My initial thoughts on my new compressor

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

PBcatfish

Contributor
Messages
1,381
Reaction score
1,431
Location
Florida
# of dives
500 - 999
Thank you again. Those are good points to consider.

The used compressors I have seen so far have carried price tags that were more than half of new. Condition did not seem to warrant that price from casual observation.

I have a pretty good mechanical background in general, but I do not have much experience with high pressure compressors, so I am not in a good position to judge the condition of a used one. I just don't know what to look for. I don't know the common points of failure & how to identify their condition. That has me thinking that for me, new might be less risky.

If 3 stage is OK, then maybe an Alkin W-31 might be an option? The price seems right. Consumables are priced right. The vertical version would be easy to move around in my shop. Most other things I have from Turkey were well made. They are said to be stocked in a warehouse in NJ.

Or maybe I should just keep looking for a better used machine?

I have some more thinking to do.
 

Tracy

Tech Instructor / Captain
ScubaBoard Supporter
Scuba Instructor
Messages
1,289
Reaction score
1,415
Location
Livonia, MI
# of dives
1000 - 2499
Thank you again. Those are good points to consider.

The used compressors I have seen so far have carried price tags that were more than half of new. Condition did not seem to warrant that price from casual observation.

I have a pretty good mechanical background in general, but I do not have much experience with high pressure compressors, so I am not in a good position to judge the condition of a used one. I just don't know what to look for. I don't know the common points of failure & how to identify their condition. That has me thinking that for me, new might be less risky.

If 3 stage is OK, then maybe an Alkin W-31 might be an option? The price seems right. Consumables are priced right. The vertical version would be easy to move around in my shop. Most other things I have from Turkey were well made. They are said to be stocked in a warehouse in NJ.

Or maybe I should just keep looking for a better used machine?

I have some more thinking to do.
I actually really like the Alkins so far. I haven't worked on any with high hours yet, but they seem to be a good quality product from the few I have seen.
Support is excellent, most parts are available to ship from NJ.
That said, Coltri support is also good, Nuvair is easy to deal with and also in country.
 

Cio

Contributor
Messages
120
Reaction score
99
Location
NJ
# of dives
100 - 199
Thank you for the reply.

I watched some service videos on the Coltri. The removable plate that housed the crank bearing attached to the block with a large pilot diameter & a flange bolt pattern. I've had good luck with that configuration in a large number of gear boxes. I saw roller bearings in the #4 cylinder con rod, where it goes to the crank. Is the bushing around the wrist pin? I didn't watch the videos for cylinders 1-3, so I don't know what they had for bushings or bearings. Parts seem available, including blocks. Top end rebuilds are scheduled at 500 hours, so I was expecting it to be only moderate duty.

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.

My interest in the Coltri began because they are a 4 stage pump, rather than a 3 stage, and the price looks good. I now have found that availability is also good. My mind is far from made up & the information you provided helps me. Again, thank you for that.

Do you have an opinion on the value of a 4 stage compressor compared to a 3 stage? Is that worth chasing? Or is the heat dissipation thing not as bad as I am thinking it might be?

4K is not that many hours for a Bauer. If you do a full rebuild on that, you will have a better compressor for less money than a new coltri.

Coltri is a hobbyist compressor, Bauer is a professional use compressor. You don't need professional use so the coltri would generally be fine, but since you have a unit on hand, a rebuild will leave you with pro version unit for less money.
 

PBcatfish

Contributor
Messages
1,381
Reaction score
1,431
Location
Florida
# of dives
500 - 999
4K is not that many hours for a Bauer. If you do a full rebuild on that, you will have a better compressor for less money than a new coltri.

Coltri is a hobbyist compressor, Bauer is a professional use compressor. You don't need professional use so the coltri would generally be fine, but since you have a unit on hand, a rebuild will leave you with pro version unit for less money.
Thank you for the suggestion.

I would be looking at a rebuild on the compressor, a rewind or replacement on the motor & a replacement of the entire filter system. At that point, I am probably close to the price of buying new, if not a little over it.

Rather than continue hijacking this thread, I have started a new discussion about my needs here- Current options for moderate duty scuba compressor?
 

SurfLung

Contributor
Messages
175
Reaction score
191
Location
Central Minnesota
# of dives
200 - 499
I have an Aerotechnica Coltri MCH-6 compressor that was made back in the 1980s. I bought it 3-4 years ago from a guy in north central Michigan... Apparently it had been used for filling tanks on a boat. But it had not been used for years. I paid only $250 for it. It DID need some fixing... The moisture condenser was actually broken inside. Maybe that's why they quit using it. I ended up fabricating a better internal condenser structure after studying some other condensers and that has worked great. The motor needed the gas tank and carb cleaned, plus new diaphragms for the fuel pump. That too... Now works great.

It's interesting that back in the '80s filtration and air quality was (apparently) not as critical as today. The air intake was a filter on top of the compressor right next to the gas engine... Apparently acceptable as long as it was upwind of the exhaust. The filter tube was filled with nothing more than activated charcoal. And I mentioned the condenser. I have upgraded all three of those aspects, PLUS I have a Back Pressure Regulator that works similar to a PMV to keep the filtering system at 99 % efficiency like modern compressor set-ups.

The MCH-6 manual states that it is intended to fill only 1-2 tanks before you should turn it off and let it cool down. That being said, we shouldn't fault it if it has problems when you run the heck out of it for long and hot periods of time. Here's a video of my filling tanks with my little Aero MCH-6...


Finally, I had some correspondence with Carlo Coltri and he was quite angry at the Chinese company that has put out the copies of the Coltri MCH-6. In response, Coltri has come out with their new "Icon" compressors to replace the MCH-6... I think it has a new 3 stage compressor head that gives 40% more performance than the MCH-6. Here's a photo and link...
2022-03-05-GP-140[1].jpg

New Coltri Pumping Group
 
https://www.shearwater.com/products/peregrine/

Top Bottom