NFPA 20 - 5% volume for sump in fuel tank Fig A 11.4.4 1

[ContractorDave]

I seem to be getting conflicting explanations for this 5% sump. On the face of it, it would appear that this sump volume is to prevent debris from getting into the fuel line. However my fire pump supplier is saying this is something built into the design of the tank and has more to do with head pressure at the outlet.

Could someone elucidate?

Regards
Dave

Regards
D

A thing moderately good is not so good as it ought to be
Thomas Paine

 

[stookeyfpe]

I would say the issue is scale inside the tank. I don't agree with the head pressure theory.

 

[ContractorDave]

That would seem to be the obvious conclusion stookey, so I was somewhat surprised by this other answer. We're doing a project where we supplied the diesel fire pumps but because of circumstances, we did not provide the fuel tanks. The ones that eventually showed up do not have a bottom side outlet, but rather a bottom of tank outlet. I'm thinking I'm going to have to thread a piece of 1" pipe extra long so it sits up inside several inches.

Regards
D

A thing moderately good is not so good as it ought to be
Thomas Paine

 

[skdesigner]

Dave, check out NFPA 20-2010 11.4.1.2.9:

11.4.1.2.9.1 The fuel supply pipe connection shall be located on a SIDE of the tank.

11.4.1.2.9.2 The engine fuel supply (suction) pipe connection shall be located on the tank so that 5 percent of the tank volume provides a sump volume not usable by the engine.

 

[skdesigner]

Just pulled out the 20-2010 handbook, and it offers this little tidbit on pg. 264:

The 5 percent sump in the fuel tank is provided for any sediment or condensation that may be in the tank. By position the supply connection to the engine on the side of the tank at an elevation no lower than the engine fuel pump the plumbing to the engine is always under a small head pressure. In the event of a leak, fuel will escape and be observed. This method is preferred to air being drawn in, resulting in the possible loss of engine prime, if the supply line is under negative pressure.

 

[ContractorDave]

Thx SK

I have that handbook on site too but damn if my supplier shouldn't be all over this.



Regards
D

A thing moderately good is not so good as it ought to be
Thomas Paine