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Old 12-05-2018, 08:04 PM   #1 (permalink)
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The "Shoebox" High Pressure Air Compressor

It should come as not surprise that I tend to go through a lot of compressed gasses- certainly not as much as some, but quite a bit nonetheless. Co2 and Argon for the welders (though I'm phasing out the CO2 on the MIGs) oxygen and acetylene for the gas torch, and of course in the paintball side there's more CO2 and just plain compressed air.

The compressed air being high pressure, not just shop air compressor pressure- like 3,000 to 4,500 psi. Years ago I had a well-used and pretty well beat up Bauer air compressor that originally came with a 5HP gas engine, but the engine was loud and didn't run well. As I didn't really need the "portability" of it (it was meant for diving, and as such, for refilling tanks out on a boat or on a beach somewhere) I switched the engine over to an electric motor.

I used that for years, but the already-loud compressor just kept getting louder and more rattly- it's in dire need of a servicing or a proper rebuild. About that time the local hobby store got a nice big professional compressor, and then not long after that, a new field opened up that had their own HPA system, so I was able to easily get my tanks filled there- including my collection of SCUBA tanks so I could continue to have regular access to HPA here in the shop.

However, the local field, thanks to a general downturn in the local economy, is basically moving to 'by appointment only', for things like birthday and bachelor parties. And the hobby shop, who once gave me air for free (at least in the small tanks) in part because I helped push business their way, now has a new guy in charge, who charges me $10 a fill. I haven't even asked what a SCUBA fill would cost.

Now, that's not terrible- and I know the hobby shop is not doing well, as many specialty brick-and-mortar stores are these days thanks to internet sales- but it's still a hassle to drive a 20 mile round trip to get a tank filled.

Buying a proper compressor like the field uses is out of the question- that'd be $5,000 at a minimum, and it's not too hard to spend twice that by the time you get to a decent amount of storage, a fill station, proper regulators, etc. And I just don't go through enough air to justify that kind of investment.

Well, several years ago, one of the sport's more famous innovators, by name of Tom Kaye, came out with a clever little slow-speed high pressure compressor he called a "Shoebox". It connects to a standard shop air compressor which acts as a "first stage", and has two very small diameter pistons moving at a relatively slow speed (600-ish RPM, I'm guessing) to produce up to 4,500 psi, which is the pretty standard pressure for paintball tanks these days.

It's also considerably less expensive than a full-on compressor, at around $600. I've been wanting one for a while, so I can finally get back to providing my own HPA. A couple weeks ago I needed to test a customer's gun before sending it back out, and every single tank I had available was pretty much bone dry- I had to go up to the local welding supplier and swap out one of my 20-pound CO2 tanks. (Which I needed to do anyway, but it's just an annoyance when you're in a middle of a different project.)

So I splurged. I dipped a bit into the cash I've been saving up for a CNC mill (the one I want now won't be released 'til May, I'm told) and picked up a shiny new, latest generation F10 Shoebox Compressor.

Is it weird that every time you buy yourself a toy, it's actually a tool?

Anyway, it arrived on Monday, well packed and with a couple of extra parts:



It's a bit bigger than you might think, and a little heavier thanks to the Dayton 1/3rd HP motor on the back, but all in all, it's compact and easily portable.



And here it is up on my workbench, unceremoniously stacked on top of the gutted chassis to my CNC lathe control box, because I literally have no other clear flat spot anywhere in the entire shop I could have set it.



Now, first thing you do is read the instructions. Yeah, I know it's not the Tim Taylor thing to do, but I just spent a great deal of blood, sweat and possible felony theft charges to get this thing, so I can swallow a little pride and do it right. Second thing, pop the four screws on the side of the silver cover and remove the front face.



Inside, you'll find this, deceptively simple and actually fairly elegantly designed.



With the cover off, the next step is to install the bleed valve knob, found in a plastic bag of included parts. Don't screw it in all the way, just 'til the threads are slightly below the surface of the pressure block.



The next step is apparently to buy a camera that can actually focus, but in the meantime, you install this little retainer screw like so, which holds the bleed knob in place. The knob is left OUT, that is, unscrewed, while running. It's screwed IN to bleed the air line when you're done.



This new version now comes with a sort of "automatic oiler", some felt wicks held to the pistons, which keep them lubricated with some of the silicone oil included with the compressor. The wicks come dry, so you have to first saturate them. The oil is a little on the thick side, and it takes a moment for it to "'wick into" the felt, so don't just start squirting it willy-nilly. The felt is a long strip folded into a V around the piston shaft, so I found that the best way was to drop the oil into the V between the two legs, which helps it soak in.



This is a regular maintenance thing, you'll want to periodically check the wicks and add more oil as needed.

And finally, the lower piston rides in a bronze guide bushing, and this needs a touch of white lithium grease. I didn't have any white lithium, so I used a tiny dab of some high-performance spindle grease.



The wicks need to get the proper silicone oil, because those ride in O-rings under a great deal of pressure. I suggest using only the factory stuff. The bushing, however, is just a bronze bushing to help guide the rod, so any decent grease should work. Doesn't need a lot, but like the wicks, will need periodic refreshing.

The kit comes with a compressor inlet fitting you have to install, but in my case, it's a fairly common "industrial"- that's a type- fitting, also known as a Milton M-style. However, all my tools and system is plumbed for the "automotive" style, or the Truflate couplers. I happened to have a spare laying about from the recent air system installation, and threaded it into place.




After that, using the compressor is easy. First, plug one end of a hose whip to an outlet for your shop compressed air system, conveniently located on your workbench.



If you don't have a conveniently located outlet on your workbench, I suppose you can just hook it up with a regular hose or something, but you won't be as cool as I am.

For a test piece, I had also splurged on getting a used Ninja 68 ci tank off of eBay, since at this point I only have like two tanks that aren't out of hydro, and both of them are 3,000-pounders. The tank, as per Post Office regulations, arrived empty. Regardless of what the gauge might say, it was bone dry- nothing happened when I pressed the pin valve.



Now, the compressor comes pre-fitted with a standard male QD nipple as an outlet, so you'll need a whip of some kind to connect it to your tank. I just happened to have this 36" double-female whip that I've been using since the CO2 days, but as you can see, it's only good to 2,500 psi.



And here it is, all set up and running. It's a simple matter of connecting the inlet air hose, the outlet air hose to the tank, flicking the switch from "off" to "run", and then clicking it momentarily (it's spring loaded) over to "start".



It starts up and goes to work, and it's quite quiet. It's loud enough I certainly wouldn't want it pumping away while I was trying to read a book or watch TV, but you can easily have a conversation while standing right next to it, without having to shout or particularly raise your voice.

I started it on an empty 68 ci tank, at 11:19 this morning.



I kept an eye on it- that is, I didn't just leave to go catch a movie or anything- and by about 11:56, or right around 37 minutes later...



The tank was up to 2,500 psi, and only maybe 2 or 3 degrees above room temperature.



Now, between the limits of the working pressure of my whip, and the fact I really needed to get going on other projects instead of babysitting this thing, I shut it off at that point. Now, to bleed it, you disconnect the input air...



And turn the bleed knob in, in order to bleed off the hose whip in order to disconnect the tank.



After that, you take your freshly-filled tank, screw it into whatever your choice of latest high-end tournament-grade marker is this week, and go play!




It's pretty useful for the player who wants to keep his or her own tanks topped up, or for those of you that don't have an easy nearby field, and it's also great for the "PCP", or "pre charged pellet" gun crowd, which as I understand it, is by far the largest segment of buyers for this kind of compressor. I'll have to dig out my Webley .22 and maybe turn myself up a fill needle adapter, 'cause using that bicycle pump is a little more of a workout than I tend to want these days.

Doc.
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Old 12-05-2018, 08:52 PM   #2 (permalink)
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A smashing good write up Doc! Thank you for posting this.
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Old 12-05-2018, 09:24 PM   #3 (permalink)
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A smashing good write up Doc! Thank you for posting this.
Seconded!
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Old 12-05-2018, 09:27 PM   #4 (permalink)
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Originally Posted by DocsMachine View Post
Tom Kaye, came out with a clever little slow-speed high pressure compressor he called a "Shoebox"
solid write-up and thanx for the effort.

Tom Kaye didn't know what to call his new compressor, so he put up a contest to the guy that came up with the best name...
you now have a "shoebox"
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Old 12-06-2018, 12:11 AM   #5 (permalink)
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It should be noted that the unit has an automatic shutoff, set to 4500 psi. You should be able to plug in your tank, start it up, and go to work/go to bed/Netflix and chill/whatever, and it'll simply stop on it's own when it's done.

I haven't tried that yet, but I have no reason to believe it'd be any less reliable than the rest of the machine. When I get a 4500-rated whip in, I'll let 'er rip and see what happens.

For those of you that may still have a 3K tank, or a PCP rifle or something, the pressure switch is adjustable- the instructions say how to adjust it, and give what I think is a starting suggestion to get to 3K, but I think there's a typo and it doesn't specify.

Personally, as my SCUBA tanks are 3K rated, and I have a pile of 3K tanks (most of which need hydro ) I'm thinking I may crank it down to that pressure, to take advantage of the auto-shut-off feature.

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Old 12-06-2018, 02:00 AM   #6 (permalink)
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Originally Posted by DocsMachine View Post
The felt is a long strip folded into a V around the piston shaft, so I found that the best way was to drop the oil into the V between the two legs, which helps it soak in.
Uhh... OK. (it's late... lol)

Excellent write-up! Thank you for this.
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Old 12-06-2018, 02:08 AM   #7 (permalink)
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Tom Kaye didn't know what to call his new compressor, so he put up a contest to the guy that came up with the best name...you now have a "shoebox"
I remember that contest! Gotta love the way the name the finger gave the finger to Smart Parts.

I like the detailed assessment, Doc, and appreciate your tips. One of these is on my list but so many other fun Mag things have popped up!
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Old 12-06-2018, 03:15 AM   #8 (permalink)
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Phenomenal! Great write up! Great note about the adjustable auto-shutoff!

I didn't know they required a common (200 psi?) shop compressor. Good to know.

When the apocalypse comes, I want to insure I can still play paintball. #lifegoals
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Old 12-06-2018, 05:21 AM   #9 (permalink)
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I'm curious to know how long it would take to fill a standard (80 cf) scuba. Also wonder how reliable they are long term.

Compressed air setups are such a complicated and expensive endeavor. My shop recently updated our compressors (previously nuvairs and whatnot), which we were constantly having issues with, to a fire department SCBA fill station. Push button start, auto shutoff, auto drains liquid, etc... it's great but it's scary how expensive the thing was. And on top of that the regs, bulk tanks, hoses, fill stations, etc, it's amazing we made the switch at all.

Assuming the shoebox holds up to long term usage (I haven't really heard much about them), $600 is hard to beat.
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Old 12-06-2018, 05:41 AM   #10 (permalink)
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Originally Posted by Bang*Bang** View Post
I didn't know they required a common (200 psi?) shop compressor. Good to know.
-No more than 125 PSI, according to the manual. It acts as a "first stage", so the 'Box is compressing already-compressed air. In this case, the Shoebox is itself a two-stage compressor; the first stage has a "piston" about 1/4" in diameter that compresses the charge somewhat, and feeds that air into a second piston whose diameter is about 1/8".

Each "stage" has smaller and smaller pistons, and works with higher and higher pressures.

Quote:
I'm curious to know how long it would take to fill a standard (80 cf) scuba.
-Not sure, this latest version runs, as I recall, a bit faster than earlier versions, thanks to better cooling and piston design. I seem to recall somebody saying they filled a half-full SCUBA tank in... 12 hours?

Quote:
Also wonder how reliable they are long term.
-Supposedly, very. The pistons are rebuildable- it's basically just some O-rings you need to replace. The pistons themselves are basically just polished hardened shafts, and are also replaceable.

The manual recommends a rebuild every 200 hours- it's basically like breaking down a 'Mag valve and replacing the O-rings every dozen cases or so.

Quote:
Assuming the shoebox holds up to long term usage (I haven't really heard much about them), $600 is hard to beat.
-Well, the original compressor was launched in 2010, and has had steady upgrades and improvements ever since. And as I understand it, they've sold a ton of them, both to paintballers and the pellet-rifle guys.

I'm by no means an expert on them- this is the first one I've ever used- but from what I've read, they're very reliable. You wouldn't want to use one to supply "all day air" to your local paintball field, but for one player, with periodic maintenance and lube, I could see this thing lasting effectively forever.

Doc.
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