True. Good point. I should've mentioned the pump is diesel. The tank is 40' high. To conform to NFPA 20, 2007 section 5.18.1.1, 121% of churn gives (105 x 120% x 121%) + (40 x .433) = 170 psi (approx), assuming churn pressure is 120% of rated pressure. Someone would have thought it was not too far from 175 psi. I wasn't involved with the original design.
Anyway the discharge from the relief valve can't be much to maintain 175 psi system pressure. But NFPA 20, 2007 section A.5.18.7 (appendix) requires "...back pressure capabilities and limitations of the valve to be used to be determined. ...". I might be wrong, but I'm assuming the reference to "back pressure" means friction loss. If it is, I can't see friction loss being a critical factor. Unless, ....as piping the relief discharge causes a closed loop, is there a concern that the pressure would keep on increasing at every cycle? Tony -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Roland Huggins Sent: March 20, 2009 9:48 AM To: [email protected] Subject: Re: Fire Pump relief valve discharge How about a more basic question. Why do you even have a relief valve? With a rating of only 105 psi exceeding 175 psi with a tank feed requires a tall tank. Roland On Mar 19, 2009, at 11:23 PM, A.P.Silva wrote: > > The building owner wants to connect the discharge piping from the pump > relief valve to the pump suction pipe, just upstream of the suction > valve. > The water supply to the pump is a water storage tank. Anyone seen this > arrangement? Is it acceptable? > > NFPA 20, 2007 section 5.18.7 mentions "Discharge to Source of Supply". > Is this to the tank or can it be also to the suction pipe? Both 5.18.7 > and A5.18.7, seems to have a concern regarding the size of the relief > valve and discharge piping, but does not provide much guidance (in my > opinion). Anyone care to expand on this concern? > > The fire pump is rated 1000 gpm @ 105 psi. The source as mentioned > previously, are gravity tanks. The relief valve is 4" and discharge > pipe is 8" corresponding to Table 5.25. The discharge piping from the > relief valve to connection at pump suction pipe has one elbow. At the > connection to the pump suction there is a tee. Is the tee to be > counted and the sizing be increased as per 5.18.6.2 ? > > Any pump experts? > > Tony > > _______________________________________________ > Sprinklerforum mailing list > http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum > For Technical Assistance, send an email to: > [email protected] > > To Unsubscribe, send an email > to:[email protected] > (Put the word unsubscribe in the subject field) > _______________________________________________ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field) _______________________________________________ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field)
