Compressor pressure

I have been toying with the idea of setting up my own fill station, thus the process began of looking into all sorts of needed gear for it.

My dilemma was with the compressor and banks (or the lack of). Can a smaller compressor be used on it's own to p/p fill tanks? Or does one actually need banks? In short, if I fill my tank with the required O2 for the EAN mix then hook it directly up to a smaller 6cfm compressor and turn it on, would it have sufficient pressure right off the bat to make sure the O2 doesn't bleed back up the line and get wasted? Or is the use of banks for this purpose needed so that one can make sure the pressure is more then the O2 in the tanks?

All scuba compressors should have a backflow pressure block that won't allow reverse pressurization of the system so your O2 shouldn't bleed back.

You can always blend your nitrox as you pump it through the compressor with a stick. They are eazy to make yourself or you can purchase one. Contrary to popular beleif you can blend in just about any compressor as long as it is lubricated with synthetic oil.

If you go oiless like the rix SA6 there is no problem at all.

As far as banks go you don't need them unless 1. the compressor pumps so much air that the heat created causes undue overheating of the scuba cylinder or you are filling a large number of tanks within a short period of time.

My personal compressor pumps 17 cfm with no banks, I really can't pump one tank without overheating it but two or more seem to work well.

The other advantage of banks is that the compressor is only responsible for filling the banks so it can run and shut off as necessary while you controll the airflow from the banks to your scuba tank via a valve that can be set to fill very slow ultimately giving you a better fill without the hassels of cooling down, This may be especially important to you if you are blending nitrox.

I thought of the check valve as well but wasn't 100% sure. My O2 supply would be from large T-cylinders (use them as much as I can, and the rest can go to the welder - of course I would be getting medical grade O2 for this).

For the compressor I thought of something smaller that can chug away at the tanks for a while, slow is good I am in no rush ($$$ is always an issue), while the banks would be nice I doubt that for 4-5 sets of doubles I would need them.

depending upon how many fills you do the smaller compressors can wear out pretty fast. most are not built sturdy enough to hold up over the long run, From what I've seen you need to go a full 5+ cfm before you get into sturdy units, A personal compressor in the 9cfm range is really just about perfect

Firstly, the compressor must be equipped with a backpressure valve, MUST. This device will prevent backflow although that is not for what it is designed. In the day, it would have been common practice to build full pressure in the compressor system before opening the tank valve, still is. Shut the tank valve when full and hook up next tank. No back flow will occur when this procedure is followed. However, PP filling is a drag. Build a stik for about $25. Basically, buy a length of PVC pipe and cut a two foot section. Stuff with four or five Gottschalk steel sponges (cleaning pads). Install a 3/16 nipple near the top and a 1 inch hose on the bottom. Go on EBay for a Miniox oxygen analyzer plus sensor. Either install the sensor into the lower end of the stik or in the output hose. Run the hose into the compressor FILTER. That will get you started, eg after you purchase a 5 cfm compressor, an oxygen regulator and some NUVAIR food grade oil. Check out the book from Airspeed Press (doh!).

You can use an existing regulator but new MIL surplus regulators can be had for peanuts. These shiny, chrome, medical regs come with two gauges, pressure and flow. However, the flow of most of these regs is limited to about 15 lpm. You need more flow. Unscrew the flow restrictor nut. This has a #73 drill hole. Using a #60 drill bit, open this restrictor disk by drilling through. It is thin and soft so take care.

Buy a length of 2 inch PVC pipe. Cut a 2.5 feet section (changed my mind). Buy two caps to fit. Buy one of those little PVC adapters that is threaded 1/2 npt female and male. It is called a "riser extender". This will screw into the bottom cap.

Drill and tap the top cap 1/2 inch npt and do the same for the bottom cap. In the top cap, screw in a Coltri intake filter housing available from Compressed Air Speciaties. In the bottom cap, screw in the adapter. This adapter is approx 1 inch diameter, perfect for press fitting a 1 inch clear plastic tube available at any hardware.

After buying a brass barb suitable for your oxygen tube (same type tube as cheap medical masks), drill and tap near top of pipe and insert barb. Using a 3/8 pipe tap, drill and tap near the bottom of the pipe. This thread will accept the oxygen sensor (close enough).

After assembling everything, Gottshalk pads installed, Caps and fittings in place, run the clear tube from the adapter to the intake filter of your compressor. If the angle is wrong, install a 90 degree elbow at the bottom. Do not glue anything unless necessary.

If you are really cheap, skip the Coltri filter. Drill many small holes in the top cap. Cut a 2 1/8 disk from thin felt. Insert this disk in the cap and press onto the pipe.

Only one comment...one (or more) pictures worth a thousand words...

Go for it!

i own a rix 6 cfm compressor and bought vince harlow's "OXY-HACKERS HANDBOOK" and built my own nitrox blend station . it was very easy. i used a analyzer bought from oxycheck.com and use aviator grade O2 . the only problem that i have is with the rix compressor not removing the moisture from the air. it almost cost me a bunch of steel tanks. When i contacted Rix industries they told me it was normal to have moisture in the air in their compressors !!! the manual states that you should drain the moisture seperators every 30 minures . that is way to much time between draining. i am currently trying to see if draining them every 3-4 minutes will work or if i need to get rid of this compressor or add another after market moisture seperator to the unit. If you need any pics of the nitrox system or info on it P.M. me and i'll be glad to talk.
steve m

I get a chuckle from RIX advertising. It is preposterous. I wonder how many tanks have rusted up due to the RIX. To anyone who bought one and doesn't know, install a proper final filter with dessicant, charcoal and hopcalite. Be careful that the RIX doesn't overheat. Running dry gas through the pump doesn't seem to agree with it. Maybe, there is not enough condensate to lubricate the cylinders, just a guess.