Water in new Magnehelic gauge

Don_175

The enemy of good is better. I replaced my existing low pressure gauge with a Magnehelic 0-3 psi. 

Last night with boiler running the gauge never went above 0.2 psi. In fact, after 10 minutes or so, the gauge drifted to 0. 

This morning I noticed water droplets inside and when I removed the horizontal nipple, water came out. Blowing into the pipe, I can get the needle to move. How would water get inside? The pigtail has water in it. The old gauge never got water in it. Will the water damage the gauge and is there any way to dry it out? Thanks 

ethicalpaul

Some of mine have done this. There is likely a leak in the seal between the glass face of the gauge and and the rest of the gauge. The leak allows, over time, steam to enter the gauge and condense in there. It doesn't seem to hurt it but yes it's best to avoid the situation.

You can shake it out and then leave it lying on your warm boiler and that will let the water evaporate out. Then when you do is put a ball valve in front of the gauge and only open the valve when you want to read it.

You can unthread the front part that holds the glass and then put some o-ring sealant on the o-ring and then spin it back on to reduce or eliminate the leak. Or just use the valve to not leave it exposed to pressure unless you're reading it.

Don_175

Thanks. I did put a valve right next to the cross tee. 

Also, why would gauge be reading 0 with main vents closed and steam actively being produced? The cheapo gauge I replaced it with was reading 0.3-.5. 

mattmia2

How long was it running with the old gauge? Did you fix anything that wasn't heating or wasn't heating well?

Don_175

Old gauge was on from last winter. Haven’t changed anything with boiler. In fact,last week when boiler had been running for a while, old gauge went from 0.4-0.5 up to 1.2 psi. I had never seen a pressure that high so I thought I would replace gauge with a real good one. This one started at 0.2 and eventually went down to0 with boiler running 

109A_5

Hello @Don_175,

As @ethicalpaul stated it may have a leak. The gauge face and indicator is on the positive pressure side of the diaphragm. If the glass face "O" ring is leaking it won't display the correct pressure (since it is leaking).

Also that style gauge often has 4 ports, 2 on each side of the diaphragm, 1 on the rear and 1 on the side. Or in other words 2 differential ports on the side and 2 differential ports on the rear. In your case the unused port on the pressure (+) side of the diaphragm needs to have a 1/8 NPT plug in it and it needs to be air tight. The 2 (-) ports (side and rear) are left unused and at least 1 unplugged, they allow atmospheric pressure on the (-) side of the diaphragm.

Don_175

109A_5 said:

Hello @Don_175,

As @ethicalpaul stated it may have a leak. The gauge face and indicator is on the positive pressure side of the diaphragm. If the glass face "O" ring is leaking it won't display the correct pressure (since it is leaking).

Also that style gauge often has 4 ports, 2 on each side of the diaphragm, 1 on the rear and 1 on the side. Or in other words 2 differential ports on the side and 2 differential ports on the rear. In your case the unused port on the pressure (+) side of the diaphragm needs to have a 1/8 NPT plug in it and it needs to be air tight. The 2 (-) ports (side and rear) are left unused and at least 1 unplugged, they allow atmospheric pressure on the (-) side of the diaphragm.

The high pressure and low pressure ports on the side have plugs in them. I unscrewed the high pressure plug on the side and it was not sealed at factory. I reinstalled it with Teflon tape. I’m trying to dry it out as the plastic face is covered in condensation. I left it on top of a warm area and it got worse. I tried unscrewing the front bezel to check the o ring but I cannot budge it. Any tricks?

109A_5

Hello @Don_175,
That may be a question for @ethicalpaul. I believe he has had his gauge glass apart. With mine I had a plug that I thought was tight enough an it was not, easier to repair once I realized what the pressure problem was. My system usually does not go over 1 inch of Water Column.

As far as drying it out. I would have left all the plugs on the (+) pressure side out and supported the gauge so it would drain out and the warm environment. Then once it dried out, plug the unused port. The condensed water in the gauge may look worse until it dries out completely.

If I were to try to remove the gauge glass assembly I would probably try two band or strap wrenches like for automotive oil filters. Or a nipple in each of the rear ports, put the nipples in a vice and one band or strap wrench. Not sure how @ethicalpaul did it.

I would pressure test it, or just try it again before I bought any special tools to remove the gauge glass. The leaky plug may be the only problem.

Having the gauge vertically higher away from the pigtail water may help too.

My gauge is significantly away from my boiler with a 3/16 silicone hose. Not that it was needed that way, I just wanted the gauge located with other instrumentation stuff I am working on.

ethicalpaul

Just keep it with an open port on the high pressure side on your boiler. It will dry out in a day or two. Seeing the condensation doesn’t mean it got worse. If it collects there, see if you can shake more out.

any leak is likely very slow and won’t affect the reading

Don_175

I finally dried the gauge and zeroed it. Reinstalled it and when boiler had been running for quite a while, I noticed the pressure hit a max of 1.2 psi. Never cycled on pressure. This morning, with the boiler off for a couple hours, it is reading 0.4 psi. Shouldn’t it be 0? The instructions said the zero with the gauge uninstalled. There is a snubber underneath it to stabilize the readings. Should I set it at 0 now?

ratio

Pull the hose off & see if zeros then. You might have condensation inside the diaphragm assembly that's throwing it off.

109A_5

Hello @Don_175, Being on that side of the pigtail the water in the pigtail does impose a bit of bias. Although that seems maybe too much or more than I would expect in your case. My gauge at +/- 1 ( or 1-0-1) Water Column seems to act like a Barometer at times even when the boiler is not in use so I just slide the silicone hose off to zero it. @ChrisJ used a Schrader valve to relieve any pressure bias as needed (see video). He has a few videos if your are interested. Eventually I'm going to move my Magnehelic gauge to use the same tapping that the 0-30 psi gauge uses so the pigtail is out of the situation. Like @ChrisJ's Magnehelic gauge is.

Pigtail siphon effects on low pressure gauge
https://youtu.be/8MLrASd2G7Q

Also those Magnehelic gauges need to me mechanically zeroed in their service position (with no pressure), which you may have done.

Don_175

109A_5 said:

Hello @Don_175, Being on that side of the pigtail the water in the pigtail does impose a bit of bias. Although that seems maybe too much or more than I would expect in your case. My gauge at +/- 1 ( or 1-0-1) Water Column seems to act like a Barometer at times even when the boiler is not in use so I just slide the silicone hose off to zero it. @ChrisJ used a Schrader valve to relieve any pressure bias as needed (see video). He has a few videos if your are interested. Eventually I'm going to move my Magnehelic gauge to use the same tapping that the 0-30 psi gauge uses so the pigtail is out of the situation. Like @ChrisJ's Magnehelic gauge is. Pigtail siphon effects on low pressure gauge https://youtu.be/8MLrASd2G7Q Also those Magnehelic gauges need to me mechanically zeroed in their service position (with no pressure), which you may have done.

It is attached via a brass elbow. Should I zero it with it hooked up to boiler? Instructions said with it detached and open to atmosphere 

ratio

If you're on the outside of a piggytail the slug of water will influence the pressure indicated, but if the volume of water doesn't change you should be able to calibrate it out -> zero it & see if it's still at zero tomorrow with the boiler at the same temperature it is now.

109A_5

Hello @Don_175,
What I would try, with the Gauge in place, Boiler off for a bit to cool. Remove the plug that is in the second (+) Pressure side port. Then verify the mechanical Gauge zero setting. If you want to you could add another valve (venting to the atmosphere) to the piping to zero the pressure when you want to.

Don_175

Thanks for the advice guys. I ordered a brass schrader valve to put in the second high pressure tapping to release any residual pressure

ethicalpaul

Honestly if you were looking for a 0-3 PSI gauge the Magnahelic was kind of the wrong gauge to get. It really shines in the 0-20 inches of water column range which is less than 1 PSI. My favorite is the -5 to 0 to 5 inch one, it shows the vacuum that occurs at the end of the cycle.

But it will at least be the most accurate 0-3 PSI gauge you could have bought.

Try to use it without the pigtail. Chris and I have it on top of a long 1/4" nipple. I then run 3/16" vinyl tubing from the top of the nipple to the gauge. The air trapped in the nipple and in my case the tubing keeps the steam away from the gauge. Put a 1/4" ball valve on top of the nipple and then you don't have to worry about a slow leak in the gauge letting steam get into the gauge.

And don't even worry about it, I have had like 1/2 of the gauge filled with water before, it's not optimal but just shake it out and let it dry if you forget and leave the valve open. These gauges are solidly built with pride in the midwest.

Also try it without the snubber. Chris has good luck with his snubber but I apparently bought the wrong one because it wouldn't let any pressure through.

109A_5

ethicalpaul said:

I apparently bought the wrong one because it wouldn't let any pressure through.

Or for example, if you bought a Snubber with a 0.004" Orifice Diameter and you had the functional equivalent of a 0.005" Orifice Diameter leak on the Gauge side, I'm thinking the Gauge would not do much.

If you can see light through it, it should let air through assuming nothing plugged it up after installation. I don't know if a droplet of water would plug up a 0.004" Orifice with maybe 1 Water Column of pressure and pretty much no flow to speak of to keep the Orifice clear.

Water will flow through a 0.015" Orifice, at a rate of about a drip every 2 seconds (pressure the same on both sides).

Don_175

Just an update. I got rid of the snubber. With boiler cranking out the steam (after at least 20 minutes) and all radiators heating, I get 0.9 psi. And gauge does not fluctuate at all. 

109A_5

Good it is all working, with a 0 to 3 PSI gauge I would not expect much fluctuation due to boiling.