Comparisons between Variable and Fixed Displacement Hydraulic Pump

A hydraulic drive system uses a pressurized fluid to deliver force to distant machinery. Each system has several common components; the most universal is the hydraulic pump. The pump’s purpose is to pressurize the hydraulic fluid so that it will travel down the line and perform work on the other side. In an ‘open loop’ system, the fluid is drawn from a reserve tank, and deposited into the same tank after it has done its work. In a ‘closed loop’ system, the fluid is brought directly back to the hydraulic pump after passing through a hydraulic filter.


Fixed Displacement Hydraulic Pump

A fixed displacement hydraulic pump has a set flow rate — every stroke of the motor moves the same amount of fluid. Fixed displacement pumps are


  • Simple
  • Relatively inexpensive
  • Easier to maintain


The simplest type of fixed displacement pump is the gear pump, in which the hydraulic fluid is pushed by rotating gears. In some models, the gears are sequential; in the quieter and more efficient version, the gears are interlocking. Another common variation is the screw pump, which uses the classic Archimedes screw, which looks much like a drill bit, to move the fluid. They have the advantage of providing a high rate of flow at relatively low pressures.


Variable Displacement Hydraulic Pump

In a variable displacement pump, the flow rate and outlet pressure can be changed as the pump operates. This results in variable displacement hydraulic pumps that are


  • More complex
  • More expensive
  • Capable of doing a wider variety of jobs


The most common type of variable displacement pump is the rotary vane pump, which is a variation of the gear pump in which the ‘gear’ is offset and the ‘cogs’ aren’t fixed, but rather extend and retract as the gear turns, allowing the pump to increase the pressure of the fluid by compacting it as it pushes the fluid through. The top-tier pumps, however, are bent-axis piston-and-cylinder pumps, much like the ones that are used in an internal combustion engine.


Simple, fixed displacement hydraulic pumps are perfect for single jobs that need to be repeated indefinitely over long periods of time; variable displacement hydraulic pumps can be used to power a wider variety of tools, but require more expense and more attention.


Anson is the professional intra vane fixed displacement hydraulic pumps manufacturer in Taiwan. We provide various intra vane pump series, including IVP series, IVPQ series, IVPV series, and cartridge kits and so on hydraulic pumps. Welcome to send inquiries and feel free to contact Anson for more details about fixed displacement vane pumps and more hydraulics.



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The Right Kind of Pressure Washer Pumps For the Right Job

Pressure washing can be time saving and can help the environment by saving water and energy. The pump is the most important part of the washer, which delivers the water, or the cleaning liquid, with high pressure. However, one must be careful in choosing the right pump, depending on the intended use of the washer.

There are basically three types of pumps for use with pressure washers:

For economic consumer pressure washers, there are pumps which some manufacturers offer in ready-made kits to replace or upgrade the pump in some models. They are designed in mind for those with little or no experience or mechanical knowledge. They are designed more for those washers used at home or for occasional use. They can also be personalized to fit certain brands and models, so the user only has to do is move aside the old plumbing, remove the old washer pump and install the new one. These pumps are intended for giving the home pressure washer more power and PSI. However, it is important to remember that these pumps are intended for occasional home use only.

If the washer will be used in a light commercial environment, and will be given a more than occasional use, then there are more powerful pressure washer pumps capable of increasing the output volume and pressure. These pumps are usually made of ceramic coated stainless steel pistons, angular contact ball bearings and are made of heat treated steel for extended life.

Generic commercial or industrial pressure washers might require some adjustments to take full advantage of them, and for these washers with a heavier and more frequent workload it is recommended to use a hi-grade washer pump. These are highly specialized and are designed to be used in particular situations: chemical spills cleaning, high temperature, oil cleaning or any other extreme conditions. For these types of pressure washer pumps, the user should definitely turn to the dealer or manufacturer for proper installation and configuration of the washer and pump.


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Something About Hydraulic Pumps

Hydraulic pump, which is a water pump that uses the kinetic energy of flowing water to force a small fraction of that water to a reservoir at a higher level, is a mechanical device used to move liquids in a hydraulic system.

It can be mainly divided into hydrostatic and hydrodynamic. The former is a kind positive displacement pumps. Being distinguished from hydrostatic pump, the later one can be fixed displacement, in which the displacement cannot be adjusted. At the same time, hydrodynamic pumps have a more complicated construction that allows the displacement to be adjusted in special need by the user.

How does the hydraulic pump work? It works based on Pascal’s Law which states “The pressure, in a static hydraulic fluid in a closed system is everywhere the same”. Generally, in a hydraulic pump, water or another fluid is highly pressurized and moved through various motors and cylinders. To control the fluid various valves, hoses and tubes block or disperse the fluid creating the pressure and force without the need of an external power source. By using the kinetic energy (molecular energy) of the water/fluid to power the pump, no electricity is needed. And according to the law, if you increase the pressure in one area of a system, it increases throughout the system.

Of course, like many other types of pumps, the hydraulic pumps also have a wide range of applications. Its application can be summarized as transferring and circulation of liquids within light industry and farming irrigation and pressure boosting. And it also can be applied tin cooling systems and air-conditioning systems.

And in daily applications, especially in the hydraulic installation, one pump can serve more cylinders and motors. However, the attendant problem is that in that case a constant pressure system is required and the system always needs the full power. The more economic way to solve this problem is to give each cylinder and motor its own pump.

The hydraulic pumps include gear pump, screw pump, bent axis pump, peristaltic pump, and so on. All these different types of pumps have many common features. Most of them are designed to be ideal for water supply, irrigation, commercial and industrial uses. Besides, most of them are made of cast iron and brass. Taking the gear pump as an example, it is the most common where pressure can remain low in simple systems. They are simple, reliable, and much less dirt sensitive.

Gear pump is also an important mechanical part; therefore, you can also learn something about it.

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