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Thread: Depressurization bleed off

  1. #1
    Insider PBSteve's Avatar
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    Depressurization bleed off

    Does anyone know how the depressurization bleed off mechanisms work? I mean, what exactly is the mechanism?

  2. #2
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    Well, it just happens that the day job is full of PSV's, or Pressure Safety Valves.

    PSV's are blow offs to vent an overpressured line on a refinery. They are actually very important, and very simple. And exactly the same device as the depressurizing bleed offs.

    A PSV is basically a surface, say a ball or piston type surface, that is connected to the process stream, held there with a spring. As the pressure increased above the set point (the tension of the spring) the spring gives way and it vents. Kind of like a backwards poppet valve, which is what it really is. The pressure is set by the tension on the surface area vs spring pressure. Take a small PSV, a .25" OD piston on the gun. Say we set to 250psi. You have .05" of area, and since you want a 250psi bleed off, you simply multiply area and pressure to get 12.5 lbs. Set the spring to about that and the piston will lift off at 250psi, keeping you from over pressuring.

    It can be as simple as a ball bearing against an oring with a spring behind it.

    Here are a couple pics of the real ones I work with:

    http://www.hpvalve.net/images/sketch/safety-valves.jpg

    http://www.spiraxsarco.com/images/re...1/fig9_1_2.gif

    Let me know if that helps -

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    Insider PBSteve's Avatar
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    Thanks for the reply! Right, that's what the Axe uses in its regulator.

    I think I asked my question poorly. I'm looking for the mechanism in regulators that keeps them from storing an "extra shot" after the marker has been disconnected from its air source/degassed.

  4. #4
    I'm not sure how the one in an Axe works as I've never handled one or taken it apart, but something like that can be as simple as a small piston acting as a normally open pilot actuated valve that uses surface area on each side of it to exposed to both the source pressure and the regulated pressure that shifts to vent the downstream side when pressure on the upstream side drops below the pressure it needs to keep it in the closed position.

  5. #5
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    Some regulators do vent automaticly, the ones that use a piston and poppet arrangement. This happens because the poppet is held tight on the seal with the back pressure from the tank. When the back pressure is removed the spring that is holding the poppet down is normally to light for the pressure in the reg in addition to the piston force, and it unseats. The AXE/Mini have this type of reg, and no extra mechanism is needed.

    DYE or PE both have a moving base style (same with the sidewinder and WGP and a bunch more.) DYE does retain air, and to release it you need to cycle the gun. PE has a small part like y0da describes, basically a piston/poppet that is connected to both sides of the pressure on the reg, the high pressure from the tank and the low pressure from the regulator side. They placed it right in the center sealing point of the adjustment pin, it is very clever. When the tank pressure is removed the piston/poppet doesn't have the 800psi push on the back side of it, and works just like a PSV, venting pressure in the reg/gun.

    Same mechanism really.

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