An OEM had a machine that developed a problem with a motor-driven porting tool in a high-production application. When drilling a hole, the motor was slow and lacked the torque needed for a quick in-and-out cycle. The positioning motor seemed to work fine — it cycled correctly, and both A and B port unloader valves would dump fluid directly back to tank (without it passing through the return filter) and releasing any force on the fixture when the porting tool was energized. The cycling rate of the machine had dropped almost 50% from what was achieved in the past.
The maintenance crew studied the circuit and felt the porting tool motor needed replacing. However, a new motor did not help the cycling rate of the porting tool at all. Both directional valves shifted fine, both manually and electrically. The only thing left in the circuit was to replace the two-stage pilot operated directional valve. They made sure the pilot pressure, (X) port and pilot drain, (Y) port both were configured for external connections. Unfortunately, this didn’t help either.
They finally decided to find a pressure gauge and flow meter with a loading valve to further troubleshoot the system. The pressure gauge was installed close to the pump outlet, and the flow meter fit nicely into the main pressure line going to the first directional valve. They found both the system pressure and flow met design specs.
Any idea what the cause of the problem might be?