two pipeSteam Fan coil unit with Pneumatic controls

Erik Richardson

I've only been in the trade for about 3 years, and don't have much experience with steam. Do you have any idea on what would cause the steam in the return? I forgot to mention that the guts to the trap had been removed prior to my company getting the contract. It would make sense that the steam in the return line is stopping the supply steam from moving through the coil. I can't explain why when I broke the union no steam went through the coil..

Erik Richardson

2 pipe Steam Fan coil unit not heating

I was sent to a new building today that is a steam system with numerous steam fan coil units, each unit is controlled bye a pneumatic t-stat and valve. my problem was that only 1/4 of the coil is hot. The valve seems to working properly along with the t-stat. So I bravely broke the union on the return side with the system running. Steam eventually came up the return through the trap, but no steam was pushed through the supply and through the coil. My thoughts are either the pneumatic valve isn't opening, or the coil is blocked. I was wondering what the easiest way to test and make sure the valve is operating, or if the coil is blocked. Or is having steam comming through the return the root of my problem??

Unknown

Erik

live steam should NEVER enter the return, I would be suspicious of the steam entering-point.

Dave

Unknown

Is It low-pressure?,

below 15 PSI? at any rate, live steam should NEVER enter the return side.

Dave

Erik Richardson

yes low pressure, operating pressure is between 4 and 7 psi. I forgot to mention that prior to us getting the contract the previous company had removed the guts in the trap.

Brad White

There is your answer

A gutless trap passes only steam....

Make sure the coil has a vacuum breaker.

Unknown

Bad news,

if you understand the workings of a steam trap. You`re on the right track,,time is the factor now.

Dave

Erik Richardson

But why would there be no steam passing through the coil with the union broken on the return side? The union is before the trap, so If I am thinking correctly steam should have passed through the coil because there would be nothing preventing it.

Erik Richardson

the trap is a barnes and jones no.41T what is suppose to be on the inside of the housing? is there suppose to be just a ball, or is there other guts missing as well? is there a thermostatic valve in there as well?

Unknown

Erik,

check the pneumatic valve, and its operator, also make sure you have enough pressure to get-it there.

Dave

Erik Richardson

Dave

What do you mean bye pressure? Steam or Air? When I tested the pneumatics, the t-stat operated the valve. The spring extended and the pressure dropped. so it takes air pressure to close the valve not to open it. so in theory if I disconnected the Air to the valve it should send the valve wide open and the steam should be cruising into the coil.It's just a little over my head and I have a boss that expects me to know everything without asking questions.

Brad White

Ah

Missed that. Coming to this late. Can you rod out the coil tubes? Some have plugs in the ends. I suspect a blockage if as you say the pneumatic valve can be forced open.

In an F&T trap, there is a float which takes care of large slugs of water and yes, a thermostatic element (metal bellows) which seals against high temperature. If air is being forced in (a trap starts every cycle as an air vent), air is passed out to either the return line or to atmosphere depending on the type. When steam hits that, the bellows expands and stops the air venting. When condensate fills the body, the float lifts and passes that out, even if the vent is closed.

Brad White

Fail Open Valve

If as you say, the valve opens when air pressure is removed, it is a fail-open valve, what one would expect for a steam coil. (Defaults to a safer mode allowing the coil to act as a radiator if nothing else.)

When you pull the air line off the valve, does steam pass then? To what point does the steam go? Sorry, coming late to this conversation.

Unknown

Erik my friend,

hi pressure goes to low, so if the valve IS opening(and nothing else is pressurizing the return), it should go there(the coil), isn`t steam FUN???
BTW- Brad White is our resident engineer,,he knows!

Dave

Erik Richardson

brad

unfortunatly I have only been in the trade for about 3 years and as I am writing on this thread I am thinking of more troubleshooting options, and I didn't pull the air completely off of the valve. I am sure I am going back tomorrow. So if I do take the air off the valve and steam passes that means the valve is junk. But when air is taken off the valve and steam still does't pass would you say the coil is blocked or are there other avenues I should travel?

Pete_31

Erik, I would try -carefully with gloves-loosening the tail piece on that valve just to rule out the valve. I believe your right most heating valves should fail open.

Erik Richardson

Dave

Steam has got to be the most brain racking thing in the heating field. MY boss is a steam guru, but get very annoyed when I don't have the answers.

Erik Richardson

Pete

What do you mean by the tail peice?? do you mean loosening the set screws and pop off the pneumatic portion, or are you talking about something else?

Erik Richardson

thanks

Thanks guys I appreciate all the advice. I am heading to bed, since 5am come quickly. I will check back in the morning for anymore advice. I will also hang a bit longer tonight for more advice on what to troubleshoot the next time I go back. thanks again I appreciate it.

Unknown

Erik,

if your boss is such a steam "guru", and you have the passion to learn, then he should "take you by the hand" to teach you.
We`ve all been through-it.

Dave

Pete_31

I was hoping that it was a valve with a built in union. Many smaller valves come with them. They are usually on the outlet side of the valve.

Brad White

Air On/Air Off

No worries on that Erik- I have been at this 30 years and am still learning every day.

If you take the air off the valve and the valve opens, that means it is working (failing in a safe attitude as far as protecting the system from freezing).

If you put air back on the valve and it closes, that means that it is also working.

If steam does not pass with the valve open, you have to find another blockage, could be debris, a strainer, a closed valve that time forgot.

Walk it through step by step. As Dave said, steam goes from higher pressure to lower pressure always. It really is very logical once you get into it. Not to say there are not real stumpers now and again.

I sense your boss does not explain things too well.

ttekushan_3

good morning!

Hmmm. Seems the guts were removed from that trap to prevent the thermostatic portion from closing as a result of steam in the returns. The steam can back up to the trap and close the thermo element (thats been removed) preventing steam entering the coil where its supposed to. Obviously, that "solution" isn't working out. BTW, at the pressures you indicate, steam vapor coming from an opened fitting on the returns can be normal. If the rest of the mains and coils are operating @ say, 5PSIG, the condensate can be above 212°F and flash into steam into the return. It shouldn't be "live" steam, but a gentle flow anywhere near another trap may be fine. This is not the problem here.

[Check out the thermal images of good and bad traps from a thread last week. I think it was "thermaljake" who posted them.]

On to solutions!

1) Could be the stem is moving on the pneumatic valve, but something inside is broken, holding back the steam. Like what Pete said. And make sure the stem is actually moving with the spring, etc.

2) The mud leg on the return side of the coil might be filled with mud up and into the lower outlet of the coil. Rodding out this section is indicated as noted by Brad.

3) You broke into the return near the F&T, but is there a strainer and/or check valve of any kind between the coil and the union you cracked open? These are usually installed along with a vacuum breaker to keep return water from being sucked backward up into the coil as the remaining steam condenses after supply valve closure. Don't forget that there's a 1700 times difference between the volume of steam and the volume of the condensate it creates! The strainer could be clogged. The swing check valve could be stuck or blocked.

4) If the items mentioned above (check valve, strainer) are there and check out OK, then check for the vacuum breaker. Check valves, thermostatically controlled supply valves and vacuum breakers go together like, uhhh, corned beef, sauerkraut and rye. Anyway, if the breaker is the only one of the group missing, the coil could be collapsed somewhere. This the worst case scenario.

5) Actually, this should be #1. This may sound stupid, but there isn't a supply shut-off lurking somewhere near the main, is there? Look closely for a bulge in the insulation with a stem aimed in such a position that you can't really see it unless you're looking for it. No offense intended on this one, but you never know... Perhaps the guts of the trap were removed for replacement and they closed a supply valve somewhere until the non-forthcoming parts arrived, and thats the way it stayed.

-Terry

Joe Billow_6

Start with the basics, check from the coil to main line for a closed manual valve, check to make sure that there are other coils working on this line. If there are and you have a hot main (use a IR thermometer). Then the problem is in this circuit. If you have a manual valve before the pneumatic one close it and physically check the operation of the pneumatic valve. I wouldn't break any fittings/unions without blocking off steam up-stream and preferably down stream too, because it sounds like there is live steam in the condensate return. With the valve out I would crack the main (making sure no one is around)and see if there is steam there, if so then your coil is probably blocked. You'll get it, just takes time.

Joe Billow

Owen

Ha Ha

Sorry, but this is way funny. I'm in your exact same boat there Eric, my compadre, and can seriously co-miserate. This stuff is very complicated, especially when you figure in all the knuckleheads who think they understand steam without serious outside study or real thought which conforms to the laws of physics. (Not the real live Dead Men of The Wall, my mentors and compadres; I'm talking about the "Turn it Up & Fuggedaboudit" crowd). Steam alone is complex enough when you start with an old, knuckleheaded building with mostly radiators. Throw in Johnson Controls pneumatics (antiquated in today's world, and maddeningly complex and complicated), convection coils, unit ventilators (#@!?$%-IT!) fan/coil units and Direct Digital Controls and you have a formula for some serious frustration.

Patience, and come here often. I've been very pleasantly surprised at how generous these guys are and how knowledgeable. I was lucky, I stumbled on this site about two and a half years ago and it has been a revelation, especially Dan and his books. I have pissed the bosses here off because I point out how poorly things have been done for too long. No trap replacement for 80 year old buildings, ridiculous pressures (14 pounds under a kindergarten!) waste, waste, waste.

I am sad though, because you work for a private sector business. Tough to tell the owners what they don't want to hear, namely they have to spend serious bucks now to save later ("What if it doesn't work! I'll lose my job!") Not that it's easy to convince public sector people either. (What if we spend all this money and don't save a ton right off the bat! I'll lose my job!) Hang in there, come here often, and good luck.