Maximum Velocity in the outletpipe of the base injection foam system

[salazarafael]

I am evaluating a base injection foam system for a diesel storage tank, where the outlet pipe velocity is 28 ft/s: According to NFPA 11, the maximum velocity for this hydrocarbon liquid, Class II, is 20ft/s.What is the problem that can cause velocity above that indicated by the standard?

 

[hfgnick]

If I remember correctly, the problem is that at very high velocities the foam picks up and absorbs the fuel so that the foam becomes in-effective. I think there is discussing in NFPA 11 or other related references.

 

[stookeyfpe]

Too small of pipe diameter.
Backpressure on the foam maker exceeds it velocity limits.
The pressure downstream of the fire pump (if provided) creates pressures that causes the velocity limit to be exceeded.