Pneumatic Thermostat System
Hi,
I am in charge of an old school in Denver. We have a hydronic boiler heating system that is thermostatically controlled by a pneumatic system that was installed in 1964. It uses Univents with air dampers and is controlled by the pneumatic system. Also fans controlled by the pneumatics. All these elements don't work anymore, but did as recently as 11 years ago.
About 10 years ago a new boiler was installed and moved into the boiler room with the steam boiler (which serves the older wing of the building . The compressor was moved also. I suspect anything that went with the compressor was lost. Currently the compressor has no dryer, pressure reducing valve, or oil remover. It runs at a high pressure and trips the breaker regularly because it runs so often and overheats.
I am wanting to resurrect this system back to working order but I have no experience with pneumatic systems. I've done some reading and looked at old textbooks and the Johnson Control book that is on this sight.
I still don't know what I need as far as an FRL system. They are not easily found online. Some are for air tools and add oil into the system rather than take it out. There is a refrigerator/dryer on Harbor Freight but it's $600 and very large. I don't know that these items are tailored for thermostatic systems.
Any help on how to educate myself or websites to look for that sell items for these systems would be appreciated.
Comments
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National Energy Controls in PA. (you can google them) is a source for all things pneumatic.
Pneumatic systems are good but fewer and fewer know how to work on them. They are fairly simple.
If the system isn't working, I would think it would overheat like crazy. Most heating valves go wide open on loss of air pressure. I attached a Honeywell Pneumatic catalog.
If your system is Johnson all the parts are basically interchangeable (not an exact fit but will work) Johnson, Honeywell, Powers, Barber Coleman, Robert Shaw
The catalog attached has a lot of good information
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If the instrument air compressor has been running without proper pressure regulation or a filter/dryer, the rest of the system may have been severely damaged and require extensive repairs.
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Bburd1 -
ive been running the system with the boiler’s outside-air adjustment, using that as a thermostat to adjust the firing rate based on the outside air temp. It also has a nighttime setback i can use to lower the boiler temp at night. Also turning on the univent fans manually as needed. Not the best but i suspect an over haul of the the thermostat system will be what’s needed and the money isnt there for that.
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@michaelmiracle Getting the OA will at least get the boiler under control to roughly control the boiler water temp. Then the day night set back. Those two things will save fuel and get things more reasonable That is a good first step.
Next step would be to get the air compressor system fixed up.
Then the unit ventilators.
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I'm seeing I probably need a PRV station that sells for $5k (Johnson Controls) and a cooler dryer that sells for another 5 or so. Am I right in that is what's needed after the compressor?
I'm thinking I can build a PRV station cobbling together the parts from eBay sellers who are much cheaper for NOS. I'm looking at the parts description on the Johnson Controls cut sheet. I only have one working compressor so it may be simpler than the one I'm looking at.
Th cooler/dryer is another story. But at least I can get the oil/water out and the pressure down as a start.
It's been 10 years like this so the system may be toast, but my understanding is that it was working a few years ago before I took over.
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you might be able to buy the parts branded as parker or whoever makes them for johnson controls for a lot less. the preassembled stations are going to be a lot more than the parts
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A lot of the older systems didn't have cooler dryers. People got lazy and wouldn't drain the tanks. I would put an automatic tank drainer on it to remove the water in the tank and let it go at that.
I mean you must have some type of PRV now? The compressors typically run at 100psi and put air to the system at about 20psi. How is it working now?
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You could do what they did in the Olden Days, the tube from the regulator feeds into the bull of a tee at the bottom of a 3ish foot long vertical piece of 2" pipe. A reducer to a small drain at the bottom, a reducer to main air at the top. If it worked with air pumps from that era, it should be fine with a modern one.
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You know, it was kind of working when I got here. The compressor was constantly tripping the breaker though. So I thought the compressor was just running too long and overheating. I shut it all down when I got the software updated on the boiler to include OA and night setback settings.
There is a setup attached to the wall just as you describe that is abandoned. Might this be what you are describing?
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It probably isn't getting unloaded properly before it tries to start again and is tripping the breaker. Or it has bad start components and can't start loaded if it is designed that way.
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Good point. It took me all day to figure this one out. I order a start cap. today. Also an unloading valve attached to a switch to replace the switch that's on it.
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if there is a bad check valve it might re-pressurize after it is unloaded.
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Grainger should have the pneumatic devices you need. When I was doing controls all the schools from the 50s-60s were pretty much laid out control wise the same at least here in the Detroit area.
For the air compressor an auto blown down would help to purge the moisture and oil in the tank. A oil separator at min if there's no budget for refrigerated dryer. If the unit vents had a night setback there most likely at some point a EP and Day/Night relay in or near the boiler room. Possibly two PRVs One for day operation to provide main air at 20PSI ish and set lower based on the operating range of the local day/ night stats. If you can go to the units and find the spring range of the valves and if they at NO valves usually 3-8 PSI or NC valves. 8-13 PSI.
If your compressor runs a ton you prob have air leaks from cut lines, bad/ missing stats or bad diaphrams on valves and dampers. It you have some fittings / gauge and squeeze bulb from a manual blood pressure cuff you can go around and test the devices. It's time consuming, but you can narrow down leaks.
Grainger / Columbus Temp Supply / Cochrane Supply / Kele all carry pneumatic stuff
Owner of Grunaire Climate Solutions. Check us out under the locate a contractor section. Located in Detroit area.
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As luck would have it. Here is an example of a small HV unit from a school built in the 60s where I did a fully DDC change over to. Hope this helps you see they did the controls via pneumatics
Owner of Grunaire Climate Solutions. Check us out under the locate a contractor section. Located in Detroit area.
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The good old days when "Blueprints " were really Blue.
Nothing wrong with Pneumatics. They do need to be tended to occasionally to keep things working right. Unfortunately, they get neglected and then its a tedious road back
@michaelmiracle.
Yes the stand pipe was used to drin moisture before the refrigerated driers. An auto drain and oil separator on the tank will help. Keeping moisture and oil out of the system lets the controls last longer.
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and cyanide…
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That's pretty much it.
I've had trouble with the compressor tripping the breaker from time to time. It always ended up being either a bad pump or a bad motor. For some unknown reason, the compressor we ended up with has a 120 volt 2 HP NEMA 48 frame motor. Not quite left-handed metric, but still not suuuper common and still too small to be worth it to rebuild vs purchase new.
BTW, it's my understanding that a "compressor duty" motor is a lighter duty rating, since there's supposed to be lots of off times to cool down. Pick general duty over compressor duty.
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