Ranhalen, here is the diagram I said I would post. This is a simple diagram for a simple solution to hooking up an airtank to a constantly running type air compressure. You will have to tap into the power cord for the compressor for the pressure switch. You will either remove the cover on the compressor where the power cord goes into it, or cut the outer insulation from the power cord to access the 3 wires. ( keep in mind that this diagram is for american wireing, black, green and white wires, if in another country, your wireing and colors may be different. you want one of the hot wires) You want to cut either the white wire or the black wire, don't cut both, you only need to cut one. Now there are 2 ways to incorporate the pressure switch. The diagram I posted, the pressure switch is screwed directly into the air tank, in wich case you have to make the hot wire that you cut, longer. You can use wire nuts to fasten extra wire to the cut ends of the the hot wire. Make the wire extensions long enough to reach the pressure switch. The other alternate method of connecting the pressure switch is to connect the cut wires right where you cut it then use brass fittings on the pressure switch and connect an airline from the switch to the airtank. With either method, make sure you insulate the wire connections at the pressure switch. Don't want to get electricuted or have it short out and blow a fuse or circuit breaker. Pressure switches are designed to open or close an electrical circuit at pre determined air pressures. For example, if you wanted the compressor to turn on at 80psi and turn off at 120psi, then you would need a pressure switch that is set for those pressures. I'll add that the pressure switch needs to be rated for 120 volts ac. The reason I mension this is because they also make them for 12 volt Dc. Now in the case of a diaphram type compressor that runs all the time. You have to determine the maximum pressure that the compressor will put out. Say the max is 60psi, you will want a pressure switch that is set for say 20psi on and 50 or 55psi off. The off pressure will need to be a little less than the max output of the diaphram compressure. (if the pressure switch's off pressure is higher than the output of the compressor, then the compressor will never shut off because it will never reach the higher pressure.) Also keep in mind that this setup does not have an unloader valve so the compressor will start with the pressure in the tank against it. The setup in the diagram is basicly the same on the cheaper piston compressor's that harbor freight sells, I know because I used to have one. This set up will work as long as the pressure switch has the proper on/off rateing. The diaphram compressor could be just hooked up directly to the air tank but the compressor would still run constantly and defeat the purpose of adding an air tank. I hope my description isn't too confusing, it realy is a simple set up if you have some mechanical experience. If I could talk to you the setup it would sound simpler, I'm not the best typing instructor. LOL. Anyway hee is the diagram.