GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: CableStop on April 01, 2021, 06:35:02 PM
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I have been receiving some concern over this design and was looking for some input on ways to improve it. I am looking to bottle a marauder pistol and this seemed like an easier way given my capacity to fabricate items. Basically it's an in-tube HUMA regulator with a drop block fitted to the end, not shown is a burst disk in the plenum which will vent out the gauge hole in the event of regulator failure. While the bottle will be 4500 PSI, as far as I can determine the only force applied to the screws on the end of the tube will be whatever is pushing on the "neck" of the regulator (face A). This diameter is 0.515" which comes out to 940 pounds of force when exposed to 4500 PSI, on the other hand a stock Marauder valve has 2600 pounds pushing on it at 3000 PSI. The screws in the drawing aren't appropriately countersunk they would be fitted similar to the stock screws in the final version.
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Areas B and C are also subjected to 4500 psi, and the seal between the drop block and the stub that goes over the regulator neck is whatever the ID of the hole in the drop block is.... If that (between B and the screws) is the same as the OD of the tube, which is 7/8", the force is 2700 lbs., so you need the screws able to hold at least 3 times that, or over 8000 lbf....
If the hole is larger than 7/8", the force is greater, of course....
Bob
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Areas B and C are also subjected to 4500 psi, and the seal between the drop block and the stub that goes over the regulator neck is whatever the ID of the hole in the drop block is.... If that (between B and the screws) is the same as the OD of the tube, which is 7/8", the force is 2700 lbs., so you need the screws able to hold at least 3 times that, or over 8000 lbf....
If the hole is larger than 7/8", the force is greater, of course....
Bob
According to my math the stock Marauder valve has 2600 pounds on the face at 3000 PSI, I could be completely wrong though. Multiply that by 3.5 and that's the ASME rated burst pressure as far as I understand.
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Misters Bob and Lloyd never cease to amaze me when they talk numbers ;D
I passed my Physics with a grade of 74.6, so it was rounded off to 75, lol!
True!
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Have you considered going in through the gauge port?
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"Marauder pistol" but you seem to be referring to the rifle sized tube (1.25"od x .095"wall) as opposed to the pistol tube (.875"odx .065" wall). I get this from your 2600lbs force @3000psi.
Face "B" is seeing 4500psi, and if it's at the tube id of 1.06" that's 3969lbs force. Is it secured in some manor (other than the screw) that is not shown?
Screws through into the tube will see the force determined by tube id and regulator pressure...or burst disc rating in worst case.
Al
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"Marauder pistol" but you seem to be referring to the rifle sized tube (1.25"od x .095"wall) as opposed to the pistol tube (.875"odx .065" wall). I get this from your 2600lbs force @3000psi.
Face "B" is seeing 4500psi, and if it's at the tube id of 1.06" that's 3969lbs force. Is it secured in some manor (other than the screw) that is not shown?
Screws through into the tube will see the force determined by tube id and regulator pressure...or burst disc rating in worst case.
Al
It would be secured by 3 screws similar to the valve. That is what the dotted circle is meant to represent, I should have clarified.
Sorry I have been crossing between the rifle and pistol. This drop block will be on a pistol, but the valve diameter I referenced was for the rifle.
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THE DESIGN itself seems overcomplicated.. This often leads to less area for pinning. the drop block ( lets call that the rectangle part ) and the insert stem ( the round part going into the p-rod tube ) can all be one piece with a lathe and a basic drill press.. Since youre using the entire p-rodd tube as the plenum - reg , you dont have to have a large port in the block.. it could be a 3/32 hole only giving room for more pinning / attachment to the tube.
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My point remains, if the drop block is made in two pieces, and those pieces joined with three screws, and sealed by an O-ring, then the force pushing the front part of the drop block off of the stub is the area where the outside of the O-ring seals times the pressure.... Your statement that....
the only force applied to the screws on the end of the tube will be whatever is pushing on the "neck" of the regulator (face A).
is incorrect, and is a dangerous assumption.... In addition to what Al and I pointed out about the forces trying to tear the drop block apart, that same 4500 psi will be pushing the regulator towards the valve.... If the reg. is not pinned into the tube, or located by a tubular spacer, the 4500 psi on the outer end of it will slide it right down against the valve on filling.... pushing it out of the O-rings after a short distance, and then applying 4500 psi against the stub of the drop block's full end area.... If there is a tubular spacer locating the regulator, then that 4500 psi times the full area of the ID of the tube is transfered to the valve screws.... Too many failure points in this design, IMO....
Bob
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My point remains, if the drop block is made in two pieces, and those pieces joined with three screws, and sealed by an O-ring, then the force pushing the front part of the drop block off of the stub is the area where the outside of the O-ring seals times the pressure.... Your statement that....
the only force applied to the screws on the end of the tube will be whatever is pushing on the "neck" of the regulator (face A).
is incorrect, and is a dangerous assumption.... In addition to what Al and I pointed out about the forces trying to tear the drop block apart, that same 4500 psi will be pushing the regulator towards the valve.... If the reg. is not pinned into the tube, or located by a tubular spacer, the 4500 psi on the outer end of it will slide it right down against the valve on filling.... pushing it out of the O-rings after a short distance, and then applying 4500 psi against the stub of the drop block's full end area.... If there is a tubular spacer locating the regulator, then that 4500 psi times the full area of the ID of the tube is transfered to the valve screws.... Too many failure points in this design, IMO....
Bob
Ok I see your point I'll just go more traditional. There will be a spacer tube behind the regular which as I pointed out somewhere else, sort of negates some of what I'm going for here which is a shorter gun. If I go externally regulated it will be more parts in line but the plenum area can be shorter since it's not taken up by the regulator and tube.
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Guys forget that a tubular spacer for the regulator transfers the force from the pressure differential across the regulator to the valve screws.... Add in the plenum pressure, and the valve screws are subjected to whatever the HP fill pressure is on the input side of the regulator.... They think that if they fill to 4500, and have the reg. set to 2000 psi, the valve screws only see the load from 2000.... but in fact they see the load from the 4500 psi fill.... In addition, the spacer has an end load on it equal to the inside reservoir tube area times the pressure drop across the reg.... Too thin a spacer tube and you can see this....
(https://hosting.photobucket.com/albums/oo221/rsterne/Important/.highres/Tube3_zpsojmxqssy.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/a8f72a68-64d3-494b-98b3-85ba6a7a34e2/p/172de1f4-1df4-4d14-b73d-548540f8bd13)
or even a complete collapse of the spacer tube, with the remains wadded up against the valve....
Bob
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If you have feed pressure of 4500psi, you need every part of the system designed to handle that pressure in case of a reg failure with proper safety margin. Or use big enough surface area burst disk downstream of the regulator. But I advise to design for the feed pressure.
Why most use bolts to pin the valves and regulators and what not in to the tubes? Threading is much better way of securing the items. If you can't then outsource the job, not too expensive if you consider the safety.
Always put seals in the pressure side before the thread.
Marko