Help with TRV's

Mark Eatherton

Close the valve between the gozinta and the gozouta of the PBV (assuming you put one there for initial fill) or crank the PBV up...

I agree with Mikes diagnosis as to why now.

ME

Unknown

I have a system nine

years old, A Buderus atmospheric gas boiler with ecomatic piped with a pressure bypass valve and TRV's on the cast iron radiators. The customer calls me yesterday and say some of the radiators are making noise, a sound like a truck or a loud vibrating sound. I ask if this just started, they said it started a little last year but is now getting worse. I couldnt make the sound happen so it is intermittent. Any ideas on this?
TONY

Mark Eatherton

Piped backwards....

A TRV is a relatively simple device. One moving part. If piped backwards, as the needle approaches the seat, it gets sucked in to the seat with a THUNK.

Depending upon how many TRVs are wide open, relieving velocity, dictates how loud and frequent the thunking gets. With just one TRV closing, and no pressure activated bypass, the thunking sounds like a small jack hammer in the affected radiator. BAM BAM BAM BAM BAM. When you open it up, and clear the needle of the seat, it stops.

If they are ALL doing it, the fix is easy. Flip flop the supply and return where it leaves the mechanical room. If only a few of the rad's thump, you have to move the TRV to the other side of the radiator (What a PAIN). If there's inadequate room on the other side of the radiator, Oventrop makes a reverse flow 90 degree angle valve.

Good luck and let us know what you find.

ME

Unknown

I will check

that out Mark, I didnt look at that. But why would it start now after all these years?

Unknown

The banging will only start when the TRVs try to throttle down the flow and reduce the heat. If the boiler stops firing before the TRVs need to throttle you won't hear the noise. Perhaps the homeowners have changed their habits and are keeping some TRVs set lower. If there's a wall thermostat used as a master, perhaps they have changed their habits.

You should be able to get them to make the noise by asking the homeowners to set all the TRVs for normal room temp for a day or so, then come in and turn them all down significantly while turning up the master wall thermostat (if used) and the boiler temperature. Any installed backwards should start banging quite quickly.

Unknown

Just a thought here guys

Could it be possible that the pressure bypass is sticking? it is a honeywell with the little siteglass and is no loger visible becaue the system water is filthy.

Unknown

I rather doubt. It's a simple spring loaded valve opened by pressure. While it might stick shut or not close completely it shouldn't "chatter" unless the circulator is really squirrely.

Unknown

Im going there

Friday Mark, First im going to check and make sure the valves are on the supply. It was an old 2 pipe system and I replaced the old radiator valves with the TRV's. But I never really doublechecked the direction of flow, so that is a possibility. Then if all is well I will isolate the PBV and clean it and test it. Question? I use the honeywell PBV with the sightglass, I open all the TRV's and allow the seat to just close all the way, I notice some manufacturers sell PBV with no sightglass. What is the best way to set these?

Mark Eatherton

It is based on your design....

If, for example, you calculated a need for 7 feet of head at design condition, and the co-relating flow at that head, you should set the bypass valve for 7'. Anything in excess of that will be bypassed.

I have heard many different ways of adjusting them, and they all make sense for the most part. It's there to keep the pump from generating excess pressure and subsequent flow, and to keep the pump from dead heading during periods of low to no call from the TRV's. I laugh whenever I see one applied with zone valves....

ME

Unknown

Why

with zone valves Mark?

Mark Eatherton

Good question...

Overzealous designer/suppliers I guess.

There is NO chance of dead heading a pump with zone valves, because the pump won't be on unless there's a zone valve open, calling for flow and heat.

If the pump is oversized, that is a design problem from the get go.If properly sized, there should be no need for a pressure activated bypass.

As Dan says, The urge to oversize heating system components is stronger than the urge to have sex...

ME

Unknown

I have been seeing

alot of drawings, of course from manufactureres, using them with zone valves. I never did because I felt if I was using a pump with a fairly flat curve and it could supply the gpm I needed, there wasnt any need for one. But I understand what they are trying to do by keeping the pressure constant. Anyway, thank you Mark and I will let you know what I find.