An Abac Compressor ‘Blows Out’

[Bramleyboy]

I inherited an ABAC air compressor. The motor works but now when it reaches a certain pressure, it ‘blows out’ and makes a hissing sound. The pressure drops and then the motor starts again and so on. I had it fixed about 8 years ago and it was quite expensive. What has gone wrong and can I replace it? If so what do I order and do I need to know any details about the machine? I do hope someone can help as I have no idea! I hope I’ve listed this in the right section. Many thanks, Bramley

[Togo]

Sounds to be like a pressure switch sensor or pressure relief valve problem. Model number of the unit would help. Some of the older ones have mechanical safety mechanisms and the later ones use electronic measures.

[Bramleyboy]

Sorry Togo. I hope this helps! The only stickers on the compressor are https://ibb.co/JjnwTYs
https://ibb.co/mRXTBDt The machine is about 30 years old. Many thanks and apologies, Bramley

[Togo]

I have had a look at the ABAC websites and cannot find a model that is the one that the labels indicate. I can find a A 39B CM3 but the company are very protective of technical information and spares options. Is the gauge showing that it has reached a working pressure in the tank before it blows off? If you are using it is it blowing off then? Is the blow off valve a metal type plug that can be screwed out? If so it could be dirty and a clean up may help it sit properly. Suspect you may need the ABAC repairs organisation. They are quite expensive bits of kit. Not really something that a non tech layman should be trying to repair I think given the inherent danger associated with high pressure air systems. Good luck Bramley.

https://www.air-compressorsdirect.co.uk/catalogsearch/result/?q=095736B-60+CM3

[Togo]

Crikey...what I can find is that pressure switches start at about £45 and go up to about £170 depending on the model, they do look like a bit of kit that belong on a machine a lot younger than 30yrs old mind.

[Togo]

I found this on a site Bramley it is quite a concise summing up of the dilemma that you have. PRV=Pressure Release Valve.

""If your PRV starts bleeding air, it could mean that the pressure in the compressor system has reached the cracking pressure setting of the PRV, and the PRV has done what is supposed to. The PRV has opened to bleed down pressure in the compressor circuit before that pressure becomes dangerous.
That the PRV bleeds air in this scenario is good.

Note the pressure on the tank pressure gauge. If the pressure level where the PRV opens is higher than the normal cut out pressure switch setting, it does indicate that the compressor switch, the device that controls the ON/OFF of the air compressor depending on its pressure set points, likely has failed. You should replace the pressure switch before using the compressor again.""

Haha you got me interested in a technical issue.

[Togo]

Now this is the way to go.

""PRV Bleeds Air before normal cut out pressure is reached.

If that happens, it normally indicates a problem with the PRV itself. That is, unless the PRV is in the line between two air cylinders on one compressor.
The piston inside the PRV is usually held in place by friction. It’s often a metal-to-metal installation, and the friction between the metal pieces makes the PRV piston resistant to movement until the pressure on the end of the piston is high enough to blow the piston off seat. If you have oil or water in the PRV that may offer enough lubrication to allow the PRV piston move sooner than it is supposed to.

With the compressor off and the tank empty, remove the PRV and rinse it in a solvent. Let it dry thoroughly. Pull out and push in on the piston a few times, then push the piston all the way in, and reinstall the PRV. Fire up the compressor.
If the PRV does not bleed air and the compressor stops at the normal cut out pressure, that may have resolved the issue. To double check the PRV operation, pull out on the pin to bleed a little air, and then push the pin back in. If the PRV does not bleed air by itself you are good to go.""

Or.

""Spring operated PRV.

The compressor may have a PRV that is held closed by a spring. If it does, when you pull out the PRV piston to test the PRV, the piston should retract by itself when the ring is released.
Follow the cleaning process as noted earlier. If that does not resolve the issue, it is quite likely that the spring may be failing, and cannot exert enough force to hold the piston closed. Replace the PRV if this is the case.""

Fingers crossed that can sort it.

[alavahalf]

Pressure release valves are often a sealed device to specifically stop you tampering. The ones I have dealt with recently need to be calibrated every 12 months, otherwise the insurance won't cover you. If they go wrong and don't release air when they should you could have a lethal situation if it goes wrong. My sons has one on top of his Autoclave, it is set to release at 220 psi. Very scary when being tested to the limit. The PRV screams as it oscillates between off and on.

[Bramleyboy]

Thank you very much Togo for you care and attention. Now I have a better idea of what to look for. I am careful! Many thanks, Bramley.

[Togo]

Cheers Bramley. Hope you get it sorted....hand bit of kit.