I have a 7 hp. 150 psi. max craftsman professional air compresser, after using it for a while it starts smoking and oil soaks the filter after the fresh air filter. It soaks the top of the head also. Is the oil to thin ? It Runs good, what kind of oil should I be using ? The recomended sears oil dose not seam to be doing the trick, I think its to thin. I didnt over fill it, but it seams to be getting by the valves. This is the second one thats doing the same thing. Do I have a good back up under the work bench. It has a 60 gal.tank, and 240 volt motor.
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If you have air blowing out of the oil filler cap, I would suspect that the piston rings are shot. The piston rings are supposed to keep the compressed air above the piston, and air seems to be leaking past the piston rings into the crank case.
If your compressor is oil-less type, most likely pressure is leaking past piston ring. To verify, remove cover to expose bottom of cylinder (unplug compressor and let out all air). With flashlight, examine the upper-most part of the cylinder (turn motor by hand till piston is at top of stroke). If top of cylinder is scratched, then pressure is leaking past. For many years now, stores are in a race to have more HP and PSI to attract customers. Customer is really the loser because components used to make the units can not handle the higher pressure. Normally small 115v compressors are set to cut out at 125psi and larger two stage units will cut out at 160psi. Small compressor set to 200psi makes for short lived compressor. Could be compared to driving your car at 100mph all day every day. Longest life is attained when unit is being used at about 60 to 75 % of capacity. To allow your compressor to reach cutout pressure and keep working for a while, lower cutout to 120psi (pressure switch may be adjustable). To restore to 200psi, replace cylinder/ ring. If your compressor is oil type, suspect leaking reed valves.
I would guess from the info supplied that the pressure switch is shutting it down at 125. Most piston type compressor only pump a max. of 175 unless it is a special high pressure unit. Also it may be shutting down on high amps, high temp etc.However with all that said Piston units are positive displacement, meanning that it should pump until something gives. Start your unit, close the discharge air valve and see what it pumps up to. May have to adjust pressure switch to get over 125. If unit runs and runs and just will not go over 125, you probably have a valve going bad. Do you have a safety lifting. if so another indication of a bad valve.
one thing that would be worth checking is the pressure release valve which is usually located on the bottom of the unit. This valve is suppose to be used each time the unit is turned off. For obvious safety reasons you should release the pressure from the tank each time you are done using it. If this valve is leaking or was left open then you will not be able to achieve the desired full pressure. Just checking if this is tight may be your solution! Hope this helps!
A piston in any engine should be around 100 psi I would guess. A Chevy 350 used to be around 150 psi. An air compressor that only pumps enough air to reach 20psi is obviously too low on compression. Nailers and the like need 80 or more psi. The intake valves may be shot, the unloader might be stuck or piston rings are worn.
The pressure switch should be at the factory setting of about 120# max. Not to be hurtful,but what you discribe is normal. Even a 2 HP 220V is minimum for a compressor.. You go by the CFM Rating. You and I can not afford a two thousand dollar 12 CFM Unit. Your compressor is simply too small, to do much. It is pushing against tank pressure so much,after 90# that the reed valves can't hold it. Set it at 100 to 120. It is not designed to run up to 150 max. Now if it is,an oiless compressor , it won't last long. My Campbell- Hausfeld lasted 31 years. Got a new one two years ago