Chattering heat trap check valves

[Lance Stronk]

hi. I have a Tarm excel 2000 wood/oil gasifier and 620 gal thermal storage. I am getting chattering in the heat trap check valves when thermal storage gets above 150 deg f. Chattering comes and goes and I am not sure of the cause.
The only thing I can think of is that the expansion tank I have in the system is too small (60?). System pressure goes from about 20 psi when cold to close to 30 when hot.
The chattering is really annoying and I can't help but think that the check valve(s) that make up the heat trap are chewing themselves up.
Any advice would be appreciated.

 

[maple1]

Not sure what your heat trap is?

Do you need pressures that high? Also not sure that has anything to do with it - but 30 is really pushing close to your blow off pressures I would think. My system stays in the 10-15 range.

 

[Clarkbug]

Agree with Maple that you can probably lower your system pressure some, unless you have a really tall house.

A schematic of your system would help with a diagnosis here for sure.

 

[Lance Stronk]

A heat trap was what was described as this paralleled arrangement of check valves.

I needed to clean the furnace. I decided to take the cover off the top front of the excel boiler to inspect an air riser- when I opened the little valve on top, quite a bit of air came out. I did not think I had to purge air from there (essentially the top of the boiler). Turns out that all the rattling subsequently stopped.
ITs hard to believe that a little air would cause the check valves to rattle.

System pressures are around 21 max and I think that is due to a small expansion tank.

 

[salecker]

Hi Lance
Is your heat trap made of two check valves in opposite directions in the return line to your storage?Or ??
The reason i ask is when i built my system i was told to build in two check valves facing opposite directions into my return line with a loop.
I had the same chattering when i had some air in the system too.My pressure is running right up against the 30psi as well.I dropped the pre charge pressure in my expansion tanks a little to get more room in the expansion tanks.But the first time i maxed out my temps this yr i did blow out some water from the relief valve.I added a little tank that came with my boiler hoping it would up my expansion volume to handle higher temps.
I added a pic,you can see the double check valves on left side of the tanks.A few people have asked what it was and i just said i was told to build and install it.Sometimes i look at it and wonder if it was just a way to sell more fittings.

 

[maple1]

I'm pretty curious on exactly what those two check valves would do for things? Don't think I've seen anything like that in piping diagrams I've seen.

 

[pbvermont]

That twin check-valve, heat-trap arrangement has been the standard piping recommendation from the company that has been selling Tarm boilers for decades. It works. It keeps heat from migrating out of storage when not called-for.

 

[Lance Stronk]

Yes - that is the exact arrangement - not really certain how it works as I thought flow through the thermal storage was only in one direction (I really should put some neon indicator bulbs or something on the pump power to see which one is on - that may help me understand the flow direction during the different phases of operation).
Unless my plumber got it wrong or unless I am looking at things wrong, the 'heat trap' is on the output of the boiler into the thermal storage. Again, not knowing how this works, maybe it doesn't make a difference whether it is the input to or output from the heat storage. The plumber supposedly followed the plumbing diagram - I would have to double check it against the diagram.

 

[maple1]

That twin check-valve, heat-trap arrangement has been the standard piping recommendation from the company that has been selling Tarm boilers for decades. It works. It keeps heat from migrating out of storage when not called-for.

Very well could be - I am just not grasping how it works.

 

[salecker]

Very well could be - I am just not grasping how it works.

Same here,but i was getting a lot of help for nothing so i just followed instructions.

 

[Bob Rohr]

If the system is air free, then sometimes swing checks rattle due to in-sufficient flow to keep then gate held open.

Really a swing check, while commonly used, is not so good for closed loop hydronic.

A swing check depends on a pressure difference to close and seal, in a hydronic system the pressure is equal on both sides of the check. Swing checks work good on sump pumps for example where the pressure drops to 0 when the pump stops, and the water in the piping above the check closes and seals it.

They also have a high Cv which means they need a lot of gpm to hold open completely. A1" swing check may have a 25 or higher Cv, so you need some good flow rates to open the gate

Really a check should be sized by the flow rate, not the pipe size. Often the check will be one or two sizes smaller than the pipe.

Lastly, since a swing check has a long travel distance, compared to a spring check you may get water hammer when they close.

Some good reading on check valves.

http://www.dft-valves.com/pdf/literature/general-information/CheckValveBacktoBasicsArticle.pdf