Around the 7 bar level the compressor safety valve blows out?

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When I start up my compressor the pressure gradually build,s then around the 7 bar level the safety valve blows out,. Then the compressor just carries on charging up again until the safety blows out again, and so the tank never reaches the red line, so to speak, when it should cut out properly. Rather it just chugs along cutting out below the 8 bar where I suppose the pressure switch should do the real cutting out process.

Is this just a rubbish safety valve or is there something more at work here ? Thanks, Jonathan.

Air compressor pressure relief valve
Typical compressor pressure relief valve.

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Hi Jonathan. If the PRV lets go before the compressor tank pressure reaches the normal cut out pressure setting, then we would surmise that it is the pressure relief valve that’s at fault.

Sometimes oil in the compressed air can lubricate the piston inside the PRV and it can let go prematurely as the pressure builds and below the normal “safety level” cracking pressure.

Try removing the PRV, soaking it in solvent, and after it dries, reinstall it and test the compressor.

If that resolves the issue and the compressor pumps up to cut out and shuts down before the PRV releases, you’re good to go. We suggest too that if that works, make sure to cycle the PRV a few times manually to ensure that it will release on it’s own if needed.

If the cleaning doesn’t work, we suggest a new Pressure Relief Valve is in order. They are easily obtainable and not expensive. Do make sure the cracking pressure on the new one is the same as the old… or within 5 PSI either side.

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Thanks willr. I’ve already ordered a brand new PRV in anticipation of some such problem. But you’ve pretty much confirmed that’s where the problem lies.

I’ll replace the PRV when the new one comes then and have another go. If there’s any more trouble I let you know.

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