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I'd recommend a 50% duty cycle or less. When you think about it, 50% running time is actually quite a lot. Reciprocating compressors need some time to cool off for best service life. It is not such a big problem on small compressors such as these since they do get a good blast of cooling air from the motor mounted fan, but a big cast-iron shop compressor gets just a mild breeze from the fins on the flywheel, which is only running about 1000-1500 rpm, so they tend to get quite hot if run hard. This is why unloading a compressor while it is running, via head unloaders opening the intake valves, makes a lot of sense if the compressor is cycling a lot. It gets the benefit of the cooling air from the fan, while drawing in and expelling cool air from atmosphere to lower temperatures inside the cylinder and head as well. Your compressor doesn't have this setup of course. Most important part is to keep the air filter clean, the oil level correct and keep the compressor level, at all costs. Many people have seized compressor pumps after taking them up on the roof. I'd stick with the factory oil until the warranty was off it. Just gives them one less avenue for trying to get out from under their obligations if anything goes wrong. That is not a knock against DeWalt by the way, it is my opinion on anything that is under warranty. After that, I don't see any problem with running full synthetic automotive oil. Just pull off the back plate on the crankcase and give it a good flush first. When you get two incompatible oils, nasty things can happen. I serviced a Palatek screw compressor last summer for shutting down on overtemperature. I cleaned the rad and proceeded to add about 10 L of oil to the compressor. I opened up a pail of PetroCanada compressor oil and added it to the machine. It was sitting next to the compressor. I started it up and it ran fine. Case closed. Till the following morning, when the shop calls and says the compressor it dimming the lights when they try to start it. I go onsite and the unit is seized tight! WTH! I couldn't turn it with a pry bar. I pulled the whole unit and took it apart. Turns out, they were using Petro Canada SUPER compressor oil, a synthetic blend. I guess one of the guys ordered a pail of oil and forgot to stipulate the SUPER part. There was a foul gummy mess all throught the compressor, and I could peel a jelly-fish like scum off the bottom of the separator tank and mold it into various shapes like translucent plasticine, before it melted Terminator 2000-like back into a flat, formless shape. So, for the low low price of a $3000 overhaul, they found out that some oils, even cheek-by-jowl products from the same manufacturer, cannot be safely mixed. I have been wrenching compressors for 9 years now, btw. Soon to be returning to school though, to make a radical change in my career path.
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