Instruction and Operation Manual
SA-07-11-37 Rev Orig
11
Jan 2009
that the pump flow is likely to drift
aimlessly and not respond to control
valve position.
Parallel Operation
Maximizing control is critical when operating
centrifugal pumps in parallel. One pump can
overpower the other in regards to head at a
lower total flow. If a simple, unrestricted manifold
connects two pumps at the discharge head, the
discharge head of one pump is imposed on the
other. All pumps will see the same discharge
head at a given time. This is demonstrated on
the following curves:
The characteristic curves of two pumps
designated A and B are demonstrated in the
Parallel Operation figure.
Since no two pumps will have exactly the same
performance, it is assumed that pump A
produces a slight amount more head than pump
B. The pumps are arranged with a common
manifold as shown in Parallel Units Common
Valve figure.
Figure 3. Parallel Operation
Figure 4. Parallel Units Common Valve
The pressure in the manifold is set at P
1
; the
flow through pump A indicated as A
1
on the
preceding curve. At the same time, the flow
through pump B is indicated as B
1
. However, if
the throttle valve is closed to cause the manifold
pressure P to rise to P
2
, then flows through
pump A and B are A
2
and B
2
respectively. If the
throttle valve were closed even further, then
pump B would cease to flow entirely. Since
pump B would effectively be deadheaded, the
fluid in it would heat up and boil. During internal
boiling, it could encounter liquid slugging and
probable damage to the pump. Proper selection
of a control system can prevent this situation.
