If you’re new to the world of hydraulics, one of the first things you will need to learn is hydraulic pump displacement. Pump displacement is simply the amount of liquid transferred from a hydraulic pump’s inlet to its outlet in one revolution or cycle. In basic terms, it’s the amount of liquid a given pump can process in per each rotation of its motor. Pumps with multiple chambers have displacements equal to the displacement of one chamber multiplied by the total number of chambers. So, if a pump has 4 chambers and one chamber displaces 5 units the total displacement for that pump is 20 units. There are two different types of displacement: fixed and variable. Let’s go over the specifics of each now.
Fixed Displacement Pumps
In this first type of pump, the displacement can only be changed by changing the drive speed of the hydraulic pump. This means that the only way to modulate the total displacement will be to either increase or decrease the drive speed. These types of systems carry many advantages in terms of hydraulic pump displacement. These include being less expensive, easier to maintain, and having a simpler design. Fixed displacement pumps are used in what is known as “open loop” hydraulic systems. In these systems the pump draws fluid from a reservoir that supplies the system.
Variable Displacement Pumps
Variable displacement pumps have a completely different and much more complicated system. These systems have an added feature that allows you to change the chamber size of the pump. Effectively increasing or decreasing how much liquid it can hold. This can change the displacement of the pump. You can also change the drive speed like with fixed displacement pumps. This double system makes variable displacement pumps complicated and prone to breakage. They require more upkeep than their fixed counterparts in exchange for finer control on their output. For most applications, a fixed displacement pump will have many more advantages than a variable displacement pump. These pumps are typically found in “closed loop” systems. These systems have a continuous flow of fluid between the pump and motor.
Hydraulic pump displacement is one of the basics of hydraulics that you just need to know. Displacement can be thought of as the amount of fluid that is moved from the intake to the output of the pump. Fixed displacement pumps are more reliable and only change displacement by changing their drive speed. Variable displacement pumps are more prone to wear and have variable chamber sizes in addition to drive speed changes to alter their displacement. Now you can shop for hydraulic pumps with confidence.
