Problem Revisit: Condensate Receiver Banging Noise...

[murphymok]

Hi,

I posted this problem before. I have a condensate receiver tank that services all the low pressure condensate return from the building, as well as a 1/2" steam trap drip leg from the high pressure steam pipe. There is an occasional banging noise in the tank, sounded like waterhammering.

Any thoughts?

Thanks.

 

[MintJulep]

Just read about this exact problem in last issue of HPAC mag, which I have now thrown out.

Problem was the the condensate returns should be flooded (water only), but at start-up it was possible to have a mix of water and steam in the return.

 

[KenRad]

Even after startup, if one or more steam traps have failed and are blowing steam, you can have this banging noise as the live steam mixes with relatively cool condenstate in the other return pipes or the receiver.

Does your receiver have a vent to atmosphere? If so, check it; if a lot of steam is blowing out, you have one or more failed traps. The best way to pinpoint a failed trap is to isolate it from the return main, and open a test valve (if you have one) to see if the trap is blowing by. You can also take temperature readings on the return piping downstream of the traps to find the culprit.

---KenRad

 

[25362]

KenRad, is it not possible that the HP condensate partial flashing, while entering the lower condensate receiving pressures, generates the steam that causes water hammering ? If your answer is affirmative, this would indicate that there wouldn't have to be a steam-leaking trap. Am I right ?

 

[MintJulep]

This might be a little far fetched.....

Does the banging correspond to the operation of the trap on the HP drip?

Is it possible that when the trap opens the pressure in the tank experiences a sudden increase, effectively sub-cooling the condensate in the tank. When the trap closes, the pressure drops again, and the condensate rapidly returns to a saturated state, with associated rapid boiling?

 

[KenRad]

25362,

Good point - this could be the case. But if the HP trap was selected properly, it provides for sufficient subcooling of the condensate to prevent this from happening. Another thing that should be checked out.

---KenRad

 

[25362]

For the subcooling to take place rather quickly, the ambient conditions might play a role. Murphymok speaks of an "occasional" bang, thus it appears it may be related to the outside weather conditions.

 

[murphymok]

Hi,

The HP trap is a thermodynamic trap and it was replaced recently. The banging frequency is irregular though and the operator told me that it happened mostly in the morning time. I was there yesterday in the afternoon and I could hear the banging noise. The weather was relatively warm, around 8C. The building uses steam for heating and domestic hot water heating.

Thanks for all your help.

Murphy

 

[Joesteam]

The problem does sound like it is originating from the trap. I would try a thermostatic trap, which has more sub-cooling than a thermodynamic, but more importantly has a modulating (ie: constant) discharge rather than the on/off style of the TD.
Otherwise, look for any areas of piping or tank where hot flashing condensate (steam) may come in contact with cooler water.

 

[KenRad]

There are some bimetallic traps that actually have an external subcooling adjustment. Here's one:

http://www.tycovalves-na.com/ld/YAWMC-0430-US.pdf

---KenRad

 

[TBP]

I would stay away from thermostatic traps for drip service (especially HP). They'll let condensate back-up into the main.

 

[katmar]

Even if the HP trap is not passing, the hot HP condensate will flash as it enters the lower pressure of the receiver. If this line is below the liquid level in the receiver the bubbles of flash steam will collapse as they are cooled by the bulk condensate from the LP duties.

Can you change the entry point from the HP line to above the liquid level? This would of course result in more of a plume from the receiver, which may be a problem in itself.

 

[tkdhwjd]

Can you isolate the 1/2" trap drip leg away from the condensate collector and drain it to the pad instead? If you system allows you to do so, you can try it for a few days to see if the problem goes away. Then you can know for sure that rapid condensation of steam (from flashing of HP steam) upon contact with LP condensate is the main culprit. Just a suggestion. I would think it would be easy to manipulate this 1/2" line.