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Questions About Vaccuum/Air Force And Its Usage

  1. Apr 20, 2012 #1
    Hello experts

    I have quite a number of questions about a project that is basically an airgun, but uses the force of air/vaccuum instead of a spring to blow the air. Here is a brief description of the whole model:

    There are two tubes, one placed in the other, such that there is some space between them.

    There are two pistons too. The first piston operates between the space between the two tubes, and the other operates in the inner tube. Note that the inner ends of the pistons fit precisely in their vicinity such that air cannot move past either of them.

    These two pistons are connected together outside the tubes for convenience so that there is only one piston handle outside the tubes.

    The outer tube has an opening at one end (the end opposite to the piston handle) while the inner tube is tightly closed on one side such that when the piston is pulled back, vacuum is created in the inner tube.

    Now we have formed a machine which blows air with the force of vacuum. When the piston is pulled backwards, the space between the two tubes will be filled with air, while the inner tube will have vacuum in it. When the piston is released, the pressure of air will push the piston inside the inner tube (because there's vacuum in it). But since the two pistons are connected, the piston of the space between the tubes is also pushed forward, hence blowing air out of the opening.

    Now I put my questions:

    1- Is this model practically attainable?

    2- Which material should be used for the inside and outside tubes?

    3- What are the advantages/disadvantages of this model against the conventional airguns which use the force of a spring to blow air outside a tube?

    4- What should be the diameter of the inner and outer tubes if we want to blow a dart of mass 50g to a distance of 200m through this device?

    5- Is there a company/firm where I can order this model?

    6- And lastly, does anyone have an estimate of the cost of a prototype?

    Attached Files:

  2. jcsd
  3. Apr 28, 2012 #2
    I would imagine that the reason nobody has replied yet is that some of your questions cannot be answered without knowing many more details. You also don’t give my mind enough information to completely understand what you are doing. I don’t know if that problem lies mostly in my mind or in your presentation.

    But you might know that there is an alternant design that is common use in the hydraulics and pneumatics industry. I used these “hydraulic intensifiers” in a previous job when my power supply put out 3000 psi, but I needed to generate a small amount of fluid at 20,000 psi. They take a small pressure to drive a larger pressure. They do not work on a vacuum. But an alternant design would make them work with a vacuum. Perhaps that is what you are presenting here, but I just don’t see it.

    Suppose you have a regular double acting hydraulic cylinder. The area of the piston is 10 and the rod has an area of 9. (Substitute any units you like.) This means that on one side of the piston, the annular area has an area of 1. So if the rod is free and not connected to anything, and I put a pressure of 100 on the large area side of the piston, then the piston area on the rod side of the piston will generate a pressure of 1000.

    An alternant means of building an intensifier is to couple the shafts of two fixed displacement pumps together. If you supply fluid to the one with the larger displacement, then the smaller displacement pump will produce a pressure that is higher by the ratio of displacements.
  4. May 3, 2012 #3
    The question is not about the pressure caused by a hydraulic cylinder. Its about the force of the vaccuum (or rather the air in fact). When you fill the needle of a syringe with dust and then pull the piston back it rushes to its original position when you release it. Due to the pressure of air around the syringe.

    The question is about using this force as a spring i.e. how much wide a tube (with vacuum inside it) would cause enough force to push the piston of another tube which is filled with air.
  5. May 5, 2012 #4
    Sounds like a simple F=P*A problem.

    You might bound your solution by assuming you can achieve a delta P of perhaps .4 - .7 bar.
  6. May 5, 2012 #5
    What is a "delta P"?

    Its not about solving some numerical problem. I'm trying to figure out a means to convert a blowgun into an airgun without using springs.

    What I really want to know is this:

    What is the relation of the area of the vacuum tube with its length? i.e. will a long but narrow tube create more force than a short but wide tube?

    How do we measure the force of air (which is pushed out through the air-filled tube) w.r.t. the speed at which it is blown out?

    How much efficiency should I expect from this model?
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