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What does it take to make a Scuba Compressor a CNG Compressor?

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  • What does it take to make a Scuba Compressor a CNG Compressor?

    I'm not sure in the wisdom of this, but I see cowboy of this parish has done this and there's a great video on youtube, see:

    http://www.youtube.com/watch?v=kzSiL...v5uHJHwtT3TPKL

    Only the thing is, hardly a week goes by when i don't see an ex government surplus Bauer or similar going for next to nothing on Ebay. Our fire stations seem to have them, and get rid of them with 300hrs on them.

    What is involved in a 'proper' and 'safe' conversion? If I had to spend another USD1500 I'm sure I'd have a stonker doing 10GGE/hr or greater, and for not that much.
    Last edited by BritCNGUser; 05-14-2014, 10:55 AM.

  • #2
    Re: What does it take to make a Scuba Compressor a CNG Compressor?

    I have a friend that has been converting high presuer air compressors stating back in the early 90's. Some work better than others & some need less that work to convert than others. These will always be low inlet pressuer compressors. The most important things to know are all in NFP 52. Its all about everything be intrinsically safe, all electrical connections, switches, motor, & motor controls. If is a natural gas drive compressor the start charging & ignition system needs to be intrinsically safe also. The compressor must also be tight, in other words no leaks from any seals or relive valves. Some compressors allow gas to escape from the crankcase seal, this is a no-no. In So. Ca. you can canot have the blowdowns go to atmosphere. I am sure there are a few things that I missed somebody will point them out.

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    • #3
      Re: What does it take to make a Scuba Compressor a CNG Compressor?

      I can see I would need a unit I can seal the crankcase, but generally I should have thought these are pretty simple mechanical issues. The 'sparks' side would need to be in separate isolated enclosure, and is likely the more difficult bit, but I see no issue. I'd liek to see the unit featured in that video close-up. Someone else must have done this, [where is a cowboy when you want one?] so now I wonder which units make a good starting point.

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      • #4
        Re: What does it take to make a Scuba Compressor a CNG Compressor?

        Are you giving up on the coltri or just trying to set up a backup compressor?
        From what I have gathered, the real work is in making it foolproof and absolutely safe. It sounds like different regions have different requirements. In a pinch I suspect you could get a scuba compressor to compress natural gas in as little as an hour or so but it wouldn't meet any safety standards.
        The fuelmaker compressor safety features can be a nuisance when they act up but it is nice to know your compressor will shut off if it overheats, if the gas pressure drops to low, if the pressure doesn't rise fast enough, etc. It seems like most scuba compressors have a skilled operator nearby anytime it is running while it seems like most CNG compressors are left to run unattended for hours on end. Setting the compressor up with failsafes to shut it down automatically would be a big concern for me.
        Karl

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        • #5
          Re: What does it take to make a Scuba Compressor a CNG Compressor?

          On a Corkin skid there are safeties for both high & low inlet pressure, oil pressure, oil flow, high discharge pressure, high discharge temp, & relief valve failure. There can be more safeties if the controls are PLC.

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          • #6
            Re: What does it take to make a Scuba Compressor a CNG Compressor?

            Karl: Not giving up on the Coltri although I am having a hard time with it. More because of the time it takes to get parts than anything, and the fact that it has no interstage gauges out of the box, it is still far from 'right'.
            No the reason I ask is that, yes i'd like a back-up and my brother has his eye on one, and I'm thinking it can be done cheaper and better by an military-surplus or fire-station scuba type.
            I can see i could have oen of those things pumping CNG inside half-hour, but best not, I may not be the world's best looking bloke but done like that I could find myself looking a fair bit uglier.

            My Coltri has pressure switches and safety valves at every stage, but comparing it to the Coltri scuba versions not much else on top as far as I can see. I have not got my head around what goes on in the 'sparks' enclosure, and the AC single phase motor I suspect is made to be ignition proof, but again, is it dfferent from the scuba, it looks not.

            As for high & low inlet pressure, oil pressure, oil flow, high discharge pressure, high discharge temp, & relief valve failure, it only only has half from that list.

            The fella in taht video is using a Bauer K15. They're common [*] and pretty bullet-proof so I'm tempted.

            A government surplus Lot 4231 - "Compressor - High pressure for the use of, parts various" would do me 'lavverly'.
            Last edited by CNGLO; 05-17-2014, 11:06 PM. Reason: TOS language violation

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            • #7
              Re: What does it take to make a Scuba Compressor a CNG Compressor?

              Cngmike- as far as not venting gas to atmosphere how does the phill get around this? The hoses I see on the fill only has a single hose and no return line, when the valve is switched from open to close after the vehicle is full the gas has to go somewhere

              Brit- send that gentleman a instant message on youtube and simply ask him what he did to convert it to safely compress natural gas...im sure he wouldn't mind sharing

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              • #8
                Re: What does it take to make a Scuba Compressor a CNG Compressor?

                The Phill and Q2 use the low pressure gas (1/4 to 1/2 psi inlet) as cooling, flooding the motor and control modules with gas and feeding that gas to the compressor module.
                When the tank is full or the stop button is pushed the gas is drawn back from the hose into the motor and control module to relieve the pressure at the connection. (provided the vehicle receptacle check valve is working properly)
                Hose length and volume contained is calculated to the volume of the modules so no more than 29.5 psi is developed inside the modules. Any pressure over the 29.5 psi would be vented. 29.5 or less psi will allow disconnect of the nozzle from the vehicle. This is why there is a maximum allowable hose length on the Q2 and only one hose available (length/style) for the Phill.
                It is all in the engineering design of the products and part of why these compressors are certified as appliances by the AGA.

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                • #9
                  Re: What does it take to make a Scuba Compressor a CNG Compressor?

                  If your coltri has adequate failsafes to allow you to let it run unattended I would just source the components and duplicate it on your soon to be acquired scuba compressor.


                  I am sure you could set up interstage pressure switches and an inlet pressure switch to shut it down should the gas pressure drop or a cylinder fail. Temperature sensors could be wired in as well. You would need a solenoid valve to shut off the inlet gas in the event your failsafes shut things down. I could picture doing this with basic electromechanical sensors on a low voltage circuit controlling a master relay which would cut all power to the system.

                  The more complicated one to figure out is how to shut the compressor down should the fill hose develop a leak. The Fuelmaker senses how fast the pressure in the hose rises and shuts down if it fails to rise.
                  I cant picture doing this with electro mechanical sensors and imagine you would have to go with a more sophisticated electronic system.

                  I hear reference to an "arduino" microcontroller that is widely used by hobbyists to design custom electronic circuits. I haven't a clue but it could be worth looking into and then you could use pressure transducers for all the pressure measurements.

                  Keep us posted on what you come up with.

                  Karl

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                  • #10
                    Re: What does it take to make a Scuba Compressor a CNG Compressor?

                    As I cast my eye around hte Coltri, within the noise cabinet per se there's not much to see. 2 x pressure switches, and safety valves that vent to atmosphere. The Coltri is designed to sit outside whereas I understand the Phill & FM et al can be put in your garage. As I said earlier the Coltri hides all its 'sparks' in a gas-tight enclsure, but have to say I'm not seeing how that makes it so differnet to its scuba-ony sister products. But I think I should do some more digging. I still ahve not got my head around how the AC motor will differ, if at all. I can see why you might need temperature compensation in the US, somethign out of he box a Coltri does not have. I believe Greenline fit this and sump heaters too.

                    You lot have soem barking-mad weather compared to us, vast extremes of hot and cold, whereas when we complain about the cold we're being namby-pamby, it is never proper cold. I was in NY one proper, properly cold winter, jeeeeez. So you might need temp compenation control etc.
                    Last edited by BritCNGUser; 05-21-2014, 03:24 AM.

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                    • #11
                      Re: What does it take to make a Scuba Compressor a CNG Compressor?

                      This particular thread is fascinating to me in that I have had a half dozen people purchase basic scuba compressors for conversion to CNG and I really don't know for sure what they are adding or changing.

                      The most basic one I supplied was the little 3.8 CFM gasoline driven MCH6 and that guy even changed the engine over to CNG as well. I had another customer that purchased a 7 CFM compressor in an open frame that was electric with automatic features (condensate drains, high pressure shutdown, high temperature shutdown) and he told me that he was adding on a couple of other safeties as well.

                      Since I sold these as scuba compressors, I asked them to just send me a note saying that they understand that what they have purchased was a "Project" compressor and it would be up to them to make it acceptable for local regulations.

                      You guys are pretty ingenious!
                      Ray Contreras
                      CompressorStuff.com

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                      • #12
                        Re: What does it take to make a Scuba Compressor a CNG Compressor?

                        Ray,

                        What do you think about the lack of customer support some of us have experienced with coltri america
                        for purchasing "illegal" compressors from ebay or other sources?

                        Personally I dont think any of us set out to piss off coltri america, but its been clear that if we need parts or service
                        we are not to seek any help from coltri

                        Ive had much more customer support from you and other forum members then I have from coltri america

                        Comment


                        • #13
                          Re: What does it take to make a Scuba Compressor a CNG Compressor?

                          I guess I can understand. CNG was not part of the ColtriAmericas (CA) plan when it was started a few years ago and what hit the US was outside of the normal supply chain. Because it has the Coltri name on it, people push for the type of support usually given by the dealer network and, because there is no network, CA has had demands put on them even though they have not made a penny on the sales.

                          Things are changing, though. Maybe not with CA in FL, but with the West Coast distribution center, they are going to be bringing in more CNG supplies (parts and compressors) for those of us that are trying to help. However, in order for me to purchase a CNG compressor, I have to provide a statement saying that I will only sell to customers that are interested in doing the conversions needed to bring it up to US specs. I also have to get a statement from the customer saying the same thing. I don't know if anyone will be willing to sign something like that, but at least the parts will be more available for Coltri customers.

                          We'll see what happens.
                          Ray Contreras
                          CompressorStuff.com

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                          • #14
                            Re: What does it take to make a Scuba Compressor a CNG Compressor?

                            It seems like a tough pill to swallow, buy a "USA" spec machine for 13,000$
                            Or a "out of network" machine for 7500$

                            Personally, I am very happy with my "out of network" machine both on price and performance

                            Comment


                            • #15
                              Re: What does it take to make a Scuba Compressor a CNG Compressor?

                              Originally posted by trdscfjc View Post
                              Ray,

                              What do you think about the lack of customer support some of us have experienced with coltri america
                              for purchasing "illegal" compressors from ebay or other sources?

                              Personally I dont think any of us set out to piss off coltri america, but its been clear that if we need parts or service
                              we are not to seek any help from coltri

                              Ive had much more customer support from you and other forum members then I have from coltri america

                              What kind of customer support are they not providing? Technical questions, parts, ???

                              I have an ancient bauer compressor that I got excellent technical input on from a scuba forum. I would figure the scuba forums would be a good source of technical info on Coltris as well??? I got aftermarket parts from Lawrence Factor for the bauer and at this point I find the internet forum and aftermarket suppliers eliminate the need for customer support from the factory.

                              Comment

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