Comparing the Fixed Displacement Pump and Variable Displacement Pump

Hydraulic systems have a wide variety of applications and are used across multiple industries. Two types of hydraulic pumps are variable and fixed displacement pumps. It is important for everyone working in these industries to understand the differences between the two pumps so that they can select the right pump for their needs. In general, a hydraulic drive system (such as the pumps discussed above) use fluid delivered under pressure to make machinery churn. These systems have a variety of components; however, these components can change depending on the job that they are asked to perform. One of these is a fixed displacement pump.

A Fixed Displacement Pump

These types of pumps have a set, constant flow rate. These means that every stroke of the machine will move the motor a set distance. Therefore, the machine will also pump the same amount of liquid with each and every stroke. Some of the important aspects of fixed displacement pumps to remember are:

  • These pumps are relatively easy to both understand and use
  • Fixed pumps are typically less expensive when compared to their variable counterparts
  • Because these pumps have fewer moving parts they are also easier to maintain

Most pumps that fit this description push fluid by rotating gears. The gears are built in a sequential pattern and fit together smoothly. Other variations of these pumps include the screw pump which moves in the form of a drill bit. Both of these descriptions are examples of fixed pumps. Their variable counterparts have some notable differences.

Comparing the Fixed Pump to the Variable Displacement Pump

The variable displacement pump is a little bit more complex. The flow rate and the pressure of the fluid can be changed even as the pump operates. This means that the variable displacement pumps are:

  • More complicated to use because of the additional moving parts and changing flow rates
  • More expensive to purchase because of the added functionality
  • A variable pump is typically capable of performing more jobs than their fixed counterparts

Unlike the fixed pumps, the gears of the variable pump are typically not fastened in place. This is because as the flow rate and the pressures change, the pump will need to change the size of its stroke. While this does give the variable pump some additional functions, it also makes it harder to use.

Selecting the Right Pump for the Job

These two pumps have some notable differences that people need to consider when putting together a hydraulic system. The fixed pump is a suitable option for jobs that are repeated in the same way over an extended period of time. Jobs that change with time might require a variable displacement pump.