Compressor pressure

[san diego diver]

do you have any idea on prices or where to look for the filters? i've looked around and seems to be too expensive !!

 

[pescador775]

Look for one of those slick, stainless steel, aircraft hydraulic accumulators, rated 3000 psi. Sometimes, they show up on EBay. Make up some filter pads from felt and separator discs out of plastic or metal. Pack whatever chemicals as appropriate. If gas powered or used in a city, include Vaporshell 13 X, next--hopcalite (expensive) and activated charcoal. If electric, hopcalite optional. Sometimes, the accumulators will have weird inputs or outlets, like JIC 5. Go to McMaster Carr for correct fittings, stainless nice but plated steel very OK.

 

[Bowzer]

RIX SA6, El Cheepo O2 meter, DIY Blend Stick (per Oxyhacker) GMC combined coalescor/filterstack (original 2nd stage coalescor still attached, this in place of the 3rd stage coalescor), priority valve, over pressure valve, electiric shutoff, magnetic starter. swapping out brass for stainless, still short a few pieces so it ain't quite finished. As you can see we use steel tanks. No problems with this setup.

Looks like attachments are down. Will try to send pix later

 

[pescador775]

Auto shutoff? You didn't say. Probably OK with RIX. I believe stainless reed valves are used. After the last tank is filled, I prefer to keep the compressor running, with petcocks open, for a minute. Running under no load extends the valve life on some compressors. This procedure doubles the life of Bauer valves which may be subject to corrosion if water is allowed to lay in the cylinders. I don't know why this works. The cylinder pressures are never really zero, but it does.

 

[san diego diver]

hey Bowzer ,
can you send me some pic's and info on the after market coalesers or filters on your rix sa6 ? i have to dry the air going into my tanks some how . draining them every 3-5 minutes seems to help, "BUT" i'm sure the air is still moist. i have the same rix sa6 and built my blend stick also.

 

[pescador775]

San Diego, let's not make a big deal out of 1000 bucks worth of filters. Heheheh. How about this--I sell you a good, used Bauer PO for $250.

 

[san diego diver]

what is a PO and will it be adaptable to a rix sa6 compressor? all i really want to do is remove the rest of the moisture from the air .could you please e-mail me and let me know the specifics? maybe pic's? what about moisture seperators ? got any ?

 

[MikeFerrara]

Depending on what kind of diving you're going to do and what mixes you need you're liable to end up doing some partial pressure blending no matter what.

Filling tanks without a bank just plain sucks. You have to listen to the compressor running all the time and unless you have a pretty serious compressor it'll be slow.

 

[Bowzer]

hey Bowzer ,
can you send me some pic's and info on the after market coalesers or filters on your rix sa6 ? i have to dry the air going into my tanks some how . draining them every 3-5 minutes seems to help, "BUT" i'm sure the air is still moist. i have the same rix sa6 and built my blend stick also.

sorry to take so long to respond, but lots going on.

if you are interested in compressors, I would recommend reading this:

http://thedecostop.com/forums/showthread.php?t=10085

I have been unable to get jpgs to upload - keep getting upload failed. I have tried several compressions, etc.. Anyone know why? If you want pics, send me an email.

as to rix, etc. No doubt this is not the least expensive setup out there, that was never the intent. If cheap was the main motivation I wouldn't have started with a Rix.

Rix has 2 centrifical moisture separaters one after the 2nd and 1 after the 3rd stage. These do a modest job of water removal. As the compressor was designed for warm water use by Navy Seals with Al tanks dry air was not a major factor in the design. I got my unit, well used, off EBAY, missing the 3rd stage separator, and needing a lot of work. As Rix separators are expensive and don't do the finest job of water removal (we have steel tanks and it is cold up here, read rust and freezeup) I decided to go the coaleser route for the third stage. I was going to build the coalescor and filterstack. The bigest problem I had was finding a suitable coalescor element. It had to be of fine enough pore size to perform well and had to fit within narrow diameter schedule 80 SS tubing. (check the price and pressure ratings of SS and you will see what i mean). I looked at a lot of sintered bronze but didn't find what I wanted. Finally I decided I was going to have to buy a coalescor. Once I decided that, the cost of the combo GMC filter wasn't much more than what it would have cost to build the filter. yeah it is expensive. I didn't buy a compressor to save money.
As to the auto shutoff, I find it very handy. I have a mix of LP and HP tanks. I set the shutoff for the LP pressure and have an override button for when I fill the HP tanks. We dive as a family so I am usually filling at least 3 tanks at a time. When the first tank fills, the compressor shuts down (right now I manually shut of the O2, but I have a valve on order to tie into the magnetic starter as well. If you go with an electric compressor greater than 3cfm or so you will want a magnetic starter). I remove the full tank and attach the next. When I open the valve, the pressure drops and the compressor kicks in. I generally bleed off the water every tank or two (probably excessive given the coalescor size) but with a 10,000 cuft stack it takes a while to fill with a 5.5cfm compressor and keeping it fully presurized helps with the quality of the filtering. BTW, Guy doing the VIP says the tanks look like new inside so the air is dry with this setup.

If you do get a coalescor, be sure to get a "Priority Valve" (back pressure) another expensive piece but you gotta have it if you want to coalescor to work well. Sorry if I am being peedantic, but a little theory may be helpfull to explain why. Colaescors function by allowing very small droplets (fog) to adhere to a surface, where they can merge (coalesce) with other droplets untill they become large enough to fall off the surface to the bottom of the coalescor from where they can be drained. Coalescors can not dry air, just remove excess water. The air that leaves them is still 100% humid. It is the job of the desciant in the filter to remove the remaining moisture. A Priority valve separates the colaecsor and filter from the scuba tank. It is set to keep the air in the coalescor/filter at a minimum pressure (generally around 1800 lbs) before allowing the air to enter the tank. The reason is two fold. 1. Filter media works better at higher pressure, there is greater dwell time (time the air remains in contact with the filter). 2. The higher the presure, the less water air can hold. Thus even though air going through the coalescor emerges at 100% relitive humidity, the air at 1800 psi will carry far less water than air going through the coalescor at 100PSI, This is a lot less water that the desciant in your filter will have to remove. Since saturated desciant is the main reason for filter failure and filters are expensive, it behoves one to have a priority valve.

Temperature also has a major effect on how much water air can hold. Bauer rates the PO at 3000 cuft, but at an inlet temp of 20C (68f) That is inlet to the PO, not compressor (rule of thumb is the compressor heats the air 15 degreed F)... thus to get a full 3000 cuft out of the filter you will have to do all your filling at 53 degrees f or colder. If I recall pumping air at 85 degrees ambient will cut the life of the filter by almost 1/2.. I believe Lawrence Factor uses an 80 degree F temp as a basics for their filter rating.

I considered a Bauer PO, but didn't like the small capacity/double pass design which makes refilling cartridges difficult (I can open/refill the cartridges in my present stack if i ever get the hankering)

Another thing that bothers me about used filter stacks is lifespan, the things are good for only so many cycles (metal fatgue). It is a high number and as a home user I will never get near it, but how many cycles are on that EBAYed unit??? They will only fail when the pressure is high !!!

Other recommended reading is the "Oxygen Hackers Companion" - Airspeed Press.

A PO is a small combined filterstack/coalescor made by Bauer. It is used on their smaller compressors. You can put it on a RIX. most stuff can be plumbed but I don't know about the metric to US conversion. My guess is that Swagelock will have metric thread fittings for 1/4 inch tube. Assuming that Bauer uses metric pipe threads. The HP side of the Rix uses 1/4 inch ss tubing.

At this point we are recreational, but we seem to be moving in technical circles so adv nitrox and PP can't be ruled out in the future. filling off the compressor isn' t that bad. with air I can walk away, but with nitrox I hang around and watch the meter. typically 15 minutes per tank. Filled 6 last night in about an hour and a half. would have taken me longer just to drive to a dive shop and back not counting the wait for the fill.

hth

 

[san diego diver]

hey pescador,
why not e-mail me (sddiverdude@sbcglobal.net) and let,s talk about the 250.00 bauer po !!