Water Gauge seals

Hello all.

I am remaking the water gauges on my 3" marshall to include shut off's

The original drawings call for 1/4" glass tube with passes through a 3/8x40 cap.

What size o ring do you think I should use and could I use 6mm instead?

Thanks all

Brian, i would use either 1/4" or 6mm, but I would use soft neoprene rings rather than O rings, and make the nuts to suit. Some suppliers stock the glasses and matching neoprene. it is important to cut the rings square, I push a piece of tube on a piece of round bar to suit, and part them off in the lathe using a scalpel mounted in the tool post.

Chris Gunn

The retaining caps should not be too tight because the glass can easily be broken, hense soft neoprene rings as Chris has suggested. Normal o-rings are hard and require reasonable force to compress. Sometimes used on full size boilers but not suitable for small fragile models.

If you are unable to find suitable neoprene tubing to make rings, you can use flat teflon sealing tape by twisting it into a string and wrapping the string around the glass. Not as good but will get you out of trouble.

Paul

I have used std O rings in the past without a problem. Chose a ring with the section just under the minor diameter of the nut thread so it slips over easilly and a neat / slight stretch fit over the glass. They do deform and go hard in use though and have to be changed whenever the glass is disturbed. Pauls comment re clearance in the bore of the nut where the glass passes through is very relevant, also don't make the glass too tight in the gauge frame bores for the same reason. I have tried the twisted PTFE tape method several times and never had any luck, my method must have been flawed! I also used some seals sliced as described by Chris from tube given to me by another club member and described as high temp silicon rubber, spectacular failure! As the boiler came into steam they just turned soggy and extruded out of the nut in a cloud of steam! So if you go that route be sure you know the tube material is the right spec. I have just bought some 9mm red line glass from LSM for the 6" with seals. Seals came as a length of clear tube, so I am hoping this is a better grade than I was given in the past!

Paul.

O rings are made in numerous materials and also hardnesses - rated as shore. 70 is standard. silicon rings are quite soft. Good luck. Noel

Thanks all for the reply, and apologies for not replying sooner.

I orders some 1/4” gauge glass, decided to go with BS010 o rings.

I have undercut the gland to take the o ring which seams to work well.

Thanks again