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Re: valves, O rings, contamination
Posted By: SVP Neon Equipment In Response To: valves, O rings, contamination (Lookin to the future)
Date: Wednesday, 14 February 2007, at 2:04 p.m.
> I have been a neon tube bender, working in a
> sign shop, for 3 years. I joined this
> company after completing a 6 week neon
> course. The course taught me the basics, but
> the experience has been a true learning
> experience.Unfortunately, to the dismay of equipment manufacturers, the quickie 6 week neon "schools" rarely cover anything on the subject of equipment maintenance. IMO that is a disservice to the student, but I won't get up on my soap box about it this morning.
> Are the "O" rings on the valves in
> a manifold comprised of some special
> material, or can I buy the ones I've seen at
> the local hardware store for less than $1?The O-rings used in the manifold system should be Viton, preferably about 75 durometer. Viton is the type of material and the durometer is how hard or soft it is. Viton O-rings are typically not available at a hardware store. For further information on O-rings, O-ring stopcocks and connections feel free to visit the Technical page on our website. There are 2 or 3 short dissertations that should be of help.
http://www.svpneon.com/technical.html
> Can the "O" rings be purchased
> separately from the valves, or does the
> whole valve need replaced if there is a
> problem with the "O" ring?First, lets clarify: The "whole valve" would include the glass barrel, Teflon plug and control knob. I believe what you mean is the Teflon plug that has the O-rings on it. Here is a link to the "Anatomy Of An O-ring Stopcock" on our website, which is also accessible from the Technical page:
http://www.svpneon.com/SC_Anatomy.html
O-ring replacements can be purchased separately. We offer a variety of O-ring sizes. Depending on what manufacturers manifold you have we may have what you need.
The Teflon plug is a rather soft material. When removing the old O-rings it is important to be very careful not to gouge the O-ring grove of the plug as this can create a leak path around the back of the O-ring.
> What is the simplist, fastest method for
> cleaning out a glass manifold that may be
> contaminated?The best method is an ultrasonic cleaner, though few shops have them and for some strange reason don't seem to want to purchase one for "regular maintenance" of their vacuum system components. I have listed an alternative method on this board several times. If you can't find it through a search let me know.
> Can too much pressure be placed on the
> valves, so that the "O" rings
> virtually get flattened?Yes, they can be tightened too much. But it is not so much a problem with the O-rings getting flattened out. You are working with a screw thread, so it is possible to exert a lot of pressure on the plug and glass when tightening it. The most common problem of over tightening the plug is damaging the Teflon - either stripping the threads, or causing the stem to "mushroom" out inside the glass barrel. In more extreme cases the glass threads on the top of the barrel may break, or the glass barrel itself may break.
> I've been told to
> just look at the valve and when the rubber
> hits the glass, stop, don't over turn it.The nice part about O-ring stopcocks is you can see how much the O-ring is compressing just by looking in the seat area when it is closed. The analogy I give is to tighten it like you would a new water faucet: Just a little snug. The tip O-ring - the one that seals against the tapered glass seat - should be compressed until it appears to be about 3/4 to 1 times the cross section width of the non compressed O-ring. In other words, if the tip O-ring has a cross section of 1mm in its relaxed state, when properly tightened the width of the seal in the tapered seat should be 3/4mm to 1mm in width. In simple terms, it is a "soft seat".
> Yet with a propane tank, or water faucet
> repair, you can't just stop when the rubber
> grommet makes contact, you have to turn it
> tight.A propane tank may have a couple hundred PSI behind it, so it may be necessary to tighten the shut off valve a little more than a water faucet. Water pressure should be ~ 40-50 PSI, so not as much tightening. (How much you tighten these first two things will also depend on what type of valve is used and the quality of it). The differential pressure on an O-ring stopcock in a neon manifold system is 15 PSI *at most*. The accepted average atmospheric pressure is 14.7 PSI at sea level. The barometric pressure on a given day may be a little higher than normal, which is why I say 15 PSI. If there was a perfect vacuum in the manifold (which is not possible), the differential pressure from the outside to the inside would be no more than 15 PSI.
Mark
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