Low pressure gauge that can handle high vacuum- is digital the only option?
I just finished a renovation of my system that involved a conversion of the entire basement and first floor to 2 pipe (most of the old piping was leaking) while leaving the upstairs radiators 1 pipe. This system runs in natural vacuum between cycles (upstairs radiators have Teflon ball check valves I designed sitting on MOM vents, more on that to come as I get this system fine tuned). The thing is, it goes down nearly to -20 inHg between cycles. It already broke my -30inWC to +30inWC gauge instantly the first time it went into vacuum. So the question is, what gauge do I get that can show the 0-4 oz/in2 normal operating pressure but not be damaged by -20+ InHg of vacuum? It doesn't necessarily need to show vacuum, as I have a compound gauge as my high pressure gauge, but it does need to stand up to that level of vacuum without breaking. I know there are digital gauges that can do this, but they are quite expensive ($300+). What would you guys' suggestion be for a gauge? Included are some pictures of the check valves I made. They are made from a Holley carburetor jet extension for alcohol fuel (5/16-32 thread), which is drilled down further and polished to make a seat for a 1/4 inch Teflon ball. A nail is pressed through a crosswise hole to retain the ball. The standard MOM orifice or MOM knockoff orifices can screw into the female thread on top. An O ring is placed around the bottom for better sealing in vacuum. More pictures of the vents and check valves and the rest of the system will be on another thread when I have time to do it on the computer. On mobile I can't figure out how to put the pictures where I want them to go and then my phone crashes trying to post the pictures. For now I just need to figure out this gauge issue.
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Could you mount a low pressure gauge on one these teflon ball check valves or some version of one to protect it from most of the vacuum? Then have a vacuum gauge or combination gauge mounted separately? I'm curious to know how this works, it sounds promising so far.
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Hello Theo_G,
I would use something like this, a Dwyer Magnehelic (see image), oh yeah I do. Many new and used on eBay. Note the 15 psi Max. -20 inHg is about 10 PSI. BTW 4 oz/in2 = 6.9 WC (inch of water) = 0.5 inHg = 0.25 PSI.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System
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If I made a 1/4 NPT version of the check valve to go downstairs, I would think that if the gauge went to peak system pressure it would just get stuck there with no way for it to escape. I will start a thread with more pictures of this system at a later point when I have it fine tuned a bit better. At this point it's only been running for a day.
The Magnehelic is a great idea. Last time I used one on the old system it got filled with water instantly and the glass fogged up. Maybe I just had one with bad seals. How do they handle being mounted on a pigtail or control tree in terms of longevity and accuracy? Is there a better way of doing it to protect the gauge from water exposure?
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The Magnehelic is a great idea. Last time I used one on the old system it got filled with water instantly and the glass fogged up. Maybe I just had one with bad seals. How do they handle being mounted on a pigtail or control tree in terms of longevity and accuracy? Is there a better way of doing it to protect the gauge from water exposure?
By "instantly" I assume you mean over the course of many hours. This is from steam getting into the gauge and condensing there, something I too have experienced.
You can try to improve the main seal behind the glass (plastic) with silicone oil, but the best thing to do is either put it above a pigtail or water seal, or if that affects your pressure reading too much, put it above a valve and only open the valve to read it.
You can also put it on top of a tall vertical 1/4" pipe which will slow down the steam that can get to it (but may not completely stop it during long calls for heat).
Longevity is fine, even full of water they just keep going. I have drained mine several times with no ill effects. On top of a pigtail they will of course be even more long-lived.
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el0 -
Good to know. The one on the old system was mounted right on the steam main and I do think it had bad seals, the fogging of the glass appeared right away, as in maybe an hour after I had started up the system or less. It was a used one in who knows what condition though. This one will be mounted on a control tree, like a pigtail made of black iron pipe. Because my MST288 only has two pressure tappings, I built two control trees for the two gauges, a manual reset pressuretrol, and a vaporstat. The manual reset pressuretrol is set at B-dimension pressure to keep water from being spewed on the floor if something goes wrong with the vaporstat (no main vent, only a check valve).
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IME, a normal 30" Hg-0-15 psi compound vacuum / pressure gauge would certainly handle any vacuum this system would see. Now, is this gauge sensitive enough on the pressure side to meet your needs, probably not.
I am not aware of a 30 - 0 - 5 compound gauge being available.
Dennis Pataki. Former Service Manager and Heating Pump Product Manager for Nash Engineering Company. Phone: 1-888 853 9963
Website: www.nashjenningspumps.com
The first step in solving any problem is TO IDENTIFY THE PROBLEM.0 -
@Theo_G yes I think you will be very happy with it on top of a control tree—you won't need the valve in that case. The water trap should protect it from getting any steam at all.
I should also have mentioned that of course the gauge's resistance to letting air out (and steam in) is also dependent on the pressures it's exposed to.
As was stated above, all Magnahelics are rated to 15 psi (and I assume similar negative pressures—they are all built to be able to reverse the pressure inputs), and the recent-vintage ones have a rubber blowout plug, so if you get a NOS or used one on ebay (highly recommended), be sure it is one with the red rubber plug on the back (and not just a hole where it's missing LOL)
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el0 -
So I couldn't find the negative pressure spec on the Magnehelic, but I found it for the Capsuhelic (500psi rated version), and it is 20inHg, exactly what my system got up to after a continuous 8hr run. I don't think my system will ever run longer than that on the tstat so it should be fine. On shorter runs it gets down to about 10inHg. The connections on the Capsuhelic also face down which simplifies things in terms of mounting (there are a lot of things jammed into that space on the front of the boiler). I don't mind paying a little extra for a Capsuhelic over a Magnehelic, there are some new old stock ones in the pressure ranges I'm looking for. I don't believe they have a blowout plug or at least I don't see one.
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That vacuum valve is fantastic! "Carburetor parts:" That's great!
I actually needed a vacuum vent once on a job, but was able to find a NOS one on ebay.
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-30" of wc is only-1psi or so.
You need a gauge that will take 30" of Mercury=Hg
You may have to use separate gauges 1 for pressure and one for vacuum. So use a 30psi+0to a -30"Hg for vacuum
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Hello Theo_G,
My Magnehelic is connected to the top of the boiler, at my boiler's pressures of less than 5" WC I noticed a slight bias in the pressure reading caused by the water seal of the pigtail when I had it connected there, which I did not like. So now I have about 8 foot of 3/16 silicone tubing between the boiler top and the Gage. I never bothered to cut it, I just looped it up high over a pipe then back down to the Gage. I think the 8 foot of thin tubing acts a bit like a snubber too.
If the Gage (or the plugged unused port) does not leak and there is a air buffer between the steam and the Gage there should not be a condensation issue. At these low pressures if the Gage leaks it may not read correctly.
Also check this out; ChrisJ 0 - 2" Magnehelic without pigtail, with and without snubber
https://forum.heatinghelp.com/discussion/158333/0-2-magnehelic-without-pigtail-with-and-without-snubber?utm_source=community-search&utm_medium=organic-search&utm_term=18%22+Magnehelic
The Capsuhelic will probably work just fine, just less versions to choose from.
Magnehelic Spec. 2021 Dwyer Catalog.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
as soon as you start doing that, you see the pressure build up before any air will exit the radiators. That’s why I gave up on this idea (I too had made some check valves that attach to the top of the MoM vents)
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el0 -
I had no clue how much vacuum would be generated as that was the first time the system was run. But that's what I'm going towards now. I already have a -30Hg-0-30psi gauge as my high pressure gauge.
I'll look at the options for Magnehelics too and see if I like any better than the 0-25" WC Capsuhelic I saw. I do like the 200F temp rating of the Capsuhelic. More confidence inspiring. Not to mention the bottom connections.
If the seat for the ball is polished enough, no spring is necessary. The ball will seat as soon as it sees vacuum, and it will unseat as soon as it sees pressure. I made the seat with a small Dremel grinding bit with beveled edges, then polished it with a soft polishing bit and compound. Having even a weak spring would impede the operation of the valve, it needs to have essentially zero resistance to air pressure to vent properly. And they do work well. I have one real Dole 2B vacuum vent for comparison and they work about the same as each other. This is just a temporary solution for this heating season. Next year the plan is to put Hoffman #3 Paul valves on each of the three upstairs radiators so that they vent out of the single point where the dry returns combine. After that I can add a vacuum pump (I found a very small liquid ring pump, or alternatively I can use an eductor/ejector in conjunction with a centrifugal pump), and a differential pressure switch and it will be similar to the Dunham Differential System where the temperature of the steam changes based on demand.
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I wish you success!
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el2 -
Hello Theo_G,
You may be interested in what @PMJ did with his system, he uses a natural vacuum, no vacuum pump needed. I guess if you don't let the air in, you don't have to vent it back out, also less oxygen in the system to cause corrosion.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
That's exactly the configuration of the system right now and it works quite well. The only thing I'm going to change with regards to system venting is I'm going to go from the large main vent check valve to a solenoid valve with a delay on make timer controlled by the limit/burner circuit. The reason for this is that the large main vent check valve has too much backpressure and i'd like to be able to run the system with a bit less pressure. I'll keep the check valve plumbed in parallel with the solenoid valve in case it fails. The homemade check valves on the upstairs 1 pipe radiators work perfectly and open with seemingly almost zero pressure, so there's no issue with those. The reason I'd like to add a pump is I'd like control over the steam temperature based on demand or outside temperature. Like a Dunham Differential System or a Vari-Vac. Probably with the pump controlled by a PLC and several sensors.
As for the gauge, I ended up going with a Dwyer Capsuhelic 4025 (0-25 in WC). I just felt more comfortable with the Capsuhelic where the system pressure is isolated from the gauge mechanism, and I happened to find one new in box on eBay at a pretty good price. A more detailed thread with information on the whole system is to come mostly after I do some cleaning up in the boiler room. There are tools and pipe insulation all over the place as I was in a huge rush to get the system running before it got really cold.
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