welding on negative pressure

[tightfits]

I was having a hard time getting an airtight hull trully airtight when I discovered that hooking vacume to the hull while zapping a small but persistant leak is very effective. Just wondering if anyone is currently using this method?

[Momo2000]

The reverse method is more common - apply the exhaust of your vacuum to the hull to build Some pressure, but without blowing things out, apply soapy water to the outside in search for the leaking holes.

[Guest62110524]

do you know how to press test?
when we get survey we always use manometer, which is simply a loop of clear tube half filled water, put 2psi in tank, and watch water go up in the second half of loop, should rise to 8 feet head, ok, then leave it settle, on cold day water will drop and hot will rise, but water should stay there, if drops and drops and drops , hey your tank it not tight, dont forget valves on the tank or water may get into it
for yachts in survey, same way they test a liferaft!!
no good just testing soap and water, this will find the big leaks, only manometer will be a true test
no charge for this info