Troubleshooting with System Tests for Hydraulic Piston Pumps When it comes to piston pumps, here at Hydraproducts we generally more experienced with pressure compensated, variable displacement piston pumps than other types. However, the information that you discover in this article can be used to test any type of pump that is of the variable displacement type. So read on to discover what you need to know when it comes to fixing piston pump issues. The purpose of the pressure compensator is to monitor downstream pressure and then change the internal configuration of the pump in order to maintain your pre-set pressure for flow. When it comes to the piston pump’s compensator setting, be aware that adding the ability to handle pressure compensation to any pump will make it necessary to check this extra loop when troubleshooting a hydraulic system circuit. A typical issue of this type of pump is that the setting of the compensator is incorrect when it comes to cutting off pressure. This is set up to work with the spring setting of the system relief valve. It’s critical that the relief valve setting is higher than the compensator by between 100 and 150 psi. If the compensator is set higher, then the flow will be too much from the pump and therefore, the compensator will be bypassed making the pressure compensation negated. The temperature of the fluid will rise and lead to loss of energy due to the pressure drop. Case drain pressure is another factor that needs to be considered. This is usually around 5 psi. In the majority of pump designs, the pressure compensator drain will flow into the case, which will mean that the pump case pressure will affect the compensator. If there is an obstruction in the line for example, this could lead to further pressure and it could result in serious issues. Be aware that the pump could mechanically be destroyed by a compensator that is not operating properly. If you’re not getting issues on the above, then you may have incorrect pressure from further down in the circuit. For example, an ‘open system’ situation where there isn’t any resistance to flow. It might be that the pump needs to be primed, this could be addressed by an air-bleed valve further downstream. If you are getting some pressure but it is not enough, then check whether something is preventing the system pressure such as a blocked pipe or inlet. There could also be some faulty components downstream. If you are not experiencing any of these conditions, then take a look at how the pump is internally. Is it worn or damaged and therefore leaking? Check if the pump outlet line is cooler than the pump case drain. If this is the case, then you will need to shut down the pump. Now remove the solid pump case drain pipe and replace it with a hose and restart the pump. If you see more than a small trickle of oil then you can safely say that the pump rotating group is not in good condition and is likely to be badly worn. Come back to visit our blog regularly for more hydraulic system troubleshooting help!