IMPROVING THE WORK OF BREATHING OF THE RGU

If you are planning to duplicate this project, it is assumed you know just how crazy you must be to dive a RGU or any other rebreather. These things can and do kill people...smart people...dumb people...experienced people...beginners alike...Always know your PPO.



My initial shutoff valve for the RGU got me quickly through the experimentation stage but there were long term work of breathing problems. The first was the limitation of the half inch orifice in the hose shutoff. Credit for the mouthpiece modification comes from my observations of the FEOR and Patrick's Oxycheck site where similar directions for the mouthpiece are found.

The other WOB problem was the inside diameter of the RGU hose. In both cases I have increased the diameter to reduce the WOB. As you can see in the header picture, the new hose is much bigger than the hose that comes with the RGU. It is a new hose that fits a US Divers regulator. It has a one and half inch opening on one end and a one inch opening on the other end. These are available from:

VINTAGE SCUBA SUPPLY

Clutching my hoses that come so fast from Vintage that they might as wll be shipped by transporter, I headed to Lowes, my favorite rebreather parts store. While I also go to the other rebreather store Home Depo, I like the layout at Lowes better and it is directly on the way to the office. Besides, they are so used to me wandering around in the plumbing department that the staff often asks me where things are. It's so nice to go some where they know your name.

I started in the PVC plumbing stock department selecting a ball valve for the mouthpiece. Rather than checking what kind of pipe would fit in a valve, I would try each one to see how much resistance to breathing each one had. The clerks just ignored me...if it had been another customer, they would have noticed. I had already determined that a three quarter valve had twice the area of a half inch valve. I could not detect any resistance to my breath with the three quarter inch ball valve. I slipped a few feet down the isle to the PVC pipe. I found that one and one quarter pipe fit perfectly into the big end of the hose. It conveniently also fit onto the ends of the ball valve. The excitement starts to rise in my sleepy brain like bubbles in the cheap champaign at a Moose Hall wedding.

I needed to celebrate so I put the one and a quarter inch pipe to my mouth and played it like one of my Didgeridoos .... that got some attention as the weird sounds traveled throught the store. Some thought the pipes were bursting...some thought the aliens were landing. If you can't guess, my theme song is Jimmy Buffets "Follow in my Wake."

Throwing four of the ball valves, a contractor pack of one half inch couplers, and the pipe into my cart I headed for checkout and my office. No real work was going to be done this day.....

The first thing I did was to drill a three quarter inch hole in the ball valve directly across from the flat knob. I was careful to center it before drilling.
The hole through the half inch coupling perfectly covers the three quarter inch hole drilled in the ball valve. Here is where my DSV differs from the others. Rather than insert the fitting, I flare the coupling so that it fits over the ball. Flaring takes advantage of the thermoplastic nature of PVC. It also creates a larger surface for glueing and a wider surface. This reduces the lever arm of the mouthpiece and the possibility of breakage. First I put the coupling in my mini lathe turning it at low speed. I use a small heat gun to warm the end of the coupling.
After the end gets soft, I expand the end with a funnel to preset the flare. This is an important step.
After a short reheat I press the ball valve in place and the coupling forms a perfect fit. I hold it until it cools.
I put some PVC glue in the flared coupling and press it onto the ball valve covering the hole I drilled earlier. I tighten the vise and leave the mouthpiece in the vise overnight.
Drilling out the cavity for the check or one way valves from the RGU mouthpiece. One end is drilled shallow...the other deep. If you have a RGU, you will note that this is the same configuration that is in the mouthpiece that comes with the RGU. I messed up half of the ball valves in this step. Thats why I bought four ball valves.
Here the RGU valve sits in the cozy cavity I made for it. The next step in the fabrication process will be to glue the valves in with some goop. That way I can get them out if I need to.
Here I am flaring one of the heat softened hose fitting cut from the one and a quarter PVC pipe. I have it in the chuck of the lathe just like the pipe coupling I modified earlier. I goop the flared fittings on the inside with PVC cement and slip one onto each of the hose ports of the mouthpiece and put it aside to the next day.
A final heating and a squeeze of the mouthpiece. This one is a little off so I will reheat it and get it even. Love things that can be fixed. After I get the whole thing finished, I take some permanent marker and make it black. Next I put the large end of the hose over the flange, slip on a mouthpiece, and clamp them on with plastic wraps.

About that Didgeridoo comment earlier. Here is a shot of me playing my favorite dige from down under. It is decorated with an octopus. Not only is it a beautiful piece of art, it really is easy to play. Note the size of the bell. It gets some attention on quiet spring nights and on Halloween...my favorite holiday.



Someday I will do a page on my dige collection and how to make one out of PVC. Not now, I am heading back to the quarry for more rebreather testing. Read that as an excuse to go in fresh water.

Enjoy,
Tom

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