2nd Relief Valve

[ashomar]

I have a customer concerned about the fire pump main relief valve failing, which may cause damage to the fire protection piping due to high pressure in the system. They are suggesting installing a 2nd relief valve as a back up. Is this a good idea, where can this be installed?

 

[NJ1]

Well typically you have a 3/4 relief valve on the discharge side and a 4" kunkle relief valve on the bypass. How many more relief valves do you want to install?
What is your actual static system pressure? What is the head pressure of this pump?
Please advise

 

[FFP1]

I assume you have a diesel driven pump and the existing relief valve is the same diameter as the discharge pipe........

If this is the case, I do not see any problem with two listed/approved properly sized relief valves located downstream of the fire pump. There is no code or specific reason why this would cause a problem. Loss history would indicate this approach is a waste of money since desiel driver overspeed incidents are rare and the listed/approved relief valves are historically reliable.

I say explain everything in detail to the customer and install a second redundant relief valve if they still want to spend the money for the "extra" level of reliability.

{If you are referring to the 1/2-3/4 in. diameter circulation relief valve on an electric fire pump, this size relief valve is simply not designed or capable of preventing excessive pressure as you have indicated.......in addition, there is really no purpose for a larger diameter relief valve IF you have an electric fire pump!}

I hope this helps.

 

[b1ueshift]

Relief valves are more likely to fail open as they rely on a small spring loaded pressure relief valve to seat properly to hold the main valve shut.

The relief valve is unlikley to fail shut and even if it did, the worst thing that is likely to happen is there will be some drips as the system should have been pressure tested to well above the maximum operating pressure when it was comissioned.

If the client has a big budget, you could install a fire pump with a variable speed drive (these have come on the market in recent years). The variable speed drive will regulate the pressure and if it fails a pressure relief valve will prevent overpressure.

 

[ashomar]

Thank you all for the reply. The relief valve is 6" mounted on a common 12" discharge from 2 elctric and one diesel pumps, all taking suction from a well. The concern is that the underground fire mains are old (about 40 years old) and any failure in the relief valve may cause a lot of more expensive leaks.
If we decide to install the 2nd relief valve, what settings should be used. The current valve opens at 140 psi. The pumps are rated 2000 gpm at 130 psi.

 

[chicopee]

Isn't the test levers designed to periodically test the relief valves?