sizing T & P valve for indirect.

Wayco Wayne_2

Got a call on a 100 gallon Indirect yesterday that had a leaking TP Valve. The existing valve was rated at 150 psi and 105,000 btu's, However the boiler was rated at 175,000 Input. btu's. Shouldn't the TP vlave match or exceed the btu raing of the boiler?

kcopp

sounds reasonale to me.

what model was it? Sounds like it could have been thermal expation to me. Did they have a potable extrol on it?

Wayco Wayne_2

Triangle Tube

Prestige 175 boiler. Smart 100 indirect water tank. No expansion tank. 

Mark Eatherton

Relief Valve Sizing....

It is supposed to be sized to the heat transfer capacity per hour.



And that depends upon where you are as it pertains to delta T. Cold tank, hot boiler, MEGA BTUH transfer.



Hot tank, Hot boiler, very little heat transfer.



This is the "dance" that indirect manufacturers are doing with the ASME folks. Code says if the indirect is operated above 180 degrees F, OR can transfer more than 199,999 btuH, OR can hold more than 120 gallons, it MUST comply to the ASME requirements.



So, if you have a run away boiler (200 degrees F) and a storage tank that is nearly as hot (190 degrees F) how many btuH will it transfer at that point? Not many, hence provided you have not violated any one of the other two ASME requirements, in their minds (indirect manufacturers) it doesn't have to comply to ASME requirements.



If it were me, I would size it for the best case heat transfer capability. Even though it is occuring at a low level heat transfer, you have it covered.

If a person were to size it based on connected energy, in some apartment settings, you would need to have a HUGE pressure relief valve, and you probably wouldn't have adequate tappings to support the relief valves needs...



Size it to the hourly transfer data as published by the tank manufacturer.



Glad to see you're back to work Wayne. Welcome back. You heal fast for an old man :-)



ME

Wayco Wayne_2

Thanks Mark

I'm just working half days then I come to a nice nap. If I could get full pay for that daily routine I'd be a happy camper.     But, It 's been 4 weeks since the surgery  and I'm understandably lacking a little energy.  This has me wondering if there's any teachng positions available somewhere. Not so much energy needed for wrench pulling. Ha!. Well what you said makes sense. I showed up on the job to fix the boiler. Their house had a voltage spike which aced a couple VCR's and TV's. It also fried the ECM blower motor of the Tri Tube Prestige. When I left the job everything was working. The  water tank was cold having been off all weekend. 3 hours later I got a call that there was water on the floor of the boiler room. (what did you do?) Come to find the pressure relief valve leaking profusely. Cold tank plus large boiler means lots of heat transfer and a small TP valve. (105,000) Replaced it with like to get them back on line. I was just wondering if I needed to go back and upgrade to a 180,000 rated valve?.