Doesn't it state in NFPA 20 that it is either bad design practice, or
maybe even prohibited to over size a pump and rely on a relief valve to
take care of the excess pressure.
I can see if you have a situation where the city water was upgraded and
now an existing pump is in this situation. However, if new design, then
alternative options from the PRelV should be taken.
4.7.7* Maximum Pressure for Centrifugal Pumps.
4.7.7.1 The net pump shutoff (churn) pressure plus the maximum static
suction pressure, adjusted for elevation, shall not exceed the pressure
for which the system components are rated.
4.7.7.2* Pressure relief valves and pressure regulating devices in the
fire pump installation shall not be used as a means to meet the
requirements of 4.7.7.1.
A.4.7.7 It is poor design practice to overdesign the fire pump and
driver and then count on the pressure relief valve to open and relieve
the excess pressure.Apressure relief valve is not an acceptable method
of reducing systempressure under normal operating conditions.
A.4.7.7.2 It is not the intent of this subsection to restrict the use of
pressure reducing valves downstream of the discharge isolation valve for
the purpose of meeting the requirements of 4.7.7.
I guess if you put it after the pump discharge control valve, then NFPA
20 no longer applies and you go to NFPA 13 and/or 14 which may allow the
device.
Travis Mack, SET
MFP Design, LLC
2508 E Lodgepole Drive
Gilbert, AZ 85298
480-505-9271
fax: 866-430-6107
email:[email protected]
On 5/20/2014 9:12 AM, Steve Leyton wrote:
Dewayne:
Why a reducing valve instead of a relief valve? If the excess
pressure is at churn only, then a relief valve would be the ticket as it
only occurs in a no-flow condition. This would mitigate Pete's concerns
about redundancy as prescribed in NFPA 14.
SML
-----Original Message-----
From: Sprinklerforum
[mailto:[email protected]] On Behalf Of
Martinez, Dewayne
Sent: Tuesday, May 20, 2014 5:20 AM
To: [email protected]
Subject: Pressure reducing valve on fire pump
We have a situation where we have a pump that produces more than 175psi
at churn. Can we put in a main pressure reducing valve after the pump
discharge to bring it all down to 175psi or do we need one for each
system?
Thanks,
Dewayne
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