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SurfLung
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Cascade or Direct Fill

Wed Aug 30, 2017 11:22 am

To Cascade or Direct Fill...
- I've been thinking that I'm adding an extra layer of moisture protection by cascade filling my Twin 38s from AL80s. But recently I realized that by doing it this way, my compressor has to pump the AL80s all the way up to 3300 psi in order to fill my 1800 psi Twin 38s... Making the compressor work a lot harder than if it just filled the Twin 38s directly to 1800 psi.
- The compressor has PLENTY of moisture protection... No need for more.
- Just thought I'd share this... :oops:
SurfLung
The Freedom and Simplicity of Vintage Equipment and
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tbone1004
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Re: Cascade or Direct Fill

Wed Aug 30, 2017 11:56 am

what is the backpressure valve set to on the compressor? It doesn't work any harder pumping as long as it is under that pressure. It needs that amount of pressure in there for dwell time in the filters as well as to balance the thing out. A lot of them have 3000psi back pressure valves so it won't be much of an issue.

Better thing you can do is to put better cooling on the system before it hits the moisture separators with either supplemental fans or more ideally with liquid cooling of some sort. Keeping the air cool is going to not only pull the moisture out, but with the moisture comes any contaminants that are vaporized *i.e. oil etc*

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antique diver
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Re: Cascade or Direct Fill

Wed Aug 30, 2017 6:29 pm

The way your drying and filtration system is put together should be pretty efficient... but knowing your propensity to improve things that aren't really a problem :lol: I do have an idea that may further extend your filter media life to some extent.

First take a good temperature reading of the aluminum on discharge side of your pressure maintaining valves (the one mounted on your compressor, and the one after your filter arrays) while your pump is running and has been filling to full warmup. Let me know what you find and I can try making a few calculations that can tell us how much theoretical improvement might be achieved by a simple method I rigged up for a dive operation in Paamul, Mexico. :)
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SurfLung
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Re: Cascade or Direct Fill

Tue Sep 05, 2017 9:22 am

Tbone,
- Actually my Back Pressure Regulator is set by the factory to 1800 psi and the check valve is set to 1500 psi. So, filling my low pressure Twin 38s to 2000 psi directly from the compressor DOES save the compressor from the harder work of filling cascade tanks to 3000+ psi.

AntiqueDiver,
- As you have deduced, I shouldn't have a moisture problem and in fact I don't. The cascade idea was sort of overkill. I'd sure be interested to know what you did with that compressor in Mexico though! :)
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 or Direct Fill

Tue Sep 05, 2017 4:11 pm

if that's the case, then I would look at how to improve cooling on the compressor and not transfill

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antique diver
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Re: Cascade or Direct Fill

Tue Sep 05, 2017 10:29 pm

SurfLung wrote:Tbone,
-
AntiqueDiver,
- As you have deduced, I shouldn't have a moisture problem and in fact I don't. The cascade idea was sort of overkill. I'd sure be interested to know what you did with that compressor in Mexico though! :)
It was so simple you will just roll your eyes. :roll: The shop in Paamul was using a Bauer K14 pumping about 8 or 10 cfm and operating for hours each day in the high heat and dripping humidity. They were constantly needing to replace their filter to keep air quality reasonable, and the costs and inconvenience were adding up. We couldn't do anything about the important factors of high humidity and high temperature of air going into the machine. The easiest thing I could control would be the temperature drop between the high pressure discharge line between the compressor and the final separator. The more it cooled before getting to the separator the more water would drop out in the separator, leaving less moisture vapor to be taken out by the molecular sieve in the filter. Result would be filters lasting longer and money saved.

It was a simple matter of coiling up about 15 feet of SS tubing into a coil that would fit into a 5 gallon bucket. Flexible hose was attached to each end of the tubing with one end coming from the compressor's aftercooler (finned tubing coil) and the other going to the original final separator. The bucket was kept full of ice and water completely submerging the coil. A finned tubing coil would have been even better in the ice water, but expensive, and I was trying to help them save more $$. So, having their own icemaker right there they had an adequate source for keeping the air cooled down way more than any air-cooled aftercooling, and dropping more water out in the separator. I don't recall the details on how much it reduced their filter purchases, but they were pleased with the results. I don't bother with all that on my own compressors as it is not really necessary for the small amount of tanks I fill.
The older I get the better I was.

tbone1004
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Re: Cascade or Direct Fill

Wed Sep 06, 2017 5:48 pm

I have liquid cooling before the filters on mine as well. It's astounding how little work the filters have to do when you get the air cool. Tobin at Deep Sea Supply has a BEAST of a chiller on his that apparently is prone to freezing in the winter *in Los Angeles mind you* when the coalescers blow out

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captain
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Re: Cascade or Direct Fill

Thu Sep 07, 2017 10:58 am

I had the idea of using a small 5000 BTU window air conditioner connected to a plenum and connect the compressors intake to the plenum. Feed the compressor cold dehumidify air. You would also need a small inlet to the plenum to replenish the air the compressor sucks out.
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tbone1004
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Re: Cascade or Direct Fill

Thu Sep 07, 2017 7:20 pm

haven't done the math for how big you need per size, but this is what you actually want

have a tank of some sort that has the coils from the compressor laid inside of it. More insulated obviously the better but something is better than nothing

https://www.amazon.com/Active-Aqua-Chil ... iller&th=1

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antique diver
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Re: Cascade or Direct Fill

Fri Sep 08, 2017 9:52 am

captain wrote:I had the idea of using a small 5000 BTU window air conditioner connected to a plenum and connect the compressors intake to the plenum. Feed the compressor cold dehumidify air. You would also need a small inlet to the plenum to replenish the air the compressor sucks out.
Cooling and drying the intake air can make a significant difference in filter life.

Here is information lifted from a chart by Bauer USA about ambient temperature and effect on filter life factors. The left column is ambient Farenheit temperature and right column is filter life factor.
Baseline of 68 degrees is factor of 1, so at temperature of 86 expected optimum filter life is only 57% of life that would be expected at 68. The cooler the ambient air the less moisture it can hold so there is less to be captured by the filter media.

Sorry the numbers run together. I couldn't get them to layout properly here.

41 2.62
50 1.85
59 1.34
68 1.00
77 0.75
86 0.57
92 0.52
104 0.43
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captain
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Re: Cascade or Direct Fill

Fri Sep 08, 2017 10:08 am

antique diver wrote:
captain wrote:I had the idea of using a small 5000 BTU window air conditioner connected to a plenum and connect the compressors intake to the plenum. Feed the compressor cold dehumidify air. You would also need a small inlet to the plenum to replenish the air the compressor sucks out.
Cooling and drying the intake air can make a significant difference in filter life.

Here is information lifted from a chart by Bauer USA about ambient temperature and effect on filter life factors. The left column is ambient Farenheit temperature and right column is filter life factor.
Baseline of 68 degrees is factor of 1, so at temperature of 86 expected optimum filter life is only 57% of life that would be expected at 68. The cooler the ambient air the less moisture it can hold so there is less to be captured by the filter media.

Sorry the numbers run together. I couldn't get them to layout properly here.

41 2.62
50 1.85
59 1.34
68 1.00
77 0.75
86 0.57
92 0.52
104 0.43
It would also increase compressor output and shorten fill times. Moisture in air occupies space, the less moisture in the intake air the more air for the compressor to pump hence more CFM output.
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tbone1004
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Re: Cascade or Direct Fill

Fri Sep 08, 2017 10:49 am

we are talking more about the outlet air though. There isn't much you can do for the intake side. That said, obviously cold/dry air is ideal for the intake portion, just quite impractical

The cooler thing about cold air going into the filters is that as the moisture comes out of suspension it takes almost all of the particulates with it so the only thing the filters have to take out is CO.

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antique diver
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Re: Cascade or Direct Fill

Fri Sep 08, 2017 12:58 pm

tbone1004 wrote:we are talking more about the outlet air though. There isn't much you can do for the intake side. That said, obviously cold/dry air is ideal for the intake portion, just quite impractical

The cooler thing about cold air going into the filters is that as the moisture comes out of suspension it takes almost all of the particulates with it so the only thing the filters have to take out is CO.
About that intake air, my small compressor is electric and I run it in my garage with doors open. I could run an intake hose through the wall into the house where the air is cool and dry. Troubling thing is that the only convenient place for the intake would be the back corner of the utility room above the cats' litter box. :shock:
I think I'll stick with the outdoor air!
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couv
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Re: Cascade or Direct Fill

Fri Sep 08, 2017 1:51 pm

antique diver wrote:
tbone1004 wrote:we are talking more about the outlet air though. There isn't much you can do for the intake side. That said, obviously cold/dry air is ideal for the intake portion, just quite impractical

The cooler thing about cold air going into the filters is that as the moisture comes out of suspension it takes almost all of the particulates with it so the only thing the filters have to take out is CO.
About that intake air, my small compressor is electric and I run it in my garage with doors open. I could run an intake hose through the wall into the house where the air is cool and dry. Troubling thing is that the only convenient place for the intake would be the back corner of the utility room above the cats' litter box. :shock:
I think I'll stick with the outdoor air!
How about a duct within a duct? Would running a duct from your compressor's intake into an air-conditioning duct be feasible providing you have a method of shutting it off when not in use?
A sincere THANK YOU to all at VDH who make this wonderful resource available and to all the thoughtful contributors.

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antique diver
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Re: Cascade or Direct Fill

Fri Sep 08, 2017 5:26 pm

couv wrote:
How about a duct within a duct? Would running a duct from your compressor's intake into an air-conditioning duct be feasible providing you have a method of shutting it off when not in use?
That would work but is just not worth all the trouble for me. It would be a nice setup for someone to do. I'm at a point that I just want to simplify things, and my filters are already holding up well with two final separators in series.

Always fun hearing new ideas though! Thanks. :D
The older I get the better I was.

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