If you are talking about the pin in the outer passage of the centrifugal bypass type of pump. It is there to keep the check ball from closing off the interconnection passage between the centrifugal bypass passage and the pressure bypass passage. Not to hold the check ball off it's seat. When the centrifugal bypass circuit is in operation (lower RPM range), the check ball will lift, reach the pin and move over (towards the outside of the pump) so that the passage is not blocked off and send the bypass oil back into the pressure bypass passage and into the return system. If the ball is not moved over it can close off the passage. If you did not build pressure in any RPM range with the pin in place and nothing else was wrong with the passage, I might look at the centrifugal valve in the rotor to make sure it is not stuck in the open position. Even with the centrifugal bypass passage open, the motor should build pressure. Even if the centrifugal bypass check ball seat was off center, the motor should have built pressure. Granted the pressure would be lower. If the centrifugal bypass valve in the rotor is working properly, it should close as the RPM of the motor increases thereby shutting off the centrifugal bypass circuit and sending the oil into the motor and the pressure bypass circuit.. If the valve in the rotor is not working properly and or stuck in the open position, more of your feed oil than you want is going to be sent back into the return system not into the motor at all times.
After reading what you posted about the passages, I would look closely at everything on the pump, check to see if the centrifugal valve in the rotor is installed correctly. Maybe its machined and installed wrong.
Last edited by JIm
on Fri Apr 25, 2008 6:32 pm, edited 1 time in total.