Boiler relief valves

Jerry_15

All good stuff. The prv's are rated for both pressure and btu's on the tag. A 1 1/2" will vent vastly more btu's than a 3/4 " one of the same pressure rating. Also note that the one's made specifically for steam are usually larger on the discharge side. I'm not a big fan of multiple relief valves. On hydro a six story building a 50lb valve would almost certainly be needed as you would have to run the pressure up to 20/25 or more to make the altitude. (Be sure to adjust your ex tank pressure to match op pressure or it,ll blow off anyway) Good luck.

STEVE PAUL_3

BOILER RELIEF VALVES

Who or what determines the capacity of boiler releief valves?
I was always under the impression that the codes require hot water boilers to be protected with 30 PSI relief valves, and steam boilers to have 15PSI relief valves. Of course the valve must be capable of discharging the BTU load required. Now I have a customer whose commercial boiler failed the Hartford Ins. Co. inspection for the wrong relief valve. The present valve is a 50 PSI valve (well within the BTU limits of the boilers input) in a 1- story building. Any thoughts?

Paul Fredricks_3

I've seen 50 PSI relief valves on boilers, and higher. I would think that if the boiler and piping is rated higher you can use higher. I'm not sure, but the BTU rating may need to be a multiple of the boiler rating. Anyone else know?
I wonder if the inspector goofed. Did he say what was wrong with the valve? Sometimes they just don't like the way they are piped.

Anna Conda

Its not just psi that's involved, but also venting capacity. The valve must be able to discharge a volume of steam or water sufficient to keep up with a run-away production. That's why some larger boilers may have two or three valves - they all have the same pressure rating, but the multiple valves are required to meet needed capacity.

seabee570

relief valves

anna is right...pressure rating is only part of the equation...on most steam boilers the relief valve must be matched to the input of the burner,and not allow the the boiler pressure to rise any higher than 6-10 percent of maximum boiler pressure...so you must look at the burner input,not just the pressure rating of the valve.boilers over 500 square feet of heating surface need at least 2 relief valves and maybe more....

Dave Belisle

50 PSI relief valve

I had a boiler room with 9 boilers with 50 PSI relief valve on them, we replaced the valves every three years.
It needed the higher pressure valves, the system was hot water in a six story building but the boilers where rated for 50 PSI.

Look at the tag on the boiler , it will say what the max boiler pressure is.

See if the valve is sized for the boiler BTUs and the boiler is rated for the pressure........

BP&H
Dave

Bill Jirik,

need further information

To properly answer one needs to know, 1, steam or hotwater,
2, BTU rating and PSI rating from boiler data plate, 3, if hot water, is the expansion tank A.S.M.E. pressure rated and what that rating is, if the expansion tank is not A.S.M.E. national board stamped many jurisdications will limit the relief valve to 30 psi

Steve Paul_4

50 PSI relief valve

We got the answer today. The inspector said that a water boiler with a 50 PSI relief valve requires an ASME expansion tank. The present tank is not ASME rated. So we must install a 30 PSI valve instead, as long as the valve is rated for greater than the boilers BTU input raing.

Jerry_15

Yeah right, and a 40 gal water heater from the home despots with a 125 psi relief valve needs to be ASME rated too. That's why they make commercial tanks in 119 gal. Change the valve, get paid, and remember that those who can; do. Those who can't; teach. Those who can do neither; become, well we all know. (steady pay and good benefits though.)

Steamhead (in transit)

Steve, in a 1-story building

you really shouldn't need that much pressure, unless you're running water temps well over 212. If the water temp routinely rises past that point, find out why. If you can reduce it, you'll save your customer a bunch of fuel.

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STEVEN MARKS

In the state of CT any building open, with access to the general public must have a ASME expansion tank if the relief valve is rated higher than 30psi. If 30 psi or less a non-ASME expansion tank can be used.

Guy_6

Hmm

So in theory, this equates to a chain only being as strong as it's weakest link. The boiler was OK, but the exp. tank wasn't rated above 30, therefore the system was technically at risk. Good to know.