Fire Water Jockey Pump Configuration

[ColourfulFigsnDiags]

In most firewater systems I've seen, the jockey pump only kicks in when required to re-pressurise the firewater mains. However, I've just been presented with a set of P&IDs for a very large fire system, for a very large plant, in which it is implied that the jockey pump operates continuously with a continuous kickback to the fire water tank. This kickback is flow controled using a FCV and FIC upstream of the offtake.

Is this normal, and if so what are the advantages of doing this over having the pump kick in when required?

As far as I can see neither NFPA, nor any other standard says anything other than the duty of the Jockey pump is to maintain system pressure.

Read the Eng-Tips Site Policies at FAQ731-376

 

[pipedream]

have been in fire protection for nineteen years and have never heard of this. is the water to only circulate in the underground mains? it could not circulate through the sprinkler system because it would set the fire alarms off on a continous basis. the only thing i can figure is that if the water is circulating there might be a possibility of stagnint water in the underground mains. if the jockey pump is running all of the time and dumping back into the tank better put two relief valves on it so that one can be changed out while the other one is in service.

just my thoughts.

 

[JonnyWill]

For what is worth, my understanding of a jockey pump is to maintain pressure in a closed system .... if there is a pressure leakage of some kind, ie, opening of a valve, the jockey pumps kicks in to maintian the pressure.. but it shouldn't be run all the time .. should it ??

 

[harrysat]

Normally the jockey pump starts at a signal from a pressure switch. This pressure switch has two pressure levels: a low level to start the jockey pump and a high level to stop the jockeypump. The two values are set close to each other (i.e. 0,5 bar) to keep the pressure in the fire mains as constant as possible.

I noticed that in very large underground fire mains systems, the pressure in the fire mains can vary constantly. The variation can be 0,5 - 1,0 bar as far as I have seen. When that happens, I can imagine that it can be better to keep the jockey pump working all the time, and to regulate the pressure via a pressure relief valve with a outlet to the water storage. I've never seen this but this can be the reasing that the engineer has chosen this way to control a constant pressure. The disadvantage are the energy costs and the maintenance of the the jockeypump because is has that many working hours. The advantage is a more constant pressure in the systems and less false alarms because of the (slight) water hammer that can take place when a jockey pump starts.