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Simair tc5000 compressor internal air leak

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I have a Simair tc5000 twin cylinder compressor with tank of unknown vintage. Recently I've noticed that it runs more often as the pressure drops off more quickly. . There is an audible air flow within the compressor itself on one of the cylinders . Also that cylinder is more noisy when running particularly when approaching 60 psi cut off pressure. I think it probably needs a replacement piston and liner/ring but cannot find any sources of parts or someone who could service it.  Any advice/ suggestions to identify/confirm the problem and how to cure it welcome.





Edited by JohnTA
correct spelling

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An undercover Sparmax AC-500 I believe.


If there is a audible leak from one of the cylinders when the compressor isn't running, it will be the non return valve for that cylinder. The NRV's aren't prone to failure, but can become gummed up with crud (shed seal material &/or mould) which prevents them from closing fully, these are pretty easy to access, strip & clean.


Remove the 8 Allen screws holding the finned cylinder covers on, lift the covers off together & you will now be looking at the black or possibly silver cylinder plates with the NRV's  mounted in the centres of the plates. Remove the cylinder plates & wash them in hot soapy water, possibly removing the NRV's for more thorough cleaning if they are obviously caked in crud.


While you have the cylinder plates off, check the condition of the piston crown flapper valves & the piston seals - flapper valves can work loose, moving into the wrong position & can snap / break, piston seals degrade with time & will eventually wear our, usually signified by obvious scoring on the liner & quite a bit of noise while running.

If you have a piston (bonded PTFE seal) or liner issue, the parts will be available (may take a bit of hunting right enough), but you will be looking at around £30/£35 for a single set & needless to say if one set happens to be toast, the other will not be far away, so £60/£70...


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A few images I've managed to dig out if they help;


Covers removed (moisture & gunk all normal);





Healthy liner / piston / flapper;


Healthy piston seal (worn seal material on seal edge);


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Hello again,


thanks for the pictures they were helpful. It looked a bit different on opening it up as shown in photos below. I've sorted it by removing all the gunk form the NRV, polishing it and turning the flap over  It all works again now, it was still at full pressure after 10 minutes with no other air being drawn so I'm happy with it now.




Thanks for your help.



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