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SurfLung
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Aerotecnica Coltri MCH-6

Tue Jul 09, 2019 9:52 am

Aero Tecnica Coltri MCH-6
Image
- I've had my eye out for one of these and when I found it, I had to buy it. The 4 stage MCH-6 has been sold under different names and even private labeled to sell by other companies. One of the older renditions was the Olmeva 6000. This one of mine is an Aerotecnica Coltri MCH-6. The current model is a Coltri Sub MCH-6. Which is also sold under the names of MaxAir 35, Nuvair MCH-6, and others.
- This is my first gasoline engine powered compressor. It's also my first oil lubricated compressor (I have an electric powered RIX SA3 oil-less compressor). Anyway, I have some questions and concerns:

1. It appears to have been used quite a fair amount but has never had an extended air intake hose like other gasoline engine powered compressors. I have since seen other gas powered units pictured this way. The latest Coltri Sub operators manual talks about "positioning" the compressor for best ventilation. They do offer a remote air intake hose for situations where the compressor cannot be positioned to avoid the exhaust fumes. The guy I bought the "Aero" from says he and his buddies used it on their boat when diving in Lake Michigan. So, how common is it to use the gas powered compressor without an extension hose on the air intake?

2. The filter cartridge on this Aero was packed with nothing but charcoal. I replaced it with a Lawrence Factor pre-packed filter that is 2/3rds 13X Sieve for moisture absorption and the remaining space has hopcalite for CO and Charcoal for tastes and smells.

3. I positioned the Aero with the intake filter into the wind and the engine exhaust flowing downwind. I then pumped and emptied a tank 3 times. Drained the moisture accumulator and the filter spigots. And then checked the filter test strip. It was still solid blue. I then pumped the tank up once again and took it diving for about 45 minutes. I smelled nothing and tasted nothing. Seemed fine.

Comments... ?
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Re: Aerotecnica Coltri MCH-6

Tue Jul 09, 2019 11:18 am

First Run

- The engine originally had some trouble getting fuel due to a rusted up and crudded up gas tank. This is a first run test of the engine after cleanup of the gas tank and fuel screens. Also first test of the compressor. The moisture accumulator and filter drains were spitting out quite a bit of moisture and foamy oil-gunk. I test filled this old Scuba cylinder at 2.9 cfm the first try. Later as the compressor began to work itself in, I filled several times at up to 3.5 cfm. That's a good-n-fast fill rate and the scuba cylinder was HOT when full.
- I changed the oil. And after some more run-time, the drainage from the moisture accumulator has become less and less mucky. It is now spraying out a watery mist with a thin film of oil. The drainage from the filter spigot has become almost totally dry. All excellent results!
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Re: Aerotecnica Coltri MCH-6

Wed Jul 10, 2019 10:39 am

Replies to Questions/Concerns...

Remote Intake Hose - Not sure if I mentioned it but, My AERO did not come with a remote air intake hose. It's apparent that the previous owner used it without an extended hose. Then, I read the latest manual from Coltri Sub and it talks about "positioning" the compressor for adequate ventilation. The accessory "Remote Intake Hose" is only offered for situations where adequate ventilation cannot be achieved. I have never seen anyone operate a gas engine powered compressor without a Remote Intake Hose... But it got me wondering if it's okay to do it... Especially with my tendency to leave things original. Nobody offers a Remote Intake Hose kit... At least not on their webstores. Nuvair, MaxAir,... North Shore compressor, etc. On the other hand, the air filter that's on the AERO is also nearly impossible to find a new filter element for... So there's really no point in keeping it original. So I asked a friend about his MaxAir 35 and he said it came WITH the remote intake hose. He sent me a photo of the connection and it is nothing more than the internal mount for my intake filter, with the center drilled out and a hose clamped onto it. CRIPES! I've been running around looking for some clever plumbing solution. So, I will soon have a Remote Intake Hose to go along with my new BPR fill whip from Mr. 6000 PSI... And this little compressor will be ready for business!

Concerns About High RPMs - I've heard the arguments about these smaller compressors running at high RPMs. I've come to the conclusion that if they are designed for the RPM that you are running them at, and you do the proper and regular maintenance, they seem to give reliable service for YEARS.

Adequate Filteration - The single little filter tube had me concerned at first. But even more of a concern was the lack of a Back Pressure Regulator or PMV to keep the filter pressure at 1800 psi or higher and give the best efficiency to the filter. In addition, this little AERO came with a filter cartridge that had nothing but charcoal in it... No moisture absorbing 13X sieve. I'm actually making some major improvements by adding a back pressure regulator and using Filtertech see-thru filters with color changing test strips. These filters are 2/3rds 13X Sieve and the rest hopcolite (for CO conversion) and charcoal for tastes and smells. Furthermore, I can easily check the status of the filter... The top comes off easily and the filter pops up where I can lift it out and check the colored strip. Changing the filter is equally easy.
- Here's an interesting aside... On another compressor, I have a 4-tube filter array that came off an older version of the MCH-6... The Olmeva 6000... Uses the same filter tubes. But, it's much harder to get the filters out to check them. I have found that it is usually only the first filter that starts the test strip turning color. So maybe Aerotecnica figured to use a single filter tube and just make it a whole lot easier to check and change?
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Re: Aerotecnica Coltri MCH-6

Thu Jul 11, 2019 9:04 am

My MaxAir 35 has one of these installed on it. https://www.leisurepro.com/p-mxami/max- ... -indicator . Carbon Monoxide is a tasteless colorless gas, so you will not detect it by scent. This gadget has a piece of litmus paper which turns red if there is Carbon Monoxide in the system. There is a little glass port so that you can check it while the compressor is in operation.
My MaxAir came with a gas engine and an extended intake hose. I have converted it to 220 single phase. The compressor is rated for 2800 rpm. The 220 motor turns it over at 2400. I see that as a bonus!
I also installed windshield wiper hose on my condensate drains. When I blow the drains I can point them down wind so the oily watery stuff does not get sucked into the intake. I got my compressor used with 11 hours on it. It now has almost 170 hours on it and works great. Quite possibly the best scuba investment I've ever made.

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Re: Aerotecnica Coltri MCH-6

Thu Jul 11, 2019 9:42 am

If there is even a small breeze just position the compressor intake up wind of the engine exhaust.
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Re: Aerotecnica Coltri MCH-6

Fri Jul 12, 2019 10:08 am

Latest Developments...
1. My Briggs and Stratton engine is now running perfectly. As mentioned before, the gas tank was rusted and crudded up pretty bad inside. After cleaning the tank and intake screens, it started up and ran OK. After running more and more, it starts up real easy now. 1-2 pulls with the choke on gets it started and a quick push in of the choke and she takes off for as long as the fuel lasts. I think running fresh fuel thru it has probably dissolved the internal varnish deposits from the old gas. Lately I'm running premium gas with no ethanol or AVGAS... These can stand storage without going bad.
2. Made Up my Extended Intake Hose... What a relief! I can quit worrying about whether I should or shouldn't. I now have AT LEAST as good separation of exhaust and intake as other gas engine powered compressors. I put a brand new Solberg 8 cfm filter on it with 20 micron polyester filter media. Test sucked through it and there's literally no resistance. And of course I'll have it positioned upwind of the exhaust.
Image
3. Filtration Realities - I have a Back Pressure Regulator coming that will improve moisture condensation and filter efficiency. But right now this compressor goes through 13X sieve pretty fast. I have a Lawrence Factor cartridge in it that has 2/3rds 13X sieve and 1/3 Hopcolite and Charcoal. I think I have filled my 38 cf test tank 4-6 times on the filter and the indicator strip is already starting to turn pink. Hoping the BPR improves filter efficiency by a lot. The current Coltri manual says these filters should last 20-30 hours at 68-86 degrees Farenheit. On the other hand, this is a portable compressor... Designed for the convenience of filling scuba tanks at any remote location. I can certainly buy and bring more filters or cut costs by re-packing my own... If I end up using it extensively. As mentioned previously, the clear pre-pack filter with indicator strip is super easy to check and replace on the MCH-6.
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Re: Aerotecnica Coltri MCH-6

Wed Jul 17, 2019 1:01 am

swimjim wrote:
Thu Jul 11, 2019 9:04 am
My MaxAir 35 has one of these installed on it. https://www.leisurepro.com/p-mxami/max- ... -indicator . Carbon Monoxide is a tasteless colorless gas, so you will not detect it by scent. This gadget has a piece of litmus paper which turns red if there is Carbon Monoxide in the system. There is a little glass port so that you can check it while the compressor is in operation.
My MaxAir came with a gas engine and an extended intake hose. I have converted it to 220 single phase. The compressor is rated for 2800 rpm. The 220 motor turns it over at 2400. I see that as a bonus!
I also installed windshield wiper hose on my condensate drains. When I blow the drains I can point them down wind so the oily watery stuff does not get sucked into the intake. I got my compressor used with 11 hours on it. It now has almost 170 hours on it and works great. Quite possibly the best scuba investment I've ever made.

North Shore has it for $70
http://www.northshorecompressor.com/pro ... cator.html

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Re: Aerotecnica Coltri MCH-6

Mon Jul 22, 2019 11:32 am

Progress is Good...
- Here's a video of the AERO filling Twin 48 scuba tanks at a little over 3.2 cfm FAD. AS you can see, I got the remote intake hose and filter system up and running. My buddy Bill AntiqueDiver helped me with rigging a Vortex Generator to replace the missing one in the moisture separator. And, I now have a Back Pressure Regulator keeping the system at 1800 psi for better efficiency at Moisture condensation and filtering.
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Re: Aerotecnica Coltri MCH-6

Mon Jul 22, 2019 2:04 pm

Compressor is lookin' good Mr. Surflung! Did you take it on the last trip?
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Re: Aerotecnica Coltri MCH-6

Tue Jul 23, 2019 10:20 am

antique diver wrote:
Mon Jul 22, 2019 2:04 pm
Compressor is lookin' good Mr. Surflung! Did you take it on the last trip?
- Thanks to you Mr. Compressor Man... :)
- I didn't bring it on the trip because I wasn't quite ready... Wasn't sure if it would start reliably and wasn't sure if my filter would last long enough. Since I cleaned up everything in the fuel tank and carburetor, the engine has been starting and running on 1-2 pulls. But if I turned it off to switch tanks, I'd have a heck of a time getting the hot engine to start again. As for the filter life... Before we made up the vortex generator and added the back pressure regulator, the filters would barely last 4-6 tanks... And my last filter already had 2 tank fills on it.

So,
1. Last night, I replaced the diaphragm in the Briggs and Stratton fuel system... The old one was crispy. This made a difference. I filled three sets of twin tanks. Ran out of gas somewhere in the middle. Refueled. And the engine restarted easily with one pull.
2. Checked the blue strip in the filter and it is just beginning to turn pink on the lower end. This is after 8 tanks filled. So, moisture removal has improved by at least 100%.

Cost Per Fill - This is looking like I'll get about 10 fills per filter cartridge. It might end up being more but I'll go by that for now. These are the very best filters available with 13X Sieve for moisture, Hopcalite to convert any CO to CO2, and Charcoal to remove tastes and smells. Cost is $31 each in qty 5 or more. So I've got about $3 in filter costs per fill. I didn't measure how much gas I use per fill but I filled the tank possibly 2 times with the best gasoline available (avgas). Lets say 1 gallon of gas for 10 fills... About $4.50 per gallon... So, 45 cents of gas per fill. So, my fills are costing about $3.55 each... Not bad. Not bad at all. And like I say, the filter life may improve... This current filter started out when I didn't have my vortex generator and back pressure regulator systems fully installed.
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Re: Aerotecnica Coltri MCH-6

Mon Aug 05, 2019 3:25 pm

The Aero Worked Well...
- We took this compressor on our dive trip to Lake Ore-Be-Gone up in Gilbert, MN. We each brought our twin 38s and twin 50s and refilled them between dives. Boy, they got hot out in the sun. But the Aero pumped them up with clean dry air and we enjoyed 5 dives each. :D
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Re: Aerotecnica Coltri MCH-6

Mon Aug 19, 2019 11:27 am

A New Moisture Dissipator for my Aero...
- I removed the make-shift vortex generator from the Moisture separator tower and found it was heavily coated with gunky condensate. So I decided to take the Moisture separator tower apart and see what could be done. Fortunately, I have a nearly identical Olmeva separator tower on the filter array for my RIX compressor. So I took the bottom off that one apart to compare. Below you see the broken Aerotecnica dissipator on the right.
Image
- The original dissipator was a micro screen with the air inlet below it. The design allowed for a chamber below the screen and condensate tends to accumulate in that chamber. I think the gunky oil and water condensate clogged the screen so eventually it blew out of its mounting, breaking the mounting in the process. So now, the gunky condensate pools in the chamber above the inlet and just keeps shooting up and down and pooling without ever completely draining the condensate.
Image
- In contrast, the Olmeva dissipator vents the incoming air through small holes in a verticle tube... The holes are located above the condensate drain pool so they're not blowing air through it AND the condensate can settled and be drained more completely.
Image
- I replaced the broken microscreen dissipator with a home made dissipator along similar lines to the Olmeva dissipator. I used a concrete floor anchor just like the one Rich (50,001 Questions) came up with for replacing a dip tube on a tank valve. You can see how the slots will dissipate the incoming air above the condensate drain pool. This allows the condensate to pool unmolested at the bottom, and drain completely when the drain is opened.
Image
- I've used this now for a couple of tank fills at home and three fills at our most recent dive trip to Fortune Pond. It seems to be working VERY well. :)
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Re: Aerotecnica Coltri MCH-6

Thu Sep 12, 2019 12:45 pm

Here's the Latest Video...
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