12
4.4 Check Valves
(Figure 8, 9, 10 & 11)
Operating experience on thousands of installations has indicated the many metering pump troubles have to do
with check valves. Problems usually stem from (a) an accumulation of trash between the valve and seat, (b)
corrosion which damages seating surfaces, (c) erosion from high velocity flow, or (d) normal physical damage
after extended service.
When reassembling after cleaning or replacement be sure to use new seals. Separate the valve assembly and
examine the components for wear, damage or accumulation of solids. A ball valve seat should have a sharp 90
◦
edge, free of any nicks or dents. Hold the ball firmly on the seat and examine against a light. If light is visible
between the two then replace the seat and/or ball.
4.5 Hydraulic Make-up Valve
Hydraulic make-up valves are designed to maintain the correct volume of oil in the hydraulic system between the
piston and the diaphragm. Pumps are supplied with one of two valve styles shown in figures 12 &13.
