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Thought I Blew An Air Hose.......

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  • Thought I Blew An Air Hose.......

    I was working in the shop the other day when Suddenly I heard what I thought was an air hose rupture. I went running in the direction of the noise, realized it was coming from the back room, opened the door and found that the relief valve on the compressor had let go. I glanced at the pressure gage around the corner and it was reading 185 PSI. WOW....... it's supposed to kick out at 120 PSI. I immediately threw the switch to the off position and it kept running. Luckily the plug was right there above the compressor so I pulled it, good thing it wasn't hard wired into the box or I would have been scrambling across the shop to the breaker box. I'm surprised the load didn't over heat the motor, stall it and trip the breaker.
    Remembering back several years ago I think this same thing happened, that is why I replaced the switch back then.
    The original switch, the one shown in the picture with the indicator was no longer available through Campbell Hausfeld, the replacement was identical but didn't have the indicator. I found that the switch it self was identical to the original so I figured I could just swap the switch out so I could use my original housing with the indicator. Well it worked out that I could and did, however........... big mistake taking the switch apart, it's like a spring loaded watch. In trying to put it back together I found that there was no way I could hold the switch parts together compressed and place it down in the box, mount the diaphragm under it and screw it all together. I had to get creative......... I had a friend wrap a couple pieces of MIG wire around the switch in two places as I held it between my fingers. I then could drop the switch down into the box and mount the diaphragm to the bottom of the box. Now, it looks like I have to go through all this again. I found a switch, but the mounting is a bit different and I would have to modify the unloader fitting. I can't swap internals on this one because they are a little bit different.

    What I was thinking of doing was replacing the contact points on the original switch with some tungsten contacts that I could make. The problem is how would you fasten tungsten to the copper strips???
    The contacts are the problem why the switch stuck on in the first place, as arcing occurs between on and off cycles they welded them selves together. I believe that if the contacts were tungsten they wouldn't pit from arcing so they wouldn't stick.
    The arcing occurs mostly from when the switch nears the cut out, not the cut in. The reason is that as the tank nears the cut off point the pressure between the contact points becomes less and less until the switch opens. During that time arcing starts.
    I think that if the switch had more of a positive cut out like a circuit breaker does it would minimize the arching. But nothing I can do to redesign the switch.

    JL.........................



  • #2
    The only way I can think of to fasten new contacts to the brass strips is to rivet them on.

    But, after two failures, I would seriously consider replacing the whole pressure switch with one that is rated for at least twice the current. Perhaps one for a larger pump. Or perhaps someone like Grainger would have one. This may cost a bit more, but it is likely to be a more permanent fix.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

    Comment


    • #3
      Same thing happened to me last year. I went to the local steel/plumbing wholesaler and they had a large assortment of universal pressure switches in various ratings. A new one cost me around $25. I did make a minor adjustment in the set-points and it works perfectly. A lot less trouble than fixing an old, unreliable unit.

      Comment


      • #4
        Could you wire in a honkin' relay so that the pressure switch does not need to control a large current? How's the shaper coming along? Bob.

        Comment


        • #5
          Originally posted by Paul Alciatore View Post
          The only way I can think of to fasten new contacts to the brass strips is to rivet them on.

          But, after two failures, I would seriously consider replacing the whole pressure switch with one that is rated for at least twice the current. Perhaps one for a larger pump. Or perhaps someone like Grainger would have one. This may cost a bit more, but it is likely to be a more permanent fix.
          You can't peen or dimple the tungsten, too hard. Perhaps either silver solder or braze may work, but the heat may take the temper out of the copper strips.

          There are all kinds of replacement switches of various voltages, pressure ratings etc. but fitting and placement of the unloader fitting become a problem.

          I like the idea of using the original switch to activate a heavy duty relay.

          JL......................

          Comment


          • #6
            Originally posted by JoeLee View Post
            You can't peen or dimple the tungsten, too hard. Perhaps either silver solder or braze may work, but the heat may take the temper out of the copper strips.

            There are all kinds of replacement switches of various voltages, pressure ratings etc. but fitting and placement of the unloader fitting become a problem.

            I like the idea of using the original switch to activate a heavy duty relay.

            JL......................
            Yes, an auxiliary contactor would be the best way. This would also allow the addition of heaters, or overload protection for the motor.

            It isn't clear, however the description "Luckily the plug was right there above the compressor" makes me think the operating voltage is 120v? If so, reconnecting the motor for operation on 240 would certainly prolong the life of whatever contacts end up doing the switching.

            Of course this may complicate other aspects such as wiring to the supply outlet, etc. or maybe not?

            In any case, I would encourage replacement of the pressure switch with something a little more robust, with a positive snap action to eliminate the problem you describe as it approaches the high pressure point. I have participated in cleaning up after a pressure switch malfunction that blew the insulation and siding off the side of the building, and in the process the motor/pump unit narrowly missing the building owner as it returned from the low earth orbit that it had aspired to.

            Dave

            Comment


            • #7
              Did that to mine years ago, as I had the same problem. A heavy duty relay is the way to go in my experience.

              Originally posted by Bob Fisher View Post
              Could you wire in a honkin' relay so that the pressure switch does not need to control a large current? How's the shaper coming along? Bob.

              Comment


              • #8
                When I put my compressor in I had some motor controllers left over from a job, wired the motor thru the controller and the pressure switch controls the starter, if I'm going away for a while I just turn off the breaker for the starter solenoid.

                Comment


                • #9
                  Just buy a good quality new switch and be done with it.

                  A relay is just as likely to fail as one of the pressure switches.

                  Comment


                  • #10
                    I work for a company that makes high voltage switches.
                    For the contacts, we use silver braze to make a little button
                    which is the contact pad. Seems low tech, but they have
                    been doing it that way since 1920. I could look if you are
                    interested in the brand/type of silver braze.

                    --Doozer
                    DZER

                    Comment


                    • #11
                      Macona, the reason for recommending a relay is not because it won't fail (it will fail just as easily as the pressure switch, depending on design load and use), but to let a cheap and easily replaced part take the brunt of the arc damage from the switching action. This is actually a common system design - and one that is used on our well with a water pressure gauge rather than air pressure.

                      Perhaps paranoid, and probably likely to silently fail from disuse, but any worth to a pressure switch after the safety valve that would kill the feed if the line got pressurized? Possibly a piece of cloth over the end of the pipe and attached with a rubber band to slow the air and provide a little pressure before blowing off without and real danger from the flying part (hmmm... seems this should just blow off and do nothing)?

                      Comment


                      • #12
                        Originally posted by becksmachine View Post
                        Yes, an auxiliary contactor would be the best way. This would also allow the addition of heaters, or overload protection for the motor.

                        It isn't clear, however the description "Luckily the plug was right there above the compressor" makes me think the operating voltage is 120v? If so, reconnecting the motor for operation on 240 would certainly prolong the life of whatever contacts end up doing the switching.

                        Of course this may complicate other aspects such as wiring to the supply outlet, etc. or maybe not?

                        In any case, I would encourage replacement of the pressure switch with something a little more robust, with a positive snap action to eliminate the problem you describe as it approaches the high pressure point. I have participated in cleaning up after a pressure switch malfunction that blew the insulation and siding off the side of the building, and in the process the motor/pump unit narrowly missing the building owner as it returned from the low earth orbit that it had aspired to.

                        Dave
                        No it's 220v

                        JL...................

                        Comment


                        • #13
                          Originally posted by Tor View Post
                          Macona, the reason for recommending a relay is not because it won't fail (it will fail just as easily as the pressure switch, depending on design load and use), but to let a cheap and easily replaced part take the brunt of the arc damage from the switching action. This is actually a common system design - and one that is used on our well with a water pressure gauge rather than air pressure.

                          Perhaps paranoid, and probably likely to silently fail from disuse, but any worth to a pressure switch after the safety valve that would kill the feed if the line got pressurized? Possibly a piece of cloth over the end of the pipe and attached with a rubber band to slow the air and provide a little pressure before blowing off without and real danger from the flying part (hmmm... seems this should just blow off and do nothing)?
                          In my experience the price of a motor contactor is about the same as a pressure switch.

                          Comment


                          • #14
                            Originally posted by macona
                            In my experience the price of a motor contactor is about the same as a pressure switch.
                            But what about time to replace? Looks like in this case the pressure switch isn't even made any more, making replacement difficult - and repair a likely possibility. As an added bonus, using a pressure switch that can handle the load and a contactor also provides a built in way to get the machine up and running immediately if needed. We actually did that once with our well when the contactor failed (broken wire in 220V winding), and were very glad to have water back without having to go buy a part or have it shipped in. Of course, a compressor like this isn't as critical to keep running as a well pump.

                            Comment


                            • #15
                              Either a contactor that is driven by the pressure switch or a solid state relay so that there nothing mechanical.
                              Amount of experience is in direct proportion to the value of broken equipment.

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