Gravity Fed Dry Brake

How big of a vent is necessary when using a gravity fed dry brake?

 

vent should be same size as dump side.

 

4.8 Gallons going in and its gravity fed not pressure fed.

 

if anything, the vent should be bigger, as the fuel is technically pressurized(inches of water) going in.
the one i used last year, and will be buying soon, was 2" outlet and vent, double dry break.

 

Not including the fuel bladder I am going to be carrying on my back.

 

We are using a single brake not a double.

 

If you look in the male part of the D/B you will see it is divided into 3 equal spaces, the fuel will take one path and the air will take another....
Some dumpcans have only a pressure vent (small) usually in the filler cap.
I can't tell you exactly how I do them cuz it is a secret.

 

the fuel outlet is the restriction, not the vent...given the vent isn't a pinhole.
air flows much more easily than fuel...particularly, downhill. in fact, that's how your engine's cylinders get filled. the air isn't sucked in...it's pushed in by atmospheric pressure. no way in hell fluid can move that fast under only approximately 14.7psi.(that bars ram-air, et al).
in other words, the vent does not need to equal the size of the fill tube.
if you're making your own system, check it out with water...if it bubbles, the vent's too small. when the vent is enlarged enough to eliminate bubbling, a bigger vent won't make it much better.

 

Thanks guys. After doing a dry run w/ water and not gas I think we may have this one nipped.

Glad we used water because in our testing we had started to fill the dump can with a garden hose without venting the DB and low and behold it pressurized and shot water all over the place.

I am sure you can imagine the jokes that started with us using gas instead of water and having old smokey joe in the pits next to us sucking on his 50th ciggarette of the day.

Good times!