Issue: We observed in one of the 7-port valves (Upchurch V-241) that the motor was not actuating it accurately. An indication of this issue is the failure of the initialization process when the syringe pump tries to move the piston to the top. This fails due to the valve not being in the appropriate position. By comparing the torque required to turn the valve with other parts from the series, the defective valve was identified to require a significant higher force.
Normal torque: 12 to 13 Ncm
Solution: By loosing the hex nut at the back of the valve by approx 1/4 turn the pressure of the rotor to the stator was lowered to this range.
Some thought about pressure: The maximal pressure the syringe is specified for is 13.8 bar, the valve 69 bar. With the actual motor current setting of 0.75A (92 in Rambo board) we produce a force of 180 N, which translates in a pressure of 108 bar. This will obviously only be reached when the capillary is blocked…