How do you tell the correct rotation of a hydraulic pump and what happens if you run it in reverse?

How do you tell the correct rotation of a hydraulic pump?

Most hydraulic pumps will rotate CW (looking at the shaft). Since most pumps are turned by 3 Phase electric motors it is easy to make the motor turn the right direction. There are exceptions, so the manufacturers ID tag and product catalog or the web can shed some light if there is doubt.

Determining pump rotation on a Gear pump is the simplest one.

The drive shaft is offset since it is driving one gear direct and they normally have a large Suction port and a smaller Outlet port. Since flow in the pump is between the gear teeth and housing, it is easy to imagine which way the pump is setup by turning the shaft so flow is from the large port to the small port.

gearpump.pngGear pumps are most often the ones that have no markings for rotation.

Also some gear pumps made for Mobile equipment have two large ports and can turn either rotation. The correct port must be connected to tank and the other port could be reduced since it will then be outlet.

These pumps have check valves in their housing to keep outlet pressure from going to case and blowing the shaft seal while bypass oil can get back to the suction port.

What happens if you run a hydraulic pump in reverse?

It would try to pump oil from the circuit and put back in the tank. After the circuit is evacuated, the pump continues to run. It would run dry until it overheated and locked up mechanically if the clearances of the running parts are minimal.

Some Vane pumps with the Vanes in the Rotor at an angle could possibly bend, break, break segments out of the Rotor etc. until the pump locked up.

If it is running reverse rotation and someone hooked up the inlet to the circuit and the outlet to tank it would pump oil, though it would probably cavitate due to the small size port connected to tank. However, when pressure starts to build most design pumps would blow the shaft seal.

An axial piston or bent axis pump would only make noise since the notches in the valve plate would be on the wrong side and each piston could have some high pressure spikes as it discharges its last bit of oil. However, these pressure spikes will reduce pump life in relation to max pressure setting.