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In reality, what is the smallest compressor I could get away with for painting with? I know it needs to be big enough to be able to move the paint but also so it's not forever running out of air.
Any hands-on experience?
Cheers
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I have a 50l tank and a 3 or 3.5hp motor, and I wish I'd bought a bigger one. It kept up fairly well, but I painted my car in sections anyway. It's much less happy running some air tools, and if I put the harder foam pads in my 3" polisher, it won't turn at all.
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Smaller tanks seem to condensate more as well so more chance of water in your paint.
A 50 litre tank is fine for little touch in jobs but 100 litre is really the minimum you should be looking at. 150 litre is a good all rounder.
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It also depends on what paint you are using and whether you need to run an air fed mask.
I have an old AID compressor which is about 50L and its fine for painting most of a car, i've done a whole MK2 Jag body shell with it (minus doors, boot and bonnet which I painted seperately) and it was great but I then had another compressor which was a machine mart one of around 150L running the mask and it was a bit awkward having two pipes.
The older 50L compressor seems much better than the newer ones of the same size that i'vre used in terms of the air it delivers and its a lot quieter to boot.
I think bigger is better and the CFM quoted on new small/cheap compressors does seem to be a bit misleading at times.
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goldnrust
West Midlands
Minimalist
Posts: 1,880
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For me a larger more powerful compressor was not in budget and I did not have space to store it, so the option was to do my best with a small compressor or to stick to aerosol cans. I’ve done all my painting with an eBay special (I think, might have been Aldi or something) 9.5cfm compressor with a 25 litre tank. This runs into a combined pressure regulator and water separator unit, then on to a cheap gun. The compressor does run almost constantly while painting, but I do not have to wait for it to charge up or anything. I have painted 2 complete small/medium sized cars, and several panels for you there vehicles with it. I’m not saying it’s the best tool for the job, but for an affordable DIY option for someone who is painting a car once a year at most, it does the job. I appreciate the need for good quality tools, especially to do a super high quality finished job, but I am also realistic that my painting skill is very much at ‘hobby level’, and I’m painting outside so will have dust / insects and other issues. At that point I do not believe my less than professional grade equipment is not the limiting factor.
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Last Edit: Mar 1, 2022 22:53:55 GMT by goldnrust
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200l with 13-14 cfm minimum.
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I use a couple of Aldi ones with 9.3 cfm displacement and 25L tanks in parallel and a low pressure compressor (unit out of a hot tub) for the breathing, also tend to do only one or 2 panels at a time. the compressors run through a length of copper to the separator which seems to keep the air dry.
A lot of the cheap ones quote displacement rather than free air delivery, mine are probably around 6cfm FAD.
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Dez
Club Retro Rides Member
And I won't sit down. And I won't shut up. And most of all I will not grow up.
Posts: 11,784
Club RR Member Number: 34
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You really need to rewind a few steps and understand a few basic principles to answer your question.
Firstly, in an ideal world compressors as we know them wouldn’t exist. You would just have an air pump driven by an electric motor that flowed enough air to deliver a constant air supply to the spray gun or whatever other air tool you are using. There would be no need for an air reservoir (the tank).
The problem is the laws of physics dictate this isn’t possible using a normal 230v domestic electricity supply. Most air tools require about 15cfm to operate and this figure isn’t easily obtainable. If you’re talking using a 13 amp plug, the highest power electric motor you can go is about 2.2kw (3hp) before startup ampages start tripping the circuit. A lot of 3hp compressors have a claimed 16cfm, but this is largely horsesh1t. It’ll be more like 12-13. With a dedicated power feed you can get to 4hp which should net your a true 15-16cfm with a decent compressor. anything over that can be a struggle as you keep finding weak links upstream in the electrical system.
So why do compressors have tanks? The job of the tank on a compressor is to mask the fact the pump can’t keep up with the demand. It’s pumped up to a pressure well above the required cfm and this is used to both smooth the air delivery and to create a reservoir to draw on when the compressor can’t keep up with the demand. The larger the tank the longer you get air usage wise.
Tank size is generally linked to motor and pump size as you wouldn’t want to try to fill a massive tank with a tiny pump as it would be running until it wore out, and putting a tiny tank on a massive pump that filled it in seconds would be pointless. In the midrange around 100-150l you do see multiple pump sizes on the same tank though. H
Now spraying isn’t as high a demand as a lot of other air tools. Compared to a sander it’s nothing. But there’s spraying and there’s spraying. If you’re painting vans where it takes 20 seconds to walk from one end of the van to the other with the trigger depressed, that’s a big draw when you’ve got to walk back and forth a dozen or more times to cover a full side. If you’re painting a single wing you’d be doing short 1-2 second bursts and you’d coat the whole panel in 20 seconds and be leaving it to dry.
So the answer is ‘it depends’. It’s always better to go as large as your power supply will allow though, as it will almost always make a better job. No one wants to be stood waiting for more air whilst watching your wet edge dry before your eyes.
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Thank you for the replies all. I had a chap offer me to borrow one but I think it's just a 25l which I had a feeling would be too small. I did look at renting a 150l one from my local HSS but for the price they want for a day, you may as well buy a second-hand one.
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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Dez has pretty much covered it. It depends how big an area you're painting. Constant painting, like doing a whole car, will push any single phase compressor to its limits. Having a larger air tank is a complete waste of time in that situation. It wont last. I have a 1000L tank in my workshop and without the compressor running I can barely paint a car door before it runs too low. A measley 20 or 50l difference in tank size is hardly going to buy you much more than a few seconds spraying time before the pressure starts to fluctuate.
If your doing small stuff having a big tank and pumping it up in advance can work but ultimately you need cfm which needs electrical power... My compressor is 18kw and can feel underpowered sometimes!
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I know of professionals who can paint a whole car using a 50l tank.
The thing which changed everything for me when it came to spraying using a compressor was employing the air regulator.
With a typical gun you find on the shelf in places where they sell them you regulate your pressure down to about 2 bar. At that rate the gun will run without any motor assistance for about a minute and that's enough time to lay down quite a bit of paint.
I've tested the limits of various compressors over the years while I was learning about it and the only thing I've found where you would say something like the advice above about getting the biggest and highest current draw you possibly can is blasting. Blasting really does use a ton of air. I've seen someone using the calor gas tanks to extend the off-motor performance of his blasting setup. With a couple of large calor tanks linked in series you get a lot more time before the pressure runs out and the motor turns on. Obviously takes longer to recharge. You can also use a gravity fed blast media tank as it lessens the energy required if the blast media is already heading in a downward direction instead of you trying to lift the media.
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1000 litre & you can't paint a door? You gun must have a massive air bleed.
I have 150 litre tank and I can paint a car door and it may not even recharge in that time. Tank is set to 110 psi and gun is set at about 30 psi normally. HVLP guns use a lot less air, but even my JGA guns don't use a whole lot more air.
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Some really good info here so far, thank you guys! I need to get a couple other bits I think before I start laying down some paint, such as regulator and water trap.
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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1000 litre & you can't paint a door? You gun must have a massive air bleed. I have 150 litre tank and I can paint a car door and it may not even recharge in that time. Tank is set to 110 psi and gun is set at about 30 psi normally. HVLP guns use a lot less air, but even my JGA guns don't use a whole lot more air. To be fair alot of it will be down the running the mask as well as the gun but the point I'm trying to make is thinking you can have a small compressor and compensate with a big tank just doesnt work. A lot of people just look at the tank size as an indicator of how good a compressor will coap but really its irrelevant. When I used to paint cars at home I had a 250l tank hooked up to two 24L hobby compressors. Still ragged the curse word out of the compressors trying to keep up.
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Ah, mask will use as fair bit of air as well.
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I've a hydrovane 23 hooked up to a 500l tank and id notice pressure drops a fair bit when spraying. I know the hydrovane are meant to run constantly but I've it set on a pressure switch. No airfed mask, just the gun.
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I don't think I would buy a massive compressor just so I could run a mask. I do have a big compressor already as I'm ex-trade and kept the tools after closing the garage so my compressor is lovely. I just wouldn't buy one only to feed a mask. There are other creative solutions you can employ such as running a hose to the exterior of the garage and using that to breathe as it's totally separate to the contaminated air.
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