10 replies to this topic

[farid.k]

Guys,

Can I have a snapshot of the clause in latest nfpa 20 saying that fire water pump shall have dedicated pressure relief valve at pump discharge. What I have with me is 1999 edition in clause 2-6.1 saying that each pump shall have automatic relief valve ( not pressure relief valve ). The problem is, when the standard says "automatic relief valve", contractor come out the design with auto recirculation valve (arv or yarway valve) which is not common pressure relief valve. I do expect to have spring loaded relief valve.
Thanks

[farid.k]

Based on my reading, No section in this standard specifically permits the use of a main pressure relief valve on an electric fire pump, except where a variable speed driver is used. 

[breizh]

farid ,

The unit I've in mind is having a PSV (pressure safety valve) at the discharge , both on Jockey pump and Fire pump .

Breizh

[farid.k]

Yea, I already include in the design however some engineer challenge my design saying that, why dont you consider auto recirculation valve? The function is the same ( can avoid overpressure ). Plus, there is no specific clause IN NFPA 20 saying that there must be PSV at discharge of fire water pump using electric motor. How do I answer their question?

[Brocklesnar]

NFPA 20 / Section 4.7.7 provides guidance for selecting design pressure of fire protection pipeworks. Design pressure should be the net pump shutoff (churn) pressure plus the maximum static suction pressure, adjusted for elevation. It further specify that a pressure relief valve should not be used to stay within design pressure.

 

NFPA allows circulating relief valve for fire pumps, to allow adequate flow of water through pump and prevent overheating. This type of valve is typically seen on motor driven fire pumps and jockey pump.

 

Pressure relief valves for engine driven fire pumps should be located between the pump discharge nozzle and 1st check valve. A open-discharge cone arrangement is allowed.

 

NFPA do not intend to restrict use of relief valves beyond the 1st isolation valve of pump discharge.

 

Hope above helps.

[farid.k]

what is the different between 

-Circulation Relief Valves

-relief valve

 

is it mandatory to have both? circulation relief valve i think more to min flow line and should be sizing based on min flow of the pump. but if we already have min flow line, do we need to have relief valve? for me, it is redundant to have both.

[fallah]

farid.k,

 

Circulating relief valve is a self regulating pressure control valve that maitains the upstream pressure at a prespecified set point and send back the flow of pressure relieving to source tank. This self regulating valve and independent to control system is to be selected for fire water pumps due to respecting the safety matters...Please take a look at the PCV on jockey pumps discharge line included in the attached PID of a fire water system...

Attached Files

•  PCV on Jockey pump discharge line.docx   233.92KB   90 downloads

[farid.k]

farid.k,
 
Circulating relief valve is a self regulating pressure control valve that maitains the upstream pressure at a prespecified set point and send back the flow of pressure relieving to source tank. This self regulating valve and independent to control system is to be selected for fire water pumps due to respecting the safety matters...Please take a look at the PCV on jockey pumps discharge line included in the attached PID of a fire water system...

Fallah, is it mandatory for main fire wate pump?

[fallah]

farid.k,

 

Yes, the main fire water pumps have to be equipped with such circulating pressure releif valve but one common can be considered for several pupms...

[farid.k]

fallah, what if they proposed to use auto re-circulation valve (arv)? and how to set pressure for both relief valve and arv?

[fallah]

farid.k,

 

Per the concept, PCV is applied to maintain the pressure inside the fire water network to go higher than a pre specified value; then an ARV that works based on the flow might not do the job properly...