Jockey Pump Pressure

[moiz19670309]

Hello'
NFPA 20 requires the head at 150% flow to be atleast 65% of rated head. It also requires the head at 0% flow to be no more than 140% of rated head.
Being client some one is installing Fire Protection System in our plant. We have witnessed the Pump tests. During the jockey pump test, its maximum pressure at 0 flow came out to be 172%. We have objected about this increase from limiting 140% to 172%. But the Fire Protection System designer says that he will install a pressure relief valve at the discharge of jockey pump and hence limit the 172% to 140%. He says NFPA allows it for pressure maintaining devices.
Is he right or should we reject the pump.
Kindly help me.

Moiz Khan

 

[SprinklerDesigner2]

There isn't an acceptance test for a jockey pump because a jockey pump is not required to be listed or approved.

The only thing that might cause me concern is if the discharge churn pressure exceeded 175 psi which only means the pressure switch isn't set correctly.

 

[MGXFP]

Your head limitations are for fire pumps, not jockey pumps.

I've used domestic water pumps as jockey pumps in scenarios where a fire pump feeds a main loop from a water storage tank. It is perfectly fine.

You can reject the jockey pump but not because NFPA 20 says so.

 

[LCREP]

The problem with jockey pump are they were not set properly, often the pressure they started at was too low resulting in a water hammer when the fire pump activates. So if the fire pump churns at say 150 psi the jockey pump should come on at 140 psi, off at 150 psi, the fire pump should come on at 135 psi. The start pressure difference on the jockey pump can be as low as 5 psi, but I found most times a mercord switch could not be set for a 5 psi difference.

Just to be clear the jockey pump is limited to about 15-30 gpm at most. Where the fire pump is in the 100's to 1000's of gallons of water per minute.

 

[DavidCR]

You could add any device to make the pressure maintaining system work fine, hydro-pneumatic tank, relief valves, controls, etc. But the simpler the better, and the simple UL jockey pump controller is the normal budget option and the normal practice.

I´d say that if the jockey pump is normally small the upper limit is not important since it should not be capable to withstand an open valve, or sprinkler flow, so the pressure will only go up if system is closed or with small leaks (depends on the system particular characteristics we don´t know) and the pressure control device have to be very well sized to warranty the right settings.

The important point that is indirectly required by the NFPA 20 is that the lower setting defines the fire pump start pressure, and if the upper limit is not reliable or if the system is unstable (too big, difficult to control how much air is trapped, etc.), the start-stop cycle will be unstable, too frecuent, etc.