casing relief valve in fire pumps

[saleh.na]

Hi.
Is the Casing relief valve or automatic relief valve(protect pump of overheating) the same as the pressure relief valve in fire pumps?
Acc. to NFPA 20 , The automatic relief valve shall have a nominal size of 0.75 in. (19 mm) for pumps with a rated capacity not exceeding 2500 gpm (9462 L/min) and have a nominal size of 1 in(25 mm) for pumps with a rated capacity of 3000 gpm to 5000 gpm (11,355 L/min to 18,925 L/min).
Please comment.

 

[itsmoked]

I kinda doubt they're the same because you can still have overheating problems with a lower pressure.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mk3223]

This type of relief valve, i.e. overheating protection of the pump casing due to the fluid heated under the sun radiation., is one type of pressure relief valve. But, it can release a certain amount of fluid enough to protect the pump for the specific purpose.

 

[Artisi]

do you have an overheating problem and why?


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[saleh.na]

No,this is not problem., each pump(s) shall have an automatic relief valve listed for pump service installed and set below the shutoff pressure at minimum expected suction pressure.The valve shall provide sufficient water flow to prevent the pump from overheating when operating with no discharge.the question is whether automatic relief valve the same as the pressure relief valve?

 

[JJPellin]

No. The automatic relief valve is there to pass enough flow under deadhead conditions to prevent the pump from burning up. The PSV is there to prevent the pump from over-pressure damage when blocked in but not running. That would be my interpretation.

Johnny Pellin

 

[LittleInch]

It would be very helpful to specify the section you refer to as NFPA 20 has many different relief valves allowable.

It's not easy to be precise, but I believe this is simply a thermal relief valve designed so that in the idiotic tests NFPA require (run for 30mins at max speed against a closed head) the water tends to get rather hot and can expand such that the pump is damaged or just thermal expansion from ambient air / solar gain.

NFPa / vendors tend not to like pressure relief valves in case they go off / leak when they shouldn't, hence the rather small size listed.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[saleh.na]

Thank you very much for the discussions you have made but the standard requires that the device be used to prevent the temperature rise in closed-circuit mode that means no pump discharge outlet.
4.13 Circulation Relief Valve.
4.13.1 General Requirements.
4.13.1.1* Where an electric variable speed pump is installed,
the automatic circulation relief valve shall open at the minimum speed.
4.13.1.2 Unless the requirements of 4.13.1.8 are met, each pump(s) shall have an automatic relief valve listed for the fire
pump service installed and set below the shutoff pressure at minimum expected suction pressure.
4.13.1.3 The valve shall be installed on the discharge side of the pump before the discharge check valve
4.13.1.4 The valve shall provide sufficient water flow to prevent the pump from overheating when operating with no discharge.
4.13.1.5 Provisions shall be made for discharge to a drain.
4.13.1.7 The automatic relief valve shall have a nominal size of 0.75 in. (19 mm) for pumps with a rated capacity not exceeding
2500 gpm (9462 L/min) and have a nominal size of 1 in.(25 mm) for pumps with a rated capacity of 3000 gpm to 5000 gpm (11,355 L/min to 18,925 L/min).
4.13.1.8 The requirements of 4.13.1 shall not apply to enginedriven pumps for which engine cooling water is taken from the
pump discharge.

 

[Artisi]

Don't really understand what your problem is, a pressure relief valve is a pressure relief valve used to limit pressure, whether its to safeguard the casing or down stream equipment from over pressure or to allow by-pass at a set pressure so as there is flow thru', the pump in the test situation, is to me - exactly the same thing.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[saleh.na]

My question was whether the two are one or not? Which is my understanding with these explanations that they are one. Thank you all dear

 

[TugboatEng]

Two different valves. The casing relief valve protects the pump when it is not operating from changes in pressure caused by solar heating of the system.

The automatic recirculating valve protects the pump from overheating while it's operating in low flow situations and aids in priming. The automatic recirc valve installs in place of the discharge check.

http://www.schuf.com/products/pump-recirculation-valve