Page 122
December 2009
Water System Design Manual
1.
Open System BPS
: PHD within the service area of the supplying distribution system
plus supply to the BPS equal to the MDD-rate in the higher-pressure service area. If the
BPS was designed to deliver a greater flow rate than the MDD-rate of the high-pressure
service area under normal operating conditions, the engineer must use the greater flow
rate to determine the capacity of the supplying system to deliver needed flow to the BPS.
2.
Closed System BPS
: PHD within the service area of the supplying distribution system
plus supply to the BPS equal to the PHD in the higher-pressure service area, or the design
flow rate of the BPS, whichever is greater.
10.2.2 Hydraulic Design for Supplying System: Fire Flow Conditions
The engineer must design the BPS to maintain at least 20 psi at ground level at all points in the
low service, or supplying distribution system, under the following conditions:
1.
Open System BPS:
Under fire flow plus the MDD rate conditions within the supplying
distribution system (WAC 246-290-230(6)), the open system BPS design should include
provisions to lock out pump operation whenever one of the following conditions exists:
a.
Suction pressure causes the pressure at service connections along the supplying
distribution system to fall below 20 psi.
b.
Suction pressure falls below 10 psi anywhere in the suction end of the BPS piping.
Storage in the high service area would provide water service during the lockout
period.
2.
Closed System BPS:
a.
Under fire flow plus the MDD rate conditions within the supplying distribution
system (WAC 246-290-230(6)) plus supply to the BPS equal to the PHD of the high
service area.
b.
PHD within the supplying distribution system, plus supply to the BPS equal to fire
flow plus the MDD rate conditions (WAC 246-290-230(6)) for the high service area.
10.3 Mechanical Design Considerations
The engineer should consider the following design issues for BPS design:
1.
Pump efficiency at the operating point(s) (at the intersection of the pump curve(s) with
the system head curve(s)).
2.
Pump start-up and performance testing requirements.
3.
Pressure rating of pump casing and end connections.
4.
Horsepower requirements at full load; identify operating efficiency at full load, and
specify service factor.
5.
Electric motor thermal overload protection.
6.
Electric supply available at the voltage, amperage, and desired phase configuration.