Current options for moderate duty scuba compressor?

[PBcatfish]

I had accidentally started to hijack another thread with questions about a Coltri MCH-6 that another board member had recently purchased. Rather than continue to drag his thread off topic, I decided to start this thread, to discuss the current options for those who are considering buying a personal scuba compressor for moderate duty use. Commercial duty scuba shop compressors are a different conversation.

Tracy had been chiming in on the other thread with advice & opinions that seemed well founded. Hopefully I will see some of those responses here as well.

At this time, my biggest question is in regards to the benefit of a 4 stage compressor compared to a 3 stage. I’m still getting my head around that one. Other major factors I’m considering include maximum pressure, fill rate, longevity, availability, available support, and cost to run.

The Coltri MCH-6 seems popular, and seems to show up under some other brand names like Maxair 35. They are stocked in the US, said to be made in Italy, and parts availability seems to be good. People like Tracy, have noted that they are not as well constructed as other brands like Bauer and Mako. Favorable reports have come in from Cathal. Motor run capacitors seem to be the most common point of failure.

I’m basically looking for something that has 4,500psi capacity for occasional use & will fill an AL80 to 3,000psi in under a half hour.

Compressors I have considered include:

Coltri MCH-3 – 3 stage, 110vac, too slow

Coltri MCH-4 – also too slow

Coltri MCH-6 – seems popular, currently available, around $3k, good for 4,500psi, probably need to change filter cartridges every 10 hours or 20 tanks filled, 4 stage head, opposing cylinder design looks like it should be efficient, build quality has been questioned by some, said to be made in Italy, but a Chinese knock off shows up on Ali Express for about half the price, some have reported good service life, everyone seems to agree that this is not a constant duty machine.

Coltri Icon - not much info yet, is this an updated MCH-6? Might it be the Chinese knockoff?

Alkin W-31 – Currently stocked in NJ, priced around $4k, said to be made in turkey, seems closer to a constant duty machine, 3 stage, 4,500psi capable, W shaped head design is a non-opposing reciprocating type that does not look to be efficient, the vertical configuration comes on wheels & would probably roll around my shop for easy storage, filter cartridges are about $50 & filter refill kits are about half of that, weighs more than other units in this capacity range.

Bauer Jr II – about $5k, about the same capacity as the last 2, said to be German made, I haven’t checked availability yet, parts support in the US is said to be good, 3 stage unit, build quality said to be good.

Thoughts?

Opinions?

Experiences?

Good Used equipment you want to sell?

 

[VikingDives]

I bought an MCH-6 and regretted it. After 25 hours of use, pressure was backing up in the third stage. Contacted coltri and ended up sending it back to nuvair via fedex.

FedEx was kind enough to loose the compressor, then pay me for it.

You probably won't have to ship one back for warranty work, but know that if you do, it's going to go to California. 80 lbs on a pallet is about 1000 dollars cross country shipping...
I ended up building a box to ship it in, so it was only about 150 dollars to ship.

I'm sure there are plenty of folks that are able to do repairs in FL, so that might not be an issue for you.

All that said, get a Bauer Junior. You'll pay more, but they are higher quality, everyone services them, you can run one from 110v and get decent performance. Plus you don't have to worry about getting exhaust sucked up into your tanks.

If you decide to get the coltri, get auto shutdown etc and make sure you order from Nuvair.com. They are the only authorized dealer in the US, and if you need warranty work, they aren't going to do it if you bought it from scuba.com or someplace like that.

 

[tbone1004]

ok so first thing

This is not like a truck where there is light, medium, and heavy duty. The compressors are rated based on a duty cycle which is their ability to run continuously. If you are filling banks, you need a continuous duty compressor. That doesn't necessarily mean it's a big compressor, but it must be rated for continuous duty if you are going to fill banks with it. If you are going to fill banks which I assume you are based on your 4500psi comment, then you need a continuous duty compressor. A good rule of thumb is that anything without auto-drains is probably not designed for continuous duty since the thinking is that you won't be walking away from the compressor for any length of time or leaving it running for any length of time. A 5cfm compressor takes about 15mins to fill an AL80 which is about the time you're supposed to bleed the system so when you stop the compressor to change tanks you will blow down the drains. Any modern pump designed to run longer than that is probably going to have an auto-drain system as standard.

Number of stages is important for final pressure and 4-stage really isn't that important for anything under 4500psi as the compression ratios are balanced. The 4-stage blocks are needed to hit 6k, and some of the real high volume lower pressure blocks are 4-stage, but I wouldn't prioritize a 4-stage block personally.

contact @iowacavediver who is up in Jax and keeps tabs on compressors in the area, you'll probably want to buy one used.

 

[PBcatfish]

ok so first thing

This is not like a truck where there is light, medium, and heavy duty. The compressors are rated based on a duty cycle which is their ability to run continuously. If you are filling banks, you need a continuous duty compressor. That doesn't necessarily mean it's a big compressor, but it must be rated for continuous duty if you are going to fill banks with it. If you are going to fill banks which I assume you are based on your 4500psi comment, then you need a continuous duty compressor. A good rule of thumb is that anything without auto-drains is probably not designed for continuous duty since the thinking is that you won't be walking away from the compressor for any length of time or leaving it running for any length of time. A 5cfm compressor takes about 15mins to fill an AL80 which is about the time you're supposed to bleed the system so when you stop the compressor to change tanks you will blow down the drains. Any modern pump designed to run longer than that is probably going to have an auto-drain system as standard.

Number of stages is important for final pressure and 4-stage really isn't that important for anything under 4500psi as the compression ratios are balanced. The 4-stage blocks are needed to hit 6k, and some of the real high volume lower pressure blocks are 4-stage, but I wouldn't prioritize a 4-stage block personally.

contact @iowacavediver who is up in Jax and keeps tabs on compressors in the area, you'll probably want to buy one used.

Thank you Tbone, as usual, you are a wealth of good information.

My need for 4,500psi is only a single little tank that is slightly less than 2 liter capacity. I would be filling that maybe 1 or 2 times per week. Unfortunately, that is the biggest reason why I want to buy some kind of compressor. I have a hard time finding a local shop that has their bank above 3,600psi & I really need the little guy to be filled to more than 4k. That little tank doesn't need breathing quality air, but everything else I have does.

 

[PBcatfish]

...

If you decide to get the coltri, get auto shutdown etc and make sure you order from Nuvair.com. They are the only authorized dealer in the US, and if you need warranty work, they aren't going to do it if you bought it from scuba.com or someplace like that.

I spoke to the guys at Nuvair the other day. At first I kind of blew them off because the price they quoted me was many hundreds of dollars higher than another price I had seen on line. When I commented on that, his reply was that - yea, that's going to be a machine shipped from Spain & if you need to send it back, the freight charge is going to be high. Sure enough, when I looked at the other source more carefully, they were based in Spain. The guy at Nuvair sounded like he knew what he was talking about when it came to the product itself too. If I do go with a new Coltri, it would either be from them, or a local shop if I can find a local shop that sells them. After sales service does seem to be a concern with a scuba compressor.

 

[tbone1004]

Thank you Tbone, as usual, you are a wealth of good information.

My need for 4,500psi is only a single little tank that is slightly less than 2 liter capacity. I would be filling that maybe 1 or 2 times per week. Unfortunately, that is the biggest reason why I want to buy some kind of compressor. I have a hard time finding a local shop that has their bank above 3,600psi & I really need the little guy to be filled to more than 4k. That little tank doesn't need breathing quality air, but everything else I have does.

so you mention moderate duty but you never mention the actual duty that you expect the compressor to run. Filling 2L bottles is not anything that the compressor is going to care about, and the smaller pumps are capable of filling a lot of tanks, just not a lot of tanks at the same time.

Can you define your actual filling process in more detail in terms of what kind of tanks and how many of them are filled at one time?

 

[PBcatfish]

so you mention moderate duty but you never mention the actual duty that you expect the compressor to run. Filling 2L bottles is not anything that the compressor is going to care about, and the smaller pumps are capable of filling a lot of tanks, just not a lot of tanks at the same time.

Can you define your actual filling process in more detail in terms of what kind of tanks and how many of them are filled at one time?

My usage would mostly be filing 80cf AL tanks @ 3,000psi, Some LP steel 72s, Occasionally a couple of HP120s @ 3500psi and occasionally a 2L 4,500psi tank for non breathing use. I would not expect to do more than 4 fills in a single day ever & I would probably expect to average 4-6 fills per week. Some day, I may do some partial pressure blending, but that is not likely in the near future. I need to buy some kind of compressor because I can't find any place locally to put much more than 3,600psi in that little 2L tank & I really need it up over 4k. I could get a crappy little Hang Seng for the little tank (of non breathing air) but blowing $400-500 on that seems silly if I could put the money towards something that would also fill my dive tanks.


I have an old Bauer Utilis (late 1990s) that is probably too far gone to save. It came off of a yacht and was given to me. The hour meter shows over 4k, The PO filter housing is frozen shut to the point where Kroil & a pipe wrench can't get it apart (and it's probably past its expiration date anyway). The electric motor needs to be rewound. When I spin the compressor by hand, it does not seem to build pressure. Quite frankly, I see very little there to salvage. This has me looking for another option.

 

[tbone1004]

@PBcatfish that's light duty use! I would look at getting the Bauer if you can swing it financially for a long term investment.
Consider the E1 which while slower to fill *would be about 30mins to fill an AL80 from empty*, it does it at a much lower RPM so it will be quieter, but more importantly it runs on 115vac and doesn't need a dryer plug in your garage. If you go that route though you may want to buy a separate motor starter depending on what else is in the circuit.

 

[Angelo Farina]

I did personally know mr. Coltri, ad his long history about developing and building compressors. At the beginning they were really terrible, always problems. I owned two of them, and both self-destroyed after less than 100 filling cycles. But it was in the eighties... Then they steadily improved the products, changed materials, etc, and nowadays an MCH-6 is a reasonable machine for light use.
Said that, after my second one failed I did buy a very old Bristol three-stages, rebranded Technisub here in Italy, which did work flawless for years.
But when I became a professional instructor, I did learn what is the only serious option: Bauer. They cost more, but you will never regret your choice. These machines are almost indestructible, and are designed for easily maintenance and rebuilding.
If you have money constraints (as me) search for a used one.

 

[PBcatfish]

This is being discussed on another thread - Scuba Diving Compressor - Mantus Marine

There is not a lot of info listed. Since it runs off 110vac & draws less than 15 amps, I can't see it putting out much more than 1.5 or maybe 2cfm, which is slower than I am looking for. The part that catches my attention, is that it's water cooled. That makes me think that the duty cycle might be good. The $2,500ish price tag has my attention too. I'm wondering if this might be based on the MCH3.