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Benefits of a Fixed-Displacement Hydraulic Pump 16## November 2016

When you need to choose a hydraulic pump solution for a hydraulic system, it is important to decide what type of pump you will require. You must also understand the basics of how pumps work and hydraulics.

Fixed-Displacement Pump
All hydraulic systems rely on pressurized fluid to create force in order to perform work that is accomplished by transforming mechanical energy into hydraulic energy inside hydraulic pumps and creating a positive displacement downstream. For example, a forklift needs to raise and lower pallets—which would be the desired work.
 
You must also choose between a ‘closed-loop’ or ‘open-loop’ system. In a ‘closed-loop’ system, the fluid passes from the pump directly to the motor before returning to the pump. In an ‘open-loop’ system, the pump draws the fluid from a reservoir or tank, and then pumps it to a control valve from where it is directed to the services being operated before returning to the tank.
 
Two of the most common pump options are fixed displacement pumps and variable displacement pumps.

Benefits of Fixed-Displacement Pumps

Fixed-displacement pumps are well suited to a wide range of functions where the amount of pressure required to perform work is the same each and every time. For instance, if the pump is rated as a 30 cc pump, it will pump 30 ml of hydraulic fluid through the system for every single rotation.
 
The pressure and flow rate will not change, no matter how the pump is operated or what occurs elsewhere in the system. If you need a lower flow rate, then you will have to divert the excess flow or use a variable displacement pump.
 
Two common types of fixed-displacement pumps you can use are the bent axis piston pump and the gear pump. The bent axis piston pump provides the added benefit of normally having a higher pressure capability than a gear pump.
 
For operations that require the same flow rate, a fixed-displacement pump is the perfect choice.
Since the pressure and flow rates cannot be changed, you need to make sure to select the correct size fixed-displacement pump to suit your needs.
 
Aside from flow rates being directly proportional to pump drive speeds, fixed-displacement hydraulic pumps have several key benefits over variable displacement pumps, including:
  • Less Expensive
  • Easier to Maintain
  • Simpler Design

Benefits of Variable Displacement Pumps

Unlike fixed-displacement pumps, variable displacement pumps are able to increase or decrease the fluid flow rates electronically, manually, or hydraulically. The method used will depend on the flow required and the type of pump being used, such as a vane pump, axial piston pump, etc.
Variable Displacement Pump
Furthermore, the method of displacement changes based on the pump’s internal structure. For example, a variable displacement piston pump is determined by the bore area of the pistons and the stroke length. The stroke length can vary to help regulate the flow rates as shaft rotation turns and moves the pistons inside the pump.
 
The control piston inside the pump also helps regular pressure and, essentially, functions as a relief valve. When pressure increases above the desired pressure compensator setting, the control piston moves outwards and slows the travel distance of the other pistons.
 
Aside from being able to regulate fluid flow rates, other benefits of variable displacement pumps include:
  • Allows for more complex designs for complex hydraulic systems.
  • Variable displacement is available in different types of pump designs—piston, gear, and vane.
  • Custom-designed variable displacement pumps can be built to exact specifications.
  • Better flexibility to regulate and change fluid flow rates for different operations.
As can be seen, fixed-displacement pumps and variable displacement pumps have their own benefits, depending on your specific needs. For further assistance in choosing the right pump or for other hydraulic system solutions, please feel free to contact White House Products, Ltd. at +44 (0) 1475 742500 today!

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