the compensator setting, therefore cutting off the pump flow but still maintaining the desired pressure. The downfall to this is that if you are running at a high pressure and are destroked at the compensator pressure, you are creating heat inside the case which will flow out of the case drain line and into your reservoir. Many may think of this as a minor amount of heat, but if a system is left sitting in this high-pressure standby state, the heat can become a major factor in your system. Below is a chart that shows just how much heat can be created at different pressures and speeds when sitting at compensator pressure.

Another option is to utilize a load sense compensator. With a load sense compensator, this compensator will include a lighter spring setting to control the swash plate. Upstream pressure is ported into a load sense port on the pump, as the pressure requirement increases, the pressure acts against the load sense piston. Once the pressure requirement is higher than the offset, the pump swash plate angle changes and the pump begins to increase flow, by increasing the swash plate angle, until we have enough pressure to balance the piston. Once balanced, the flow remains steady until the load changes.

The offset pressure is normally 200-300 PSI. With a load sense compensator, the pump produces what the load requires plus the spring offset, normally 200-300 PSI.

This system will also utilize a standard compensator so if the system pressure increases enough, the pressure compensator will take control and reduce the swash plate angle to reduce the pressure.

Let’s look at my initial application but this time, it has a varying load. They conveyor requires 1500 PSI to move 50% of the time, but the balance of the time the system requires between 2250-2500 PSI to move the load.

With a standard pressure compensator, you would have to set the pump at 2600 PSI to accomplish the work. When the work only requires 1500 PSI, the pump will be trying to produce 2600 PSI. Fifty percent of the time, your system will be operating at 1100 PSI of inefficiency, which means heat. With a load sense compensator, when the load requires 1500 PSI, the pump will actually produce about 17-1800 PSI. Yes, this is 300 PSI inefficient, but that is much better than 1100 PSI inefficient.

With a varying load, the load sense is a much better system. For additional control, you can utilize an electronic proportional flow control or throttle. You can use an electrical signal to vary the hydraulic signal which is received by the pump’s load sense line. This would give you full electronic control of the amount of flow the pump produces.

There are additional control options which allow you to remotely control the pressure compensator. With this remote compensator control, you can set 2 or more different system pressures. With the ability of a variable piston pump to build 5,000 or more PSI; the additional setting can be used when operating components with a much lower pressure requirement.

The next control is a torque limiting or HP limiting control. By adding an additional spring and piston, you can set a pump to always maximize its allowable input torque, therefore, maximizing output flow and pressure at a defined setting.

In this application, you are operating large bore, long strong cylinder. The cylinder has a 10” bore and 150” stroke. During most of the stroke, the cylinder is not doing very much work and can operate at 800-1200 PSI. During the last 20” of stroke, we want to hit our system pressure of 4500 PSI, but we can move much slower.

Our pump has an output of 15 CIR, a maximum flow of about 113 gallons at 1750 RPM. Our prime mover is an electric motor, 75HP with a 1.15 service factor. I want to keep my cylinder moving as fast as possible, but I also want to ensure that I never exceed a power demand 82 HP.

At 82 HP, the pump can produce 1254 PSI at full output, 113 GPM. As the load requires more pressure, the pump will begin to reduce flow and increase pressure. At 90 GPM flow, the system will produce about 1560 PSI; at 60 GPM we can get almost 2350 PSI. At 4500 PSI, the pump flow will be reduced to about 31 GPM. The advantage of this pump is that the internal controls of the pump are adjusting to maximize flow and pressure at all times without exceeding the available HP.

If I wanted to use a pump which could produce 113 gallons of flow at 4500 PSI, I would need 296 HP. If I choose a 75 HP motor with a pressure compensated variable piston pump, the motor would stall before the pressure compensator could kick in and reduce the pump flow. Depending on the load, a load sense pump could also stall the 75 HP motor if the load pressure is high enough to use up the HP before the pressure compensator kicks in. With a torque limiting (HP) control, we utilize the full limits of the prime mover and maximize power usage.

series: PCP10max flow: 10.5 GPMHyvair’s line of pressure compensated industrial piston pumps (PCP) are stocked with displacements from 0.49 cu.in/r. (8.0cc) to 4.27 cu.in/r. (70.0cc) and continuous pressure up to 3,000 PSI. All sizes in our industrial line are available with multiple control options from load sensing to dual pressure solenoid. Through drives are available on all pump sizes except the PCP33. The semi-cylindrical swash plate design allows for smooth, stable operation, increases efficiency and reduced noise by sealing pressure on its face. catalog pdf Cad File

Hyvair Corp. distinguishes itself from other component and system companies with total customer service. From design support in the earliest phases of your project, to just-in-time deliveries to meet your customer"s production schedule, Hyvair works with you as a team member - not just a supplier.

series: PCP8max flow: 7.8 GPMHyvair’s line of pressure compensated industrial piston pumps (PCP) are stocked with displacements from 0.49 cu.in/r. (8.0cc) to 4.27 cu.in/r. (70.0cc) and continuous pressure up to 3,000 PSI. All sizes in our industrial line are available with multiple control options from load sensing to dual pressure solenoid. Through drives are available on all pump sizes except the PCP33. The semi-cylindrical swash plate design allows for smooth, stable operation, increases efficiency and reduced noise by sealing pressure on its face. catalog pdf Cad File

Hyvair Corp. distinguishes itself from other component and system companies with total customer service. From design support in the earliest phases of your project, to just-in-time deliveries to meet your customer"s production schedule, Hyvair works with you as a team member - not just a supplier.

Flexible and high-performing, the PVP Series hydraulic piston pump increases uptime with fast and reliable variable volume pumps engineered for medium pressure applications. PVP pumps feature thru-shaft capability and high-strength construction for greater productivity, while improving the work environment with quiet pump technology for reduced noise levels and easy-to-service components.

By maintaining the pressure and flow when demanded, internal leakage is reduced, generating less unwanted heat. Also, less strain is put on hoses and seals, providing a more reliable system. The use of flat-face O-ring face seal fittings and snap-to-connect fittings provide leak-free connections.

The integration of pumps, filter housing, and priority valve results in fewer and shorter lines, providing added reliability for greater productivity and less pressure loss and less flow restrictions.

The integrated pump assembly is attached to the right side of the pump drive housing. The charge pump section is a constant-flow gear-type pump. It draws oil through a suction screen from the rear differential case, providing low-pressure oil to the dual filtering system and to the integrated axial piston pump. Filtered oil not required by the integrated axial piston pump is routed to the clean oil reservoir for transmission and ground-drive pump usage.

Integrated axial piston pump is available in two sizes, 63 cc and 85 cc displacement. They are pressure-flow compensated axial piston pumps and provide oil to steering, brakes, hitch, SCVs, as well as ILSTM, ActiveSeatTM, and for power-beyond functions if equipped.

All functions return oil to the integrated dual filtering system, making oil available to the integrated axial piston pump. Oil not required by the integrated axial piston pump is supplied to the clean-oil reservoir.

Clean-oil reservoir is located in the top portion of the pump drive housing and holds 9.5 gallons of filtered oil. It receives excess oil that the integrated axial piston pump does not need. It serves as a reservoir for filtered oil to be used by the transmission pumps. When needed, it also supplies filtered oil to the ground-drive pump and the integrated axial piston pump. Also, with the use of large single-acting cylinders, the integrated axial piston pump may draw oil from the clean-oil reservoir as needed. Reservoir overflow oil provides lubrication for spiral gear set in differential.

Hydraulic system protection is provided by an oil level switch located in the clean-oil reservoir. If oil level is low, secondary functions (SCV, hitch, power beyond) will be reduced, maintaining oil for steering and brakes. At the same time, an indicator light and code will be generated, notifying the operator of a low-oil situation. This is to assure oil will be available for steering and brakes. Once oil level is satisfactory, secondary function will be restored and the indicator will stop.

There is also a temperature sensor located in the clean-oil reservoir. It is there to protect the transmission. The engine rpm will be reduced to 1500 rpm and only certain transmission speed will be obtained with cold oil. Once oil temperature is acceptable, complete engine and transmission functions will be resumed.

Priority valve is also integrated with the hydraulic pumps and the filter housing, resulting in fewer and shorter lines providing added reliability. It ensures that oil supply is available for steering and brakes. Excess oil is then available for other hydraulic sys­tem functions such as SCVs, hitch, power beyond, ILS, and Active Seat.

Filters: Two 10 micron filters working in parallel filtering hydraulic and transmission oil results in 17% more flow capacity and extends filter service interval to 1500 hours.

IVT and PST transmission pumps are constant-flow gear-type pumps located on the left side of the pump drive housing. The inside pump section of the tandem pump on IVT"s supplies the transmission hydro unit. The outside pump section on IVT"s and the single pump on the PST"s perform the same functions. Not only do they provide oil for transmission functions, but they also supply hitch and SCV pilot stage oil and PTO and differential lock control oil.

Hydraulic systems are safer and easier to control than traditional motors. However, any machine can have issues. For instance, what should you do if the shaft seal fails on a pressure compensated pump?

A pressure compensated pump is a complex type of pump. For simpler pumps, turning it 360° will always release the same amount of oil. With a pressure compensated pump, however, the flow is adjustable. Sometimes it will release a certain amount, sometimes a different amount.

A pressure compensator is a device built into some pumps. It automatically reduces (or stops) pump flow if system pressure rises above a preset maximum (sometimes called the “firing” pressure). The compensator prevents the pump from being overloaded.

Most hydraulic industrial equipment is designed to work at about 2,000-3,000 PSI (pounds of pressure per square inch). There are two main ways a system can fail: having too little pressure or having too much.

When most pumps fail, pressure drops as fluid leaks out. But when pressure compensated pumps fail, they fail high. They build up too much pressure. This can cause many problems including shaft seal failures, where the shaft seal comes off and slings oil everywhere.

Such accidents are extremely rare, but it’s good to be prepared. A relief valve on your hydraulic system will prevent the pressure from building up too much. The valve will return liquid to the tank when there’s too much in the system. This will not only prevent your shaft seal from coming loose but will protect your whole system from a catastrophic failure.

When hydraulic industrial equipment fails, you can lose a lot of time and productivity waiting for repairs. Our certified team will come to you, performing on-site troubleshooting to minimize downtime and get your equipment running.