Tanker Venting

[DD]

Is there a formula to determine the area for the opening of a tanker vent? Does it need to be equal to the cross section of the discharge 10" dump valve (actually 9.75" opening) = 97.06 sq inches.

[S. Cook]

I've heard it needs to be 4 times the discharge.

[Dalmation90]

Hi Guys:
Didn't have a "formula" but do have some more information. It does need to be four times the cross section of the INTAKE --
4" intake =8" round or 7.1" square

NFPA 1231 notes a 8"x8" square vent is usually adequate. I'd at least equal, and preferabbly go 1.5 times the size of the dump just to have a comfortable margin.

When designing a truck to move water, it's no time to skimp on the plumbing and venting.

NFPA 1231, Water Supplies for Surburban and Rural Firefighting, Appendix C.1.6:

Proper venting is a prerequisite for filling and emptying tanks, but it is imperative for rapid filling and discharging of tanks. There must be adequate provision for air to be driven from the tank when it is being filled with water and for air to enter the tank. IT IS RECOMMENDED AS THAT, AS A MINIMUM, THE VENT OPENING SHOULD BE AT FOUR TIMES THE CROSS-SECTIONAL AREA OF THE INLET. (emphasis mine) Inadequate venting can result in the tank being bowed outward when it is being filled rapidly, or in impairing the discharge flow when emptying.

(Next paragraph notes 8"x8" is normally adequate)

And:
C-1.12.1 Mobile Water Supplies Equipped with Large Gravity Dumps.
...Adequate air intakes and tank baffle cuts should be provided, or inefficiency and possible tank damage can result...

[DD]

Thanks to all for information on venting tankers. Dick