now for a little banging

jacobsond

Same college as described in previous posts. Central heating plant 80 psi pressure out.All buildings set at 8 psi. My next challenge is a building that has been banging for years. According to one instructor banging ever since he started 7 yrs ago. The building is used to teach repair to large equipment. Tractors and loaders. The 4 shops are very large. Ceiling height 20-25ft or more, 50+ft long 30+ft wide aprox for the shops. Each shop has steam unit heaters in the ceiling. 8-10 of them Hoffman traps on each one. Draining into a common return I believe 2 1/2 inch. All joints welded There are several classrooms on the 2nd story in the center of the building. 2 AHUs on the roof in doghouses. Everything installed 30-40 yrs ago. One of the shops bangs a lot. Not much at startup mostly during the midday. The ceiling unit heater fans are controlled by thermostats. They do not have control valves on them. AHUs have a control valve that the heating plant controls. At night the AHUs are for the most part shut down. The AHUs start up at 7am banging starts usually by 11am. I have temp tested all the traps I could get to. I also have ultrasound data. Temp across traps is 20 degree difference. 220 on the input 200 on the output. Ultrasound inclusive for my newly trained ears. They are all good or all bad the way it sounds. I did find a bad disc on one of the Dunham bush 30-7a traps on an AHU. The return in the banging shop sounds really quiet except for the banging around 5dB at 25khz. It sounds really full tho. The other returns are louder. 13+dB with not much for condensate noise. Still trying to figure the piping. The shop returns join together about the 8ft level then run to a condensate pump. So If you had to guess is it going to be bad traps, bad slope on the return or possibly pressure to high. Should I concentrate on the noisy shop or maybe its elsewhere? I dont want to have the attitude its always been banging so don't worry about it.

EBEBRATT-Ed

The telltale sign for bad traps is do you have any steam coming out of the condensate tank vent? If you do you have bad trap(s)

Make sure someone didn't "master trap" the main return line near the condensate pump.

Make sure the return lines drain by gravity to the condensate pump.

With all the equipment well up above the condensate pump this should be an easy fix. No reason this shouldn't work quietly

nicholas bonham-carter

Is there a partial restriction in the return line which allows it to gradually fill up with water, and back up into the coil?—NBC

jacobsond

There has been some steam coming out the vent. None really now since I changed the disc on the dunnham-bush at one AHU. I regraded some of the lines where I could. A lot of them are pretty level. not much slope. Since I started the banging has gone from constant from startup to around 10:30 there is some pinging and gets louder as the day goes on. Partial success yesterday. I found 2 Hoffman 53 traps bad. One had a disc blowing and one had a surging steam sound. Going over my notes and wav files on the outputs I think there is at least 1 more Hoffman surging. There are at least 4 condensate lines going into the pump. I have been following the loudest lines. As I find things the condensate line goes quiet. Getting to the traps is difficult I have to work around large equipment in the way and there is school on so I cannot always get into the room. Since the traps have never been serviced I believe there are multiple issues. I will keep plugging away while the heat is still on. Im learning a lot about the ultrasound. Previous repair attempts only used the IR tester. All the traps temps are good. I have already found that all the traps are not good.

EBEBRATT-Ed

@jacobsond

Sounds like you making progress. Traps seem difficult as you go through it after a while you will get better at it.

Good job tracking thing down. 1 bad trap can make other traps act funny

dopey27177

Can you get pictures of the piping connections to the condensate pump.

Jake

jacobsond

Yesterday I continued on my quest. I repaired one more surging Hoffman that was on my suspect list from my original survey. Still the banging returned right around 10-10:30 just like clockwork. I continued to follow the steam sound in the returns following the loudest. Narrowing it down found unit heaters 2nd floor hall were pretty noisy even when valved off. Bathroom one on the end of the hall very noisy when valved off. Whats under the bathroom the entryway. Heater in the ceiling of the entryway. Success!! There were 2 Hoffman 1E disc traps. One on a drip and one on the heater. Both bad. Blowing steam hard into the little 1/2 in return. 50dB for those that use ultrasound.That return met the 2 1/2 return from a couple shops 30ft down the hall. Repaired those traps and the building went silent. Interesting how 2 little traps could make such a loud banging in every shop and hall. Now it makes sense on the timing. As students showed up for class the entry heater came on more so the 2 failed traps into the small return made a really large impact. Needless to say I know just about every inch of the steam piping in that building now.

retiredguy

Do you have any steam lines that run horizontal and then turn upward that do not have a steam trap at the point of the up turn? Also do you have any zone valves that open to control the steam flow that do not have a steam trap just before the zone valve? I am also going to say that if the system is 30-40 years old, most or all the steam traps should be rebuilt/replaced. F&T traps and bucket traps usually have little temperature difference between the in and out when the trap is at or near it's normal working load, unless there is a problem with that trap. If, most of the systems are utilizing 8 PSIG steam pressure at the coil inlet and outlet you will most likely get steam out of the vent in the condensate tank unless the return runs through a conditioned space and the return line is not insulated. Pictures of the pipes that make the most noise, the AHU's and the condensate tanks would be helpful. If you have noisy AHU's that you valve off and are still noisy the valves that you turn off probably leak through and the trap and drain line need to be checked. One last thing what boilers do you have, what is the fuel and the input, are you making dry steam, is the condensate held in an atmospheric tank, heated tank or deareator and do you have a good treatment system?

Gsmith

Good news and bad news, you’re now the go to expert on that system. Congrats.

ethicalpaul

Yeah, now you have earned the right to be cranky for decades whenever someone asks you about it!

This is a great reminder that steam really isn’t mysterious, or that noise is “just the way it is”. There’s always a cause. Something I constantly have to remind myself when chasing software bugs

jacobsond

On my follow up visit today I decided to check the other end of the building where there used to be an entrance to the outside. What did I find in the ceiling? Another disc trap on a drip leg blowing 50dB just like the other side. Repaired that also. Now the 2 floor hallways are starting to cool down. Go figure stop blowing steam into the return and things start to work. Other problems like why are the halls so hot correct themselves. I don't mind being the expert. When things don't operate normal I will work until they do. By the way no hammering at all. 1st time in many years I have been told.

EBEBRATT-Ed

@jacobsond,

Most problems are lack of maintenance. Most jobs , especially larger ones designed by engineers are usually (but not always) installed right.

Tracking down trap problems isn't easy. Crawling in crawl spaces filled with broken glass, wires and left over pipe, working on ladders trying to get 60 year old stuff apart that's never been apart. Crawling through cobwebs and moving all kinds of stuff taking out painted over screws............did i miss anything?????

jacobsond

No I think you hit it all. With the exception that everything is over 200 degrees and one drop of "water" will leave a mark. Welcome to my world now. Its funny that I really like the challenge.