Jockey Pump Req'd for Wet Supply to Dry Valve?

4/9/2020

In regards to a dry-pipe system with a fire pump on the supply; is a jockey pump required on the wet portion between the pump and the dry-pipe valves?

I have to assume the answer is yes, since pressure needs to be maintained in this line if leaks develop over time. Please confirm/advise. Thanks in advance!

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9 Comments

Mike ike

4/9/2020 10:13:33 am

Not nessasarily. I've designed monitor systems without a jp since the system was manual and pump would turn on from the pressure drop after the control valve is opened.

Franck

4/10/2020 04:48:30 am

That's weird
If the system is manual, why the start of the pump is not manual as well?
In your case, a possible issue would be a leak on the main between the pump and the manual operating system. The water pressure will drop and your pump will start automatically on pressure drop.
And because your fire pump is not supposed to stop automatically, this means that it will operate, at almost no flow, until somebody shows up and stop the pump.
In extreme conditions (not continuously attended location), it can creates serious damages to your fire pump (overheating of the pump casing for electric pump if no adequate circulation relief valve is provided, or, in a very bad scenario that happened once in a plant with a diesel fire pump, the destruction of the engine with loss of raw cooling water : the pump operated during the entire week end and emptied the water supply tank (limited capacity) via the raw cooling water supply... no more cooling for the engine).

Pete D

4/9/2020 10:20:18 am

A jockey pump is a high pressure low capcity (flow) pump. The reason they're included is to make-up pressure that bleeds off of the private service main network without hammering the system with the full power of the fire pump in a no flow condition. Their necessity exists independently of the type of overhead system connected.

Franck

4/10/2020 04:40:35 am

Fully agree with that comment.

The purpose of the Jockey pump is not to cope with leaks (even though in case of leaks it will do it !).

The purpose of the Jockey pump is to maintain the pressure in your system so that you fire pump will start only in case of a large flow, because sprinklers are operating.
The setting of the pressures (start/stop) of the Jockey pump is then determined, based on the churn pressure of your fire pump, to avoid water hammer (that could lead to spurious activation of deluge/preaction/dry systems or sometimes damages on piping) when the fire pump automatically start.
It will also prevent that a small leak in your system will start the fire pump to compensate the pressure (all the more since fire pumps are normally not supposed to be equipped with an automatic stop at a preset pressure).

It is therefore necessary for all fire systems with a fire pump (alternative could be a pressure tank, with the same purpose of keeping the pressure under normal conditions at a level above the start pressure of the fire pump)

FIREPE25

4/9/2020 12:54:14 pm

In my opinion the best way to deal with a system in which you have a very small amount of wet pipe after the fire pump is to install an excess pressure pump. NFPA 20 does not require pressure maintenance pumps to be listed. An excess pressure pump utilizing a pressure switch will save you money. Also, Jockey Pumps on this arrangement have been known to short cycle. An excess pressure pump will alleviate this problem as well.

sean

4/9/2020 07:41:41 pm

a pressure maintenance pump is there more for longevity then anything else.

Mark

4/10/2020 02:10:05 pm

FOr that or a deluge valve header application I like the excess pressure pump option FirePE25 suggests. Albany pump makes one and could control start and stop with Potter PCS switch.
If you go full blown jockey pump and controller with the small volume of piping have had to put extra (two instead of just one) check valve in the jockey pump discharge pipe spaced as far apart as practical to help stop the short cycle issues mentioned. Helps keep the water hammer off the mercoid or transducer switch in the jockey pump controller.

FIREPE25

4/10/2020 02:13:07 pm

Mark, good point about the deluge valve. Most of the projects we have done this on are large freezers with pre-action systems.

5/19/2020 02:38:43 pm

Dear All,

The primary purpose of Jockey Pump (JP) is to prevent inadvertent operation of main FW pumps unless it is really required to operate (i.e. only in emergency scenario).
Main FW pumps will only intend to start when there is real crises/ demand from Hydrants, monitors, Sprinklers or deluge system which is possible in case of emergency scenario only whereas JP starts due to minor leakages on prolonged stagnant water in wet pipes, inadvertently hose reel open by operator or any other cause which is non-emergency scenario. The sizing of JP, there are number of ways to do, like thumb rule, leakage calculations or equivalent of one hose reel capacity (say 100 gpm or less) but should be less than one hydrants. The pressure, as it is called pressure maintenance pumps (another name of JP) is only maintains the pressure in the wet system in non-emergency scenario and it will stop once main FW Pumps comes into operation/during emergency. The on-off pressure settlings should be slightly higher than main pumps operation settings (NFPA 20 have numerical values to do this). Since JP need not to operate in emergency, so not required to be comply with NFPA 20. JP is API pumps (Conventional process pumps), generally follow API 650 nothing to do with NFPA 20. The operation can be continuous or intermittent depend of power availability.

Trust this will help.

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