Air Compressors

>>1204638
why not use that engine to drive several air pumps at once? 2 or 3 10-13 cfm pumps should be more than enough

>>1204646
I'd prefer to have a single general-purpose compressor that operates on electricity.

>>1204653
it seems much easier to just have 2+ piston compressors and motors operating in parallel on separate 220v circuits all feeding into a single tank

how do you convert an engine? put a plate over the exhaust, put npt fittings over the ports with one way valves and pipe it to the tank? you'd also need to pipe unloader ports too. wouldn't you need several horsepower to crank it?

>>1204638
you're going to need at least 12CFM @ 90psi(25CFM for 100% duty cycle) which is putting you into industrial sized compressors.

>>1204638
you can hook up that domestic '3hp' compressor to a cabinet and do your blasting in bursts of thirty seconds every two or three minutes. might be ok for a home shop.

somewhat paradoxically it's easier on a single phase induction motor to keep the compressor running all the time and never let it fill up, even though that seems like 'beating on it'. stop-starts are what burns them up.

>>1204638
>you need a screw compressor to get enough airflow

You definitely do not. At least, certainly not for garage use. A 5hp (ACTUAL 5hp, continuous-duty, not the "5hp peak" crap you see on big box-tier compressors) unit would be good for occasional cabinet use.

>>1204717
>somewhat paradoxically it's easier on a single phase induction motor to keep the compressor running all the time and never let it fill up, even though that seems like 'beating on it'. stop-starts are what burns them up.

Only if the pump/motor are rated for continuous duty in the first place, which a lot of the cheaper ones aren't. Most of the ones that are rated at 100% duty cycle tend to be large enough to manage a decent duty cycle at the actual blasting cabinet.

>>1204638
>I also had an idea about converting a 1.3 liter VW air-cooled engine from a Beetle into an air compressor and driving it via an electric motor. Has anyone here done anything similar before?

I thought about something similar, actually. Engines do make extremely nice compressors if you put in the work and can find a motor big enough.

>>1204660
>how do you convert an engine? put a plate over the exhaust, put npt fittings over the ports with one way valves and pipe it to the tank?

Basically.

But to do it "right" you re-make the camshaft and timing belt/chain/gear so that the valves actuate in an intake/exhaust pattern on every stroke instead of the usual intake/compression/power/exhaust cycle seen in a 4-stroke engine. Obviously, how easy this is to do is greatly dependent on how the engine itself is constructed.


I ended up discarding the idea because I ended up finding a pair of 10HP industrial compressor pumps and associated motors. They need some work, but I got them at what may well be less than scrap value.

>>1204732
How about this for a conversion:
>grind exhaust lobes on camshaft completely down so they don't contact
>install fittings in spark plug holes with a check valve
>spin motor

This should work in theory. I don't have a beetle engine to test it on though. If you put a large enough crank pulley on it with a handle you may be able to operate it by hand, like starting an old model T.

>>1204920
That's sorta what I had in mind, but instead of grinding the camshaft I thought about just removing the pushrods for the exhaust valves.
You could use any 4-stroke petrol engine I guess, but a Beetle engine is air-cooled so it might be better suited for compressor use.

File: mark-mini.jpg (119KB, 1645x1353px) Image search: [Google]

119KB, 1645x1353px

Does anyone have experience with Mark compressors? I'm looking at their screw compressor range and the prices aren't that bad.

Not OP but I got a compressor question.

What level of filtration and water removal do I need to achieve piano black quality finishes with a 5hp/60 gallon tank and HVLP gun? I can't justify refrigeration for my hobbies.

>>1204653
Google some shit on compressor theory.

You'll have a to look at the compression ratio of the motor in this hypothetical. That will determine more or less the max pressure you achieve.

Then the power source (electric motor in your conversion) determine how quickly you can get to that pressure, and continuous delivery after that.

>>1204695
But let's be honest, he's going to blast what, car or motorbike parts?

The largest thing I can imagine doing backyard is a boat hull.

He's not getting paid by the hour for it so hue only has to manage whatever duty cycle he has instead of getting the maximum.

>>1205955
>You'll have a to look at the compression ratio of the motor in this hypothetical. That will determine more or less the max pressure you achieve.
wouldn't the max achievable pressure for an engine be far greater than any general use compressor?

anyone have thoughts on the costco compressor?

>>1205910
>What level of filtration and water removal do I need to achieve piano black quality finishes with a 5hp/60 gallon tank and HVLP gun? I can't justify refrigeration for my hobbies.

Piano black isn't sprayed, it's a gorillion extremely light coats of very thinned-out paint, brushed on. Just FYI.

Anyway...for automotive-quality spray paint jobs, you usually use a particulate filter, then a coalescing filter (these are sometimes the same filter), then a dryer (desiccant is the preferred method for painting), then another, finer particulate filter.

Sometimes there's a carbon filter after that, which scrubs out damn near everything remaining. Refrigeration actually isn't that great for painting. They can't achieve dew points as low as desiccant or deliquescent dryers.


For home use, you should be alright with a regular 5-micron filter, followed by a desiccant dryer. Readily available as combo units. You may want to put a sub-micron filter after this, if you've got a decent budget for it.

>>1205962
>wouldn't the max achievable pressure for an engine be far greater than any general use compressor?

It would actually be quite a bit less.

Typical consumer engines usually sit around, what, 10:1 compression ratio? And that's at 0 actual flow out of the exhaust. 10:1, at sea level, barely gets you 140PSI, max.

An ideal air compressor has an infinite compression ratio, because they would have no unswept volume in the cylinder. In an air compressor, any unswept volume is wasted power, because the air that's left in it is compressed, but isn't actually moved out of the cylinder. This is one of the main problems with using an engine as a compressor. While they're very sound mechanically, all of that unswept space in the cylinder hampers their efficiency a fair bit. I don't actually know by how much, but it does.

For reference, the last compressor pump I took apart (a small, 1HP-ish unit) probably has a "compression ratio" of 40:1 or higher. The piston comes to the very top of the block, so the only unswept volume in it is the space created by the paper gasket and the small, 0.5cc exhaust hole in contact with the reed valve.

>>1206305
8.5-9.5:1 for most regular cars on the road