Nitrox blending, cascade filling????

[divetheworld]

OK, I've been blending a while now with my single 'J' that I get through every 1-2 months. I have heard it said that using more than one J in a cascade system will allow me to recover more O2 from my supply cyls.
I dont get it, maybe I have brain lock, but i just dont get it.
When I have used my supply cyl down to the lowest usable pressure, thats it. I rack up a new one and continue, how would I get more from two manifolded together?
All I can think of is when you have tanks that have a residual mix left in them, you would top up from the J with the highest pressure, the J with the lowest pressure would be for filling dry or nearly empty tanks. Is that it? But that would not need manifolding, just swapping.
Please explain.

[Padowan]

Originally Posted by divetheworld

OK, I've been blending a while now with my single 'J' that I get through every 1-2 months. I have heard it said that using more than one J in a cascade system will allow me to recover more O2 from my supply cyls.
I dont get it, maybe I have brain lock, but i just dont get it.
When I have used my supply cyl down to the lowest usable pressure, thats it. I rack up a new one and continue, how would I get more from two manifolded together?
All I can think of is when you have tanks that have a residual mix left in them, you would top up from the J with the highest pressure, the J with the lowest pressure would be for filling dry or nearly empty tanks. Is that it? But that would not need manifolding, just swapping.
Please explain.

As far as I know you have hit the nail on the head for how a cascade is used. It's like having different pressure banks - the High Pressure gas is the most valuable to you, so if you have say 50 bar in a second J, you use this first, then use less of the higher pressure J.

[David Martin]

With the cascade you just use sequentially, starting with the cylinder with the lowest supply pressure (above what you're filling into) and working up.

For nitrox "bottom mixes" such as Nx36 or weaker, a cascade isn't going to help much. Your J is still fully useful down to 30 or 40bar. However for deco mixes (eg 230 bar 50% requires 84bar O2) a cascade is essential to get make use of the bottom half of the supply cylinder. At these higher pressures it also becomes more useful to be able to move the whip between cylinders without depressurising the whole whip.

Move into trimix PP blending, and the number of "J"s to get efficient gas useage seems to go up considerably :-(

David

[Mark Powell]

You don't necessarily need to manifold them together. For a permament installation it's true that a cascade may have all the supply cylinders connected together but with individual valves so that that you can choose which supply cylinder is feeding the target cylinder.

The idea is to use the supply cylinder with the lowest pressure first, then once the target tank has equalised with this cylinder, shut it off and then open the next lowest pressure supply cylinder. Keep doing this until you get the fill you want.

The advantage is that you keep the head pressure in the highest pressure cylinders as you have already put in some of the O2 from a lower pressure cylinder.

For garage blending 'cascade' is rather a grand word for it. Connect your filling whip to the lowest pressure cylinder and fill until equalised, then disconnect from the supply cylinder and connect to the next cylinder, etc.

A whip which allows you to keep the O2 pressure in the filling whip between supply cylinders is a good idea.

Usual disclaimers: This information only to be used by suitable qualified gas blenders. Pure 02 is a fire hazard and should be used with the appropriate caution.

[chrisch]

There you have the answer. If you want to get the last dregs of O2 out the cylinder you need a gas booster. This little baby will increase the pressure of the remaining O2 to a usefull level.
That said you still can't get the last 5 bar or so out.

There is a small KISS booster that will do the job and runs from a compressed air source.

I doubt the economics stack up on the level of use you mention.

One thing though, a more powerful booster will do away with the need for an HP compressor. You can use it for the air top off from a tank of air from your LDS. An LP compressor would then suffice and they are cheap (about 150 quid from machine mart).

If starting from scratch its an interesting strategy.

Fess up though - I have never used one of the damn things (they are expensive) so I don't know how easy/difficult it would be to get an accurate final pressure for the PP blending. I would be very grateful if anyone has a view or experience on this as I have thought about buying a booster for this purpose.

Chris.

[Padowan]

I've just got YBOD and am now thinking about getting a KISS nanobooster to allow me to get nice, decent 200bar O2 fills in my garage as not all dive centres are able to boost HP O2, and are only really set up for PP blending nitrox, decanting straight from J's.

I think that you can get a Nanobooster and whips from the states for about a grand. A lot of money, but think of the convenience!

[chrisch]

Originally Posted by Padowan

I've just got YBOD and am now thinking about getting a KISS nanobooster to allow me to get nice, decent 200bar O2 fills in my garage as not all dive centres are able to boost HP O2, and are only really set up for PP blending nitrox, decanting straight from J's.

I think that you can get a Nanobooster and whips from the states for about a grand. A lot of money, but think of the convenience!

More here:

http://www.derwentelec.clara.co.uk/h...s_booster.html

Chris

[Fiona]

Originally Posted by Padowan

as not all dive centres are able to boost HP O2, and are only really set up for PP blending nitrox, decanting straight from J's.

Hi there not really sure where you are based but I get my O2 from Aqualogistics in Stockport, Geoff has no porblems getting me over 200 bar. He has just put in a haskel pump to be able to do this.

I can't find the price on the Jetsam site for the nanobooster but it seems to be $1250 canadian. Is this right?
Anybody bought one recently?

[Padowan]

Originally Posted by FionaB

Hi there not really sure where you are based but I get my O2 from Aqualogistics in Stockport, Geoff has no porblems getting me over 200 bar. He has just put in a haskel pump to be able to do this.

During the week, when in Manchester, I also use AquaLogisics and have had very good service there, but back down in Kent I usually go to Kent Diving, and they've not got a booster, so I have to go to Dive Machine instead....

But I like the idea of being able to do this myself, anyway!