what would cause low pressure in the system for the fire pump 1

[Jaystam1]

At our facility we had a supervisory alarm go off for fire pump running due to low pressure. We had the same problem couple weeks ago with our jockey pump low pressure. The fire alarm is not going into full bells and whistles just a supervisory and after a little bit the pressure goes back to normal. Could this be from the suction side if we are not getting enough pressure from city or is there something in the sprinkler lines itself? Thanks Jay

 

[skdesigner]

Are you sure it's pump running due to low pressure? Might the controller be set to do an automatic weekly run test?

It shouldn't be the city pressure fluctuating. If you look at your pump layout, you'll see that every time a pipe connects the discharge to the suction (Bypass, pressure sensing, thru the pump) there is a check valve.

When you say "the pressure goes back to normal", do you mean that the fire pump shuts off? If it was indeed a low pressure condition that started the pump, it should not be able to automatically shut down (got to keep dumping the wet stuff on the red stuff if a fire happens).

The operation manual for the controller should be behind the front door of the controller. The first thing I would do is read up on the automatic weekly run test.

 

[TravisMack]

I have seen some pumps with automatic shut off. Very bad idea in my opinion. If that pump is on, I want some one to have to shut it off manually. I would bet that there is a leak, or some one is taking water from a hydrant downstream of the pump if it is connected that way.

And, get that fire pump changed to manual shut off. The jockey is fine as automatic shut off, but fix the fire pump to manual shut off.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[cdafd]

Have you sought professional help??

Contact the company that does the annual inspection and have them trouble shoot

Before something gets messed up and dOes not work when it needs to

 

[skdesigner]

Yes, have the inspection company in. If it's a leak starting the pump, it has to be big enough to drop the pressure faster than the jockey pump can maintain it. Jockey pumps usually pump a little less than the flow of one sprinkler. This means a.) this is not a small amount of water, and leaks don't fix themselves and b.) a leak like this would likely trip a flow switch, in which case you would get an alarm. Same if somebody opened a downstream hydrant.

Look through your controller configurations. Pressure points should be set as follows:

Fire Pump Stop: Churn pressure (data plate) + Static Pressure (inlet gauge)

Jockey Start: Pump Stop minus 10 psi

Fire Pump Start: Jockey Start minus 5 psi

After typing all this out, one more thought. Do you have pressure relief valves on your system? One small half inch one not set properly could potentially dump enough water to start the pump. But then your flow switch should pick it up...

 

[TravisMack]

Not all underground that feeds hydrants will have a flow switch on it. I am always a fan of putting a flow switch on any bulk pipe, but it is not always done. I have seen several projects with a main pump house feeding and underground fire loop with hydrants. The flow switches were on the system risers. In that setup, you could open the hydrants and not trip a flow switch.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

 

[NJ1]

If you are dropping pressure that fast but can visually find the leak You should start by:

Troubleshooting Mercoid Switches
Troubleshoot system check valve

 

[bobinillinois]

Is there a backflow preventer on the system?

I've been testing fire pumps and had alarms go off in neighboring buildings because I sucked water out of their buildings. I also had one customer whose system had a single check valve that had disconnected their waterflow alarms because every time some one used the car wash down the street, their alarms would sound.

I've encountered similar problems to what you describe in small loop systems that are usually attatched to dry systems. Small volume systems are way touchier than similar systems hooked to wet systems.

 

[MGXFP]

Just to be clear: is the pump feeding a sprinkler system only or something else like an underground fire line?

 

[EGFPE]

You need to determine if the low pressure is on the suction or discharge side of the pump (fire/jockey). Also, are you certain that you had a low pressure alarm for the jockey pump? Better yet, are you certain you are getting a low pressure alarm. It is not usual to supervise a fire pump controller for low pressure. Unless NFPA has changed, I do not believe this is part of the required system monitoring. If the jockey pump cannot keep up with the flow, then the system pressure will continue to drop if the system cannot keep up with the demand. Then the fire pump should start. If the fire pump does not start you would then get a supervisory alarm indicating a failure to start (diesel) or loss of power (electric).

 

[FIRESPRINK]

We had the exact scenario discussed, a private fire hydrant downstream of the pump was having water removed and the main booster pump would cycle on. However with what is being described, I would consider any check valves on the booster pump suction line. If there is a backflow prevention device it should be tested and/or inspected as well. In a normal situation the jockey pump kicks on and pushes everything up, the expected ways to relieve/lose pressure are (1) No water seen, the pipe and/or fittings are leaking in a place not seen-the underground (2) No water seen, the PRV on the discharge side of the booster pump (or on the systems) is set too low and is relieving pressure-not uncommon (3) No water seen, any/all of the supply side check valves are not water tight and the boosted pressure is leaking back into the lower pressure inlet (4) At the test header water is seen, have you confirmed that after the last fire pump test was the test header valve totally closed, often these can be left cracked open and this will drain pressure out the test header and most fitters leave the lowest test hose valve open and the cap loose so that condensate and leakage will not build up and freeze. If the test hdr valve is cracked and a hose valve cap loose there will be water building up under that hose valve.

If it is underground leaking there is a company called Leak Detectors in Illinois. I have used them 5~6 times in 34 years when we could not find the water leaks but Nelson works around the country and all I can say is he has always helped us AND he has helped those I recommended him to. I suspect he has some kind of electronic dowsing rod, he says no.