This could be caused by an excessive amount of air pressure.

All air hydraulic pump manufacturers recommend the operating air pressure be in the 90 to 120 psi range.

The air motor on all air operated hydraulic pumps must be able to dissipate air for it to run efficiently. With high air pressure the motor cannot dissipate the air quickly enough and this will cause back pressure and an eventual stall or air bypass.

This can be prevented two ways.

1.      Adjust the regulator down on your air line or compressor to the recommended range of 90-120 psi.

2.      Make up a regulator and gauge kit with air quick connects and attach it to the air inlet side of the pump. Then adjust the regulator to 90-120 psi. This will also allow for easy connecting and removal for proper storage in your tool box when not in use (please see attached photo).

Note: Draining water from the shop or truck compressor daily and applying a good air tool oil (Marvel Mystery oil) into the air inlet once a day will also help minimize air bypass.