Kick back line in Fire pump piping

[nabeel3]

The attached photo and drawing is from my project fire tank piping. The nozzle is near to bottom of a 15 meter high tank. The tank nozzle N2 connected with pipe and valve is suction line of the centrifugal fire pump. Next to it is seen a nozzle, N9 which will be connected with a discharge line from pump. It is mentioned as Kick back line in the drawing. The pump discharge is networked through underground piping into various building. This kick back line is a branch from the main discharge header and connected with the tank nozzle N9 which is blinded in the pic. I am unable to understand the purpose of Kick back line. Any thoughts learned members.

 

[skdesigner]

Is there a flow meter called out on the line? Fairly common to pipe flow meter discharge back to a tank to minimize water wastage.

 

[LittleInch]

Give us more of that drawing where the kick back line is attached to the discharge line.

This snippet is really no help, but given that the diameter is the same size as the suction line it's clearly meant for some large flows.

I suspect it's some sort of "spill back" line designed to allow some flow through the pump when dead heading the pump, or maybe used as a full flow test of some sort, but without more data impossible to say.



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[nabeel3]

Dear skdesigner,

There is no flow meter in the line. But there is another dedicated test line.

 

[nabeel3]

Please see the attached photo. The connected pipe is suction of the pump. The blind nozzle is the kick back line.

 

[LittleInch]

Unfortunately whilst an interesting photo it tells us nothing.

Please send us the p&id of the discharge pipe where this line originates.

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Also: If you get a response it's polite to respond to it.

 

[nabeel3]

Dear little inch

Please see the attached. The blue line indicates kick back line. The pump discharge into under ground fire pipe network

 

[LittleInch]

OK, That looks like a full flow pump return line to the tank.

The P&ID may tell us a bit more, but you probably need to look in the Operating and control philosophy or process description to discover why it's there.

It's very curious as to why there are two lines, presumably one operating, one standby and the valve looks like a fail closed isolation valve, but the layout drawing doesn't give us that sort of information.

So it could be there to test the pump without dead heading it or be used to switch on the main electric pumps before you need the supply and then as soon as you do then close the flow return lines.



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Also: If you get a response it's polite to respond to it.

 

[nabeel3]

Dear little inch

Can u look into this attached photo. This is the client fire water system standard.

Thanks

 

[LittleInch]

That makes sense now we have all the relevant information.

What you have is a pressure regulated fire main, so if the flow in the main is low then the pumps could produce a higher pressure than parts of the system are designed for. Hence some water flows back to the tank to move the flow along the pump curve and results in lower pressure.

It also means that during a test, if the pumps are running but no fire water flow, there is water flow through the pumps.

It also limits the pressure in the system to some unspecified pressure so that presumably it doesn't exceed a certain pressure at the hose connections. Does your system have a lot of elevation change?

I'm no expert on NFPA systems, but those valve will need to be certified by the approved bodies (UL or FM) because if they fail open they could reduce pressure and flow in the fire main.

See NFPA 20 and NFPA 14.

https://blog.bermad.com/fire-protection/meeting-nfpa-20-compliance-standards-prv-vs.-pcv

NFPA standards are free to view on line

https://www.nfpa.org/codes-and-stan...ds/list-of-codes-and-standards/detail?code=20

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.