Fire pump and jockey pump

[leo2011]

I’m designing fire sprinkler system for 5 story residential building in NY (only sprinkler system No fire cabinets).

The existing fire hydrant flow test is 40 PSI static pressure. The residual pressure is 37 PSI at 500 GPM

I ran my Hydraulic calculation and came up with 247.97 GPM and 75.61 PSI.

Should I size the fire pump for 247.97 GPM and 75.61 PSI?

Should I size the jockey pump for %10 of the flow and 84 PSI?



Please comments

 

[Artisi]

I would size the sprinkler pump 250 gpm @ 80 psi - assuming your calc's are correct this should be OK. The jacking pump only needs to be minimal flow rate, maybe 3-4 gpm @ 84 / 5 psi. You need to check the appropriate code for the detail.


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

interesting to know how you've spread out the flow or pressure over a building 5 stories high. This would generate a considerable difference in pressure from ground floor to top floor.

Be careful to differentiate required pressure from differential pressure required from you pump.

If you've got 37-40 psi coming in, your pump only needs to add 40 odd psi differential head which is how pumps are specified.

Jockey pump can be any size, but <5% (1 to 2% is ok) is a good idea otherwise it will only turn on for a few seconds before hitting the high pressure switch.

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

 

[leo2011]

Thanks! Now i have 2 different answers!
should I go with %100 of the pressure drop OR the differential head between the required Pressure and the street pressure?

What would happen if the street pressure drop below the test pressure?

Please Advice!

 

[Artisi]

You have to design for the minimum inlet pressure.
However-- as you are designing a life saving system you need / must get professional advise - not really of guess work etc.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

I'm assuming you've used something like NFPA 13? It's even free.

http://www.nfpa.org/codes-and-standards/document-information-pages?mode=code&code=13

Pumps are sized on differential, so as artisi says, minimum differential on inlet plus pump differential pressure = discharge pressure

If it's a bit high, you might get a bit more water - probably not a bad thing, but too high and you might spring a leak or burst a pipe - bad thing. SO also check max pressure plus pump at no flow < max system pressure on the ground floor.

I don't know much about sprinkler design but would imagine a lot of the pressure is lost over the sprinkler as opposed to friction in the piping? so a bit more pressure than the min is ok.

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