Old Johnson Controls Residential Pneumatic System

JimRafferty · May 2017

Greetings, All!
In need of a little wisdom.
We picked up a "new" account and a new homeowner who wants to update his system. The system is controlled by a Johnson Controls Pneumatic system, vintage 1950. In the basement is a compressor and a control panel that kinda looks like Captain Nemo's dashboard. Banks of old pressure gauges, Mercoid controls, etc. piped in with multiple 1/4" copper tubing going up into the house. Each room has it's own pneumatic thermostat and each radiator in that room has a pneumatic rad valve. The system is still operational and is a thing of beauty. It really hurts to shut down such a cool retro relic.
When we killed the air pressure and fired the boiler, we found that the rad valves are Normally Open.
Rather than cut out 35+ pneumatic rad valves, the customer would like to leave the rad valves in place, but wants the pneumatic thermostats in each room removed.
What potential downside is there to just cutting the T-stats loose from the copper tubing? Could one of the rad valves leak from the water side into the now abandoned pneumatic tubing? When we killed the air pressure in the system, we could hear water (condensate) trickling back through the pneumatic tubing into the compressor.
If anyone has had any experience shutting down, abandoning or decommissioning a system like this, I'd appreciate your input. Thanks in advance.

EBEBRATT-Ed · May 2017

Most pneumatic heating valves are normally open as you have found. This provided freeze protection and would cause the building to overheat if compressed air was lost. This was called "fail safe " operation.

The pneumatic valve is operated by air pressure (to close the valve in your case). Compressed air from the air compressor feeds each thermostat in the building (this is called main air). There are two types of thermostats single pipe or two pipe.

In a two pipe system compressed air is piped to each thermostat (main air) and a branch line is piped from the thermostat to each valve. As the room temperature changes the branch pressure changes to the valve as the air pressure is regulated by the stat.

with one pipe thermostats the main air from the compressor is piped to a tee through a restrictor. 1 line from the tee goes to the stat and the other line from the tee goes to the valve. The thermostat bleeds off the restricted air supply to regulate the valve.

If you decide to abandon the system you can shut down the compressor and remove the stats. Nothing will happen and every radiator will get full heat........but you will now have no temperature control of the building.

It is not possible for condensate to get into the pneumatic tubing....that just cant happen. If there is fluid in the pneumatic tubing it will be oil and/or water. The water is from condensation in the air tank and failure to drain water from the tank occasionally will cause this (they make automatic tank drainers now).

Oil comes from a warn out compressor.

oil and water in the system are bad for the controls

If it was me I would fix up the pneumatic system and keep it working.
Once it is fixed up a pneumatic system used for heat only would probably need to be serviced once a year to keep it working properly.

Sounds like this was a Cadiliac system in its day. it will still work why destroy it. parts are available

ratio · May 2017

There shouldn't be any water in the pneumatic side of things. It's just this side of impossible for heating water to leak into the air side of the valve. Any water in the there is condensation from the air compressor, an automatic blowdown valve and dryer are indicated.

Why're they decommissioning the system? It'll cost far more to replace it with a comparable electronic system than it will to repair the pneumatic system. It may even be cheaper to add on whatever remote access they want than to change out the whole system. If the system was originally designed with individual controls on the radiators, it might not be possible to balance it without that control, you'd need to duplicate that. You could use DDC transducers to operate the pneumatic valves, & keep the compressor, or change out all the valves.

ScottSecor · May 2017

Cool system, never saw a house with it but most of the local public schools had the same basic system until the last fifteen to twenty years. I agree with above, not dangerous at all to remove the copper (later plastic or rubber) pneumatic tubing.

Biggest problem I see is that the systems we serviced were not balanced at all, practically every classroom got the same size unit ventilator, regardless of heat loss. Not really an issue with individual control for each classroom. BUT, when the original tubing started to fail many rooms would hit 85 or 90 degrees on a cold day. My point is you will need some sort of control on every radiator in the future.

tim smith · May 2017

You could probably come up with a conversion linkage and 24volt operators, one way or the other you can very likely come up with a operator that would work. Then install 24 volt stat and relays. A thought? I have seen these in a couple houses and quite a few commercial bldgs. Always enjoyed dabbling. The real challenge would be probably getting wires where you need them.

Jamie Hall · May 2017

Totally agree with @EBEBRATT-Ed . If it ain't broke, why fix it?

If the present owner wants shiny new electronic controls, I expect the simplest thing -- by far -- would be to find air valves and electronic thermostats which would perform the same function as the existing pneumatic ones. Leave the radiator valves controlled by air. Less reliably, probably, but much better bling...

bob_46 · May 2017

Those are modulating valves so forget residential controls .
Unlike modern electronic controls replacement controls and even rebuild kits are available .

JimRafferty · May 2017

Thanks all for your comments.
And sorry for any confusion. I meant to say condensation from the compressor.
Yes, I agree that it's a Cadillac. And way cool to boot. The more I see of this system the more impressed I am with the engineering and the individual room control capabilities.
In a nutshell, the new owners are a younger couple and are looking for convenience, connected home type stuff and, yes, bling.
They want to be able to turn down one thermostat when they go away for the weekend rather than fifteen stats.
And the compressor noise is also a factor.
I'm recommending a system with outdoor reset and non-electric rad valves to try and preserve the controllability it has now.
I feel like I'd be desecrating a monument by shutting down this work of art. But like Dr. John says, if I don't do it somebody else will.
Thanks

nicholas bonham-carter · May 2017

Real bling is having a vintage system in perfect working order, which no one else could have!
What about putting a wi-fi thermostat in front of the whole system. That way they have the room stats set the way they wish, and still be able to have some upper limit control over the whole system.
If you dismantle the controls, and remove valves, etc, can you consider making those parts available on the buy, sell part of the website here? Metered valves, or orifices could enable you to fine tune the output of the rads.--NBC

ratio · May 2017

Don't forget that pneumatics has had setbacks from like The Beginning. If that system doesn't have it already, it for sure can be added with off-the-shelf parts. But you won't be able to set the temp from your iPhone 42 without a little custom work. There are threads around here somewhere illustrating similar custom work...

We understand that you probably won't be able to change their mind about this, but it's always sad to see a '68 Vette go under the knife. It's bound to come out the far side to the less.

ttekushan_3 · May 2017

Modulating pneumatics like that are beyond Cadillac. (No offence!)

Day night setting is accomplished with dual pressure stats.

There are any number of internet capable switches that can cut in and out the electro solenoid for night setback.

I can't begin to venture a guess what it would cost to replicate this system.

Besides, you can still use a normal thermostat to set high enough for the pneumatics to prevent overheating and when set low enough the valves simply open but the house is cooler.

I just don't see here what necessitates the destruction.

Furthermore, since there will no longer be room control (which is the holy grail of modern heating control that we all would kill for-- and they want it destroyed) I predict that this mistake will be followed by a bigger one:

The removal of the entire system within a couple years "because steam heat can't be controlled. "

And all this will cost a ton of money. Do they really want to step on that rake?

MilanD · May 2017

Goes to show that because one doesn't understand something, doesn't make the "something" be at fault. Try convincing the customer to keep this. As others suggested, same wifi access and control can be accessed without killing the Dodo. From what you said, they really want a remote on/off and high/low switch. Once temp is set in each room to a desired temp, it'll never need changing.

JUGHNE · May 2017

Is this steam or hot water?
I have a school house with Powers controls. They only use one classroom. All main rooms have day/nite Tstats.
The entire building is set on nite pressure except for one day a week. The day/nite stats each have an over ride lever to call for day temps if needed. There is a master day/nite switch in the boiler room that is used to bring the entire building up to temp when desired. Each stat has 2 choices of temp.
This building is hot water with reset on boiler temp. Pumps run on outdoor reset stat.
These stats will modulate the water flow very accurately. Breathing on the sensor will cut the water flow.

I think you need the 2 tube control system for the day/nite stats.
The day/nite function could be electricfied with timer, wifi....so you could run the system with your phone......that turns the crank for a lot of younger ones.

If you have 1950's rads the stats would match the décor. As NBC said that is real bling that would be unique.

JimRafferty · May 2017

Thanks all for your comments.
With the cost involved in replacing the Johnson Pneumatic system with outdoor reset and non-electric rad valves, we may have convinced the customer to keep the Johnson System.
The system is hot water with Johnson Outdoor reset, has 3 circ zones total, 2 heat and 1 DHW.
My though is to let the Johnson Pnuematic system do it's thing and to make/break the space heating circs with a TACO multi circ relay and (2) digital stats up in the house.
The digitals can act as master stats and allow the owner to lower 2 digital stats instead of 20 pneumatic stats when they go away for the weekend.
Anybody see a downside to this?

ttekushan_3 · May 2017

I see no downside to that. I've used the master thermostat method for deeper setbacks. The pneumatic system doesn't care if the valves operators are relaxed (open) indefinitely until called on to prevent overheating of the room.

Your plan will work, the comfort of the modulating thermostats is retained. It's both an economical and effective solution. Win-win.

EBEBRATT-Ed · May 2017

that should work. The Johnson system will limit overheating but the master stats would have to be in the coldest rooms

Old Johnson Controls Residential Pneumatic System

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