Hi, Sit back as this might take a while to explain. It is so easy to show you at the actual pressure switch. The air you hear escaping is the relief valve which takes the pressure away from the compressor head. The pressure switch is mounted direct onto the tank and gets full tank pressure on the switch part and this does the on / off trick. When it switch to off it also triggers the relief valve. Usually place at the underside of the switch and coupled trough a small tube to an delivery valve placed at the point where the delivery tube of the compressor head enters the tank. You problem is most likely at this point. The action of that delivery valve is such that when the compressor switches off the valve closes the tank and the relief valve in the switch lets out the air in the delivery tube. Thus making it possible for the compressor to start against zero pressure in the head. Usually there is a problem with the delivery valve at the tank. Worth checking by letting ALL the pressure of the tank and unscrewing the big closing nut on the valve. Inside you will find a spring and a small rubber pad. Most likely there is some dirt inside or the rubber pad has a dent in it. This can in most cases corrected by rubbing over a piece of sand paper. Clean the lot, mount and try again usually problem solved. If not cry for help this evening and I see what I can come up with. Regards Wilfried Vermeiren http://users.skynet.be/modelbouw.wilfried -----Oorspronkelijk bericht----- Van: modeleng-bounce@xxxxxxxxxxxxx [mailto:modeleng-bounce@xxxxxxxxxxxxx] Namens The Sheppard Residence Verzonden: zondag 3 oktober 2004 1:10 Aan: modeleng@xxxxxxxxxxxxx Onderwerp: [modeleng] SIP Compressor Problem MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.