User guide

Glossary
G - 3
Pump Shift A midship pump is usually mounted with a split gearbox installed in the drive shaft.
The pump shift moves a sliding gear in the gearbox that transmits power either to the
pump or the rear axle. In road position, power is transmitted to the rear axle for driving; in
pump position, the rear axle is disconnected, and power is transmitted to the pump shaft.
Relay Movement of water from apparatus at a water source to additional apparatus until water
Reaches the fire ground.
Relief Valve An automatic valve which, when activated by the relief valve control, will hold pump
pressure steady when discharge valves or shutoff nozzles are closed. The valve maintains
its given pressure by dumping the pump discharge flow into the pump suction.
Relief Valve A handwheel adjustment valve which, set to control the desired pressure, will control the
Control relief valve to maintain the working pressure.
Series Pressure position in which the first impeller’s discharge is fed to the eye of the second
Impeller in a two-stage pump which then discharges the water from the pump.
Service Test Pump test performed to determine if the apparatus can deliver its rated volume and pressure.
Shrouds Sides of an impeller that confine the water.
Slinger Ring Prevents water from continuing to travel down a shaft to the gears and ball bearings.
Stages The number of impellers in a pump that are used in series; that is, one following another
in terms of flow. Each impeller develops part of the total pump pressure.
Tachometer Indicates the speed of the engine crankshaft in revolutions per minute.
Torque The force that acts to produce rotation.
Transfer A two-position valve in a pump that changes the operation from parallel (volume) to series
Valve (pressure) operation and vice versa (not used on single stage pumps).
Vanes Guides inside an impeller that direct water to the volute.
Volute Gradually increasing discharge waterway.
Water Amount of work that a pump can perform.
Horsepower
Wear Rings See Clearance rings.