Air Compressor Are SEPARATOR,MOIST,W/TRAP,0.75NPT is oil filter for QR25 model 310 and 340?

I am assuming the oil in the air filter, if its a beltless style would be to keep dust from going inside, like the really old cars were, they called them oil soaked filters. better at trapping dust and dirt.

you're oil separator has failed or the machine is not scavenging back to the compressor

If it is a screw compressor and by you saying you replaced the seperator i would say it it you need to check the scavange line. This is a pipe that goes to the bottom of the seperator filter and sucks any excess oil back into the bottom of the element (pump ) if this is blocked oil will pass down the line insted of going back into compressor. Check pipe on seperator and flex hose going from seperator vessel to bottom of element.

Check the fan

check the oil air seperator if it has oil inside it, if so replace it

you stated you replaced the filter.Was it the separator filter? the separator filter is located inside the separator tank. the separator tank is where you add oil. If this filter is bad it will cause oil and air to mix and get into the air. Also there is a 1/4 inch line that comes from the top of the tank . this line has an orffice in it If the orffice plugs oil can carry over into the air.

There are oil separators that go on the discharge of compressed air lines before the end use.

An in-line water separator should be used before the supply line, a good air filter wouldn't hurt either.

It is normal for these units to pass osme oil. If you have had the machine awhile, and think that the problem has gotten worse, start by changing the oil separator filter (inside the oil tank). Also check the scavenge line that dips to the bolltom of the serparator it must be unblocked. There may be a nozzle and/or strainer in the scavenge line as well. Make sure they are clear.