Hale DSD - Manual (Page 12)

Pressure (Series) Operation
Pressure operation, Figure 1-11, finds the impellers connected in series. That is, the output of the
impeller supplied from the pump intake is supplied to the input of the next impeller. The pressure at
the pump discharge is the sum of the pressures of the two impellers plus the pressure at the
intake. The amount of water delivered to the discharge is the same amount that entered the first
impeller. Using the example above when in series operation. The discharge pressure will be 330
PSI and the discharge volume will be 500 GPM.
Volume Versus Pressure Operation
Selection of volume versus pressure operation is determined by three factors:
• Generally, the pump should be operated so that the pump gives the desired result at the
lowest engine speed
• Transfer to volume (parallel) operation for higher flows (see below).
• Transfer to pressure (series) operation when higher water pressures are required (see
below). .
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 operation. 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.
TRANSFER VALVE
Figure 1-11. Two-Stage Pump Pressure Operations
SUCTION
CHECK VALVE
(CLOSED)
FIRST STAGE
IMPELLER
SECOND
STAGE
IMPELLER
CHECK VALVE
(CLOSED)
SUCTION
DISCHARGE MANIFOLD