Steam system return issues air vents leaking

Everything_HVACR85

this is one of the highest risers 20 feet max. Each heater has a vacuum breaker on the inlet at the top, thermostatic air vent on bottom followed by a steam trap and a piston check valve. Initially I found all air vents closed, suspect due to leaking as well as some vacuum breakers missing. This building is fed from a pressure reducing station and the pressure was raised to 80 psi. I corrected the missing vacuum breakers and opened all air vents, this reduced the pressure to 60psi by letting the air out. I was then able to lower the pressure to around 30psi. Replaced a few new check valves that were not working.  Building is operating much better but a few air vents still spit condensate periodically. Is this just another problem with check valve/ steam traps not working or could there be something else I have missed. I do not know the original design,  pressure settings or installing contractor. I have improved the operation but am curious if this design position of all valves ect. Is correct.

Everything_HVACR85

EBEBRATT-Ed

How does it work with the air vents valved off?

Lifting condensate with steam is problimatic but can be done. Yours is piped exactly right.

Are there control valve on the inlet to the heater? I don't think so.

As long as the steam is on there is nothing to vent. Shut the air vents off. Keep the vacuum breaker though. Shouldn't need an air vent

You can't drop the steam pressure to low because that is lifting the condensate. If the condensate riser is 20 feet you need 20/2.31= 8.65 psi of steam pressure to raise the condensate. add to that for pipe and fittings so you need 12 psi to raise the condensate

Should be ok as lon as the bucket trap works properly

Everything_HVACR85

Thanks! It was running with the air vents off, I assumed they were there for a reason. There are actuators that feed steam to these heaters they close/open on outdoor temperature. I did the math on pressure to return the condensate, as I said it is working better at a much lower pressure than before. If these actuators close obviously they fill with condensate and leak out the air vents. At this point they are just leaving open for winter and will close in summer and have to drain condensate. I believe this is where the problem started, too many maintenance guys messing with this and didn't know how it was supposed to work. So actuator closes, controlled by set point in BAS, condensate builds up and leaks from air vents, they close air vent and somewhere in between began raising pressure. 

luketheplumber

I've been a subscriber on your YouTube channel for a couple months, love your videos keep them up.

Everything_HVACR85

EBEBRATT-Ed, what you are saying makes sense, if the steam stays on there is no need to vent, I did not consider this. It seems I may not need the actuators or air vents once the air is bled. I still dont see the original design, with the air vents being low anytime the actuator would close the vent would drain the condensate. This may be my approach next heating season, thanks again for the knowledge. I was trying to get back to design which may have been flawed from the start.

EBEBRATT-Ed

@Everything_HVACR85

Technically it SHOULD have air vents there (and I am sure a piping book or engineers drawing would show them their) especially because bucket traps don't handle air well and can get air bound. And normally they would be fine. But this is a different application your below the main and it will fill with water.

Since the valves are mostly open I think your fine with the vents off.

I thought about piping off the air vent valve and go way up above the main condensate return but that won't keep them from spitting.

An F & T trap instead of a bucket would vent air better you could try one in a problem unit if you have to

I am sure on that job the return goes back to a condensate tank or boiler feed tank so the air will vent there

But if you think about it when the steam comes on condensate will come down that pipe first and get the trap going

Everything_HVACR85

I thought about raising them as well but they would have to go way up. This is a different application than most and yes they to run back to a condensate tank. I dont really need the actuators and can control on and off due to season so I think the best plan is just to schedule a seasonal start up and shut down. Thanks again for the insight. 

ChicagoCooperator

Off topic, but that is some impressive cross bracing and framing (working on a project with some right now, but nowhere near that hefty).