Loud Whining Noise two-pipe Fin Tube

will_the_thrill

Hello,
Recently replaced the heating system for a NYC School. Replacement included Boilers, Boiler Feed, Duplex Vacuum/Condensate Pumps, Radiator Valves and Traps. Once the traps were replaced and we operated the temp boilers, there is this high-pitched whining noise that lasts for about 10 minutes and then disappears. This noise continues throughout the entire day and even after the boilers are turned off. Its a very strange phenomenon. i uploaded videos of this noise at the following links: https://youtu.be/qJK7jq1E2dAhttps://youtu.be/enZ0nCnG3xw

We have tried various methods in resolving this issue but haven't found a solution:
1) We operated the condensate pumps to run with no vacuum, only condensate.
2) We have lowered the steam boiler operation from 7 psi down to 4 psi.
3) The traps have been serviced and inspected by the trap manufacturer, Mepco & Dunham, they have found no fault with the installed traps.

A solution we haven't checked yet are the air vents. the noise sounds like air is travelling through the radiators at an extreme velocity and thus producing a sound, the loud high pitched whining noise.
There are no air vents installed at the ends of the main. i could not locate if you should install air vents at the ends of the main for two-pipe pumped return systems, thoughts?
Heating season is almost over, so hoping to find a solution soon to close out this project.
thanks.

Jamie Hall

Yes indeed you need vents at the ends of the mains. Big ones. Several of them. No way do you want the air in the mains to be being pushed out through the radiators! If you send us the size of the mains (length and diameter) we can help figure out how many of what size.

What is the reason for operating the boiler at even 4 psi? Are there fan coils or something like that involved?

JUGHNE

Are there traps at the ends of the mains?

Steamhead

First of all, if you're running that system up to 4 PS!, that's too much.

Second, is this a variable-vacuum system (as Dunham Vari-Vac) or does the vac pump simply exhaust the air from the system?

nicholas bonham-carter

Can you give us any information which identifies this particular system, by manufacturer.
The high pitched noise sounds like air being expelled by high pressure through a restriction, such as almost closed crossover traps.
Try setting down the pressure to 4 ounces with a vaporstat, see what difference that makes.--NBC

MilanD

Aaand? Has this been resolved?

will_the_thrill

Thanks for all your responses. i will have the Contractor install air vents at the ends of the mains to see if this resolves the issue. Contractor already replaced F&T traps at the ends.

The system operates on Honeywell pressuretrols. Cut in is 2 psi and cut out at 7 psi. Its a 150,000 sq. ft building, so running on two (2) 250 hp boilers on lead/lag.

No variable vacuum pump installed, simply exhausts the air, operates average 5.5" hg vacuum.

Jamie Hall

Be sure the vents are rated for the pressure. You might check with Barnes & Jones (@Sailah) on that.

JUGHNE

TRV's on the fin tube?

will_the_thrill

@JUGHNE mepco TRVs and mepco traps were replaced with new for all fin-tubes throughout the building.

JUGHNE

Could a TRV not being completely closed due to debris on the seat be squeaking some steam by?
Does lowering the pressure change the pitch of the noise?

will_the_thrill

thanks @JUGHNE i was thinking the same. This noise is easily repeatable by turning the temperature up, thus opening up the TRV. If there was debris, shouldn't it have passed through the trap into the condensate return and not reappear? i have suggested to the Contractor to lower the steam pressure further and see if this resolves the issue.
one other thing, client requested the temp boilers be installed on grade above Design Flood Elevation. the noise first started when operating the temp boilers above grade. the pipes that were once dry returns may have became wet returns. what does Dan H. recommend to do when this happens? i have the LAOSH book, do you know what page where he makes these recommendations?

JUGHNE

If returns went from being dry to becoming wet and you had cross over traps perhaps their life has changed to cause them to whistle.

Jamie Hall

Changing dry returns into wet returns may have really messed up the venting. There is a solution, though: restore all the returns to run to a condensate tank with its water level held at the original system water level -- all of them, dry, wet, whatever! -- and replace the vents and traps which have been operating flooded. Then pump (use a boiler feed pump setup) up to the boilers.

will_the_thrill

MilanD said:

Aaand? Has this been resolved?

i found the trap that was installed and causing the noise was Mepco TH1A SW. This is a trap that has a replaceable cartridge with integral disc assembly. The noise went away once trap was replaced with Mepco 1ESS, a trap with only replaceable stainless steel disc/seat. Both traps are used in low pressure applications.

Any thoughts on why the trap with integral disc type trap causes this noise is beyond me.