Loud noise possibly Air Vent on Hoffman Differential loop

HVAC003

We have a customer complaining of loud noises coming from Steam Heating System. A brief description of system Weil Mclain EGH 85 gas fired steam boiler installed about 20 yrs ago, two pipe system with mostly C.I. Radiators and two pieces of baseboard each with radiator traps, Hoffman differential loop with Hoffman #75 vent installed on the top of the loop, pressure is controlled with a vaporstat set at 10oz. with a 6oz. differential, boiler installed so water line match's original water line, water line is stable throughout cycle and no makeup water was added during 45 minutes of operation, burner cycles on vaporstat properly. I was present when noise was heard but could not get to repeat. Sounded like the Hoffman steam vent was rattling or pounding. Unfortunately I was not close by when noise happened.
Steam vent seems to be working well venting air no steam or water venting. Suggestions?

Jamie Hall

Chances are the noise you are hearing is related to the Differential Loop tripping and the vent closing and reopening. It can make quite a nice little gurgle and sometimes -- depending on the vent -- whistle.

10 ounces is too high. If you don't want that noise -- and I=blame you if you didn't, the cutout pressure must be 6 ounces per square inch. The differential should be around 4 ounces per square inch. Use a low pressure gauge to determine that the vapourstat is properly calibrated; if it is the mechanical sort, it can be recalibrated and probably needs to be. If it is the older mercury sort, calibration is controlled by how accurately it is levelled.

Unless your system is very small, that vent is probably too small. I'd add a Gorton #2 to it, using and antler.

While you are at it, check and make sure that the crossover traps are operating properly, and be absolutely certain that there are no other vents of any kind anywhere else on the system.

Steamhead

Jamie Hall said:

Chances are the noise you are hearing is related to the Differential Loop tripping and the vent closing and reopening. It can make quite a nice little gurgle and sometimes -- depending on the vent -- whistle.

10 ounces is too high. If you don't want that noise -- and I=blame you if you didn't, the cutout pressure must be 6 ounces per square inch. The differential should be around 4 ounces per square inch. Use a low pressure gauge to determine that the vapourstat is properly calibrated; if it is the mechanical sort, it can be recalibrated and probably needs to be. If it is the older mercury sort, calibration is controlled by how accurately it is levelled.

Unless your system is very small, that vent is probably too small. I'd add a Gorton #2 to it, using and antler.

While you are at it, check and make sure that the crossover traps are operating properly, and be absolutely certain that there are no other vents of any kind anywhere else on the system.

This.

HVAC003

Thanks for the advice. I have revisted the job and determined the the vent rattles when the pressure rises high enough to push steam through the differential loop to the return. You can hear the steam moving and feel the rapid temp increase in the loop and return. I will lower the vaporstat setting. I also noticed during a heating cycle after the pressure has reached cutout pressure the system is cycling fast on the vapor stat less than one minute on, less than one minute off. I skimmed boiler yesterday and plan on adding cleaner to system.

Jamie Hall

That fast a cycle rate indicates one of two things: either the vapourstat is subject to a lot of rapid pressure variation in the boiler; skimming will help that, as would a snubber on the pigtail -- or, more likely, a seriously oversized boiler. Have you compared the EDR rating of the boiler to the actual load on the system? That is, added up the EDRs of all the radiation? Vapour systems -- like this one -- tend to be happiest when the boiler EDR is no more than 5% over the system EDR to about 15% under. Bigger is definitely not better!

What cleaner are you planning to use? Unless you have a very significant sludge problem, I really can't advise any cleaners for a steam system. If you do decide to add a cleaner, however, be sure that you drain and refill the boiler several times to get it all back out. Skim first, thoroughly -- most cleaners will emulsify any oils, which is exactly what you don't want.