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  • SCUBA Air Compressor?

    I’m thinking of buying and using a Scuba air compressor to pump natural gas. Breathing air compressors of the 5 HP size pump 3000 psi at about 3.5 cfm and new are about $3000+. I have tested a 1/3 hp air compressor to pump the 7” WC natural gas from my meter to the propane tank for the B-B-Q to 100 psi. Aren’t propane systems designed to max out about 250 psi? Anyways I won’t be taking propane camping with me anymore now. SO, if I use a 250 gal propane tank as a reservoir, I can give the scuba compressor an increased inlet pressure to facilitate a faster fill. What pressure should I try?
    I’m thinking of routing the natural gas through a 1” drier to the Scuba’s compressor’s intake manifold, and bypass the breathing air filters on the output side. Doing this may allow some oil mist in the natural gas that may be just what the Doctor ordered for car engines. Or would it be wiser to convert the high pressure breathing air filters to driers and eliminate the intake drier? OR just use the breathing air filters to filter the natural gas?
    How fast might this 1/3 HP + 5 HP system fill a 10 gal car?
    For a faster fill, I’ll but some Scuba tanks together in a cascade system with a CNG fill coupling at the end, then add some pressure on/off switches to make it automatic. WHAT DO YOU GUYS AND GALS THINK? Should I try it and let you know what happens? Any advice and recommendations may be the difference between success and failure and or something damaged or not. Whow, I bet someone is doing this already, are you out there? Sincerely D.Rierson

  • #2
    Re: SCUBA Air Compressor?

    Bad idea unless your planing to blow your self up.

    No way is a SCUBA compressor designed to do CNG.
    John

    Comment


    • #3
      Re: SCUBA Air Compressor?

      The first thing is the motor and controls. all of the controls and must be intrinsically safe or explosion proof the same with the motor. Your other choice is a remote control panel in other words a panel with all contacts mounted at least 12 feet off the skid (This all falls under NFPA 52) at least here in southern Ca. a home compressor can be no more than 2 cfm. Storage is forbade. If you do make sure you have PRD's on the tanks. Breathing air machines are designed to operate on atmospheric pressure. By upping the inlet pressure you increase the rod load. putting more wear and tear on the bottom end of the machine, cutting the life of the compressor or worse. you will be able to operate at standard presser, 7 inches of water column, but not much more. depending on the outlet filters you can get high pressure dryer cartridges that will also coalesce oil from a man I know locally and there is another manufacture in Florida whose name escapes me.

      What is the make of of the breathing air compressor you have and how about some picts. Both Ingersoll Rand and Baure make NG compressor based on breathing air machines.

      Comment


      • #4
        Re: SCUBA Air Compressor?

        Thanks for great reply. There is a 5HP Max-air 35 and a Bauer used for sale on Craigslist LA listed under Sporting Goods- compressor, for $2200 each.
        The remote control panel would be no problem, then replacing the Gas or Electric motor that comes with the compressor for an explosion proof one is possible but adds cost. What if the motor and control panel was remote from the compressor? Long drive belt would be a problem but could be solved. Can you give supplier for the high pressure dryer cartridges you had in mind? As you said that storage is forbidden and 7” WC is OK for the compressor I would need to adapt a CNG filler coupler to the output side of the high pressure dryer. Where would I buy one new or used, any ideas?
        I appreciate your positive feed back and knowledge in this mater.
        Sincerely D.rierson

        Comment


        • #5
          Re: SCUBA Air Compressor?

          I am certainly no expert, but you might consider a used fuelmaker product. They are specifically designed (safe) for the job intended. An unintended accident is bad for the whole cng community.

          Comment


          • #6
            Re: SCUBA Air Compressor?

            That sounds like good advice to me.
            I remember Ron (where are you?) was talking about the same thing, I believe he is a CNG technician.
            I'm sure is is quite possible to build a device, but at what expense?
            Even if we got all our sharp and creative minds together to design a fueling device, could we do it for less than Fuelmaker?
            I would be willing to put up my mechanicals design skills to help, that's what I do for a living.
            On top of everything else, to do it legally, what kind of beauracratic red tape would you have to go thru?
            J
            BLUE 09 GX

            Comment


            • #7
              Re: SCUBA Air Compressor?

              Some general thoughts:

              The idea of using a Scuba Compressor is not new; a lot of manufactures that offer NG Compressors also selling Scuba equipment as well, but you may have noticed that the NG equipment comes with Explosion proof motors, panels and pressure switches. Also they come with gas recovery equipment for the oil separator blow down cycles as well. The equipment also comes with built in diagnostics so that the compressor will shut down automatically when it malfunctions (not if it malfunctions).

              Actually the oil separators on decent scuba equipment will also work for NG as well, but you definitely do not want Compressor oil in your NGV, or storage bottles.

              You'll also need to evaluate your available flow rate from your utility meter. Bigger isn’t always possible. A typically house meters won’t flow more then 250,000 btu/hr at 0.25psig. You'll also need to subtract out of that flow rate your household gas loads (furnace + water heater + clothes dryer + stove/range + etc). Whatever is left over is all you’re going to be able to safely draw or you'll start starving your appliance's pilot lights for fuel, and worse yet, with a missing or defective check valve, each appliance may start "leaking" air in along with the gas into your compressor intake. (Obviously a potentially hazard).

              Assumptions:
              1 therm NG = 100,000 btu
              1 therm NG = 100scf
              1scfm = 0.01 therm/min

              3scfm = 0.03 therm/min

              0.03 therm/min * 60min = 1.8therms = 180,000 btu/hr

              Assuming the 3scfm compressor is going to be drawing about 180,000 btu/hr at 3000 psig, but it will likely draw even more when the output pressure and compressor load is very low.

              I assume the max flow at 200psig output is 4.9scfm (just guessing)
              4.9scfm = 0.049 therm/min

              0.049 therm/min * 60min = 2.94therms = 294,000 btu/hr

              At this flow rate the compressor will start to draw a vacuum on the 250,000 btu/hr meter and all the pilots will starve for fuel in the house. In other words, this is very bad.

              One solution to this problem is to have your utility come out and upgrade your meter to a larger flow rate and supply pressure. A typical upgrade could be a 800,000 btu/hr @ 2psig supply pressure, but you will still need to install regulator for the rest of your appliances in your house that run at 0.25psig, not a big deal, but the entire upgrade can typical cost about $1000.00. Also this potentially may cause your utility to also switch you to commercial billing which might cost you more per therm at the lower monthly usages for these billing tariffs. Not to mention they (the utility) are going to want you to explain your plan to their engineers who will also need a warm fuzzy.

              Let’s not forget if you’re going to be running an electric motor, you'll like want it explosion proof, and likely single phase for residential use. This combination is going to make it harder to find motors much more then 3HP which for a 3scfm compressor you can actually just sneak by with, for about another (+$700-1k new). As for a gas engine on the other hand, this is going to create heat around your compressor which is going to make it harder to actually compress the gas into your storage tanks, and possibly the potential gain in compressor performance you hoped for might not actually materialize, also they are noisy and could cause your neighbors unwanted frustrations, especially if you’re filling up every day.

              Explosion Proof 5000psig pressure switches ($350 ea); you'll need at least one.

              You'll also still need a way to recapture the blow down gases from the oil separators. Some High Pressure plumbing and a large air compressor tank on the supply side. ($?)

              Explosion proof enclosure and motor starter contacts ($?)

              IMO using a scuba compressor would work, but its probably not going to end up being cheaper unless you can justify a real need for the additional capacity, and in those cases there are always used Fuelmaker or other Brand Compressors ready to go on the market, and if one Fuelmaker doesnt do the job for you, you could always get two.

              If you bought a used Fuelmaker they seem to hold their value quite well. So a decent resale value is a real option if you want to upgrade or just sell your equipment someday.

              Scuba compressors also hold their value, but what is the resale value of a jerry rigged scuba compressor once converted to breathe Natural Gas? (not so good I imagine)

              Just my 2 cents, but I want to know how it turns out for you if you decide to go that way though, it sounds like it could be a fun project.

              Be safe.
              Last edited by MrComment; 02-04-2008, 09:01 PM.

              Comment


              • #8
                Re: SCUBA Air Compressor?

                There's been little to nothing for used compressor's on the market is the problem. Whats out there is selling for way too much. I'm wondering if someone could utilize a old diesel engine as a compressor. Get one that died and just use a couple of the cylinders for your compressor............
                I would think the internals of the diesel would handle the pressure given a compression test on one can be in excess of 500 PSI. I'd imagine that the actual forces the engine see's on an ignition cycle would be much higher and the rotating assembly would handle it.

                Comment


                • #9
                  Re: SCUBA Air Compressor?

                  What the market needs is a competitior to FM. There is nothing about a FMQ-2 that should make it cost $11k other than their monopoly. Maybe a knockoff from China?

                  Comment


                  • #10
                    Re: SCUBA Air Compressor?

                    Danger! Danger! Will Robinson!!!!!
                    Please do not use the acronyms SCUBA and CNG in the same conversation on this forum! Short of a few stainless steel high pressure fittings these two technologies are totally different animals. Two different facets of the compressed gas industry.

                    First off, I am no fan of Fuelmaker and thier monopolistic policies and barely capable equipment that was deliberately engineered for the replacement parts market. Nor am I a fan of thier piss poor excuse of the difference between the Euro and the Dollar as a reason for nearly doubling the cost of some of thier parts. Or thier attitude and lack of attention to thier "Neighbor to the South" as they spool up thier international marketing efforts.

                    "What the market needs is a competitior to FM. There is nothing about a FMQ-2 that should make it cost $11k other than their monopoly. Maybe a knockoff from China?"

                    A knock off from China would certainly knock Fuelmaker off thier pedestal. So would any of the other offerings from Europe, The Netherlands and Australia.

                    Problem: None of them are capable of passing AGA, CGA, CSA, UL, NFPA safety standards. You remember, the standards that keep you, your family and your neighbor's family safe and from being subject to imported I.E.D.s.

                    That's an Improvised Explosive Device. Which is what you've all been talking about making. The engineering involved in building safe flammable materials handling equipment that can operate in a residential area is intense. The one and "only" justification that Fuelmaker can use in it's defence of high pricing.

                    Sure, an auto or diesel engine (basic air/gas pumps) could work. Hurricane used/uses a modified Ford 440ci engine for thier portables. They are high maintenance and don't last long. Kind of like when GM tryed making a diesel out of a small block 350. And people wunder why Americans don't like diesel engines.

                    Sure, air compressor companies could adapt thier products to gas compression. Just like Bauer or Ingersoll Rand did. They make nice little, affordable 25cfm compressors that work on a 5psi supply and a 20hp explosion-proof three phase motor. You just have to have a technician on staff to monitor it's operation and do a valve job every 500hrs.

                    "There's been little to nothing for used compressor's on the market is the problem. Whats out there is selling for way too much."

                    The problem is called supply and demand. Last year you could steal Fuelmakers and NGVs because nobody wanted them. "What's CNG?... Why would I pay $5,000 to convert my vehicle to a fuel it's hard to find...Why would I buy something like that when gas is only $2.65 a gallon?"
                    Good supply but no demand. Certainly no shortage of short sighted individuals.

                    A discussion of homebrewing your own CNG raises more questions (and dangers) than it answers and unless you have deep pockets, an engineering degree and a longing desire to bang your head againts a brick wall, I would suggest you leave the answers to those who do.
                    Your Friendly Nazi Squirrel Administrator

                    Comment


                    • #11
                      Re: SCUBA Air Compressor?

                      Originally posted by cnghal View Post
                      [B][COLOR=red]A knock off from China would certainly knock Fuelmaker off thier pedestal. So would any of the other offerings from Europe, The Netherlands and Australia.
                      The Chinese plants are more than capable of passing CSA, UL, etc. they do it all they time. I would like to find a solid design for a VFA and have it produced in China for a target of $1500 retail. Certainly doable. I do a lot of work with Chinese manufacturing of engineered products. You get what you ask for is the bottom line. If you don't ask for it you don't get it. FWIW their CNG tanks pass CSA, TC, DOT easily, and have an excellent safety record.
                      I would have to look at the FM design and patents and see what room we would have to produce a similar product.

                      Comment


                      • #12
                        Re: SCUBA Air Compressor?

                        Please try to get a Chinese version made. I'll buy one

                        Comment


                        • #13
                          Re: SCUBA Air Compressor?

                          CanAm,
                          Pretty bold statements, which are you addressing, VRA design or manufacturing, because plants and manufacturing might pass an ISO standard, but it takes an actual presented design to pass CSA and UL. And several imported designs have tried. Where are they?

                          BTW, where are these Chinese CNG tanks that so easily pass CSA/ANSI NGV-2 2007 & DOT FMVSS 304 or CMVSS 301.2. I keep hearing claims and promises, but every time I ask for proof, the silence is deafening.
                          Just take a picture of one of these Unicorns and make a copy of thier pedigree the next time you see one.
                          Your Friendly Nazi Squirrel Administrator

                          Comment


                          • #14
                            Re: SCUBA Air Compressor?

                            Originally posted by cnghal View Post
                            CanAm,
                            Pretty bold statements, which are you addressing, VRA design or manufacturing, because plants and manufacturing might pass an ISO standard, but it takes an actual presented design to pass CSA and UL. And several imported designs have tried. Where are they?

                            BTW, where are these Chinese CNG tanks that so easily pass CSA/ANSI NGV-2 2007 & DOT FMVSS 304 or CMVSS 301.2. I keep hearing claims and promises, but every time I ask for proof, the silence is deafening.
                            Just take a picture of one of these Unicorns and make a copy of thier pedigree the next time you see one.
                            I am not here to sell anything, so I don't know why the attack. But many of the Chinese/Argentine tank mfrs have NGV2 certs already in hand and 571.304 is not a tough challenge to any tank manufacturer.

                            ISO is hardly a standard these days. Most factories seems to gain ISO compliance now. It has very little to do with the actual product being turn out.
                            Last edited by CanAm; 06-28-2008, 03:10 PM.

                            Comment


                            • #15
                              Re: SCUBA Air Compressor?

                              CanAm,
                              I beg to differ, you are selling the viability and intergity of, until actually proven otherwise, unsafe and potentially illegal equipment which violates the Terms of Service of this forum. There are no attacks intended here. I just ask that if you are going to vigorously claim a fact, that you substantiate it in truth with some form of evidence as to not confuse other forum users as to what is fact and what is opinion.
                              As to ISO, I mention it because it is the only standard that some of these imported products can stand on which doesn't amount to much when a toothpaste factory is ISO compliant and is also producing high pressure regulators.
                              Your Friendly Nazi Squirrel Administrator

                              Comment

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