pressure compensated hydraulic pump how it works pricelist

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.

Piston pumps are durable and relatively simple devices. A basic piston pump is made up of a piston, a chamber, and two valves. The pump operates by driving the piston down into the chamber, thereby compressing the media inside. In a hand pump, this is usually air. Once the pressure of the air exceeds that of the outlet valve spring, the compressed media goes through the open outlet valve. When the piston is drawn back up, it opens the inlet valve and closes the outlet valve, thereby utilizing suction to draw in new media for compression.

Although somewhat expensive, piston pumps are among the most efficient types of pumps. They have an excellent pressure rating (as high as 10,000 psi), but their design makes them susceptible to contaminants. They provide an excellent solution for many high-pressure hydraulic oil pumping applications.

Axial piston pumps are positive displacement pumps that use multiple cylinders grouped around a central axis. The group of cylinders, usually containing an odd number, is called a cylinder block. The pistons within each cylinder are attached to a swashplate. The swashplate is also known as a cam or wobble plate and attaches to a rotating shaft. As the shaft turns, the angle of the swashplate changes, which drives the pistons in and out of their respective cylinders.

Since the swashplate is at an angle to the axis of rotation, the pistons must reciprocate axially as they orbit around the cylinder block axis. The axial motion of the pistons is sinusoidal. As a piston rises, it moves toward the valve plate. At this point in the rotation, the fluid trapped between the buried end of the piston and the valve plate is expelled to the pump"s discharge port through one of the valve plate"s semi-circular ports. As the piston moves back toward the valve plate, the fluid is pushed through the discharge port of the valve plate.

Axial piston pumps can be designed as variable displacement piston pumps, making them very useful for controlling the speeds of hydraulic motors and cylinders. In this design, a swashplate is used to vary the depth to which each piston extends into its cylinder as the pump rotates, affecting the volume of discharge. A pressure compensator piston is used in some designs to maintain a constant discharge pressure under varying loads. Cheaper pressure washers sometimes use fixed-rate designs.

In a typical pressure-compensated pump, the swashplate angle adjusts through the action of a valve using pressure feedback to make sure that the pump output flow is precisely enough to maintain a designated pressure. If the load flow increases, the pressure momentarily decreases, but the pressure-compensation valve senses the decrease and then increases the swashplate angle to increase the pump’s output flow, restoring the desired pressure.

Axial piston pumps can contain most of the necessary circuit controls intrinsically by controlling the swash-plate angle, to regulate flow and pressure. They are very reliable and can allow the rest of the hydraulic system to which they’re attached to be very simple and inexpensive.

They are used to power the hydraulic systems of jet aircrafts, being gear-driven off of the turbine engine"s main shaft, and are often used for automotive air conditioning compressors for cabin cooling. The design of these pumps meets the limited weight and space requirement in the vehicle"s engine bay and reduces vibrations.

Pressure washers also use these pumps, and axial reciprocating motors are used to power many machines. They operate on the same principles as axial piston pumps, except that the circulating fluid is provided under substantial pressure and the piston housing rotates and provides shaft power to another machine. A typical use of an axial reciprocating motor is powering small earthmoving machines such as skid loader machines.

This guide provides a basic understanding of axial piston pumps. To find out more about other types of pumps, read our guide here. For more information on related products, consult our other product guides or visit the Thomas Supplier Discovery Platform to locate potential sources or view details on specific products.

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.

EasyProg is offered together with a complete range of control units, driver boxes and sensors to make system programming and machine installation fast and easy with the highest accuracy.

A machine"s quality and reputation is often measured on how well the load is controlled at different stages of the moving cycle and at different speeds. This requires the valve not only to control the load well when in a single step operation, but how well the valve performs when multiple functions are activated at the same time.

Nimco Controls offers valves which can be tailored to each machine"s specific function and through our special spool design software. We can tailor every function to perform at the optimized speed and with a positive influence of all other functions.

Our Post Compensated Load Sensing valves offer superior load control with their unique design. Each spool has two compensators allowing customization of both the pressure and the flow.

With consistently improved, special design concepts and manufacturing methods, we are able to offer our customers as low as 1 cc/min at 46 cSt leakage rates for certain products and an average of less than 2 cc/min leakage rates for larger valves.

The advantage of low leakage rates over the spool is that the load does not drift when the spool is in neutral position. Leakage rates as low as 1 cc/min allow customers to avoid using costly, over center valves where they would otherwise be necessary.

At Nimco, we combine our knowledge of hydraulic valve design, system and application, and electro mechanics into one solution that will achieve the best performance for our customers.

We work closely with our customers to understand and improve their machine design and performance not only for single products, but also their entire system optimizing hydraulics, electronics, and how well all parts work together.

Our philosophy of designing with only the best materials and products, that will withstand the toughest demands and environments, has made Nimco products synonymous with quality. This is the main reason why our products are found on the most demanding and reputable machines in the market today.

With energy prices continuing to climb and resources becoming more scarce, we focus our R&D resources on the development of components which will contribute to lower energy consumption.

Our target is to assist our customers (and in turn, their customers) with saving money by consuming less fuel in their daily operation at the same or higher output levels. We also strive to increase our customers" daily productivity while minimizing their Co2 footprint.

Nimco"s Open Center Valves are all designed to minimize pressure drop and to contribute to overall efficient system performance. Valve designs are optimized to give excellent load control in combination with optimum energy usage.

Our LS Pressure Compensated Flow Sharing Valves are designed to only make use of the flow and pressure required to work a machine at optimized levels at all times.

Our EasyProg software will optimize machine performance and load control functions with minimal energy consumption by controlling the flow outputs and diesel consumption in every work cycle and condition.

We offer all valves with standard spools which have high resolution metering as well as specially tailored spools which are specifically designed to meet any machine"s specific load control needs.

In addition, we offer all valves with spools that do not have metering functions, but where spools are designed to allow for maximum flow at the lowest possible pressure drop.

Most of our open center valves can be equipped with secondary valve functions such as relief and anti-cavitation. Electrical unloading valves in the valve inlet and in any other sections needed are also available.

We offer a wide range of Spool Controls including Hand Levers, Cable, Pneumatic and Hydraulic Controls, as well as Electro Hydraulic on/off and Proportional Controls.

Most of Nimco’s open center valves as designed so that they can be ordered in a load sensing version which we call ‘’ On Demand Load Sensing’’. On Demand Load Sensing valves enable the valve to work in a system where a variable displacement pump is the source of oil and pressure supply.

The On Demand Load Sensing valves will activate the pump when the spool is shifted from neutral position, but does not offer individual pressure compensators for each spool.

Nimco offers post compensated flow sharing load sensing valves which have the unique feature of two compensators for each spool, thus better load control and welcome cost and energy savings for the machine builder. For applications where no flow sharing is needed, uncompensated sections are available which can be combined with full flow sharing sections in one valve.

Inlet functions for fixed and variable displacement pumps with electrical off loading valves and HPCO (Power Beyond) functions are available as standard as well as special high flow inlets where a LS compensated spool eliminates the pressure drop between the pump and the valve.

Other unique features with the Nimco LS valves include two compensators for each spool. This makes it possible to equip the valves with LS pressure reducing valves for each cylinder port and thereby limit the internal pump pressure to be exceeded without consuming any pump flow while still ensuring the maximum flow desired for each function is not exceeded.

Other standard equipment for the Nimco LS valves are; Manual Override Hand Levers with integrated Stroke Limiters and SRV’s with integrated A/C functions.

By combining a traditional directional control valve with a pressure compensated flow control valve and a traditional fixed displacement pump(s), load speeds can be maintained without the use of a more expansive load sensing system including variable displacement pumps.

Why would we want to add this extra complication to our hydraulic systems?Having a hydraulic pump which reduces its output to near zero when the system pressure reaches maximum saves the system from pointlessly forcing oil over a relief valve.

Whenever a system is at maximum pressure, and the pump is a fixed displacement model, like a gear pump, then the system is at maximum displacement as well.

The combination of these two maximums also means that the power requirement from the prime mover (diesel engine or electric motor) is at maximum as well.A prime mover at maximum power is consuming maximum energy (fuel or electricity). Much of this energy is being used for nothing other than a conversion to heat.

You could compare this to operating a truck at maximum throttle while it is parked against a solid wall of rock. You"ll burn a lot of fuel but you won"t be doing any useful work!

Working oil: A mineral based oil with additives to resist corrosion oxidation, & foaming is recommended. Viscosity at any running condition should be 60 SUS minimum & 250 SUS maximum. 180° F is the maximum recommended system operating temperature

This SAE Aerospace Standard (AS) establishes the general requirements for the design, construction, acceptance, and qualification testing of flat cut-off pressure compensated, variable delivery hydraulic pumps used in military aircraft hydraulic systems. It also provides parameters for a Procurement Specification to be used in conjunction with this AS.

The hydraulic pumps defined by this AS are generally for use in aircraft hydraulic systems conforming to and as defined in AS5440 and MIL-H-8891, as applicable.

The proportional directional spool valve type PSL is suitable for constant pump systems, while type PSV is suitable for control pump systems with a pressure/flow controller. The flow rates and load pressures for the individual consumers can be individually adjusted. The proportional directional spool valve types PSL and PSV can be adapted to various control tasks, e.g. for safety functions.

The proportional directional spool valve type PSLF is suitable for constant pump systems, while type PSVF is suitable for control pump systems with a pressure/flow controller. The proportional directional spool valve types PSLF and PSVF are available as individual manifold mounting valves in valve banks. The flow rates and load pressures for the individual consumers can be individually adjusted.

The proportional directional spool valve type MICK is a combination of the proportional directional spool valve type PSL and specially designed 8/3-way diverter valves which are flanged-mounted on the PSL sections. The PSL sections proportionally control the flow rate and the downstream diverter valves distribute it to the individual consumers. Up to three dual-acting consumers can thus be supplied with one valve section.

The directional spool valve type EDL with series connection is actuated directly. The flow rates for the individual consumers can be individually adjusted. The proportional directional spool valve can be flexibly adapted to different control tasks by means of additional functions in the intermediate plates and ancillary blocks.

The directional spool valve bank type CWS with series connection is actuated directly. The consumers are black/white controlled. A range of connection blocks and mounted blocks offer a wide range of applications. The valve bank CWS is used mainly in mobile hydraulics. In stationary hydraulics, the direct mounting on the compact hydraulic power pack results in an extremely compact system solution.

Load-holding valves are a type of pressure control valve. They prevent loads on cylinders or motors dropping in an uncontrolled manner. For this purpose they are pre-loaded with a pressure setting that is higher than the largest possible load. A hydraulic piston controls the opening of the valve to achieve the required lowering velocity.

The load-holding valve type CLHV is suitable for applications with low and medium tendencies to oscillate and is used especially in connection with proportional directional spool valves, e.g. types PSL and PSV. It is also available with return pressure compensation and spring chamber relief.

The type OSCA-D load-holding valve is especially suitable for applications that are either particularly susceptible to vibration or that work with very high load pressures. The valve is designed as a screw-in valve and is easy to install and remove. Choose from a range of connection blocks. Matching tools for producing your own blocks are available.

The load-holding valve type LHDV has special damping characteristics. It is suitable for applications that are highly prone to oscillations, and is used especially in connection with proportional directional spool valves, e.g. types PSL and PSV. When the valve is closed, it is completely tight and prevents all leaks. Shock valves and shuttle valves with or without restrictor check valves can be fitted in the load-holding valves, e.g. to relieve hydraulic brakes with a delay.

Axial piston pumps have several pistons that are arranged parallel to the drive shaft. They are available as either variable pumps or constant pumps. Variable displacement axial piston pumps adjust the geometric output volume from maximum to zero. As a result they vary the flow rate that is provided to the consumers. Fixed displacement axial piston pumps have a constant geometric displacement and convey a constant flow rate depending on the rotation speed.

The axial piston pump type V60N is designed for open circuits in mobile hydraulics and operates on the swash plate principle. It is available with an optional thru-shaft. The pump is fitted mainly to the power take-off on commercial vehicle transmissions. The large selection of different pump controllers allows the type V60N axial piston pump to be used in a variety of applications.

The axial piston pump type C40V is designed for open circuits in mobile hydraulics and operates on the swash plate principle. The large selection of different pump controllers allows the axial piston pump type C40V to be used in a variety of applications.

The axial piston pump type V30E is designed for open circuits in mobile hydraulics and operates on the swash plate principle. It is available with an optional thru-shaft. The sturdy pump is particularly suitable for continuous operation in challenging applications. The range of pump controllers allows the axial piston pump to be used in a variety of applications.

The axial piston pump type V80M is designed for open circuits in mobile hydraulics and operates on the swash plate principle. It is available with an optional thru-shaft. The sturdy pump is particularly suitable for continuous operation in challenging applications. The range of pump controllers allows the axial piston pump to be used in a variety of applications.

The axial piston pump type K60N is designed for open circuits in mobile hydraulics and operates on the bent axis principle. The pump is fitted mainly to the power take-off on commercial vehicle transmissions.

The axial piston motor type M60N is designed for open and closed circuits and operates based on the bent axis principle. The motor is particularly suitable for usage in mobile applications.

HAWE Hydraulik offers additional electronic components tailored to our hydraulic components. These include mobile controllers, which actuate complex hydraulic systems. The range includes electronic controls, proportional amplifiers and line connectors.

The programmable logic valve control type CAN-IO 14+ is a freely programmable PLC with integrated proportional amplifier. Highly precise functions are possible thanks to the feedback measurement at the valve outputs. The number of digital and analogue inputs and outputs can be configured variably. It also offers a comprehensive range of settings and programming options.

The mobile controller type ESX is a freely programmable PLC with an integrated proportional amplifier. The programming languages LogiCAD, C++ and CoDeSys are available for application programming purposes, depending on the type. The valve control type ESX has been certified according to ISO 13849 (PLd) and ISO 61508 (SIL2). It can be used in safety applications.

Proportional amplifiers actuate proportional solenoid valves by converting an input signal into a corresponding control current. The proportional amplifier type EV2S-CAN is a plug amplifier designed to be fitted directly on a proportional single-stroke or twin solenoid. Parameters can be configured either using the pushbuttons and an integrated display or via CAN bus using computer software.

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High Pressure air operated hydraulic pumping systems are complete, self-contained units and ready to operate. Just hook up standard shop air supply (maximum 100 psi) to connection supplied on the side of the console. Discharge capacities range to 64 in3/min.

System includes hydraulic oil reservoir, oil filter, air operated hydraulic pump, pressure gauge, panel mounted high pressure valves, safety head assembly, panel mounted air regulator and gauge and air line filter and lubricator. All components are enclosed in a steel console with only the back exposed. Dimensions of standard systems are 26" wide, 24" deep and 40" high.