bluespanner Posted February 17, 2009 Share Posted February 17, 2009 I have an old Hydrovane, and my switch leaks air and the electrics are shot, you have to wiggle the wires to make them work. I have found this:MAchine mart switch I see the port which connects to my tank, but what does the little one to the right do? My original one only has one port which goes straight into the receiver. Cheers Roland Quote Link to comment Share on other sites More sharing options...
upnover4x4 Posted February 17, 2009 Share Posted February 17, 2009 1 is the pressure switch(largeconnection) the 2nd smaller connection to unload the compressor on start up. Quote Link to comment Share on other sites More sharing options...
steve_d Posted February 18, 2009 Share Posted February 18, 2009 Learn something every day. Did not know it was to unload the compressor but that small pipe connects to the non return valve which is where the compressor outlet connects into the tank. If you don't have that already then I don't know if the switch will still work without the connection. I suspect it will because in it's correct application there may or may not be pressure on that line but the switch will still work. Steve Quote Link to comment Share on other sites More sharing options...
bluespanner Posted February 18, 2009 Author Share Posted February 18, 2009 So do you guys think i could just vent it to atmosphere? Quote Link to comment Share on other sites More sharing options...
steve_d Posted February 18, 2009 Share Posted February 18, 2009 Following my logic of how it must work. Pipe connects to the compressor side of a non return valve into the tank. Other end of pipe into switch. I assume when the pump comes on the switch must wait until pressure is detected on the small pipe at which point it closes the pipe so it does not continue to vent pump pressure. So if left open to atmosphere it will just continue waiting and never close off that fitting but the pump will still be running. Does that make sense? Steve Quote Link to comment Share on other sites More sharing options...
bluespanner Posted February 18, 2009 Author Share Posted February 18, 2009 er no not really steve... Quote Link to comment Share on other sites More sharing options...
pete3000 Posted February 19, 2009 Share Posted February 19, 2009 if you don't need the unloader valve connection. As i understand it you only have a screw in pressure switch like the one at mattsavage? http://www.mattsavage.com/acatalog/copy_of...r_Fittings.html ref 90100 I think machine mart do them but not easy to spot. http://www.machinemart.co.uk/shop/range/de...ies-consumables ref 000320100 website is a bit sketchy but catalogue describes as a 1/4" bsp 1 port. £16.99 inc hth Pete Quote Link to comment Share on other sites More sharing options...
bluespanner Posted February 19, 2009 Author Share Posted February 19, 2009 That is helpful, thanks. Although the picture for the machine mart one shows a big port and a little port! not sure if its just for illustration though. Quote Link to comment Share on other sites More sharing options...
bluespanner Posted February 19, 2009 Author Share Posted February 19, 2009 Bought the one you suggested Pete. It works fine. I havnt connected the little port to anything. I reckon this type of switch would be good for onboard air applications too. £19 Thanks all. Roly Quote Link to comment Share on other sites More sharing options...
pete3000 Posted February 20, 2009 Share Posted February 20, 2009 glad to be of help Roly, the picture wasn't the best, my 4 port one had the same unloader valve and I managed to break the casting on it, so took it to bits to have a look. My take on the little valve. The little valve is an inlet from the back of the 1 way valve (compressor side). once the pump is switched off and the air has gone past the one way valve into the tank, the little valve opens and allows the pressured air that didn't make it into the tank back to atmosphere to relieve pressure on the comressor allowing it to restart not under pressure? I had to buy another 4 port as my compressor needed a pressure relief, gauge, 3/8" bsp, and tank connection. I forgot the casting was white metal and over tightened the npt/bsp taper splitting the casting. I now use 1 or 2 wraps of ptfe plumbing tape and not 5 or 6. I also tried samsonal red which is supposed to be the muts danglies, but is actually useless. Pete Quote Link to comment Share on other sites More sharing options...
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