Hale DSD - Manual (Page 11)

TWO-STAGE PUMPS
There are two series of two-stage pumps:
• 750 GPM to 1250 GPM
• 1000 to 2000 GPM
Hale two-stage pumps are of a size and design to mount on the chassis rails of commercial and
custom trucks The pump is driven from the truck main drive line. Generally, the pump consists of
the following major components:
• Pump Body
• Impeller and Shaft Components
• Gearbox
• Priming System
• Pressure control Device
• Valves
Two-Stage Pump Operation
The primary difference between a single-stage and a two-stage pump is that the former has only
one impeller and no transfer valve to switch between volume and pressure operation. A transfer
valve is a two-position valve that permits the impellers in a two-stage pump to be operated in
parallel (volume) or series (pressure). Both types of operation are explained in the following
paragraphs.
Volume (Parallel) Operation
Volume operation, Figure 1-10, results in the pressure at the pump intake being added to the
pressure developed by both impellers, and the amount of water delivered to the discharge being
the sum of the flows of the two impellers. For example, if the inlet pressure is 30 pounds per
square inch (PSI), and the flow of each impeller is 500 GPM at 150 PSI, the pressure and volume
at the discharge is 1000 GPM at 180 PSI:
500 GPM per Impeller X 2 Impellers = 1000 GPM
30 PSI Inlet Pressure + 150 PSI Pump Pressure =180 PSI
TRANSFER VALVE DISCHARGE MANIFOLD
SUCTION
CHECK VALVE
(OPEN)
IMPELLERS
CHECK VALVE
(OPEN)
SUCTION
Figure 1-10. Two-Stage Pump Volume Operation