Leaking pressure relief valve

targetman

At the end of the day yesterday, I was sent to replace a relief valve.  It's a county run old folks home and there maintenance guys hired us to replace the valve.  Turns out that my employer installed this DHW storage tank 3 years ago.  Maintenace man lets me into the boiler room and tells me that he replaced the same valve last year and doesn't understand why his Boss subbed it out this year.  Well I told him that it may have been subbed out so if it does leak again within a year, we will own the problem.  Sure enough the new valve started leaking in a few minutes.  Please take at these photos and let me know what you think. 

RobG

Thermal Expansion

It sounds like when your boss put in the storage tank he did not take into account for the additional volume of the system. That looks like a Hydrotherm modular boiler set-up with their MC heat exchanger (esentialy a reverse indirect). That building should have a backflow preventer on the domestic side and with the additional added storage the water volume of the system increased therefore increasing thermal expansion. Put a gauge with lazy arm on the domestic side, wait 24hrs and check to see what your max pressure was. If it is as high or close to the relief valve setting add a larger expansion tank.

Rob

Mark Eatherton

It could also be...

That the diaphragm on the expansion tank was never properly adjusted when new. (You have to adjust the pressure on those things???)



Check the residual static potable water pressure. Adjust the diaphragm to that same pressure, and anything above that will flex the diaphragm and accept expanding water.



Love your avitar Rob...



ME

targetman

expansion tank

There is only one expansion tank.  It connects into the heat exchanger.  Does that tank serve the boiler or the DHW side?

RobG

expansion tank

The red expansion tank in your photos is for the closed loop (boiler side only). There should be a potable expansion tank somewhere in there I would think. The original design of the system does not appear to include storage of domestic hot water (think tankless, hence the reverse indirect). If there is no domestic expansion tank I think your problem would be solved by adding one. Be sure and size it accordingly and as Mark suggested, ensure it is charged to the correct system static pressure.

Thank for the avatar comment Mark, it reflects how I feel at the end of the day.

(and it is a classic photo:)



Rob

targetman

reverse indirect

I'm beginning to understand.  I can see the tankless coil.  It's just outside the boiler.  Then this system had no storage tank originally.  Boss added that big storage tank without an expansion tank and the problem was born.

RobG

expansion tank

That's what it sounds like. I would still look around for for a potable expansion tank and check the charge( it doesn't have to be in the mechanical room). Even though it probably started out as a low volume system there should still have been an expansion tank. If you cant find it (if it's there) adding another won't hurt and will only help. But yes, as you stated, adding the storage tank = adding the problem. I hope that makes sense. Let us know

Rob

icesailor

Leaking Relief Valve:

You don't have any potable DHW expansion equipment. I ran in to the same situation in a similar facility you have. I installed an Amtrol domestic Extrol type hot water tank that was the equal size to a WX-203 well tank. I never had another problem after that though there were circulation problems. I had to drill a 1/8" hole through the flapper in a 2" cold water check valve to let the expansion pressure out of the closed system. This is legal in Massachusetts with the inspectors approval. Which I received.

This Extrol sits on the floor and you can connect it into any part of the hot water system. I haven't changed a TPR valve since installing the tank.

targetman

backflow preventer

Just another thought.  Could the lack of a backflow preventer be causing the leaking valve.  I didn't have time to check the expansion tank on the boiler, but I will if I'm sent back.  That feed line with the PRV comes from the back side of the storage tank.  It branches off of the recirc pump line in the next to the last pic.  It is also pictured in the last pic bottom left corner.

Mark Eatherton

Color means nothing...

Amtrols commercial DHW potable water expansion tanks are also painted that red, primer coat looking stuff...



http://www.amtrol.com/thermxtrolasme.html



ME

RobG

Expansion tank

It APPEARS that the expansion tank in the photos comes out of the shell of the heat exchanger in black iron with a tee coming into it for the boiler feed. That set-up should work fine for your closed loop side. The backflow preventer that I was reffering to is on the main water line coming into the building. It stops thermal expansion (pressure) of the domestic water from bleeding back into the city supply water. Without a backflow preventer, If city water pressure was 60psi, as the domestic water heated and the pressure of the domestic water exceeded that of the city, due to thermal expansion the excess pressure would push back out into the city side potentialy exposing the city water to whatever contaminants may be present in your buildings water supply. With a backflow preventer this cannot happen. So as your buildings pressure increases due to thermal expansion, without an expansion tank, the water has nowhere to go besides out the domestic relief valve. Hope this helps.

Rob 

icesailor

Leaking PRV:

Which is why you need to install a thermal expansion device on the DHW potable system. You increased the amount of stored water to be heated in the DHW system. The boss should have known that you need an expansion control device when you add water storage to a closed system.

If in Massachusetts, with the inspectors approval, you can drill a hole in the check valve flapper to let the thermal expansion back out into the cold water side but some water systems now are putting check valves on water meters and there is no place for the expansion to go. Then the only recourse is a "Extrol" type tank designed and sold for domestic potable water use and with the bladder pressure properly adjusted.

RobG

PRV

Lastly, it's POSSIBLE that the city water pressure is VERY high (close or over 150psi) AND you have a bad pressure reducing valve. It's easy to test and I would hate to get egg on my face by installing the expansion tank and still having the same problem (either way though, the expansion tank is necessary to the system and should be installed if absent). Let me know if you have any questions.

Rob 

targetman

update

Turns out the problem as the buildings PRV.  Street pressure is deliverded at 130.  The relief valve is 125.

Charlie from wmass

This is why test gauges should be on the truck

Here we all are chasing our tails when a simple gauge test on the domestic side would have found the issue. Glad you found the problem. This is why they say do it by the numbers. The solution is often the simplest answer. It is always easy when you think back on it. It is thinking forward that is the tricky part. I bet you look like superman next time you get a call like this.