Hale DSD - Manual (Page 13)

When shifting the transfer valve from volume to pressure operation, the pressure will be doubled.
You may hear a metallic click or two clicks, which will be the check valves closing. If the clicks
sound too harshly, you are changing the transfer valve while the pressure is too high. This happens
when the truck engine is running at high speed.
Refer to your fire department policy for when to use volume operation and when to use pressure
operation.
If your fire department does not have a policy to follow, here are general guidelines:
1. Hale pumps are designed to pump up to 200 PSI net pressure in volume operation at
reasonable engine speeds.
2 Generally, volume operation should be used at any net pump pressure under 150 PSI, especially
when pumping from a hydrant
3. When pumping from draft or a water tank, pressure operation may be used when the volume is
less than one-half the pump capacity and when the desired pressure is over 150 PSI
4. Be certain to warn everyone involved before changing pump range.
Transferring Between Volume and Pressure Operation
Transferring between volume and pressure operation is evidenced by a metallic click, which results
from the check valves closing. If the click is too loud or perhaps, somewhat violent, the pumping
pressure is too high for switching. In this case, you should ease back on the engine throttle.
Switching between volume and pressure operation is generally governed by prevailing fire
department policy. However, here are some general guidelines if your fire department does not
have an established policy:
1. The pump should be operated so that engine speed is within its best operating range.
2 Transfer to volume (parallel) operation if the pump has to discharge more than 50 percent of its
rated capacity. Be certain to warn everyone involved before switching between volume and
pressure operation.
3
. While the switch can be done at any pressure, it is highly recommended to reduce the pump
pressure to 50 to 60 PSI before switching. The engine speed should especially be reduced when
switching from volume to pressure operation with hand held hoses in use.