Owning a Compressor

[bmoore_cave_diver]

Does anyone own their own compressor? My buddy and I are toying with the idea of having our own fill station.

I would be interested in hearing some suggestions. Pros? Cons? Unforseen issues?

We want to pretty much get rid of our reliance on dive shops and blend our own mixes.

 

[Wookie]

I have lots of them, at home, in the shop, and on the boat. I can show you how to spend a lot of money real quick. Remember, air fills is a loss leader for dive shops. They fill your cylinders as a customer service, not to make money. Course, if you want fills at midnight, it may be worth the extra expense. If you dive trimix 2 or 3 times a week, it might pay for itself in 10 years.

 

[Surface Tension]

I purchased a compressor a few years back and haven't looked back. I blend my own nitrox and dive probably 15 to 20 times a year. I fill my tanks whenever I want to whatever pressure I want. I don't have some shop guy telling me why I have to pay him for a sticker in order to get them cleaned, inspected, blessed by a priest.....you get the idea.

I may not have "saved" any money but I certainly haven't lost any considering I could sell the compressor for what I bought it for at any time. If you shop around you could get a decent deal on a used one. I would definitely recommend buying a used one. You better do your homework because you could really hurt yourself or someone else if you don't know what you are doing; it isn't rocket science though.

Even if you aren't going to be filling with nitrox I would still by this book and read it.

Vance Harlow's OXYGEN HACKER'S COMPANION From AIrspeed Press

Where are you located? I actually just bought a bigger compressor and have two smaller compressors for sale both Bauers; Junior II and a Utilus.

Dave

 

[dannobee]

I bought an older Utilus because of the lousy air fills I was getting from the dive shop(s). I wouldn't go back. I have added a nitrox/trimix stick and regulators. I'll be getting the bigger filter stack soon as the Bauer one is rather small.

No regrets at all.

 

[Surface Tension]

Danno,

Do you have a Utilus 10 or a full sized Utilus (Capitano Block)?

 

[dannobee]

Capitano block.

 

[DA Aquamaster]

Compressors are probably not cost effective if you consider the purchase price and the number of fills needed to pay it off. On the other hand, around $2000 will get you a decent portable compressor that will let you fill when ever you want and that can be worth a great deal of $ to some divers.

If you stay with a reliable compressor and a hand packed filter stack, the maintenence costs are not all that high given the limited use that 1 or 2 divers put on it and owning your own will not be all that costly, so if you don't consider the acquisition costs, filling your own tanks is very affordable.

A nitrox stick is a low tech but effective way to mix nitrox up to 40% on just about any compressor and that may also increase the cost effectiveness over nitrox fills at the local shop.

 

[dannobee]

Compressors are probably not cost effective if you consider the purchase price and the number of fills needed to pay it off. On the other hand, around $2000 will get you a decent portable compressor that will let you fill when ever you want and that can be worth a great deal of $ to some divers.

If you stay with a reliable compressor and a hand packed filter stack, the maintenence costs are not all that high given the limited use that 1 or 2 divers put on it and owning your own will not be all that costly, so if you don't consider the acquisition costs, filling your own tanks is very affordable.

A nitrox stick is a low tech but effective way to mix nitrox up to 40% on just about any compressor and that may also increase the cost effectiveness over nitrox fills at the local shop.

I think you're failing to account for the residual value in the compressor. If you buy it used, there's a good chance that it will retain all of its value if you ever sell it. If you're mixing nitrox or trimix, the payback will be a lot faster than if you're just pumping air.

Each tank of nitrox (32%) costs me less than $1 when factoring in filtering and compressor maintenance, oxygen, and electricity.

The nitrox stick works equally well for trimix. There's no need for a helium sensor, there's a way to use just the oxygen sensor to calculate the helium going into the compressor's inlet.

 

[DA Aquamaster]

I think you're failing to account for the residual value in the compressor. If you buy it used, there's a good chance that it will retain all of its value if you ever sell it. If you're mixing nitrox or trimix, the payback will be a lot faster than if you're just pumping air.

Each tank of nitrox (32%) costs me less than $1 when factoring in filtering and compressor maintenance, oxygen, and electricity.

The nitrox stick works equally well for trimix. There's no need for a helium sensor, there's a way to use just the oxygen sensor to calculate the helium going into the compressor's inlet.

I'd be interested in learning more about that technique.

Alternativey, you can also just transfill the required amount of helium into an empty tank first and then top it off with the required percentage of nitrox run through the stick. High O2 amounts in the nitrox are not required (nor desireable) and filling the He first reduces the need for a booster to get the most out of a K bottle of helium. As long as the math is right the trimix will be right and verification with an He analyzer, while nice for verification, is not needed for mixing.

 

[dannobee]

I'd be interested in learning more about that technique.

Alternativey, you can also just transfill the required amount of helium into an empty tank first and then top it off with the required percentage of nitrox run through the stick. High O2 amounts in the nitrox are not required (nor desireable) and filling the He first reduces the need for a booster to get the most out of a K bottle of helium. As long as the math is right the trimix will be right and verification with an He analyzer, while nice for verification, is not needed for mixing.

It goes something like this:
Start up compressor, calibrate O2 sensor to 21%, add He until you get the reading you want (i.e. 13.7% for 21/35, 11.6% for 18/45 or 9.5% for 15/55), then add oxygen until you get the correct mix (21%, 18% and 15%, respectively).

For 45% He, for example, that means O2+N2 = 55%. 0.21 x (1-.45)= 0.1155 or 11.6%.

Since you're using a stick and plumbing into a slight vacuum from the compressor, you can use all of the He in the source tank (even pulling a vacuum if you design the inlet correctly). You obviously can't do this when PP blending He and the source tank goes back with usable He still in it. You also don't need to empty the fill tank when using the stick.