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Anti-vac valve

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  • Anti-vac valve

    Hi all,
    Does anyone know what material the anti-vac valve O-ring is made out of? Is this standard 70 durometer rubber, or is it neoprene? Mine has gone hard and is leaking.

    Also, should there not be a spring inside the valve to hold it against its seat? When I took it apart there was just the brass bell with o-ring behind it and it was just dangling loose agains the e-clip. The NS Appia parts book does not break down the valve and I'd rather just replace the 2¢ o-ring than wait for the valve to come in. Nothing wrong with the valve just needs a new o-ring and (possibly) spring.

    Thanks again

  • #2
    It is a high-temp rubber ring--and there is no spring. When there is no pressure in the tank the piston drops down. When the tank heats up, the force of the steam lifts the piston against the seal.



    • #3
      What upper-temperature limit should I be shooting for? I'm going to go in to a local MRO shop that specializes in bearings, seals and gaskets. Also, I heard about the Giotto machines having an updated antivac design that makes it more reliable. Would it be possible to interchange it with this one?


      • #4
        Not sure what you mean by upper temperature there? You may like to elaborate.

        The revised anti-vac goes back quite a few years now. We have been using this one which is a better quality all rounder. The bonus is that it's better quality and more reliable. It will also fit earlier giottos which didn't have the hole cutout in the cover plate under the top cover.


        • #5
          Just trying to determine what to ask for when I visit the MRO supplier on Monday. It could be a regular 70 or 90 durometer rubber O-ring, a silicone one, a neoprene one, it is black so Im pretty sure it isn't silicone though.

          By upper temperature I mean the highest temperature the o-ring would be exposed to. Thanks


          • #6
            You'll want a Viton O-ring, sizing (for most anti-vac valves ) is 007 (5/32" nominal internal diameter).


            • #7
              In my Grimac the o-ring some time ago made the piston stick. I simply dug into my collection of various size o-rings for all purposes and found one which fit.


              • #8
                Do you change anti vac valves as preventative maintenance or wait for it to go wrong. Thanks in advance for any replies.


                • #9
                  Originally posted by adjiland View Post
                  Do you change anti vac valves as preventative maintenance or wait for it to go wrong. Thanks in advance for any replies.
                  The machine will tell you when the valve needs attention. Perhaps a clean o,r fine emery cloth polish of the cylinder or a new o-ring.