Installation and Operation Manual
SA-07-11-87, Rev A
18
January 2019
Parallel Operation
Maximizing control is critical when operating
centrifugal pumps in parallel. One pump can
overpower the other in regard to head at a lower
total flow. If a simple, unrestricted manifold
(Figure 8) connects two pumps at the discharge
head, the discharge head of one pump is
imposed on the other.
In Figure 8, two pumps operating in parallel will
never have exactly the same performance
curves. At the design point (Q1), with the valve
open, both pumps are operating at the same
flow and head. However, as the system curve
changes with the valve positioning (Q2), pump A
can produce a higher head than pump B. In this
case pump B will stop flowing altogether,
causing it to operate in an unstable minimum
flow condition.
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.
Figure 8. Parallel Units Common Valve
Figure 9. Parallel Operation
