Fusor Forums

Many industry/lab grade mechanical pumps don't come with muffler/oil-mist-filters.

Mine sure didn't. So I made my own.

Two identical medicine bottle caps, one with a 5/8 hole bored through the center, and epoxied to a short section of 5/8 OD (i.e. "1/2 inch") copper pipe, which has had the end capped and numerous holes bored in the sides. The pipe is then wrapped in many layers of paper towels ("cellulose fibre") and an outer single layer of cotton cloth from an old, the upper medicine bottle cap is added (scrunching down any irregularity at the end, and the expanded metal (from hardware store gutter-guard) is wrapped around the assembly and secured top and bottom with hose clamps.

The copper pipe is press-fit into a KF16 nipple to secure it to the vacuum pump outlet.

It substantially reduces (but does not completely eliminate) oil mist when pumping down or when the gas ballast is open, and it also greatly reduces noise.

Total cost around 10 bucks.


This device

A good piece of work, for sure. I have commented on oil mists in the past.
Systems inside a living space within a dwelling that have the forepump run for long periods, (hours), must have a mist filter of some sort.

Richard Hull

Nice work there, Ian.

I believe Richard's vacuum pump exhaust goes to a vent outside the building.
Let's hope it is screened to exclude oil-hungry earwigs crawling the wrong way.

Wait, insects will be attracted by hydrocarbon vacuum pump oil residue????

I have a very small pump (chosen for weighing less than 10 pounds) and need to move it frequently since I don't have much space. I can't really rig up an exhaust system, but a combination of this and good ventilation should do some good.

I thought about this bug entry issue way back in 2004, the day I put in the copper vent pipe line. I took a right angle copper bend and soldered a piece of fine copper screen wire to one end-arm. I then slipped the open arm onto a 6" length of matching copper pipe and sweat soldered it to the screened bend. The pipe exits the lab with only a 1" stub exiting the building. (The screened end is turned down towards the ground, obviously.) I used a pliable clay rope, (a form of putty), found at hardware stores to mold and ooze around the small air space around the hole to seal the pipe and make it weather and bug tight through its exit hole. All of the remaining short lengths of pipe and small ball valve in the vent line are just slide fits, within the lab. In this manner, when new oil is added I can just slip the parts loose from the vent opening/oil fill port on my precision fore pump. The ball valve in the line is left closed when the pump is not on to prevent our typical muggy moist air from foiling the oil. In this manner I have had no bugs or airborne moisture enter the oil-fill vent opening in the pump.

Super tiny midges and the like, entering through the fine screen openings would, in theory, immediately stick to the thin film in the oily copper line due to the viscosity of the oil and die. I have changed oil exactly 4 times since 2004. Each time the old pump oil is clean and free of debris. Likewise, I clean out all of the 4 slide fit pieces in the lab with acetone and observe the liquid that washes them out and not even midges, other "buglettes" or their body parts are seen. Thus, this system seems to be working just fine for me.

Note: I used all 1/2-inch copper pipe and fittings. Commonly found and very inexpensive at any hardware outlet.

Mom and dad will not let the younger folks here bore a hole in the house walls to the outside and this is where a mist filter is a must have item as noted in the previous posting in this thread. All fusor work will cease if mom comes in to pick up your dirty clothes while you are running your pump and sees a fog in your room.......Nervous Nelly's, those parents. The thought of you filling your lungs, long term, with oil distracts them a bit.

Richard Hull

What also works is a engine oil filter, screw a 1/2" NPT nipple into the center thread of the oil filter and connect that to your exhaust. No more smoke. A lot of people with SEMs do this.

I did the oil filter bit back in the 90's. I used a Fram PH8A which was a large block Ford filter from the 60's. I had several on hand left over from my days of collecting Lincoln Continentals. However, when I decided to modify my attached lab for fusor work, I cut a hole in the back wall and vented via the method above.

Richard Hull

Here's my solution. It's a 2 micron water filtration cartridge. No oil mist is getting thru that. Had a bunch of these left over from a pond filter project- so it was "free". Plus a 2" PVC test cap glued on one end. Attached the cartridge output w/ o-rings to the pump's NW16 with a piece of plastic tubing- didn't even need clamps. No sign of oil getting past. The filter material is either still soaking the oil up, or it's running back down into the pump. One could get a similar 10 or 20 micron cartridge at Home depot for 5 or 10 bucks.

Yeah, the filter just absorbs the oil mist, eventually it will plug up. I just run a piece of drain hose out my garage door for the big pump. Makes some interesting sounds when I am roughing from the accordion shape of the tube. On my SEM I found an Edwards scroll pump so I dont have to have oil in the living room.