saftey valve

[johnp]

How do i determine what size saftey valve i need, not pressure size. it`s a 20 sqft vft i plan to run at 100-125 psi.

[daysaver1]

That depends on your boiler plumbing. Whatever size the nipple or threaded port is.

ie: if you have a 1/2" nipple from the tank, use a 1/2" valve. A larger valve will work but definitely don't use a valve with smaller inlet than the cross section outlet from your boiler.

[fredrosse]

The ASME Boiler Code required a safety valve capable of passing 108 PPH if hand fired, 173 PPH if fired with Gas / Oil / or PC. Our boiler sizes are very similar, I have 20 ft2 tube surface, 1 ft2 furnace surface.

[87gn@tahoe]

Safetys have a Pound Per Hour (PPH) rating. The rating corresponds with the evaporation rate of the boiler it is suitable for. As detailed in the other "Safetys" thread, this rating is critical, as too little will not vent enough steam and too much will vent too much steam and cause water to carry over.

Just because it corresponds in size with a nipple or outlet on the boiler, it does not mean it is the correct size for the boiler

[DetroiTug]

The 42 sq-ft VFT in the tug has a 6010DC 1/2" Kunkle/640 pph, it will drop the boiler pressure 10 psi in very little time - like 10 seconds. I was unaware at purchase, someone mentioned they are also rated in % of let-off. This is a 10% which means it drops boiler pressure 10% before re-seating. Would rather have a 5% let off if there is such a thing.

-Ron