What minimum psi should an air compressor have for spraying.

I've got a little one but i'm not sure if it's good enough..

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It's not so much the psi , more how many cubic feet per minute (cfm) it can compress in order to keep up with what your spraying . Most semi-professionals will tell you 15cfm minimum but you can use less , just might have to wait a little bit longer between swings with the gun to keep the pressure up .

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so is that likely to be a number printed on the compressor?

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Probably on the little plate or sticker they put on them with the spec's , if it's a really cheap brand one it may not be there but look anyway . How big is the tank on it ?

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it's a ye olde thing....


about 40 psi and about 30 cm long and 15 wide..

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I'm sure someone will dissagree with me but I'd say that'd be a too small . Have you got access to a spray gun , hook it up and spray something (anything) through it , see if it can hold the flow evenly or if it surges and loses consistency in the spray pattern . DOn't know about high volume low pressure guns though , haven't used one of them but I'd say it'd be too small for a conventional type spray gun .

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Are any of these el cheapo direct drive 2 or 2.5 hp compressors sold by Repco or Supercheap worth buying? Can they be used for cars or are they mainly for painting hgouses, fences, etc

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Slide
1965 Mini Van (1360)
1970 Mk2 Cooper S (1310)
1978 Rover SD1 V8 (4.6)
1996 Land Rover Discovery V8 (4.0)

I have one & have used it for all sorts (including 2 pack), but they are flat out keeping up.
Get the next size up

When I paint the moke I have made a T-piece up so that I can use 2 of those small compressors (mine+borrowed one). Shouldn't burn them out then!

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Too many cars, and too little time.

Anton sprayed JAM with a 2HP? direct drive one.
He sprayed our Clubby with my `SIP' 2.5HP belt drive, said it was much better at holding pressure up. Paint on both cars was acrylic, with a top feed gun.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

CFM of 16 will do just about anything. Having a tank can give you a higher flow rating for a shorter time. The 2hp supercrap units are about 8cfm so 2 of them running together gives you 16CFM.

Funny how the air shops want $600 for a 16cfm and you can get 2x8CFM for $250 from supercrap.

Fittings is a big issue. Make sure you get the 8mm frlow through fittings not the jaymec which are about 5mm the air will flow faster and free.

For sand blasting run a pipe direct from the tank with big fittings and the flow will be perfect only your going to have to wait for the refill period of the pump

When looking at compressor ratings the important bit is the FREE AIR DISPLACEMENT not the compressor displacement. The free air displacement is the actual air delivery the unit is capable of delivering at a particular pressure. A bit like the breathing efficiency of an engine.

The compressor displacement doesn't take into account the efficiency or losses and is used to make you think the compressor has more actual capacity than it has. It measures the volume of the compressor cylinder at its operating RPM which isn't the same as the actual air delivery.


Regards
RonR

i have sprayed both my mini (enamal ) and mums austin 1300(acrylic ) with a 2hp 40l compressor from supercheep ($89Nz), with a normal gun and a finishing gun, it will spray all day long with the finishing gun, but does struggle with the larger gun, especially when spraying the roof of the 1300. next time (when i scrape the enamal crap off my mini) i will buy a top loading gun and as aomone else said, use a T piece and two compressors.....89x2 is cheeper than a bigger compressor...

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speed costs....how fast do you want to go...