The Difference Between Hydraulic Pumps, Cylinders, and Systems

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Understanding the different components in hydraulic systems can be daunting at best. Here we break down the differences between hydraulic cylinders, hydraulic pumps, and hydraulic systems, as well as answer some common questions, and dig into some misconceptions.

Hydraulics 101

Before we get too deep down the rabbit hole, it’s important to make sure you have a good understanding of the basics of a hydraulic system.

A hydraulic system is a series of components that use compressed fluid to create or transfer force from one point to another. These components generally consist of:

  • a pump
  • a reservoir
  • valves
  • fluid
  • hoses
  • motors
  • cylinders
  • filters

For now, let’s focus on the pumps, cylinders, and two types of systems.

The pumps are important because they are the mechanism that transfers the fluid from the reservoir to the system.

The cylinders convert the pressure of the fluid into the force the machine needs to work.

The two different systems discussed here will determine how exactly the hydraulic system will work and the amount of wear and tear the components will go through.


One-Stage Pump Versus Two-Stage Pump

A one-stage pump has just a single setting. This means there is only one flow rate that peaks out at one maximum pressure.

A two-stage pump has a second stage or setting that kicks in once resistance is met.

A one-stage pump is typically found in simple industrial machines whereas a two-stage pump will be found in applications that require lifting and other additional movements.


Single-Acting Cylinder Versus Double-Acting Cylinder

A single-acting cylinder is used when the application only requires the work to be done in only one direction. This is because the cylinder only applies pressure to one side of the piston. In a double-acting cylinder, the pressure is applied to both sides of the piston allowing work to be done on either side.


Open System Versus Closed System

When the terms open system and closed system are used, they are not referencing the actual opening or closing of the system.

These systems actual reference the ability to reduce pressure on the pump during use which minimizes wear and tear on the equipment, as well as the components of the system.

An open system means there is a valve that connects the lines directly to the reservoir, bypassing the pump as long as the system is in neutral. This reduces the strain on the pump. A closed system, when in neutral, blocks the oil flowing from the pump. The oil then routes to an accumulator where it is stored.


How do you convert an open system to a closed system?

You can change your open system into a closed system by removing the conversion plug that is found in the open center valve. You can then replace the plug with a closed center plug.

It’s important to change the relief valve as well. This requires a “no relief” plug to be installed on the handle end of the relief valve. Because you are converting to a closed system, you’ll need to plumb a reservoir or outlet tank for the oil to be emptied into.


There you have it, a quick intro to Hydraulics 101!