Fire Pumps and Overpressure 1

[AdamMurray]

We have building with several double interlock preaction systems all served by one common riser. This system is boosted by an electric fire pump complete with a pressure relief valve set at 170 psi.
The problem we are having is to do with system overpressure at pump start up. When the pump starts it provides a "bump" on the system raising the system pressure above the check valve to approx. 245 psi. Conversations with relif valve manufacturers indicate that these valves do take a second or two to open.

My question is: How can we contain the initial bump without modifying the pump. My initial thoughts are some type of retard chamber, however I am not familiar with these with such a pressure bump. Any ideas?

 

[scotty409]

First, find the engineer who designed this and slap him for over-sizing the pump then quick-fixing it with a pressure relief valve. NFPA 20 is quite clear that this practice is not acceptable.

There are surge suppressers available for this type of application. I don't know of a mfg off hand, but I do have a picture of one and will be glad to send it to you. Let me know.

 

[AdamMurray]

Pics would be nice and a great place to start, tks.

 

[scotty409]

what is your email address?

J. Scott Mitchell
Fire Protection Engineer

 

[AdamMurray]

adam_murray13@hotmail.com

And thanks again.

 

[gouveia]

A late post, but the two manufactures I know of are Greer and Young Engineering. These companies have UL listed equipment. They are very pricey. Other companies make ASTM compliant tanks.

I agree with Scott, the original designer screwed up big time. I recently worked on a project very similar. The only solution other than replacing the pump that I know of is to add a pressure-reducing valve. I personally think it is a poor solution but have seen other people use them. Then in addition to the pressure-reducing valve they installed a couple surge tanks.

Good Luck.

 

[pierrepaul]

What is the order of price of those pumps ?

Bryce
SPK Engineering

http://www.spk.fr/index.htm?referrer=securite_incendie

 

[TonyinNY]

Hi everyone.

Is this a combined sprinkler and standpipe system? If so how about pressure reducing valves at sprinkler system connections?

 

[thijsie]

Hi,

I heard they sometimes solve this problem wit a jaw-way valve (don't know if I spell it correctly) . This is a valve with a quick response time, to relief the pressure in the system.

This bump could also be the result of water hammering. Check literature how to prevent this from hapening.

bye

 

[LCREP]

What pressures does the fire pump come on and what pressure does the jockey pump come on at? If the fire pump is coming on at a too low pressure, it will cause a water hammer. NFPA 20, 2003 sectionA14.2.7 indicated a 10 psi difference between the jockey start and fire pump. I see many pumps where the difference is sometimes 100 psi ( client does not want the fire pump to come on!). I have also have found pumps were the set point for the fire pump is below the incoming city pressure. This is not good either.