Columbia Concrete Products
Page 6
1/04
HYDROSTATIC PUMP
PREPARATION FOR ADJUSTMENT
The control piston has strong centering springs to ensure that once the pump is
adjusted for the neutral position it will always return to neutral. If an adjustment is
necessary follow the steps listed below.
To ensure there is equal pressure on both sides of the control module during the
centering operation, it is necessary to connect the X1 and X2 ports together by means of
hose or tubing (No less than a ¼ inch ID). The port sizes are as follows:
Size 28 90
7/16-20 UNF
Size 125 & 250
9/16-18 UNF
Pump Size
Allen Wrench
Wrench
28 56
6 mm
19 mm
71 906 mm
24 mm
125 2508 mm
24 mm
With pressure gages installed at Ma and Mb, and with A and B ports blocked (or motor
stalled), and with the pump running loosen the jam nut. Turn the mechanical centering
adjusting screw until 1000 psi is read on Ma or Mb then turn screw opposite direction
until 1000 psi is read on other pressure port. Turn the screw back, splitting the distance
between the previous two positions. This should be the neutral position. Pressure on Ma
and Mb should be equal.
Tighten jam nut, stop the pump drive, remove the hose connecting ports X1 and X2.