Water System Design Manual
December 2009
Page 125
10.4.6 Pump Protection
In addition to check valves listed in Section 10.4.3, each pump motor should have protection
from power supply disruptions. Such disruptions include, but are not limited to, lightning, loss of
voltage, or loss of phase.
10.4.7 Piping Material
The engineer should use appropriate materials for interior BPS piping designs, such as ductile
iron, steel, galvanized iron, or copper piping. PVC piping should not be used. The design should
also address special anchoring or support requirements for equipment and piping.
10.5 Backup Power Facilities for Closed System Booster Pump Station
Because the service area of a closed system BPS depends entirely on the continuing operation of
the BPS, the engineer must consider standby power facilities (WAC 246-290-420). The BPS, in
effect, acts as the only source of supply and pressure for the area served. Backup or alternate
power facilities should have an automatic transfer switch that starts the moment the utility power
supply is interrupted. Manual transfer may be sufficient if it occurs in a reasonable period
according to established operating procedures. If fire flow is required, closed system BPSs must
have backup power unless specific reliability requirements are met (WAC 246-293-660(1)(c)).
10.6 Booster Pump Station Structural Design
The engineer must consider seismic risk when designing a BPS (WAC 246-290-200). See
Section 13.5 for guidance on seismic design of BPSs.
10.7 Multiple Pump Design Considerations
A water system may include multiple pumps designed and operated to provide variable design
flows to its service area. The configuration of a multiple pump operation can be "parallel" or in
"series." The design engineer should be familiar with the procedures for sizing multiple pumps
under either the parallel or series operational modes.
Parallel pump operation:
The combined pump head-capacity curve is determined at the same
head. Just add the capacities of the individual pump curves after they are modified to account for
ordinary friction losses that occur as part of the system head-capacity curve. The point where the
combined curve and the system head-capacity curve intersect yields the total capacity of the
combined pumps and the modified head at which each operates. The actual total capacity is
normally less than the sum of the individual capacities of each pump.
Series pump operation
: The combined head-capacity curve is determined by adding the head of
each pump at the same capacity (pumping rate). This mode is used to increase the head capacity
of the pumping station. The combined operating head will be greater than each individual pump
can provide, but not as great as their sum.