Dumb Q's on DIY dive compressors

[Dave_S]

I've seen the threads on DIY hookah systems. Is there a similar way for DIY systems to fill tanks ? To save money can you buy the components and put it together yourself.

I'm wavering between the two and leaning one day towards tanks for the freedom of them and the next day towards hookah because tank systems seem power hungry, expensive and heavy. Points that concern me are:

• weight on the boat
• depth of dive - most of the hookah gear seems too shallow
• time to fill - not so much recharge batteries but using a noisy compressor
• power consumption - how big a generator needed to drive the electric motor on a compressor
• price - total cost of ownership

I guess it would have to be petrol motor drive unless you can make an electric one that draws less power but over a longer time (I see the petrol ones are 6hp / 4.5kw even for small ones).

Also it seems a waste to have a petrol motor for the air and another for a generator.

Have I just talked myself out of tanks ?

[Jammer]

Originally Posted by Dave_S

I've seen the threads on DIY hookah systems. Is there a similar way for DIY systems to fill tanks ? To save money can you buy the components and put it together yourself.

I am in the process of building up a "homemade" system consisting of a military surplus 4-stage compressor and a 2 HP electric motor. Filtration and fittings will be the major expense. I have been unable to find any filter towers that I would trust at prices materially lower than new prices.

Some of the ex-military compressors are built to be light. Most of the compressors in dive shops are based on industrial and fire department systems, which are built for reliability, long life, and low cost, without regard to weight.

Most compressors can be run below their design speed to allow the use of a smaller horsepower motor, if electrical capacity is limiting. A good compressor dealer can tell you how much you can reduce speed without affecting lubrication etc.

[Uncle Bob]

Originally Posted by Dave_S

I've seen the threads on DIY hookah systems. Is there a similar way for DIY systems to fill tanks ? To save money can you buy the components and put it together yourself.

I'm wavering between the two and leaning one day towards tanks for the freedom of them and the next day towards hookah because tank systems seem power hungry, expensive and heavy. Points that concern me are:

• weight on the boat
• depth of dive - most of the hookah gear seems too shallow
• time to fill - not so much recharge batteries but using a noisy compressor
• power consumption - how big a generator needed to drive the electric motor on a compressor
• price - total cost of ownership

I guess it would have to be petrol motor drive unless you can make an electric one that draws less power but over a longer time (I see the petrol ones are 6hp / 4.5kw even for small ones).

Also it seems a waste to have a petrol motor for the air and another for a generator.

Have I just talked myself out of tanks ?

Hi if you want a hookah dive system that will supply the volume and pressure to enable a deeper dive then you need to source a compressor that will deliver the volume as well as the pressure. Second stage regs used to run at 100/120 psi (presume they still do) therefore you need a higher volume compressor to continue that pressure delivery at depth.
2 divers will dive comfortably on an 8 cfm compressor.

[denverd0n]

The issue is that for hookah you only need a couple of hundred psi at most. There are lots of oil-less, hobbyist compressors out there that can provide that, and which sell for very reasonable prices. This makes a DIY hookah system very feasible.

To fill a SCUBA tank you need 3,000 psi (or darned close to it). To get that you have to go way beyond the reasonably priced hobbyist compressors. I don't know of any oil-less compressors that will deliver that, which means you are into serious filtering equipment to get the oil out of the air. All this combines to make DIY of a tank compressor far, FAR more complicated than DIY of a hookah system.

Not that you can't do it. You can. It is just going to be a project that is orders of magnitude more expensive and complicated than a DIY hookah system.

Good luck.

[toddster8]

One sure-fire way to quickly become the most-hated boat in the anchorage: Drop your anchor then fire up the gas-fired compressor and start filling scuba tanks. Even those guys who were previously hated for running their generator all night will now throw shade on you.

[donradcliffe]

Originally Posted by toddster8

One sure-fire way to quickly become the most-hated boat in the anchorage: Drop your anchor then fire up the gas-fired compressor and start filling scuba tanks. Even those guys who were previously hated for running their generator all night will now throw shade on you.

Actually, I was the most loved boat in the anchorage, as my neighbors dinghied over with their empty tanks. Try getting your US or Australian certified tanks filled in a French country sometime.

[captlloyd]

Yes, echoing denverdOn, unless you are pretty handy and knowledgeable, you need a lot of guidance building that type of compressor. The process of filling high pressure tanks can be very dangerous from both an explosion standpoint and a clean end result concerning the air itself.

[Dave_S]

Originally Posted by Jammer

I am in the process of building up a "homemade" system consisting of a military surplus 4-stage compressor and a 2 HP electric motor. Filtration and fittings will be the major expense. I have been unable to find any filter towers that I would trust at prices materially lower than new prices.

Some of the ex-military compressors are built to be light. Most of the compressors in dive shops are based on industrial and fire department systems, which are built for reliability, long life, and low cost, without regard to weight.

Most compressors can be run below their design speed to allow the use of a smaller horsepower motor, if electrical capacity is limiting. A good compressor dealer can tell you how much you can reduce speed without affecting lubrication etc.

I'd be interested in how this turns out, especially how long it takes to fill a tank with 2hp, sounds like the perfect setup for what I'm after. Have you calculated any times on it ?

[Dave_S]

Originally Posted by toddster8

One sure-fire way to quickly become the most-hated boat in the anchorage: Drop your anchor then fire up the gas-fired compressor and start filling scuba tanks. Even those guys who were previously hated for running their generator all night will now throw shade on you.

Not just other people it would tick me off too.

[Jammer]

Originally Posted by Dave_S

I'd be interested in how this turns out, especially how long it takes to fill a tank with 2hp, sounds like the perfect setup for what I'm after. Have you calculated any times on it ?

The compressor I'm using is rated 2.4 cfm. I'm running it at 3500 rpm which is slightly below it's design speed and I've been told to expect 2 CFM actual output in practice, so in a typical situation with AL80s that aren't completely empty, 2 cylinders per hour.

It's going to be in my garage for now where it will be attached to a 4000 PSI bank system. Most of my cylinders are steel 120s plus some twinsets and some steel 72s, and some oddball little stuff like pony cylinders and SCBA cylinders for my projects involving hardened paint. I figure on having the compressor running all day on days when I'm around and able to go out and drain the moisture separator periodically.

[toddster8]

Coincidentally, there appears to be a new generation of sketchy-looking Chinese "scuba" compressors on eBay for about $800. 2.2 kw electric motor. 30 MPa capacity. Claims to fill a scuba tank to 20 MPa (about 3000 psi) in 42 minutes.

If I had a 5 kw generator on board, I'd be tempted to try one. I could probably squeeze in a generator or a compressor, but not both.
Seems to me that the most tempting DIY lash-up would to be to run a belt drive directly from the main engine. But if you had an engine room big enough for that, you'd probably have room for a generator too.

[jlcnuke]

Originally Posted by toddster8

Coincidentally, there appears to be a new generation of sketchy-looking Chinese "scuba" compressors on eBay for about $800. 2.2 kw electric motor. 30 MPa capacity. Claims to fill a scuba tank to 20 MPa (about 3000 psi) in 42 minutes.

If I had a 5 kw generator on board, I'd be tempted to try one. I could probably squeeze in a generator or a compressor, but not both.
Seems to me that the most tempting DIY lash-up would to be to run a belt drive directly from the main engine. But if you had an engine room big enough for that, you'd probably have room for a generator too.

Adding on significant loads to the engine like that could be problematic for the existing engine components as well.. I am intrigued by those Chinese compressors. Not enough to spend the money on one just yet, but I'm hoping some people do so I can find some reviews on them eventually.

[Nani Kai]

Originally Posted by Dave_S

I've seen the threads on DIY hookah systems. Is there a similar way for DIY systems to fill tanks ? To save money can you buy the components and put it together yourself.

I'm wavering between the two and leaning one day towards tanks for the freedom of them and the next day towards hookah because tank systems seem power hungry, expensive and heavy. Points that concern me are:

• weight on the boat
• depth of dive - most of the hookah gear seems too shallow
• time to fill - not so much recharge batteries but using a noisy compressor
• power consumption - how big a generator needed to drive the electric motor on a compressor
• price - total cost of ownership

I guess it would have to be petrol motor drive unless you can make an electric one that draws less power but over a longer time (I see the petrol ones are 6hp / 4.5kw even for small ones).

Also it seems a waste to have a petrol motor for the air and another for a generator.

Have I just talked myself out of tanks ?

Before answering your question permit me this mini-rant: Unless you are a knowledgeable, experienced high pressure breathing air engineer/mechanic, you are risking your life and the lives of those on your boat if you try to cobble together a compressor system from spare parts. It is nothing like working on the compressor you used to put finishing nails into that bookcase you built. High pressure air can kill or maim you in a nano second if it becomes un-contained and that is what it desperately wants to do. (To become un-contained, not to kill you, but the effect is the same). A friend once had his arm ripped open from wrist to elbow when a metal wrapped regulator hose let go while he was servicing it. And this was only 120psi intermediate pressure coming from the first stage. Breathing air contaminated with carbon monoxide or carbon dioxide can kill you. Oil contaminated air can cause your mouth to froth, also killing you. A high pressure air filter canister blew up at a dive shop where I once worked and it sprayed the whole compressor room with shrapnel and moved a wall off its foundation. Just don't understand why folks want to put their lives at needless risk to save a few bucks. Spend the money, stay alive. Okay, rant is over.

The question of diving with auxiliary air off your own boat always comes down to two choices: surface supplied or SCUBA. Recreational surface supplied is either hookah or SNUBA. SNUBA involves floating a tank over your head and breathing from a long hose so essentially it’s the same as SCUBA as far as having to refill tanks. Hookah, as noted, has depth limitations due to the pressure and volume restrictions of typical rigs. There’s also the noise issue if you’re diving in an anchorage with other boats around. You’re also restricted in your ability to penetrate wrecks, tunnels and overhangs and run into challenges with snagging the hose, especially while night diving or in limited visibility. It’s also much more challenging to assist your diving buddy in an emergency if one or both of you are on hookah. In my experience hookah is shallow water repair and maintenance equipment and is not truly a piece of sport diving gear. At least not the way I dive. That leaves you with SCUBA. If you are a SCUBA diver you will have to own tanks if you want to dive in remote areas. You either own a few and dive ‘til they’re empty or own a bunch and put up with the weight and stowage issues. If you are in remote areas for extended periods and cannot imagine being in such places without being able to dive (that would be me) then you will need a compressor. If you put a compressor on your boat see “my rant” above.

[jlcnuke]

Originally Posted by Nani Kai

Before answering your question permit me this mini-rant: Unless you are a knowledgeable, experienced high pressure breathing air engineer/mechanic, you are risking your life and the lives of those on your boat if you try to cobble together a compressor system from spare parts. It is nothing like working on the compressor you used to put finishing nails into that bookcase you built. High pressure air can kill or maim you in a nano second if it becomes un-contained and that is what it desperately wants to do. (To become un-contained, not to kill you, but the effect is the same). A friend once had his arm ripped open from wrist to elbow when a metal wrapped regulator hose let go while he was servicing it. And this was only 120psi intermediate pressure coming from the first stage. Breathing air contaminated with carbon monoxide or carbon dioxide can kill you. Oil contaminated air can cause your mouth to froth, also killing you. A high pressure air filter canister blew up at a dive shop where I once worked and it sprayed the whole compressor room with shrapnel and moved a wall off its foundation. Just don't understand why folks want to put their lives at needless risk to save a few bucks. Spend the money, stay alive. Okay, rant is over.

The question of diving with auxiliary air off your own boat always comes down to two choices: surface supplied or SCUBA. Recreational surface supplied is either hookah or SNUBA. SNUBA involves floating a tank over your head and breathing from a long hose so essentially it’s the same as SCUBA as far as having to refill tanks. Hookah, as noted, has depth limitations due to the pressure and volume restrictions of typical rigs. There’s also the noise issue if you’re diving in an anchorage with other boats around. You’re also restricted in your ability to penetrate wrecks, tunnels and overhangs and run into challenges with snagging the hose, especially while night diving or in limited visibility. It’s also much more challenging to assist your diving buddy in an emergency if one or both of you are on hookah. In my experience hookah is shallow water repair and maintenance equipment and is not truly a piece of sport diving gear. At least not the way I dive. That leaves you with SCUBA. If you are a SCUBA diver you will have to own tanks if you want to dive in remote areas. You either own a few and dive ‘til they’re empty or own a bunch and put up with the weight and stowage issues. If you are in remote areas for extended periods and cannot imagine being in such places without being able to dive (that would be me) then you will need a compressor. If you put a compressor on your boat see “my rant” above.

What compressor setup did you go with?

[Maka]

If you are wanting to fill tanks, be sure you are PADI certified 1st.

Hookah is more than adequate for most Sailboat needs. Cleaning and inspecting hull below waterline, and checking anchor. Basic reef diving.
IMHO.