Manual

of large piston fast stroke rate pumps, the dumping pressure is an instantaneous pressure generally experienced

only in the first discharge stroke of the pump since the make-up valve cannot replace the displacement of the

piston in one stroke.

It is unusual for a hydraulic bypass valve to operate during normal pump operation. The following conditions will

cause bypass pump operation.

1. Excessive pressure buildup in the process which the pump is injecting into.

2. A plugged discharge line or someone shutting off a valve in the discharge line while the pump is operating.

3. Restricted flow to the pump causing the make-up valve to operate. If an inlet strainer is plugged, or someone

closes an inlet valve thereby restricting the flow of fluid to the pump, the diaphragm is then unable to follow

movement of the plunger. The vacuum created between the diaphragm and the plunger upset the make-up

valve allowing oil to replace the vacuum condition. This excess oil will be displaced through the bypass valve

on the discharge stroke of the plunger. Undersized (restrictive) piping must be avoided (see “Piping” page 5.)

Any unusual condition in the system which prevents free movement of the diaphragm will cause a

recirculating condition between the make-up valve and the hydraulic bypass valve. Continuous oil

recirculation against the bypass valve will eventually cavitate the hydraulic prime plus introduce unnecessary

load conditions within the pump mechanism.

4.8 Automatic Bleed Valve (Figure 14)

The automatic bleed valve is a gravity operated ball check valve designed to displace a small quantity of hydraulic

oil or air on each pump stroke.

Any accumulation of solids can cause malfunction. Unscrew the valve and clean it with kerosene or solvent. If

solids cannot be removed, the valve must be replaced since there is no means of repair.