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Converted low pressure air compressor

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  • Converted low pressure air compressor

    Hi All

    Have been toying with the idea of a bi fueled vehicle for a while. The main problem with CNG was there is no fill stations close by.So with no way to fill your tanks a CNG vehicle is useless. I was waiting for the $500.00 home fill station to come about but we all know that aint gonna happen. I would even settle for a $1500.00 fill station. So what did I do, I built my own. Bought an inexpensive 2 cylinder compressor and converted it to a high pressure compressor capable of pumping pressures of 4500 lbs. I studied the bower series compressors how they worked and built one. I bought the 3rd stage cylinder head and valves built my own .500 inch bore piston and cylinder. bored and honed the cylinder built the piston and rings. It is a free piston design just like the bower. intercooler between the stages first stage has 275 LBS of pressure the second is 4500+ lbs a safety switch between the stages and one on the high pressure output set to 3600PSI
    second stage is also intercooled it pumps 1.5 GGE per hr the compressor turn 1100 RPM so its nice and quiet turning the compressor slow keeps the heat generated down to an acceptable level. It would have been easier to buy a breathing compressor and convert it for CNG even a bare bones high pressure compressor is $3000.00+ dollars.
    I have about $1500.00 tied up into building this one. Now I have all kinds of compressed CNG Now its time to convert the car over to CNG. most likley will use an impco set up. in my opinion they are old technology but well proven.would like to try one of those electronic ones that have a stepper motor valve and an oxygen sensor that can adjust the AF ratio.

    Thanks DAS

    Just my uneducated opinion
    Just my uneducated opinion

  • #2
    Re: Converted low pressure air compressor

    I think you are going to have heat problems. I hope not but keep us posted good luck

    Comment


    • #3
      Re: Converted low pressure air compressor

      post pics of this, seems interesting

      Comment


      • #4
        Re: Converted low pressure air compressor

        Originally posted by cowboy View Post
        I think you are going to have heat problems. I hope not but keep us posted good luck
        Hi All

        Heat so far has not been an issue.I designed the compressor with cooling in mind.The compressor is in its own enclosure. One large inlet for the flywheel/ fan. with 3 ducted outlets.
        one for the electric motor one for the low pressure cylinder head. the last for the high pressure cylinder head and check valve.
        all the air coming in must pass over these three parts to get out. with the majority of the air passing over the high pressure cylinder and head.

        DAS

        Just my uneducated opinion
        Just my uneducated opinion

        Comment


        • #5
          Re: Converted low pressure air compressor

          My my my DAS sounds like you are having too much fun. Wish I had access to a machine shop!

          Comment


          • #6
            Re: Converted low pressure air compressor

            What an adventure!

            My only concern is that LP compressors are designed for a certain amount of stresses. I expect that the life expectancy of the main bearings, rod bearings and crank shaft is going to be dramatically reduced. But, at that price, what the heck!
            Ray Contreras
            CompressorStuff.com

            Comment


            • #7
              Re: Converted low pressure air compressor

              well he has reduced the bore that will in turn lower the rod load I dont know what the stock piston bore was that he removed as long as the % smaller the new 1/2 inch piston is than the stock piston is as great or greater % than the rod load will not be higher. it might live a long and happy life

              Comment


              • #8
                Re: Converted low pressure air compressor

                I've been amazed over the years by some things prototype machinists and toolmakers will do , to prove it can be done in a garage size shop with a lathe and a mill. Never mind that these guys can bill out at well over $150 hr , making plenty of $ buy something, they just like to make it themselves.

                Comment


                • #9
                  Re: Converted low pressure air compressor

                  Hope you place this thing outside

                  And be sure to temperature compensate below 3600 psi in ambient temps below 70F, or you could overpressure the cylinder(s) when temps heat up (for example if you then park in a warm garage). See the chart below:
                  cng_tempcompchart.jpg

                  Comment


                  • #10
                    Re: Converted low pressure air compressor

                    Any chance you can take a couple good pictures of this setup and post them for us?

                    Comment


                    • #11
                      Re: Converted low pressure air compressor

                      Hi All

                      The compressor will be mounted outside. you would be nuts to mount it inside a building. The regulator is easily adjustable. I had thought about putting in another pressure switch and a selector switch one position for 3000 and the other for 3600 most of my filling would be done through the day when is usually is the hottest. I.ll need to watch how much variation there is in pressure through the day. I ll try to post some pictures if I can figure it out. It will not let me post a picture from a file only from a URL any ideas???

                      DAS

                      Just my uneducated opinion
                      Just my uneducated opinion

                      Comment


                      • #12
                        Re: Converted low pressure air compressor

                        you need to compensate 18 psi for every degree. I have thought about doing the 3000-3600 switch. for filling my older cars but most of the 3000 tanks are rapidly approaching end of life If I were going to do this I would use a latching relay to parallel the 3600 pressure switch and use a momentary push button to latch it. as that way you would have to latch it every time you wanted 3600 and not have any boo boos.and to why do this. to see what is over the next hill,to climb to the top of a mountain,drive around a circle in a fast car to end up where we started BECAUSE WE CAN. If you cant understand that I feel sorry for you as you never will.
                        Last edited by cowboy; 01-09-2015, 07:39 PM.

                        Comment


                        • #13
                          Re: Converted low pressure air compressor

                          Posted the pics for DAS

                          DAS, what horsepower is the electric motor turning this thing?

                          101_0386.JPG

                          101_0389.JPG

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                          101_0387.JPG

                          101_0385.JPG
                          Last edited by trdscfjc; 01-09-2015, 12:27 PM.

                          Comment


                          • #14
                            Re: Converted low pressure air compressor

                            very very bad. I see that the motor is a open frame even worse if it is single phase as every time it starts the starting points draw a arc that would ignite any gas that might be leaking. change the motor and I like it. it may need a little polish and a little safety stuff but he has proven that it can be done. more that ge did trying to get to 500 dollar home compressor

                            Comment


                            • #15
                              Re: Converted low pressure air compressor

                              The motor is a 5 HP 3450 RPM 220 volt single phase motor. I have also had concerns about the open motor. with a 14 Inch air inlet on the side and 3 air outlets two on the sides and one on the bottom. the case is not totally sealed up tight. the top is hinged and can be opened up to vent the case of any accumulated gas before starting. All the fittings and lines were leak tested with an electronic leak detector. there was a few minor leaks that the detector picked up that the nose did not. There is no leaks now. thats not to say that some may develop.I'll pop the top to vent it and give her the old sniff test. If I smell gas I'll think twice about pushing the start button.

                              DAS

                              Just my uneducated upinion
                              Just my uneducated opinion

                              Comment

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