Hale MG - Manual (Page 13)

Muscle Pumps
1-6
Transfer Valve
A transfer valve, which is controlled from the
apparatus pump control panel, allows the operator
of a two-stage pump to select volume or pressure
operations. This valve is an all-bronze waterway
device that can transfer between pumping modes
with two and one-half turns of its control hand
wheel. The position of the valve is indicated on the
apparatus pump control panel via a positive
mechanical indicator. An optional power transfer
valve is available.
Choosing Between Volume and Pressure
Operation
In deciding which range to pump (pressure or
volume), choose the one that gives the desired flow
and pressure at the lowest engine speed. When a
change of range is desired, slow down to idle
speed, and shift the transfer valve to the desired
range. 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
operations. 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 (13 BAR) net pressure in volume
operation at reasonable engine speeds.
2. Generally, volume operation should be used at
any net pump pressure under 150 PSI (10
BAR), 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 that one-half the pump capacity
and when the desired pressure is over 150 PSI
(10 BAR).
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.