RUNAMUCK Posted June 8, 2016 Share Posted June 8, 2016 So I loaned outy compressor to a mate about 6 years ago. He had it for a very long time. When it came back, it had a fault. When it reaches shutdown pressure, the unloader on the pressure switch just keeps on venting untill the receiver pressure drops to start up, and it cranks up again. And it I switch it off at the switch, the unloader does the same. It's a cunt because it's handy to have a belly full of air up while working in the shed, But hissing/ the fucking compressoe running all the time Is a pain. The only saving grace Is that the unit Is a home made jobbie, and the motor came off a petrol pump. So there's an external switch lever on it which used to be operated by a lever from.where the nozzle hung up. So I can shut it down before the pressure switch unloader opens. But it's still a bag of dicks. Anyone know about pressure switches? Quote Link to comment Share on other sites More sharing options...
yetchh Posted June 8, 2016 Share Posted June 8, 2016 that's what mine was doing (precision air) loading up to 125 psi then venting back down to 90, just randomly started doing it. Pulled the pressure switch to pieces, it was pretty clean in there, but I coated everything with silicon spray and now it works fine.. well it did when I last used, I'll go out there tonight and try it and the fucker will do it again I bet.. 3 Quote Link to comment Share on other sites More sharing options...
Hemi Posted June 8, 2016 Share Posted June 8, 2016 Yeah, check what pressure it does start venting at. If it's above 120 then the unloader is your issue, if not then it's your pressure relief. The unloaders can get gummed up over time/ the grease loses its lubricant and leaves the soap behind which will gum the shit out of everything. If a cheap trick but putting a little bit of atf into the valve and manually working it will free it up easy as. Quote Link to comment Share on other sites More sharing options...
Hemi Posted June 8, 2016 Share Posted June 8, 2016 Pressure switch? It's not mechanically unloaded? Damn Quote Link to comment Share on other sites More sharing options...
Frosty Posted June 8, 2016 Share Posted June 8, 2016 What's used as the intake filter? Could be as simple as some grit in the switch mech. Most are serviceable so a good clean and lube should sort it out. Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted June 8, 2016 Author Share Posted June 8, 2016 It used to run an air tool silencer for an air filter. But now it runs the filter off a cheap bunnings compressor which no longer needed it. So the old pull it apart clean her up and see trick. It's defo the unloader, as it only begins venting once the pressure switch cuts the motor out. Quote Link to comment Share on other sites More sharing options...
datlow Posted June 8, 2016 Share Posted June 8, 2016 It's the Non return valve at the tank end Quote Link to comment Share on other sites More sharing options...
datlow Posted June 8, 2016 Share Posted June 8, 2016 The valve at the pressure switch end should be open when ever the switch is off or at pressure to make sure there's no back pressure when it starts up, but if the nrv valve is leaking it will back track Commonly happens if a bit of rust flake gets stuck in the valve or it's been run to hard and melted the disk thingy inside Dump the tank pressure and pull apart hopefully just give it a clean otherwise buy new Teflon/rubber disk 1 Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted June 8, 2016 Author Share Posted June 8, 2016 Thanks man. That makes perfect sence. Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted June 8, 2016 Share Posted June 8, 2016 Oops Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted June 8, 2016 Share Posted June 8, 2016 It's not the NRV. That has nothing to do with it at all. That just stops the storage pressure bleeding back through the cylinders. I had exactly the same issue with mine up untill about 6 weeks ago. Adjust the switch right off, allow the switch to run and work. Wind it right up till the safety vents work, and then wind it back down to about 120/90 or whatever u want your pressures at. Just doing that may fix it, otherwise you'll need to pull it apart and clean it up and regrease. But it's definately fixable! I'm sure the NRV has everything to do with it.If it leaks it won't bleed air back past the pistons- it will leak out the unload valve before it gets to them That's what I remember anyway. They are right up there - the unload valve stays open. It's the NRV spring that often rusts to shit and causes issues Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted June 8, 2016 Author Share Posted June 8, 2016 Believe Datlow Is on the money. But something NZed said has rung a bell too. After I got it back, the pump unit has always looked a bit wet/ oily. I figured the gaskets were getting past it. But if the nrv Is the problem, then the pump will be Working harder, possibley increasing crankcase pressure. The oil level on the dipstick hasn't gone down. It's just damp looking. Quote Link to comment Share on other sites More sharing options...
Rookie Posted June 8, 2016 Share Posted June 8, 2016 Yup I'll third nrv. 1 Quote Link to comment Share on other sites More sharing options...
yetchh Posted June 8, 2016 Share Posted June 8, 2016 It's not the NRV. That has nothing to do with it at all. That just stops the storage pressure bleeding back through the cylinders. I had exactly the same issue with mine up untill about 6 weeks ago. Adjust the switch right off, allow the switch to run and work. Wind it right up till the safety vents work, and then wind it back down to about 120/90 or whatever u want your pressures at. Just doing that may fix it, otherwise you'll need to pull it apart and clean it up and regrease. But it's definately fixable! Â Â Â Yeah, I also adjusted my switch way back a bit and then back to just below the sv pressure, it seems time had made it creep over the safety valve pressure.. Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted June 9, 2016 Author Share Posted June 9, 2016 I guess I'll have to take a look and report back I thought the unloader dumps the air between the reid valves in the head, and the. Nrv. ( which makes sence) My original thoughts were that the unloader valve only opened momentarily when eitjer the switch was turned off manually, or the pressure switch shuts the motor off. (Either way when it turns off, it bleeds down) If the unloader Is only supposed to blip open to unload, then the problemo lies there. And it it stays open while switched off, then it'll be the nrv. Quote Link to comment Share on other sites More sharing options...
datlow Posted June 9, 2016 Share Posted June 9, 2016 Yeh have a look and let me know what your ones are, i'm interested to know how yours is plumbed!  The unloader that is part of the pressure switch only operates the tank side. Well on the few compressors that we have at work and my 2 at home. It's not even plumbed between the motor side of the NRV, therefor it's can't even access that air.  The unloaders on ours are just part of the switch that the piston is held up due to pressure, as soon as it comes up it switches theelectric motor off. if it is held up then it allows the air to vent. and that is where they get sticky and hold open. This is how adjusting it up and down a little can help. if not, pull it apart and clean it and will fix it. It also did to mine, and that was without touching the nrv at that stage. I did have to fix that also as it was slightly leaking but I couldnt hear that untill I had fixed the unloader from jamming because it was so loud.  Happy to be proven wrong, just my experiences! Of the few thousand I've worked on/ built its the nrv, as they have a line to the p.switch which is open when ever the comp gets to pressure or is turned off at the pswitch, if you turn it off at the wall or as op said a switch on motor it won't open the valve thus it won't leak air, you may have a self unloading nrv that isn't connected to the pswitch but they are generally more troublesome to set up hence we only fitted them when requested 2 Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted June 9, 2016 Author Share Posted June 9, 2016 I had a very breif gander at the fucked tonight. Built up about 60 psi, and Shut the motor off. Then I cracked open the line from the cylinder head to the nrv. Air did leak out. The air line to the unloader Is teed into another discharge port off the head. I removed the nrv and stripped it. The nylon(?) Sealing disc looked a little used. But I.wouldn't say it looked fucked. So I cleaned tje Fuck.put of everything, and threw the valve back.together. then paced arpund the garage looking for my thread tape. Before I could find it, her indoors hollered out that we needed bread. So that was the end of shed time for tonight. 2 Quote Link to comment Share on other sites More sharing options...
CUL8R Posted June 10, 2016 Share Posted June 10, 2016 I had the same problem once Bartman, Diaphragm needed replacing where the pressure switch is, only a pin hole bit it pissed me right off. Â Less than $20 and 5mins to fix.. Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted June 10, 2016 Author Share Posted June 10, 2016 Thanks Chris. Where did you acquire the replacement diaphram from? I doubt I'll get the chance to fuck with it again until sunday now. Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted June 19, 2016 Author Share Posted June 19, 2016 How right I was. Sunday week though. The jury Is in. The nrv Is defective. I wonder if I can buy/make a new poppet for it. 1 Quote Link to comment Share on other sites More sharing options...
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