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SurfLung
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Cascade Storage Banks

Thu Apr 25, 2019 11:58 am

Cascade Storage Banks... Proper Use.
- I'd like to know how dive shops use cascade bottles systems... Is it different from the way I use AL80 Scuba tanks to cascade fill my Twin 38s?
1. For example, I have found that the most efficient use of a cascade tank is to fill my Twin 38s when they are almost empty. With the full tank emptying/cascading into the almost empty Twin 38s, I get the most possible pressure transfered.
2. After this first cascade, both the filler tank and the receiving tank are at about half full. And, I need another FULL AL80 to add more pressure to my Twin 38s. This gets it pretty close to 3/4 full and leaves the AL80 about 3/4 full.
3. After this second cascade, I need one more FULL AL80 to top off my Twin 38s at 2,000 psi BUT the AL80 is still almost full.

Now is Where I wonder About the Difference Between Me and a Dive Shop Cascade.

1. For my next fill, I'll again try to start with nearly empty Twin 38s. This time, the first cascade will come from the first half empty AL80 and will fill my Twin 38s to about 1/4 full and leave the AL80 at about 1/4 full
2. The 2nd Cascade will come from the 2nd 3/4 full cascade and will bring my Twin 38s up to about 1/2 full and leave the AL80 about 1/2 full
3. the 3rd Cascade will come from the 1st almost full AL80 and will bring my Twin 38s up to about 2/3 full and leave the AL80 about 2/3 full.
4. And now I take another FULL AL80 to bring my Twin 38s up to a full 2000 psi... Leaving the AL80 at about 3/4 full

This continues, on the next fill much the same way... Using the cascade tanks from lowest pressure first on up to highest pressure.

Is this the way a dive shop does it too?
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

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rhwestfall
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Re: Cascade Storage Banks

Thu Apr 25, 2019 3:04 pm

I was taught to use lowest pressure tanks first until they can't push, and then move up to the next for each and every fill...
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Bryan
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Re: Cascade Storage Banks

Thu Apr 25, 2019 5:40 pm

What Rob said.... I have 8, 3600psi 250cf bank bottles.

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Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

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captain
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Re: Cascade Storage Banks

Fri Apr 26, 2019 10:51 am

rhwestfall wrote:
Thu Apr 25, 2019 3:04 pm
I was taught to use lowest pressure tanks first until they can't push, and then move up to the next for each and every fill...
This^
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tbone1004
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Re: Cascade Storage Banks

Fri Apr 26, 2019 11:10 pm

what was said above is accurate, also how auto cascade systems from Bauer work.

If you are running the compressor though, you keep it running thru the entire filling process, but as soon as you are ready to take the tank off, you need to leave the compressor filling the highest pressure bank for as long as possible. It seems somewhat counter-intuitive to be filling the highest pressure tank, but that tank is the one giving you your final fill pressure so it needs to be kept up as high as possible.

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Re: Cascade Storage Banks

Sat Apr 27, 2019 10:48 am

tbone1004 wrote:
Fri Apr 26, 2019 11:10 pm
what was said above is accurate, also how auto cascade systems from Bauer work.

If you are running the compressor though, you keep it running thru the entire filling process, but as soon as you are ready to take the tank off, you need to leave the compressor filling the highest pressure bank for as long as possible. It seems somewhat counter-intuitive to be filling the highest pressure tank, but that tank is the one giving you your final fill pressure so it needs to be kept up as high as possible.
True
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rx7diver
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Re: Cascade Storage Banks

Sun May 12, 2019 5:13 am

It's probably obvious, but I'll write this anyway: Make sure the particular cascade cylinder you start with has *greater* pressure than the starting pressure in your dive cylinder.

For example, suppose you have four 3,000 psig cascade cylinders containing 500, 1000, 2000, and 2800 psig, resp., at the start. And suppose your Steel 72 has 600 psig to start. Then skip the first cascade cylinder, and begin filling using the second (or else you risk contaminating your cascade system with impurities that might be in the air that's already in the scuba cylinder from a previous "dirty" fill).

That is, don't *automatically* begin "filling" a scuba cylinder using the very first cascade cylinder. Always check the starting pressures first.

rx7diver

tbone1004
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Re: Cascade Storage Banks

Sun May 12, 2019 9:15 am

better solution to what was said above, put check valves on your fill whips. IMO it is 100% critical to have them on there for the contamination issue.

Flow diagram in the big cascades should look like this
Compressor
PMV
Filters
PMV
Check valve
Manifold block with x-number of cascade bottles on it
Regulator
Check valve
Fill whips

The check between the cascade and compressors allows you to disconnect the compressor if you have to, but also prevents needlessly cycling the pressure in the line between the compressor and banks during filling. Cycling is what kills pressure devices, so want to minimize that.
Check between the regulator and fill whips prevent any contamination coming back from the tanks which is critical regardless of whether you only ever fill your own tanks from your own compressor. Cheap insurance from dumping large quantities of gas.
If you have multiple whips, each should have it's own check valve to prevent them from equalizing as well and contaminating each other.
SS, 1/4" mnpt check valves with 1psi springs are about $30 from Swagelok. Cheap insurance.

rx7diver
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Re: Cascade Storage Banks

Sun May 12, 2019 12:55 pm

A hobbyist might not have/need the "complete" system that @tbone1004 describes above.

A hobbyist might just have a more basic cascade set-up--you know, a competent compressor system (3-to-6, maybe up to 8, scfm), and a few (three or four or five, say) cascade cylinders (3,500 psig service pressure, perhaps filled to a max of 3,000 psig) connected in series with pigtails, and ending in a single fill whip. No manifold per se. No check valve just upstream the fill whip. Such a basic system is adequate for filling quite a few single 72's (2,250 psig + 10%) in fact, before needing to be recharged, depending.

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tbone1004
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Re: Cascade Storage Banks

Sun May 12, 2019 2:30 pm

why not put the $30 check valves in there and not have to worry about it?
The manifold is certainly unnecessary so long as you have easy access to the cylinders valves and aren't doing a high quantity of tanks.
The regulator is good piece of mind IMO, though if the compressor has a shutoff at 4k and you keep the banks there, then there is little concern for filling anything since it is either at or below the test pressure.
The check valves though are important IMO and cheap security for any contamination risk.

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SurfLung
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Re: Cascade Storage Banks

Mon May 13, 2019 9:16 am

I haven't thought of contamination risk because I'm only using air from my own compressor. But I saw a video on those Chinese compressors where the airgun guy said his tank smelled like oil and the dive shop refused to fill it because of the risk of contamination. Kind of makes you wonder, how is a dive shop to know unless you tell him? So there most definitely would be a need for a check valve... Probably right on the end of the fill whip.
SurfLung
The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

tbone1004
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Re: Cascade Storage Banks

Mon May 13, 2019 9:37 am

The check valves are typically on the leading end of the fill whips at dive shops.
Typically the whips look like this, at least on shops that charge per cubic ft.
Check valve
Line Valve
Pressure Gauge
Hose
Fill adapter

Reason being that the gauge needs to register tank pressure prior to filling. Two schools of thought there, one is to open the line valve first to pressurize the line, close the line valve, then open the tank valve. This puts cascade gas into the line, then will drop the gauge down to tank pressure when it is opened. This is arguably better. Other is to just open the tank valve and read it directly. In either instance the check valve will prevent anything from going backwards.

rx7diver
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Re: Cascade Storage Banks

Mon May 13, 2019 10:34 am

A hobbyist might first gauge his/her scuba cylinder(s), using either his SPG or his stand-alone tank pressure gauge, before attaching the fill whip to the scuba cylinder. He then would know which cascade cylinder to begin the fill with. He would pressurize the fill whip with air from this particular cascade cylinder before opening the valve to his scuba tank. Simple.

Fewer unnecessary components in the system means a less expensive system initially, fewer components to monitor and maintain, and fewer components that could fail. Keep in mind, the "real" running cost of the system includes the cost of system downtime as you're replacing even a relatively inexpensive component that has failed.

Good thread!

rx7diver

tbone1004
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Re: Cascade Storage Banks

Mon May 13, 2019 11:31 am

one thing to think about if using a standalone pressure gauge is to make your whip adaptable and dual use.
One of my whip ends is from an XS transfill whip and has a 1/4" NPT port for the pressure gauge on it. Right behind that I put a check valve and behind that a Swagelok QF4 quick disconnect. This is the same QD used by Bauer which is why I standardized on that, but you can use a myriad of others. The nice thing there is the whip end can also double duty as a pressure checker so I keep that with me when diving.
Bank outlet has a QF4 as well so I can connect the whip to that and now for the price of the quick disconnects I have something that can work as a fill whip, transfill whip, and pressure checker.

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SurfLung
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Re: Cascade Storage Banks

Tue May 14, 2019 1:08 pm

Vintage Valves May Need To Be Opened First...
- One of the issues I encountered when filling my vintage tanks was a stuck seat when the valve on the tank (low pressure) was left shut until after the whip valve was turned on. I learned from old guys on this forum that sometimes old valves have to be opened first, or else the higher pressure from the whip will hold the seat closed when you try to open it. This solved a problem for me. Now I always open the tank valve first.
- But if the whip is higher pressure than the tank, that should keep the good air moving in the right direction and avoid contamination, right?
- I've been letting the whip pressure climb to the desired fill pressure before opening the whip valve.
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The Freedom and Simplicity of Vintage Equipment and
Vintage Diving Technique are Why I Got Back Into Diving.

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