Fire Sprinkler Waterflow switch activation with jockey pump

[Mike Cole]

Hi guys,

I need some input here. I have a client that has a waterflow switch at the base of the riser activating when the jockey pump runs. I need to provide him some sort of solution to get this alarm device into service.

A little history about the building...

It's an existing Library that recently had an addition... With the new addition, it was required the Fire Pump be upgraded. The fire pump and jockey pump were both replaced and a connection to the new addition was added. This is when the issue arose. The riser flow switch in the existing building is at the base of the only riser feeding wet systems for the floors (7 floors in total). Due to the increase in size of the jockey pump, the amount of water going past that flow switch is now activating it. Never had and issue with the old jockey pump.

We've tried everything. The operating time of the jockey pump from On pressure (160psi) to off (175psi) is about 5 minute, which eliminates the dialing up the flow switch to 90 seconds. We've considered installing check valves on the feeds to both buildings to cut down on the volume of water being pressurized. We still can only get the run time down to 4 minutes and that's not a full proof solution.

What would you do here??? I don't want to replace the jockey pump to a low GPM pump, I'm afraid it will decrease fill times significantly. Do you adjust jockey on/off pressures to the minimum and adjust the flow switch up???? With that, I still don't like the idea of that flow switch moving every time the jockey pump runs....

My engineer recommends to install a lower GPM jockey pump, and be done with it. I need a second opinion.

Any help would be appreciated.

Thanks in advance.

Michael Cole
Vice President
Cole Fire Protection, Inc.

Chicago IL

 

[cdafd]

Why can't the flow switch be at 90 seconds??

 

[skdesigner]

cdafd: I think he's saying that it doesn't matter if the retard on the switch is set to 90 seconds, because the jp takes 5 minutes to complete its cycle.

Mike:

What is the capacity of the jockey pump? If it's moving enough water to activate (I'm assuming) at least a 4" flow switch, it's probably quite a bit over-sized.

Here's the annex commentary from NFPA 20-2013 regarding sizing of pressure make-up pumps:

For situations where the pressure maintenance pump serves only above ground piping for fire sprinkler and standpipe systems, the pressure maintenance pump should be sized to provide a flow less than a single fire sprinkler. The main fire pump should start and run (providing a pump running signal) for any waterflow situation where a sprinkler has opened, which will not happen if the pressure maintenance pump is too large.
One guideline that has been successfully used to size pressure maintenance pumps is to select a pump that will make up the allowable leakage rate in 10 minutes or 1 gpm (3.8 L/min), whichever is larger.

Since your system is above ground, allowable leakage would be 0 gpm. Fairly unlikely that a 1 gpm jockey is going to activate a flow switch.

Does the switch only activate when you drain and then fill the system, or does it do it whenever the jockey comes on to boost the pressure back up automatically?

If it only happens when you are re-filling the system, I'd say just shut the jockey off and let the system fill as much as possible from city pressure. Once the system is basically full of water (albeit at a fairly low pressure), turn the jockey on and let it pump the couple dozen more gallons in to crank the pressure up to where it needs to be. With a 7 storey building, you'd probably only need about 40 psi static from the city to fill the majority of the system.

If it's the other scenario, I'd be curious to know why an above-ground system in a conditioned building is losing 15 psi with any amount of frequency. Presumably it isn't leaking. Do the new zones have the little 1/2" relief valves on them? The cheap factory-set ones are notoriously imprecise, and can start pissing as low as 150 psi, and maybe close around 180.

Sorry for the long winded post. Short answer is, (a) find out why that 15 psi drop is occurring, and (b) put a smaller jockey in.

 

[Mike Cole]

They're losing 15psi every.... maybe month.... It's an extremely small leak.

If I remember correctly, its a 10GPM jockey pump... I'm guessing that's where my problem lies....

Michael Cole
Vice President
Cole Fire Protection, Inc.

Chicago IL

 

[skdesigner]

Yep. Potter VSR's operate around 10 gpm, and System Sensors operate from 4-10 gpm. A 1-2 gpm jockey would do the trick.

Your cut-in and cut-outs are pretty far apart. The fire pump is going to slam the system pretty hard if it starts at 155 or less. I'd set the new jockey cut-in to 170, and fire pump start at 165. Even if the jockey operates a little bit more frequently, there would be less water to pump in each time.

 

[Mike Cole]

agreed.... I'm not a fan of the pressure settings... That will be in my list of recommendations.


Michael Cole
Vice President
Cole Fire Protection, Inc.

Chicago IL

 

[LCREP]

A few things to consider look into....

How old is the flow switch, if it is the original perhaps the spring is weak and is contributing to the problem. Do you have a retard chamber if so maybe a pressure switch on top of the chamber to replace the flow switch. Or can you install a retard chamber and pressure switch?

 

[LCREP]

The other thing to consider is a pressure pump on the system side of the check valve above the alarm valve/check valve. They used to use them with the old gamwell pull box system to prevent false alarms. Pump it up to 172 psi and the should take care of it.