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Re: valves, O rings, contamination

Posted By: Lookin to the future
Date: Thursday, 15 February 2007, at 12:29 p.m.

In Response To: Re: valves, O rings, contamination (SVP Neon Equipment)


Wow, alot of great technical information. Thank you. I have found some prior links about cleaning that I will try. Now if I could only figure out the business and liscensing side of this. What city permits I would need, do I need to be a liscensed electrician, all that red tape.
Thanks again.

> 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.

> 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
> 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.

> 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.

> 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.

> 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".

> 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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