Fire Water Pump Test at non flow as per NFPA 25

[thkurian]

Hi,

We have a motor driven horizontal split casing (BB1)fire water pump in a new project under construction with rated capacity = 1136 m3/hr, Head = 131.5 m, Motor rating = 780 kW. As per NFPA 20, only a 1" relief valve is provided for minimum thermal flow. As per NFPA 25, pump is to be tested at non flow (only 1" relief valve is open) weekly for 10 minutes. Is this an acceptble practice for such high capacity pumps? Why a non-flow test is specified by NFPA 25 with 1" relief line instead of a separate test line with full pump capacity? In this project a separate test line is provided connected to suction tank which allows weekly pump testing at rated capacity. Please advise we can waive nonflow test as per NFPA 25 and conduct pump test at rated capacity for weekly run using test line.

Regards
Thomas Kurian

 

[LittleInch]

I've often despaired at what NFPA do to pumps but they seem to survive. Given that NFPA packages are very common, it is probably best to talk to the vendor and make sure they think it will survive this regular testing and at least there is some flow... Given that NFPA requirements are there it will need someone to waive the requirement and most fire people seem unwilling to do this and don't really seem to care about the pump being chewed up on a regular basis. Having said that, most fire pumps are pretty sturdy beasts and hence might survive much more than a more typical pump.

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

 

[thkurian]

Dear LittleInch,

Thanks. Vendor confirms that pump can work at about 6 m3/hr flow ( flow for a 1" relief valve). We requested Vendor to measure vibration during shop test at 6 m3/hr flow, but Vendor is not agreeing. Instead pump will be opened and checked for any rubbing after test since NFPA 20 says pump should not have excessive vibration only. What is excessive, NFPA is silent and not calling for vibration measurement. We would like to know, if such high capacity pumps are subjected to non flow test in any installation as per NFPA 25 and any feed back on pump bearing life. In US, NFPA is mandatory requirement for fire water pumps.

Regards
Thomas Kurian

 

[Artisi]

Not being an expert on NFPA I can understand the need for the pump to run at near to shut head to prove it's capability as this could well be a real operating condition but certainly not a weekly occurrence. The complete unit would be better run at its maximum / designed operating condition on a regular basis as this proves it's capability should it ever need to run as a firepump and not a maybe it will need to be a firepump one day. I would query this requirement with the approving authority who have the final say.

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.)

 

[bimr]

No, that is not accepted practice. Since the 1999 edition of NFPA 20, a circulation relief valve has been required.

To prevent water overheating at churn, a circulation relief valve located between the fire pump and fire pump discharge check valve is required to operate at churn pressures, but should not operate when the fire pump is flowing water. When water is flowing through a pressure relief valve or a test loop piped back to suction, the pressure will be lower than churn pressure and the circulation relief valve designed to operate at churn will not operate

"14. Chapter five of NFPA 25 requires a weekly fire pump test to be conducted without flowing water. Does this include the circulation relief valve?

No. The standard says "without flowing water" so no one flows water at minimum, rated and peak flows each week as required for the annual flow test. The circulation relief valve must flow water anytime the pump is running to provide proper cooling of the pump. Without this small flow of water, the pump will overheat resulting in damage to the pump shaft or other components."

http://www.nfpa.org/assets/files/aboutthecodes/25/25_faqs.pdf

 

[LittleInch]

Interestingly the section dealing with testing is now section 8 and I agree, 8.3.2.5 says a valve installed as a safety feature shall be permitted to discharge water. However it is accepted practice that you start fire pumps and run them for 10 minutes every week with generally very little flow going through them other than this 1" valve. Fire pumps are often fairly basic units which actually run for only a few hours in their lifetime so have different issues than pumps which run 95% of the time.

The purpose of the test is a little obscure, but basically hydrotests the system without needing any flow through a sprinkler system or hydrants. The ban on flow back to suction is because some systems just opened up a bypass and the pump would run to end of curve...

Artisi - I would agree with you, but the NFPA codes were designed by fire fighters and not pump designers. I've not come across many authorities which will go against whatever NFPA XX says.

I reviewed a "standard NFPA" pump package a few years ago and had three pages of comments and changes, many to do with the test re-circ loop and basically got told that this was a standard "NFPA approved design" and they weren't going to change a thing.... They ignored all the HAZOP comments as well....

The firewater pump package market seems to be very tight and all you get is a set design which matches NFPA to the letter and no more. The pumps do seem to work though and if you need new bearings every 5 years then so what?

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

 

[thkurian]

Thanks LiitleInch, bimr and Artisi. NFPA 25 requirements are more clear now. NFPA 25, 2014 Edition Clause 8.3.1.2 requires "A nonflow test shall be conducted for electric motor fire pumps without recirculating water to the pump suction .." and Clause 8.3.2.1 requires "A test of fire pump assemblies shall be conducted without flowing water..". This installation has another 6 engine diven pumps of same capacity, with engine cooling water flow of 30 m3/hr, hence weekly pump nonflow testing (30 minutes)is also questionable.
In the past, minimum stable flow protection with a PCV was provided for similar installations. Does this practice not followed now by the introduction of 1" recirculation relief valve as the stable minimum flow protection is not included in NFPA 20.

 

[Artisi]

Am I missing something here, what is a nonflow test/ without flowing water?

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.)

 

[thkurian]

Nonflow test is running the pump at shut off with discharge valve closed. Only the recirculation valve flow for motor driven pumps and cooling water flow for engine cooling are permitted. My concern is running such high capacity (5000 gpm) pumps at shut off with NFPA 25 permitted water flow may damage the pump.

 

[Artisi]

Sounds like shear stupidity to me running 780 kw pumps at effectively closed valve conditions. But after 40+ years involved with pumps - what would I know?


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.)

 

[nabeel3]

Dear Kurian,

In which Region are u testing these pump. In U.S or Europe or in M.E???

 

[thkurian]

Now pumps are undergoing shop tests in Europe. Pumps will be installed in Middle East.

 

[Artisi]

What does the pump manufacturer think about running at nearly closed valve for such a lengthy period - if the manufacturer is ok - then you can assume it's ok.

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.)