Author Topic: Making of a MARAUDER "Cobra" conversion  (Read 288 times)

Motorhead

  • Sr. Member
  • ****
  • Posts: 406
  • Older & Slower ... Field Target Shooter
Making of a MARAUDER "Cobra" conversion
« on: October 13, 2018, 08:49:40 PM »
 ;D After a good year or so playing with the "Cobra" air spring tech have figured out what configurations give the best results.
Placing the tube on the poppet dictates the weight/mass of the tube becomes part of the cyclic mass in motion  :P  The vent hole must pass threw the root of the o-ring groove limiting what o-ring sizes you can fit.
Alignment and rigidity become more critical too  >:(

So ... having nothing to do on the bench today figured it was time to address the MARAUDER valve once again.
Understand this mod at this level is for those with Machining skills or access .... no way one can cobble together whats shown without some precision made parts.
* The point here is TO SHOW what the devise is and how it can be adapted to a valve design that really does not cater to such a devise .....   ;)

We start by having some ground .125" rod and machine up a poppet head ( PEEK ) that carries the cobra tube o-ring that was set @ .050" behind the depth of the stem within the poppet head.
My sealing surface required @ .315" of diameter and the tube to be used was .312" o.d. with an I.D. of @ 280" ... Thus the step between sealing surface and o-ring area to be within the tube.
By having no vent hole was able to use a 007 poly 0-ring which with a light interference fit to tube I.D. seals well and is near drag free.

The real TRICK part is the miens in which we get air INTO the valve body while still supporting the Cobra tube via the valves end cap.  This done by first drilling the end cap to 3/8" and removing 3/4's of the thread length used to secure it.  This buys us intake area and internal length that will be filled soon enough by the parts required to go "Cobra"  ;)  Tube is a press fit onto the stub and held rigid via the end cap.

The BLACK piece shown was machined from glass filled acetal to be stiff & strong being it becomes pretty thin wall and lightly structural to hold the cobra tube and deal with the pressure pulse differential happening.
What we ended up with is an intake hole of .300" radially dispersed via 4  slots of .187" x .250" feeding HPA to the valves interior.  The "Vent" sits in the center where I used a stub of a .040" I.D. WD-40 type spray tube.
This was extended out of the intake throat of valve into the plenum away from the localized low pressure drop of the valves inner space / intake path.
« Last Edit: October 14, 2018, 01:04:53 PM by Motorhead »


  • Old Hangtown ... California
"Home of Motorheads Air Gun Tuning Service"
    ***** Airguns need love too !! *****

Alan

  • Administrator
  • Hero Member
  • *****
  • Posts: 2015
  • Set the example... Don't be one!
    • Mobile Amateur Radio
Re: Making of a MARAUDER "Cobra" conversion
« Reply #1 on: October 14, 2018, 05:56:32 AM »
Ingenuity at its finest!
  • Roswell, New Mexico
Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.