Should your next airbrush compressor be oil-filled or not? I’ve owned both types, and I've had a Sil-Air 15D for the last six years, so I can give you some insight into what oil-filled compressors are really like to live with.
Noise
This isn’t the only reason why you might choose an oil-filled type, but it was certainly mine. I replaced a Sparmax with a Sil-Air 15D, and when it ran for the first time, the loudest sound in the room was me saying “ooooh, what a difference!” 😁
Using a calibrated phone app, I measured the Sparmax at 61dBA and the Sil-Air at 39dBA. This is louder than advertised, but the comparison matters more. Each 10dBA increase is considered to be perceived as twice as loud, so a 22dBA reduction is hugely significant.
It’s not just about noise in the room, though. Dry piston compressors generate vibration which makes the noise travel through buildings; but oil-filled rotary compressors operate very smoothly.
Even placing the Sparmax on isolating foam pads didn’t improve it enough. It annoyed me and I knew that my attached neighbour could hear it, though he was too polite to say so: whenever I switched it on, he’d go out to his garden! I can’t stand noise or being the cause of noise, so it had to go.
Typical setup
This type of compressor tends to be bigger and very HEAVY, as will become apparent when you have to shift one from wherever the delivery driver dumped it. Mine was described as 20KG, but I don’t have scales large enough to verify this and it feels even heavier to me.
Setup begins with adding the oil, which turned out to be awkward and time-consuming. The filler tube lurks behind a gap in the casing with only a length of narrow plastic tubing to help, so I had to dribble the oil in slowly. If I poured too much at once, it just took longer to flow through.
A 500ml bottle was supplied, but I knew that it would need almost all of it so I ordered a spare. Luckily, I also thought to check whether I’d need to buy a different air hose adapter.
Build quality
All that weight must have been put to good use somewhere, right? It certainly has because this machine has been built like a Soviet tank. I can’t point to any component and fairly accuse it of being flimsy. The overriding impression during use is one of solidity.
That said, much like Soviet tanks, it has a few unrefined edges — literally in some areas — which I doubt whether you’d find on an Iwata. They don’t impede its core function or durability, though, so in six years of ownership, nothing has failed and it's as sturdy and dependable as ever.
I’ve only needed to buy consumable items: a couple of oil bottles and air filters.
Usage
Oil-filled compressors often have bigger air tanks, which doesn’t exactly help with the size and weight, but they have advantages.
The 4 litre tank takes about 1m, 40s to fill from empty, but after that it refills infrequently. Pressure is maintained between 60 and 90psi, which gives plenty of headroom. Performance is excellent with my Eclipse airbrush — it outperforms the Sparmax, especially during refilling — but users of larger spray-gun types would probably want a higher flow volume.
Refilling
I say that it refills ‘infrequently’ but this wasn’t so initially. It would top up after being left unused for a while and I didn’t know why, beyond recognising that it must be leaky. I had fitted the hose adapter with PTFE tape and that was snug. Eventually, I tracked it down to a poorly fitting pressure gauge, so I refitted it with PTFE and I’ve had no trouble since.
Each fill concludes with a “pfffffffft!” as it releases pressure from the compressor — it’s comparatively loud, but not obtrusive. Rotary oil-filled compressors typically do this to relieve pressure on seals, I think.
A less pleasant side-effect is a puff of oil from the release valve, which will spray over the inside of the casing and out through the adjacent grille. I cover the area with a taped-on wad of paper towel, which has to be replaced periodically. I don’t know whether all oil-filled compressors do this, but it’s something to be aware of.
Ergonomics
Contact points are generally positive. The pressure regulator is taut, smooth, and provides fine control; the spray pressure gauge is large and fairly legible; and the moisture trap release is a little quirky but easy to use.
There are a few niggles, though — some minor, some major:
- The oil level bulb is around the back where you can’t check it in situ
- The power switch is tucked out of view, so I leave it on and use the wall switch
- There are some poorly finished sharp edges inside the case
- The air tank’s pressure gauge is positioned high and far back, so isn’t easy to see at a glance
- The air tank’s drainage plug sits right behind the moisture trap, above a hole which is a bit too small to be practical
- There’s no oil drainage plug, so oil changes are hard work (see below)
Maintenance
Because of the weight and ergonomics, maintaining a Sil-Air 15D isn’t as easy as what you’re probably used to.
For that reason, and because I’m an infrequent user, I’ve been a bit slack with the scheduled drainage and oil changes. Almost no water appears in the moisture trap, so I don’t drain the tank very often, and I change the oil every other year, but it has coped happily without complaint.
When I do drain the tank, its quality is apparent in the lack of rusty water. Most of what comes out is emulsified oil. Drainage is an awkward and messy task, partly due to the location of the plug, partly because you shouldn’t tip an oil-filled compressor very far over.
My solution? I empty the air tank until there is roughly 25psi remaining; place the compressor on a plastic sheet; tape a clear plastic bag to the tank, covering the drain plug; then gradually unscrew the cap through the bag, which catches the mess.
Oil changes
This is the elephant in the room if you buy an oil-filled compressor. The instructions tell you to remove the outer casing, optionally remove the compressor unit — ! — undo the lid from the motor, and tip the oil out.
I’m not going to disassemble it any further than necessary and even with the casing off, it’s a beast. You may as well ask me to tip the aforementioned elephant. 🐘
My solution was to buy a gearbox oil syringe — these are widely and cheaply available via your favourite online marketplaces. With the compressor on a plastic sheet, I remove the casing and lid, draw the oil out with the syringe, deposit it into a container, and pour in new oil before refitting the lid and casing. I then shove it back into position with some swearing.
Value
Oil-filled compressors are not cheap. My Sil-Air was at the low end of the scale, yet it was still a jump up from mainstream modelling brands. However, anecdotal evidence from owners suggested that it would be a wise investment and they were proved right, as I’ve had six years of trouble-free — and peaceful — usage so far. To me, this is well worth the cost and outweighs the drawbacks, so I can’t envisage going back.
Tips
- If weight is a significant issue, consider a smaller tank
- If space is very limited, your options may be as well
- Models without a case may be easier to use and maintain
- Check suitability and compatibility before committing
- Be aware that oil may be expelled from the pressure release
If you have any questions which I haven’t answered, you’re welcome to post a comment. 🙂
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