3 replies to this topic

[Ghasem.Bashiri]

Dear Process/Safety Experts
I checked different code and practice for Fire Water Jockey Pump capacity.
But there is not a unique procedure for this issue.
Some practice recommends 1% of main fire water pump.
Also I found some practice as 15, 30 and 60 m3/hr for this pump.
I wish you can share your experince about this issue to find a suitable solution or procedure applicable to all process/safety engineers.
Ghasem Bashiri

[breizh]

Hi ,
Let you get a copy of NFPA 20 , it will support your query.
Breizh

[fallah]

Dear Ghasem,

It should be sized such that to make up the allowable leakage rate within 10 minutes or 1 gpm (3.8 L/min),whichever is larger.

Fallah

[kkala]

In addition to previous advice, it may be worth while noting (even known) that purpose of jockey pump(s) is to avoid operation of main fire fighting pump during small fire water consumptions, or leakages from fire water distribution. A jockey pump can start and stop automatically; a main fire fighting pump (of much higher flow) can start automatically or manually, but stops only manually (according to usual practices); so irrelevant starts of the latter have to be avoided.
Now "small fire water consumptions, or leakages from fire water distribution" is a bit subjective, also depending on length and conditions of fire water network. In a known case , jockey pumps had a capacity of 2x90=180 m3/h, while max fire water demand was about 2000 m3/h. But initial capacity of jockey pumps was 2x25 m3/h (on same max fire water demand), which changed later during design phase. So capacity of jockeys increased from 2.5% to 9% of max fire water demand (covered by main fire water pumps).
NFPA 20 may define % range, (but I am now aware of its content).
The 10 min time to restore leakage rate is not known to me. A jockey pump will not stop until its discharge pressure P gets the set value, e.g. 8.3 Barg. Does this requirement mean that "even if P increases, main fire water pump will start in 10 min if P does not reach 8.3 Barg"?
If P continues decreasing, main fire water pump will start as soon as its set point is approached, which happens much sooner than in 10 min in case of a strong fire.

Edited by kkala, 12 March 2011 - 07:32 AM.