Pressure releif valve

larry_9

I recently moved to farmland USA one fo the things I have noticed is that the plumbers in this area are putting the pressure relief valves at the same piont as the expansion tank. In other words were you normally put your releif valve they add a tee and then go up to the expansion tank, putting the expansion tank and relief valve on the same line. I know this is the point of no pressure change, so I can see it as a potential danger. I was wondering if anyone had any data on this. Is it covered in National Plumbing or Mechenical Code books? I couldn't find anything in NFPA or any of the other books I have.

Thanks for your help

Larry away form the cities

Mark Eatherton1

Provided that...

there are no valves that could possibly take the relief valve out of the picture, that location is OK.

The PONPC is only relevant to the circulator. The pressure at that point would be the same as the pressure in the boiler.

In other words, the pressure there WILL change, but it cannot be affected by the circulator, hence the term point of no pressure change.

Just make sure there are no isolation valves that would keep the relief valve from seeing the boilers operating pressure.

The 2003 UMC states under 1012.2 Boilers and pressure vessels shall be provided with the required number, size anda capacity of safety or pressure relief valves to insure proper relief of overpressure in accordance with nationally recognized standards, as applicable. Valves so employed shall be installed, constructed and sealed in accordance with nationally recognized standards, as applicable.

My guess is that youu'd have to go to the ANSI standards to get an accurate interpretation. Within 6"s of the top or outlet of the boiler sticks in my head for some reason.

ME

J.C.A._3

Hey Larry,

Are you sure this is a "relief valve", and not really a backflow prevention device?

Both will have a drip tube going to within 12" of the floor when piped properly. A relief valve needs to be AFTER the pressure reducing valve as the PRV somewhat acts as a "one way valve, as long as it's working properly. Just a thought. Chris
OOps, I missed the placement of the tee thing. Most here put the expansion tank at a place under the air seperator and have the PRV and backflow tied in along the way. JCA

larry_9

pressure relief valve

I have been in the trade for almost 20 years I know the differance between a pressure reducing valve B&G B-12 for example and a releif valve. Mark, even though it is the PONPC for a pump, wouldn't it increase the pressure at that point until the expansion tank was full not showing the potential pressure in the system? creating a bigger problem until the presusure releif valve finially popped off?

Larry

Mark Eatherton1

NO...

So long as the gauge and the pressure relief valve are both connected to the boiler, what you see is what you get. If the gauge is showing 20 lbs, then the relief valve is seeing 20 pounds regardless of whether it is on the outlet of the boiler or the expansion tank connection.

ME

Mark Woll_2

I'm certain it's in the ASME B&PV Code

To be technical, it should be covered in the ASME B&PV (American Society of Mechanical Engineers Boiler and Pressure vessel) code, Sections IV and VIII, Div 1 which may or may not be applicable to your particular device.

Larry Weingarten

T&Ps

Mark: There is a 6" rule for T&Ps in tank type water heaters. They need to be in the top six inches of the tank for temperature sensing. But, perhaps there are other six inch rules as well! ;~)

Yours, Larry

larry_9

thanks Mark

After reading your reply and putting a little thought to it I could see that it really doesn't matter.

Thanks

Larry