Diesel Pump Req' Relief Valve for Governor Fail?

3/28/2022

Does a diesel-powered fire pump require a full flow relief valve to prevent over pressurization due to a RPM governor failure?

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7 Comments

Alex

3/28/2022 06:18:02 am

Hi,

A relief valve should be added, when there is a chance of failure that would in turn cause over pressurization that exceeds the maximum pressure for which the system components are rated. [NFPA 20 (2016) 4.19]

Thanks,
Alex

Anthony

3/28/2022 08:13:37 am

Ales got it in one. Diesel runaway is a legitimate risk for diesel engines, you don't want that over pressure to hit your sprinkler system.

Glenn Berger

3/28/2022 08:34:10 am

Alex and Anthony are spot on.

Jesse

3/28/2022 09:08:59 am

A relief valve is typically necessary when there's the chance that a failure can create an overpressure situation higher than the rated maximum of components.

Jesse

3/28/2022 09:10:51 am

Well goodness. I guess that's what I get for opening the blog in my browser, getting a cup of coffee, and not hitting refresh when I sat back down. Alex and Anthony nailed it.

Franck

3/28/2022 10:46:34 am

Everything is said.
But it is only required when the pressure at 121% exceed the maximum allowable pressure.
As for most sprinklers, the max. allowable pressure is 175 psi (12 bars), you provide a PRV when the pressure delivered at churn may exceed 145 psi (145 x 121 = 175 psi) or 10 bars.
Note that this is the pressure delivered by the pump, taking into account the possible head lift from the water tank.
If the water tank gives 15 psi (1 bar), this is when the net pressure delivered by the pump at churn is as low as 130 psi (9 bars).

Phil W

6/20/2022 04:03:23 pm

Don't forget to add static gain from your fire water tank when calculating the churn pressure. This static pressure plus your theoretical closed valve pump pressure is the total figure to start with before multiplying by 1.21.

Also, bear in mind some actual pump delivery pressures are higher than stated on initial curves which can throw you outside of maximum working pressure of components!

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Diesel Pump Req' Relief Valve for Governor Fail?

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