One relief valve for two diesel twin pumps

[DavidCR]

Hi everybody.

In an installation of two twin diesel centrifugal split case pumps, one as main and the other as back up. Both take water from the same suction tank and both supply water to the same fire water system.

In case we need a relief valve to protect the system from overpressure. We plan to connect the relief valve to both pumps discharges with tees, and the relief valve discharge pipe is one pipe that goes to the suction tank.

As per NFPA 20. Can I use one relief valve to protect the system for both pumps?.

Is OK to size the relief valve as for one pump only, to protect both?

Thanks in advance for your comments.

 

[cdafd]

Do not know the answer , but if you put a tee between the pumps and one kicks on won't you pressurize the other pump piping???? Possible problem????

 

[Jondoeiowa]

This is not a confirmation that you can use one, but as to CDAFD's remark, would it be possible to put a check va. after the pump but before the relief piping it joined as to prevent the water from going from one pump right to the other?

 

[DavidCR]

Thanks, cdafd. I was thinking of the concept of using one relief valve and not the other implications, my mistake.

It looks that the check valves would solve the problem, but is there something in the NFPA20 that obligates you to use individual relief valves.

 

[cdafd]

Have to look at 20

If it says each or similar wording or specifies where it has to be, looks like you could do it.

Is there a problem if both pumps are running, and hey need relief either the pressure against the check would not allow one to relieve, or the relief is not big enough for both at the same time???

More than likey once you pipe all this and get it set up, buying two will be cheaper

 

[DavidCR]

Ive just got a response from the NFPA technical staff that says that in his opinion the intention of the code is the use individual relief valves. And that the discharge hast to be independent. Thanks a lot for your comments.

 

[cdafd]

It was an idea