swash plate hydraulic pump animation manufacturer

A hydraulic pump is literally the heartbeat of your hydraulic system. If you’re new to hydraulics, you’d be surprised at how many ways you can push fluid under pressure. The rotating and/or reciprocating of gears, vanes or pistons offer a designer constrained by any performance or budget envelope the options to best suit any application, especially since each of the primary pump construction styles offers unique options within each series.

Piston pump technology exclusively employs axially or radially reciprocating pistons relative to the input shaft. Fixed and variable displacement pumps are offered in all three primary construction variations — axial swashplate, bent-axis and radial. For both axial and bent-axis piston pumps, you will notice their pistons reciprocate in parallel as the rotating group orbits the shaft. Radial piston pumps look more like old wartime engines from aircraft, with their pistons reciprocating perpendicular to the input shaft. Although the most complicated design, piston pumps enjoy power and efficiency not possible in gear or vane pumps.

Axial-piston stylesThe fixed-displacement piston pump offers designers a relatively inexpensive entry point to the piston pump. They provide reliable, high-pressure fixed flow for open-circuit hydraulic systems with no fancy controls. However, the control options available to piston pumps offer many clever tactics to control your hydraulic system, from pressure compensation to electrohydraulic proportional control with onboard pressure transducers.

A pressure compensator is a relief valve for the control piston of the variable-displacement pump. The compensator is a very low flow component that essentially controls the swashplate angle to modify displacement in such a way as to maintain a set pressure. Any downstream flow demand lowers pressure drop at the pump, causing the pump to increase flow to maintain pressure. So long as downstream flow demand does not exceed the pump’s maximum flow rate, the pump can compensate and remain at full pressure. However, any flow exceeding its maximum rating will be subject to the downstream actuators’ load pressure.

Manufacturers offer various forms of displacement and pressure control. For example, load sensing control allows the pump to read downstream load pressure signals to reduce flow during off-demand periods and at reduced pressure equal to a few hundred psi higher than the highest load. A step further, you’ll find horsepower limiting (sometimes called torque or power limiting), which provides the machine maximum flow and pressure so long as the total demand is less than the prime mover’s capacity. Should a machine, such as an excavator, demand higher flow and pressure than the engine can supply, such as when multiple high-pressure actuators are simultaneously activated, the pump will automatically restrict flow to reduce the total power required.

Regardless of compensator type, each variation achieves its result by varying only the swashplate angle. For axial piston pumps, the swashplate pivots to increase or decrease displacement as required by the compensator as directed by the control piston. As a result, the control piston moves in the same axial plane as the rotating shaft, serving up a compact and powerful package.

Bent-axis piston technologyAlthough axial piston pumps are easily the most popular, other piston pump designs are offered with variable displacement. You may be aware of the bent-axis piston motor (Figure 1), which is famous for its high power and high-speed reputation. Its shaft and bearing assembly rotate at a taper relative to an axial piston motor. Despite their high-pressure design, the bent-axis configuration offers 25% higher rotational speed than straight-axis motors, and their bearing design is better suited to pulley or gear-driven applications. The force vector from a gear or pulley must oppose the bent direction of the motor (Figure 2), much like your arm pulling against a surgical band from underfoot to do bicep curls.

The tapered, oversized roller bearings inside a bent-axis piston motor provide superior side load protection to resist the steeply angled rotating group side load. For example, a swashplate on an axial piston motor may allow a maximum of 15-22° angle, while the bent axis piston motor operates at 40° or more. This extreme angle allows the motor to achieve high displacement in a small package, resulting in a high radial load on the input shaft. Resisting these side loads requires the heavy-duty tapered bearings like those you see in Figure 3 and explains the necessity to pull from the opposing direction as the motor angle.

The same benefits of the bent-axis piston motor apply to its pump kin. Superior power density, high-speed operation and high resistance to radial load make these the top choice for mobile hydraulic designs driven directly by diesel or gas engines. In addition, their inherently robust design makes them the top choice for gear or pulley-driven pump applications (as long as the installation recommendations are adhered to). Although the tapered roller bearings provide high side-load resistance, because the bearings are loaded to remove excessive clearances, excessive wear may occur. As a result, you’re more likely to replace the bearings on a bent-axis piston pump than in other designs.

You may be surprised to know that variable-displacement bent-axis piston motors are offered by manufacturers. Unfortunately, their appearance doesn’t seem to offer any place to mount any useful swashplate angling device. Their construction varies significantly from a swashplate variable-displacement pump, where instead of varying swashplate angle, the entire lens plate slides up and down inside the port plate.

A stroke piston opposed by a bias spring and control piston works much the same as in an axial piston pump. The compensator receives a pilot signal from the pressure port to balance the pressure drop at the pump’s outlet, varying the angle of the rotating group as required to maintain pressure.

The leading manufacturers of piston pumps offer most, if not all, control options for their bent-axis piston pumps. Basic pressure compensation with no other function often goes by pressure cut-off in product literature (or pressure override). The basic pressure cut-off control simply observes outlet pressure and adjusts the swashplate angle to alter flow rate, thereby maintaining a set pressure drop. So long as system demand is less than maximum flow, the outlet pressure remains at compensator set pressure. However, should demand rise above maximum pump flow, your circuit is at the mercy of the path of least resistance.

To be honest, selecting a pressure-compensated bent-axis piston pump for anything other than high-speed belt or pulley driven applications is an expensive bit of overkill. The control devices of variable-displacement bent-axis piston pumps are often quite advanced; you can expect various advanced controls such as horsepower limiting, hydraulic proportional control or even electro proportional control. I’m aware of one particular manufacturer that offers no less than seven kinds of horsepower-limiting controllers for one pump!

Proportional pump control uses proportional pressure-reducing valves in place of standard pressure compensators. For example, imagine a bent-axis piston pump where the spring offset stroke piston fights against spring pressure by infinitely varying the pressure inside the control side of the piston. Precise pressure observed by downstream transducers offers a closed-circuit feedback loop for the machine controller to adjust the proportional valve setting to match the desired outlet pressure. Some pumps may even take it a step further to include a linear transducer to provide precise displacement feedback, guaranteeing your circuit precise output flow and pressure despite fluctuations from the load, temperature, or viscosity.

With so many pump options on the market, do we really need so many advanced options for a single pump style? My vote is yes because the bent-axis piston pump offers unique advantages over other designs. The variety of control options available ensures that your system, no matter how complex, has the pump design you need.

Axial piston pumps are a common part throughout construction machines and across construction equipment brands. Their design allows them to be used from the cooling system to the steering system to a multitude of places throughout a machine. Anyone who has worked in construction equipment has certainly come across an axial piston pump, but one might still wonder, “What exactly is going on in this little box?” That’s why we’re here to help.

Whether you’re researching an axial piston pump problem or you’re just inquisitive about this widely-used part, read on for a short explainer on how they work and what they do.

At its most basic, an axial piston pump turns mechanical energy (the turning of a shaft) into hydraulic output (the moving of fluid). The use cases for an axial piston pump are wide-ranging, leading to the adoption of this pump design throughout construction equipment types and across construction equipment brands. An axial piston pump provides advantages in dependability, simplicity, and efficiency leading to its use in handling a wide range of tasks on a machine.

The basic mechanics and design of an axial piston pump are also commonly combined with gearing designs to create axial piston motors. An example is the swing motor commonly found in excavators which combines the design with planetary gears to power the rotation of the house at the point where it spins relative to the tracks.

Seeing the rotation of the piston barrel and the back and forth action of the pistons clearly illustrates how the axial piston pump works. » Click video to play/pause animation.

To convert mechanical energy into hydraulic output, an axial piston pump utilizes a rotating, splined drive shaft that connects to and turns a piston barrel. To create the pumping mechanism of the pump, piston pumps can use either a swash plate design (featured in video) or a bent axis design.

In both designs, as the pistons rotate they are repeatedly drawn away from a valve plate and then pushed closer to the valve plate. This variation in distance alters the size of the chamber available to hold hydraulic fluid. At times when the gap between the end of a specific piston and the valve plate is decreasing, the chamber will shorten, and hydraulic fluid will be expelled through the valve plate. As the piston rotates, it will eventually reach a point where the gap is increasing, leading to a longer chamber. This vacuum will cause hydraulic fluid to be drawn into the chamber through the valve plate.

Since the valve plate acts as a divider between the input and output sides of the pump, as the pistons and piston barrel rotate, hydraulic fluid will be continuously cycled through the pump as it is drawn from one connection and directed with force into another.

Since the rotating of the pistons and piston barrel is determined by the rotation of the shaft, the pump"s output can be controlled by increasing and decreasing the speed of the shaft. In the swash plate design, further control of the pump is possible by adjusting the angle of the swash plate, changing the distance of the pistons from the valve plate, and, in turn, increasing or decreasing the size of the chamber available to hold hydraulic fluid.

The shaft distributes mechanical, rotational force to the pump. Splines on the shaft interconnect with splines in the piston barrel to turn the barrel and pistons while splines on the part of the shaft that extends from the housing connect to the machine.

Pistons inside the pump rotate around the center shaft. Since the plane at which one end of the piston is attached is set at an angle determined by the swash plate, the pistons also vary their distance from the valve plate as they rotate. This variation causes a continuous alternation in the depth of the cavity available to hold hydraulic fluid inside the piston barrel and leads to their continuous looping through the pumping process.

In an axial piston pump utilizing a swash plate design, the swash plate is responsible for setting the angle of the piston’s container and, in turn, the amount of variation in depth the pistons will move through. Altering the angle of the swash plate allows the action of the axial piston pump to be further controlled.

The valve plate sits on the end of the piston barrel opposite the pistons. Slots in the valve plate allow fluid to be directed to specific connections for intake and discharge.

Axial piston pumps feature a number of moving parts which always require lubrication and other techniques to decrease friction between moving surfaces. Because of the often rapid speed at which they operate, if an axial piston pump operates in an environment with less than ideal lubrication wear can happen rapidly and even lead to catastrophic failure.

An axial piston pump is often subject to repetitive, long-lasting, and high-pressure work, and with any part subject to those conditions, the buildup of heat over time is always a possibility. Overheating of the pump can be further amplified through inefficiencies developing inside the pump and issues with the overall hydraulic system with which the pump is connected. Examples of each would be: a bearing failure that forces the pump to work harder to maintain expected output and bubbles in the hydraulic fluid inside the pump (cavitation) from operating in a system low in fluid.

Like any part in the hydraulic system, containing hydraulic fluid and directing it in very specific ways is necessary for consistent and expected functioning. If fluid is allowed to flow in unintended ways, the pump will lose efficiency or even lose the ability to provide adequate output. Seals and gaskets are used in axial piston pumps to ensure proper operation, but over time (or due to neglect) seals and gaskets can reach a state of failure that will affect the working ability of the pump.

While a full determination of why an axial piston pump failed can involve a removal and disassembly of the part, often there are simple signs to watch for when one suggests an issue with an axial piston pump, namely:

If the pump begins underperforming during operation and other issues that could affect output like loose hydraulic connections are eliminated, a lack of power can be a sign of internal problems in the pump.

Most axial piston pumps can be expected to create some level of noise, depending on size and design. A pump that has suddenly become louder or begins broadcasting an erratic noise can be a sign that internal parts of the pump are operating outside of proper conditions.

Friction is almost always a byproduct of moving parts and, if unchecked inside the part, it will often show its effects on the outside of the part through heat and/or vibrations. While some heat and vibration is to be expected, especially if the pump is called upon to work for an extended period of time, excess vibration and heating are both a symptom of a problem and a possible escalation of issues.

Most hydraulic systems connect a number of parts in a machine and contamination from failure can often come from any of them. The discovery of fluid contamination can be combined with the previously mentioned signs to narrow issues to the pump.

An H&R tech is at work in the shop rebuilding an axial piston pump, a fairly common sight in the shop because of the wide use of axial piston pumps in construction equipment.

Here’s to hoping you read this article on axial piston pumps because of a pure curiosity about how they work and function. If though, you’ve arrived here in search of a diagnosis for axial piston pump problems, hopefully, with this information in hand you’re closer to solving your troubles.

As a top dismantler and parts rebuilder for construction equipment, axial piston pumps are a frequent rebuild project in the H&R Recon and Rebuild shops. Big parts to small, our parts technicians brings decades of experience to our rebuild project and we take pride in knowing that experience leads to a part that will outlast and outperform the competition. If you’re in search of a replacement axial piston pump, our Parts Specialist are here to help in your search. Just give them a call.

Piston design - Solid, hollow, or with piston rings. The design and weight of the pistons will have a major effect on pump efficiency. The Parker F11 design with its lightweight head and retained balls can reach significantly higher speeds than swashplate pumps with their longer, heavier pistons.

Some pumps and motors can run over-centre, which means they can provide flow or rotate their drive shaft in both directions. These are commonly used in closed circuit, mobile vehicle drives systems.

Bent axis designs tend to have much heavier duty shaft bearings than swashplate pumps. This is because they are more commonly used as motor drive units and have to take the wheel loads against their shaft. Swashplate pumps, on the other hand, tend to be driven through flexible couplings that will remove any side loads, so the internal bearing is sized just to take the internal loads from the dynamic and pressure loading forces.

Noise level can be an issue with piston pumps. The noise is generated by the discontinuities in the flow e.g. as the pistons move forward and backward they create a pulsating flow that passes into the complete hydraulic system and vibrates or radiates from other components further down the circuit. This flow discontinuity is further complicated by the supply port which connects and disconnects each piston as it rotates. The timing of the opening and closing can create other, higher frequency flow discontinuities. Often different timing plates are available for different operating conditions e.g. fixed speed or variable speed applications.

Case leakage line pressures are critical for controlling the pressure balance of the slipper against the suction pressure. Care should be taken with some pump controllers as the valves exhaust into the pump casing and can create dangerous pressure spikes. Make sure case drain lines are sufficiently sized. One possible solution may be to use a more compliant, clear plastic hose for the case leakage line which will have the effect of damping out these peaks before damage the slippers. Case leakage line temperatures are also a good way of monitoring the health of the pump as discussed in the vane pump section.

If you are in doubt about the most appropriate pump to use in your application then always talk to manufacture or distributor who should be able to offer the most appropriate pump range and advise the expected service life.

Swashplate hydraulic pumps have a rotating cylinder containing pistons. A spring pushes the pistons against a stationary swash plate, which sits at an angle to the cylinder. The pistons suck in fluid during half a revolution and push fluid out during the other half. The greater the slant the further the pump pistons move and the more fluid they transfer.

Electro-Hydraulic Controls for Model (A)A4VSO (Sizes 40...1,000), Model A4VSH (Sizes 40...250), Model (A)A4VSG (Sizes 40...1000) and Model (A)A4CSG (Sizes 250...750) Swashplate pumps

In an axial-piston pump, the pistons and cylinder rotate around the center, longitudinal axis. The pistons and shoes move in and out of the cylinder because they are sliding upon a stationary, variable angle, swashblock.

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.

The displacement of a pump is defined by the volume of fluid that the gears, vanes or pistons will pump in one rotation. If a pump has a capacity of 30 cm3, it should treat 30 ml of fluid in one rotation.

In axial piston variable pumps, the flow is proportional to the drive speed and the displacement. The flow can be steplessly changed by adjusting the swivel angle. Axial piston variable ...

... axial piston pump type V60N is designed for open circuits in mobile hydraulics and operate according to the swash plate principle. They are available with the option of a thru-shaft for operating additional ...

Variable displacement axial piston pumps operate according to the bent axis principle. They adjust the geometric output volume from maximum to zero. As a result they vary the flow rate ...

... piston pump type V30D is designed for open circuits in industrial hydraulics and operate according to the swash plate principle. They are available with the option of a thru-shaft for operating additional ...

... circuit axial piston pumps are used as hydrostatic transmission components in self-propelled machines and for rotary drives in both fixed and mobile equipment of all kinds.

Axial piston twin flow pump. With a very high performance in all job conditions. Due to its twin flow configuration this pump allows a great variety of solutions in different job applications.

Air hydraulic pump, double pneumatic motor, double effect, foot operated with lock-up function, lever distributor valve (4/3), 10L tank, oil flow 8.5 / 0.26 l / min

... customer system options for mechanical, hydraulic and electric input solutions are available. Further special regulating features like torque control and pressure cut-off are also available. The reliable ...

... needs of truck hydraulics, the TXV variable displacement pumps with LS (Load Sensing) control allow flow regulation to suit the application requirements. The pump ...

... rev. displacements, these pumps are designed to operate in both directions of rotation (clockwise or counter-clockwise). Only one reference regardless of direction of rotation. The TXV indexable pumps ...

... PVG is a variable-displacement axial-piston pump designed to take on your most demanding applications. It offers high-pressure, superior performance in a compact design ...

Variable displacement pumps in closed loop; 3 basic design units and 8 max. displacement sizes of 14, 18, 21, 28, 35, 46, 56, 64 cc/rev; various control options; max. ...

Parker P2/P3 High Pressure Axial Piston Pumps are variable displacement, swashplate piston pumps designed for operation in open circuit, mobile hydraulic ...

... Series pump offers variable displacement axial piston pumps for open-circuit applications. Featuring a compact footprint and continuous operating pressure ...