Fire pump test header sizing

[Rolland1]

NFPA 20-2007 allows the designer to hydraulically size the pipe for the test header art. 4.20.3.4(2).

There's no mention of the acceptable pressure. Figure 4.20.3.4.(2) identifies the elements that must be included in the calculation, but there's no design critereas.

Should I consider that the acceptable pressure drop is the residual pressure of the water source at a flow of 150% the nominal pump flow?

Thanks

 

[pipesnpumps]

Size such that it is possible to flowtest at 150% of nominal pump flowrate.

Use minimum suction pressure possible, which is residual pressure (at pumping flowrate), at the residual hydrant tap-in, less losses between the residual hydrant and the pump suction flange. To the minimum suction pressure, add 65% of the rated TDH (total dynamic head) of the pump.. That is the minimum discharge pressure.

Size the test header to be able to flow 150% of pump flow with this discharge pressure you calculated.

 

[Rolland1]

Thanks.

If you look at figure 4.20.3.4.(2) in NFPA 20-2010 the last line showns a minimum pitot tube pressure of 18 psig.

Does this means that the minimum pressure at the flow measuring location is 18 psig? FM global recommends a minimum of 10 psig.

Adding all pipe length, fittings and elevation in this form, we will get a calculated pressure drop at 150% pump's nomial flow ,from the discharge of the pump to the flow measuring location (hose nozzle).

Am I right to assume that we must make sure that the pump and water source can deliver such a pressure at the 150% flow?