Air brush compressor.

[Ian.M]

*AND* a burst disk for belt&braces protection.

Re: your reply #46 compressor photos,

The underslung cylindrical metal can indicates the presence of a starting cap^*, and the presence of a control box means its most likely to have a current relay or potential relay, as  a PTC starter can be integrated on the three pin motor connector.

For the second one, if its actually got the same model number the plastic box may simply indicate cost reduction and/or the advance of housing technology, or it may conceal an OEM customised electronic starter and overload board.  If its a different model number it may be an integrated 'brain-box' for the whole system its from.  You'd have to open it or find a wiring diagram to tell the difference.

* Can't be anything else as the ones in the background clearly show there's no plumbing to it.

[sureshot]

Burst disk for protection, no idea what your reffering to. I know any system must have the requisite safety hardware incoperated in it. Yes "The brain box" that was what I thought when I saw that larger grey box. I didn't want a compressor I couldn't get up and running. That one is a bit steep at £160 delivered. The best new unit that would fit our requirements is about £380 new. But that's only got a small receiver. Anything a fare margin under that figure is worth a go. Dam that grey box... The slightly less 1hp at £125 also has a similar grey box near it in the picture. The seller is a refrigeration hardware dealer. I don't think I can ask, what is the grey box. Mainly because of the intended non standard use it would be purposed for.

[Ian.M]

'burst disk' aka 'rupture disk' = non-reclosing pressure relief device
https://en.wikipedia.org/wiki/Rupture_disc

Because of their extreme simplicity, if mounted as specified, short of major debris in the system large enough and flat or round enough to physically block the port, there's no way for them to fail closed,

[sureshot]

Ah ok, never heard of those before, thanks for the info on that Ian. Well I was bold enough to ask the seller of the fridge compressor, what is the grey box for ? As he's selling to refrigeration customers I doubt I will get a reply. I did explain briefly what my non standard use was, I wasn't asking for advise. Really just enquiring what the grey box is for. I thought some Google terms like " refrigeration control systems" and similar might have thrown something up, but no nothing really. If I can't find data on the grey box, I won't proceed with that type of unit. Expect all large units of 1hp to 1.5hp all have them. It's only the chance that the host equipment is needed for that type of compressor to function properly,  I really don't know.

[james_s]

Thanks for the replys and ideas, my Son does code at school, I think he could help me out along the way for any Audino projects. It is to complex for this project, I'm  certain there are simpler options. I've found a compressor, it's a bit steep at £130 delivered, and regulator and control valve gear at £25 which isn't terrible. That just leaves the air receiver, I've seen examples around £60 or so for 25 to 50 litres units. I might be worried about nothing over the frequent stop starts, but messing about with our old fridge compressor some years ago.. 15 minutes on and 5 off and it would not restart, just overloaded and clicked off. From memory a few more minutes was needed. I think it hinges on how quick the air is used up. The idea of a different starter is an in interesting idea though. I just thought if that PTC was cooled quicker the start winding would be available sooner, and less likely to overload and trip out. The compressor I'm looking at is 1/2 horse power 370 watts, it's a bit bigger than your normal fridge compressor. I think it will move more air faster, so with the price of a receiver it's quite a bit under the retail price of a similar semi professional compressor.

For £130 I would expect you could get a pretty decent ready to use quiet air compressor rather than having to build anything yourself. You should be able to get an old refrigerator compressor for peanuts, is there a scrapyard nearby? Maybe try asking at a HVAC shop or appliance repair place.

You don't want a PTC starter, you need either a current relay or an electronic starter, I have a circuit somewhere that works, it's just a triac and a couple resistors and capacitors. With a proper starter the cycles won't hurt it, you can cycle it on and off all day long without any trouble. You do need a pressure switch that has a load dump to release the head pressure though.

I'd have to ask but I think my friend spent about £30 building his, most of that was for the pressure switch and regulator. The other bits were all salvaged, including some steel tubing he welded together for the frame.

[sureshot]

Thanks for that James, well I've got two appliances, fridge and a freezer. Both are getting replaced. I've got no means of safely removing the refrigerant,  i know some would just cut them out, but I'm a bit more responsible than that. I'm very interested in the alternative starting device, current relay and or triac circuit. That sound like it won't trip out with moderate time interval. Other scrap parts, not really. Here in the UK years ago you could take stuff from the tip or old scrap yard, but there so hot on health and saftey these days that many sites won't entertain removing scrapped stuff. Its like the air receiver, i don't have equipment to weld it myself. I can find any number of old empty gas cylinders, even large out of test dive cylinders.  No welder i know would touch one with a barge pole. So only option is to find a dead work shop compressor, the control gear pressure switch dump valve is easy and cheap to source. Where that ridiculous here in the UK that the seller i doubt would reply to my grey box question, mainly through fear i joe public me that is, blowing myself up. He'd see his answered question as a liability risk, which is just ridiculous.

[sureshot]

Won't drag the thread on further, just wanted to say thank you for all the help and advice, much appreciated. I think I've found the grey box purpose, it looks like the control electrical gear. For some strange reason i started looking at 3 phase compressors and VFD's.... Back down to earth now lol. The images are 3 phase units up to 4.5hp. I'm sure now i can fashion something together. Thanks again all.

[james_s]

Thanks for that James, well I've got two appliances, fridge and a freezer. Both are getting replaced. I've got no means of safely removing the refrigerant,  i know some would just cut them out, but I'm a bit more responsible than that. I'm very interested in the alternative starting device, current relay and or triac circuit. That sound like it won't trip out with moderate time interval. Other scrap parts, not really. Here in the UK years ago you could take stuff from the tip or old scrap yard, but there so hot on health and saftey these days that many sites won't entertain removing scrapped stuff. Its like the air receiver, i don't have equipment to weld it myself. I can find any number of old empty gas cylinders, even large out of test dive cylinders.  No welder i know would touch one with a barge pole. So only option is to find a dead work shop compressor, the control gear pressure switch dump valve is easy and cheap to source. Where that ridiculous here in the UK that the seller i doubt would reply to my grey box question, mainly through fear i joe public me that is, blowing myself up. He'd see his answered question as a liability risk, which is just ridiculous.

My friend who built his compressor is in the UK so he had access to the same resources you have.

What is the refrigerant? In some UK/Europe units they use hydrocarbons like propane or butane, which obviously you can just vent. Others frequently use R134a which due to the way the laws are written you're not supposed to vent it from a refrigeration system, however it's perfectly legal to use a can of it as airbrush propellant or to power one of those air horns where it is obviously vented, so unless it is R12 (CFC) or R22 (HCFC) I would not worry about it. Surely you could also take the thing to a recycler or refrigeration shop and have the refrigerant removed, they usually charge little or nothing because the recovered refrigerant has value.

There should be no need to weld the cylinders, I'm not personally comfortable welding pressure vessels. I think my friend drilled out the original valve and tapped the hole to fit whatever standard fitting he used.

[sureshot]

I might look at getting the refrigerant removed, as I do have two compressors going free soon. I've not looked at the back to see what the refrigerant is yet, there quite old so might be lucky on a non toxic harmful variant. As for air receivers I'm looking at single cylindrical types, these heave no feet and generally no more than a single main opening of quite a large diameter. Old gas cylinders would still need a bit of prep work before being suitable for use, same with an old diving cylinder. Scrap yards round here won't let you take anything because of HSE regs.
Just another question..
I don't want to take up to much forum space. Those DOL motor starters of single phase, would one of those be suitable as a motor starter for a compressor ? And if they are, what happens when the compressor reaches pressure and blows down. Does the motor starter just default to it's off status as the pressure switch has shut off power to the motor ? I really don't know. Or does the motor starter status stay engaged and on until the pressure switch kicks back in. I'm not sure.

[james_s]

He used a pair of cylinders like this:
https://www.walmart.com/ip/Torch-Kit-Pencil-Flame-Propane-BERNZOMATIC-UL100/295966342

I think they are just strapped to the frame he built, I'd have to check though.

For the motor starter the old style used a current relay which was wired in series with the main winding. When power is applied the locked rotor current is high enough to pull in the start relay which connects power to the starting winding. Once the rotor starts turning the current falls and the start relay drops out.

These are the old style magnetic starters.
https://www.amazon.com/Compressor-Relay-Starter-Refrigerator-Black/dp/B00W8UCPS0

[sureshot]

Thanks for the links James, there's a guy on YouTube that used similar cylinders with brass fittings and nylon air line, compression fittings I think. The relay link I will try and find UK sales for it, thanks for that.
I'm only going to do this once...
A bucket list thing if I'm around long enough. Some years ago I got interested in airbrushing from a library book lol, before computers where around. Some years later I pulled a fridge compressor and fired it up, with a plan to build a unit for airbrushing, it never happened.
This time I was hoping to get my Son interested, he's into the Marvel stuff and super hero's etc, thought he might want to try airbrushing some stuff. As I'm only going to get one chance at this, and after looking across the web, I've kind of got taken with 3 phase. I know it cost a fare wack more, but I wanted a unit my Son could still use in years to come. So at the moment VFD's look the best option for this, the only slight off putting thing is the winning you get from the frequency carrier, I think it's that. But hoping the better quality ones are not so noisy. 3 phase fridge compressor, VFD control, usual pressure switch and regulator for output air. Coupled up with a 25 or 50 litre air receiver. I did briefly look at 100 litre air receiver and quickly worked out that's just daft. The VFD would just offer better control of the compressor. 3 phase as these look like much higher volume of air output. The idea being some quite times between compressor filling the receiver,  although there fairly quite anyway. As it's something I want to last I might as well throw a few bob at it.

[sureshot]

This really is a final question before I throw all sensibility out the window, spend to much, and get horse whipped by the misses So I've been doing a bit more searching on a switching system to start up the smaller compressors. After seeing a couple of videos of starting with out a PTC relay, the start winding was briefly shorted. I think I might have found a suitable timer relay to achieve this, but that would look something like the pressure switch voltage low at 12 Volts. I'm not sure in the scheme of things if that's a viable option. I think it might be, as the pressure switch is mechanical I believe. Just the contacts breaking and making the compressors circuit.
There is an image of the timer relay I'm considering, so my question is, do you think it's usable / suitable to switch the start run windings in and out of circuit ?
Thank you for reading, thoughts on this last question appreciated.

Ps. Just a correction, I think the pressure switch would need to break the mains to the compressor timer relay, and the mains side of the 12 Volts supplying the timer relay board. Think that the right way.

[Epatsellis]

When I airbrushed a lot, I found very quickly that the best air supply was a 5 ft tall co2 bottle. Quiet, cheap to refill and as long as you had good ventilation, far better than any compressor I used, including compressors from Badger, California Air Peoducts and several refrigeration compressor based ones.

[coppercone2]

When I airbrushed a lot, I found very quickly that the best air supply was a 5 ft tall co2 bottle. Quiet, cheap to refill and as long as you had good ventilation, far better than any compressor I used, including compressors from Badger, California Air Peoducts and several refrigeration compressor based ones.

You have the benefit of a really clean gas here if you get it from a welding supplier.

[sureshot]

We have an industrial gas supplier / welding company up the road here, its called SIP Analytical. I'm not comfortable using C02, my place is quite small, i also have cardiac issues, don't want it affecting blood gases. I've been up to SIP Analytical in the past to look into compressed air control gear, it is doable but outlay a bit pricey. But the biggest factor would be how quick I'd get through 3480 litres of air 232 bar 15 litre cylinder and 4500 litres of air, same size cylinder at 300 bar. Then the hassle of taking it to my diving club house for refill. But i did look into it. What I've noted is airbrush artists have a flow of air continuously with the trigger on the brush, only pulling it back for paint delivery. They don't seem to cut the air during painting. This uses the avaliable air up much faster. I'm not sure on a 3 phase compressor build yet, from what I've seen the VFD to drive one could be whiny powering the motor windings. So i might go with single phase still, but try to get the higher end unit of about 1hp if i can find one. I did find a thread in another electronics forum where another guy had the same start stall problems with a PTC relay, he also used the air up quickly before the PTC had chance to cool off. He's solution seemed to be a timer relay, and he done away with the PTC relay.