Observations of a new owner of a used Shoebox

[sperho]

Putting some in the tank would work. I don't know how long it would take to equilibrate, but shouldn't take too long I would think. Putting them in some kind of pouch to keep them from rolling around would be advised. They are friable and you wouldn't want the dust making it to the gun or having any ill effects on air channels in the plumbing. I would use the round beads instead of the pellets - the pellets are typically a bit more dusty out of the container. Oh, and you are correct, they don't get mushy and sticky - they stay rigid and shouldn't cake up in use.

[gene_sc]

Hey Lloyd, I finally saw your post here on the Shoebox. Had mine for about 3 years now. Guess it is an early model like yours. Last week I needed to top off one of my 4500 cf tanks. It was down to 3200 psi. I hooked it up to my Shoebox and turned everything on. Well it shut off at 3500 psi. This is the third time in two years that this has happened. So furtunatly I had bought a couple kits when it happened the first time and had fresh spare parts.

I reubuilt the top and bottom cylinders and adjusted the chain tension. Hooked everything back up and away she pumped. Got my 4400 psi top off on my tank and I am happy now.. I have two 3000 psi tanks that I use in the shop for testing and keep them both topped off as well. I have to say that the Shoebox has saved me lots of mony over the last three years. No 70 mile round trip scuba shop runs now to fill them any more.

I also use two external fans blowing on the cylinders. I normally run the compressor around 6-7 hours to top off my big tanks and the cylinders never get more than luke warm to touch.

The grey stuff you find in your cylinders is a combination of moisture and Lythium grease. I found the same thing you refered to in mine each time I rebuilt my cylinders. You also may notice that the inner most oring is the one that gets the hotest, It discolors more thatn the outer o'rings.

One very important thing is using the water absorbing crystals or dryer setup. I ues two inline and keep my pancake compressor lower than my Shoebox .
I would think you would be very happy with yours since you do allot of testing and need plenty of HP air around the shop.

Knowing you Lloyd you will probably come up with a better Shoebox sooner or later..

Gene

[lloyd-ss]

I only have a few hours operating time after the rebuild, but so far, so good.  Plenty happy.  I definitely want to get some moisture control in place, maybe the silica gel on the input and molecular sieve on the output.
Still in the process of moving and setting my shop back up.... and finding everything that I boxed up.  Wow, I'll be glad when I get settled back in.
Lloyd-ss

[sperho]

Didn't identify a true expert in high pressure drying, but if I run into an Air Products expert onsite at my workplace, I'll corner him to find an answer.  I did, however, do some more digging in the open literature and aside from the one paper that indicated a fall-off in the adsorption capacity at >60 bar, I found no other papers corroborating this.  I also looked in to commercial systems for drying relatively high pressure air (1 system up to 6,500 psi) and they mostly used mol sieves.  I'm 99% confident that the best "cheap" drier will be a good bed of packed sieves at the high pressure side of the compressor.  Mol sieves for 2 reasons:  (1) they can achieve a lower dew point than silica and (2) they retain their absorption at much higher temps than silica, so you don't have too worry too much about cooling the dryer in the event it warms up if it is positioned near the outlet.  Downside if you want to regenerate:  mol sieves take about 525F to regenerate.  Probably several hours at that temp at RT.   So, if you don't have access to furnaces like I do,  you can probably get buy with an oven at full bore.  Might be beneficial to do a self clean before regeration so that the headspace isn't littered with organics from all that cheese that fell off the pizza during baking!