How does a hydraulic power pack work?

In simple terms, a Hydraulic power pack pumps hydraulic oil. In this article we explore how each element of a hydraulic power pack works and why they are needed.

In more detail a hydraulic power pack is a piece of machinery that pumps hydraulic oil from its own reservoir through filters and valves into a hydraulic system.

How is hydraulic oil pumped?

The hydraulic pump is central to the hydraulic power pack, and takes many forms and configurations depending upon the pumping rate, pressure limits and environment. Most common types are Gear, piston and Vane pumps. They all pump by the rotation of their input shaft, this is normally by means of an electric motor, but can be other machines such as a combustion engine or pneumatic air motor.

The hydraulic oil is drawn from the Oil reservoir into the pump and pushed out of the pump at a higher pressure than the suction side.

What happens to the oil when it exits the hydraulic pump?

In most conventional hydraulic circuits you would expect the pumped oil to pass through a check valve. This is not ensure that pressure is not applied back onto the pump by any actions of the hydraulic actuators or equipment, therefore protecting the pump.

The next features commonly encountered would be a Hydraulic pressure filter. Ensuring clean oil is supplied into the rest of the system is important, and more on this can be found here. A hydraulic pressure relief valve is normally placed in this situation; this is to limit the maximum pressure that the hydraulic system can generate. It main function is to protect the system and its hydraulic components, more about relief valves can be found here.

These hydraulic features are common, but beyond this a hydraulic can take many forms and complex directional or control systems can be built using a vast range of Hydraulic control valves


How does the hydraulic oil return to the reservoir?

When the oil has done its work, that is when it exits from a hydraulic actuator or hydraulic motor it is not lost like a pneumatic system. The oil needs to be returned back to the reservoir to be used again. But before this happens it needs to be conditioned so it is ready for use. Any contamination must be filtered from it by using a hydraulic return filter. This will ensure any dirt that is picked up around the system is removed.

The other operation that is often carried out is cooling. After the oil has done some work it will often be hot and it should be cooled before it is re-used. Typically an Air blast cooler, which his essentially a radiator element with a fan blowing at it, or a water/oil cooler which is more efficient.

 What is the job of the hydraulic reservoir?

Once the oil is clean and cool it will return back into the hydraulic reservoir, but it will often have entrained air in it. One of the jobs of the reservoir is to remove the air. This is done by the use of a diffuser or a baffle system, allowing the oil time to release it air to the surface before it is sucked back into the pump.

These summarises the main elements of how a hydraulic power pack works and what the oil does as it passes into and out of it.