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Here's a thing, why don't the scuba boys post queries on running their compressors?

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  • Here's a thing, why don't the scuba boys post queries on running their compressors?

    Here's a thing, why don't the scuba boys post info on running their compressors? This mystifies me. I mean, there's a thousand scuba compressors to each CNG jobby, and no doubt an equal heap of problems keeping them going. Yet go on a Scuba forum, and you'll not see any mention of the problems they must get. More so when you consider that most of us, Joe excepted , don't go breathing from ours.

    Fact is, if you've a small scuba compressor, and you need to get your head around keeping it running, you''ll not find much info.
    Dare I say this, but here's the truth...

    This here CNG forum, and a few videos by Coltri on Youtube, is about your best shot.

    But why?
    Last edited by BritCNGUser; 03-11-2018, 08:14 PM.

  • #2
    A couple things different with Scuba and NGV is inlet pressure and inerts from natural gas. A scuba unit runs off ambient presser. When you start adding inlet presser the rod load goes up and crates heat on all the internal parts. Over the years I have watched well known compressor companies come and go from the CNG world, they just can't make the jump. with Arial compressor, a well known oil patch compressor company and a leader in the CNG world, they use different materials in their rings for natural gas. another difference is the way you operate a scuba compressor compared to a CNG compressor. with a scuba compressor you have shorter run & rebuild cycles.


    • #3
      I see your point, I don't suppose too many scuba blokes run five hours solid, and if they do, not every time they switch on. Thinking about it, Coltri's diddy MCH6 model is not continuous-duty, For the job intended, one diver's worth of air, that's not really an issue. Those pumps get an easier life.

      But whatever the pump, they must wear and go wonky all the same. Judging by the number of tired out scuba pumps on eBay, it seems the simple answer is that in the scuba world, they just don't bother to fix them. Pumps get left to pros, which, and who can blame them?, aren't about to discuss what they know on any forum.
      Last edited by BritCNGUser; 03-12-2018, 02:42 AM.


      • #4
        I actually spend a TON of time o the scuba boards instructing Coltri owners how to troubleshoot and fix their stuff. There are just so many compressor owners, that most problems are already covered in the older threads and you can find what you need before posting a question. There is a bit of machismo in scuba and nobody wants to look ignorant and get beat up for the questions.
        Ray Contreras


        • #5
          OK, I stand corrected. Only I've done a fair bit of searching and I'm not really seeing the kind of 'hands dirty' tales of woe and success that lives on here. As I said, there must be thousands more scuba blokes and their pumps. Ray, I suspect if you were waiting to sell parts solely to us CNG blokes you'd be in hte soup-kitchen. Yet relative to their number, they seem very quiet about fixing their pumps.

          You say: " There is a bit of machismo in scuba" so I'm guessing it's not unlike the 'psuedo-tech' surrounding the 'I was never confused' lycra-clad cycling-brigade we get here in the UK. They tend to mince about, spending thousands to save less weight than they could by taking a p*ss.

          On here, I don't know how many lurk around us, but we've got less that half a dozen true heavy-weight contributors. I've yet to find a detailed thread fixing Coltri, Bauers etc elsewhere.Certainly nothing near as detailed as the very exceptional stuff our very own trdscfjc has scribed, or even my own more lack-lustre stuff - at least I try...
          Yes, seems I stand corrected, clearly I've not been looking in the right places, these days I've got my head around most of it, nonetheless I'd like to read these threads and particularly your posts. Where do we look?
          Last edited by BritCNGUser; 03-21-2018, 03:58 AM.


          • #6
            Probably the most active board is the scubaboard Beware of the members. There are quite a few that don't welcome CNG folks and others that are just plain butt heads. You will find that quite a few treat their compressor brands as if they were religions and anyone talking bad about them are INFIDELS!!
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            Ray Contreras


            • #7
              Thanks Ray,

              I've found which is the Coltri section of their site.

              It does seem that you can get yourself into trouble suggesting buying anything that is not a Bauer, or worse, It would appear your blasphemy was to suggest running redundancy, in comfortably overspec'd kit, of whichever manufacturer is best supported on their respective far-flung island. All to keep air running for the season in a 5-Star Hotel set-up.

              I mean, how very dare you?

              It's clear, you don't know a thing... so whilst I have your ear, I see the MCH13 is being made NLA. With our trusty MCH5 being the same crankcase that doesn't bode well. Or are they keeping the MCH16
              Last edited by BritCNGUser; 03-24-2018, 12:35 PM.


              • #8
                The MCH13 is actually the 16 with smaller first and second stage pistons. So now, they are going to just have the 16 and run it at different speeds for different capacities. Basically, that means that the MCH13 price if going to go up a few hundred bucks.

                Ray Contreras


                • #9
                  Ah, interesting. Thanks. Coltri seem to do much the same with the MCH5 & 3. In fact I now run a smaller diam. motor-pulley on a MCH5 to make it a MCH3, simply because my supply wasn't always matching the demands of the MCH5. (that was isolated as a major source of the woes with my pump). I was warned by Coltri techs. not to lower to any less than 1000 rpm . Lubrication at lower speeds being 'splash' might be an issue. I'd be interested to see what rpm they design a MCH16 to get its output to match an MCH13.

                  Spent time browsing your posts and others. I was hoping to learn a bit more. Broadly speaking, the 'scuba boyz' don't seem to get to the nitty-gritty of faulting and sorting their pumps, which is a shame.