Forrester Booster Station Wat...r Tech Memo Final 4_24_08EN6INEERIN6 . PLANNING .ENVIRONMENTAL SCIEN~~t'i'~~
1231 FRYAR AVENUE
SUMNER, WA 98390-1516
T. 253.863.5128 F.253.863.094G
www.parametriY.com ,
TECHNICAL MEMORANDUM
Date: Apri124, 2008
To: Jim Gibson, P.E., City of Yelm
From: Joel Linke; Ray Nickel, P.E.; Randy Raymond, P.E.
Subject: Downstream Transient Hydraulics
Project Number: 247-1781-024
Project Name: Forrester Booster Pump Station
1.0 INTRODUCTION
This technical memorandum summarizes the hydraulics downstream of the Forrester Heights Booster
Pump Station. This memorandum includes hydraulic transient analysis for four skid-mounted booster
pumps and the water main into which they discharge. It is based on the September 2006 Forrester Heights
Water Force Main Plan and Profile drawings, the March 2008 drawings for the Forrester Heights Water
Booster Pump Station, and the March 10, 2008, Forrester Heights Water Booster Pump Station Project
Report.
The currently proposed Forrester Heights Booster Pump Station includes a normal operation firm capacity
of 117 gpm at a minimum pressure of 60 psi at all service connections as directed by the City of Yelm
and calculated using the Washington State Department of Health: Water System Design Manual
(WSDM). In addition to the normal operation capacity, the station also includes a fire flow operation firm
capacity of 750 gpm, for a total flow of 867 gpm, at a minimum pressure of 20 psi at all points in the
distribution system. Firm pumping capacity is based on the largest unit out of service. This requires each
operating condition to have a sufficiently sized standby pump to be able to handle the flow in the case that
the largest pump fails.
Recommendations are summarized in Section 5.0 of this memorandum.
2.0 ASSUMPTIONS AND DATA
2.1 Static Head
Calculation of static head at the rated duty point for the pumps assumes the following:
• Pump suction pressure at elevation 354 feet is assumed to be 60 psi for normal operation and
20 psi for fire flow operation.
Discharge hydraulic grade line for the force main at elevation 411 feet (the last fire hydrant
height) is assumed to be 60 psi for normal operation and 20 psi for fire flow operation.
• Total Static Head = 57 feet.
TECHNICAL MEMORANDUM (CONTINUED)
2.2 Force Mains
The force main data from the pump-to-discharge is based on the September 2006 Forrester Heights Water
Force Main Plan and Profile drawings and the March 2008 drawings for the Forrester Heights Water
Booster Pump Station and is shown in Table 1.
Table 1. Force Main Data
ID Total Modulus of Estimated Wave
Pipe (in) Length (ft) Elasticity (psi) Speed (ft/s) Class
8" DIP 8 75 24,000,000 4,000 50
10" C900 PVC 9.78 1,030 400,000 1,350 150
The diameter and modulus of elasticity of each type of pipe is used to determine the water hammer wave
speed. The length and class of each pipe are used to determine if the pressure ever exceeds or drops below
the rated pressures of each pipe along its entire length.
2.3 Pump and System Curve Data
The pump and system curves were obtained from the March 10, 2008, Forrester Heights Water Booster
Pump Station Project Report.
3.0 HYDRAULIC TRANSIENT ANALYSIS
The hydraulic transient or water hammer analysis used Flow Science software. Steady state base
conditions stated earlier in this analysis were coordinated with conditions resulting from operation of the
pumps described in the March 10, 2008, Forrester Heights Water Booster Pump Station Project Report.
Based on review of pump station operations, it was determined that the most extreme water hammer
events will occur during a sudden power-outage pump shutdown or normal pump start-up. Absolute
maximum and minimum limits for transient pressures were set at 346 feet (150 psi) above and 32 feet
below centerline of the pipe respectively. Acceptable minimum transient pressure was set at 20 feet below
centerline of the pipe.
3.1 Power Outage Pump Shutdown Results
Power outage pump shutdown was modeled and analyzed in Flow Science software. The shutdown
analysis was done by stopping all three large pumps at once. This shutdown resulted in acceptable
pressures for the system without a pressurized surge tank, or any vacuum relief valves. The results of this
analysis can be found in Appendix A.
However, according to the analysis, it is recommended that the connection from the force main to the
proposed 132-gallon pressure tank included in the KPFF design be increased from 1-1/4 inches to
4 inches. The pressure tank included in the KPFF design will reduce frequent pump cycling, dampen the
pressure surges during normal operation and shutdown of the pumps, and provide smoother operation.
The larger connection will improve the ability of the surge tank to perform these functions. The results of
this analysis can be found in Appendix B.
During analysis of the shutdown conditions, it was noted that flow through the booster station would be
severely limited in a total failure condition by the small size of the pump volutes. It is, therefore,
recommended that an 8-inch check valve with normally open isolation valves on either side be provided
to allow flow from the suction side to the discharge side of the pump station. This valve would allow the
City of Yelm 247-/78/-024
Downstream Transient Hydraulics 2 April24, 2008
TECHNICAL MEMORANDUM (CONTINUED)
Forrester Heights system to maintain some minimal domestic flow and allow fire flows to be pumped
through the station (using a pumper truck) in a complete pump station failure situation, and could provide
a small measure of surge protection to the upstream systems. A sketch of this installation can be found in
Appendix D.
3.2 Pump Start-Up Results
Pump start-up was also modeled and analyzed in Flow Science software. Since the proposed design
desires the capability for across the line starting in the redundant pump, the start-up analysis was done by
starting all three large pumps at once without the operation of variable frequency drives. This start-up
resulted in acceptable pressures for the downstream system. The results of this analysis can be found in
Appendix C.
4.0 OTHER ISSUES
The upstream system was not modeled in detail as a part of this analysis. Both pump starts and stops can
affect the upstream system. Hand calculations indicate that a power outage shutdown of the pumps is not
likely to result in damaging conditions in the upstream system. However, hand calculations of pump start
(based on across-the-line start-up conditions) indicate a potential for damaging conditions in the upstream
system. Therefore, it is recommended that a soft starter be provided on the redundant CR90-1 pump.
5.0 RECOMMENDATIONS
The recommendations made in this memo are summarized in the points below.
5.1 Water Hammer Protection
Shutdown: To improve the ability of the surge tank to dampen the pressure surges during normal
operation and shutdown of the pumps, it is recommended that the connection from the force main to the
132-gallon pressure tank included in the KPFF design be increased from 1-1/4 inches to 4 inches. To
maintain some domestic flow and allow fire flows to be pumped through the station (using a pumper
truck) in a complete pump station failure situation, installation of an additional 8-inch check valve with
two normally open isolation valves from the suction to discharge side of the pump station is
recommended.
Start-Up: When provided with the enlarged connection noted above, the proposed pressure tank provides
adequate protection to the downstream system for pump start-up.
Normal: It is recommended that the City consider requesting a spare 132-gallon pressure surge tank to
minimize down time so that the facility can continue to operate smoothly when the tank needs to be taken
off-line for maintenance or repair.
Upstream: It is recommended that a soft starter be provided on the motor for the redundant CR90-1
pump.
APPENDICES
A -Power Outage Pump Shutdown Results
B -Power Outage Pump Shutdown with Pressurized Surge Tank Results
C -Pump Start-Up Results
D -Recommended Check Valve Configuration
City of Yelm 247-1781-024
Downsdeam Transient Hydraulics 3 Apri124, 2008
APPENDIX A
Power Outage Pump Shutdown Results
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