Author Topic: My .257 Condor Build  (Read 873 times)

rsterne

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Re: My .257 Condor Build
« Reply #15 on: January 31, 2020, 10:49:18 AM »
While I was poking around the internet looking for information on removing the Condor valve, I ran across a YouTube video, and took this screen shot from it....



Here is the Video, in interest of full disclosure....
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This is, quite obviously, a regulated valve to fit INSIDE the Condor tank.... The regulator is at the bottom of the tube, and the tube between the regulator and the valve is the plenum....  :o

I have never seen or heard of anything like this before, but it seems a quite brilliant solution for that particular PCP, and in fact could find use in other bottle guns where there is insufficient room for a decent sized plenum.... It does give up some of the reservoir volume, of course.... but the ability to have a decent sized plenum might outweigh that in many instances....

I have a 250 bar 500 cc bottle here that is 3/4" longer than a Condor tank.... That is less length than you would add with an external regulator, which would have NO plenum.... The neck is just over 5/8" ID, and it is 12" long from the inside bottom to the top of the neck.... With care, deducting an inch each for the regulator and valve, that would leave you a maximum of 10" of length for the plenum.... If the wall thickness was 0.065" (ID of 0.495"), the plenum volume would be 32 cc.... That would probably work great for a .22 cal, and could work with a .25 cal by increasing the setpoint about 5-10%, depending on FPE level....

Calculating the external crush pressure of a tube is much more complex than the internal burst pressure, but many I checked seem to be about 40% of the burst pressure.... If we made the assumption that the minimum regulator setpoint pressure was 1600 psi, inside a 3600 psi tank, the greatest pressure differential would be 2000 psi.... Therefore a tube with a decent safety margin to burst with 5000 psi of internal pressure would probably be OK.... Since it is contained inside the bottle, the worst that would happen is that it would flatten, and be impossible to remove from the bottle....

You can get 5/8" OD 2024-T3 tubing in either 0.058" or 0.065" wall, and you can get 4130 CrMoly tubing in those, plus 0.049" wall.... The thinner the wall, the greater the plenum volume, but even going down to 0.049", the volume would only increase to 36 cc.... With the thicker wall, you could use threads to attach the plenum tube to the ends (regulator and valve), as those would provide additional crush support, so the simplest might be to use the 0.065" wall 2024 aluminum.... That should give about a 2:1 safety margin with a 2000 psi differential, so should resist collapse even if the regulator vented.... The same applies to the CrMoly tube at 0.049" wall....

I don't plan on building such a device.... but I thought it was worth posting about it, since I have never seen this idea before....

Bob
  • Coalmont, BC

rsterne

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Re: My .257 Condor Build
« Reply #16 on: January 31, 2020, 11:34:42 AM »
I had one more thing I wanted to try this morning.... I removed the O-ring from behind the Top Hat.... I was wondering if that 1 mm thick, 70D rubber ring was absorbing enough hammer energy to reduce the velocity.... I filled the gun to 3000 psi (for each shot), loaded an 82.5 gr. slug, set the PW to 8 and took a shot across the Chrony….

768 fps instead of 872 with the O-ring.... I repeated at PW = 7 (793), PW = 6 (maximum recorded at 800 fps), PW = 5 (785) and PW = 4 (733 fps)…. I then put the O-ring back on, and checked at PW = 4 and PW = 6, and those shots were 868 & 869 fps....  :o

OK, so that is quite a revelation.... The O-ring appears to be slowing the hammer gently, instead of letting it drive the top hat hard enough to bounce off the valve.... It appears that with the larger, angled ports the breech volume is filling much more rapidly, causing a faster pressure rise.... This drives the top hat back harder/faster, blowing the valve open much more quickly, which is why the valve can't be tuned for a bell-curve now.... If the hammer strike is too light, and barely cracks the valve, it slams shut and you get really low velocity.... Once the valve opens past a certain point, you get that fast pressure rise behind the slug, and the valve gets blown open and you get full power.... almost regardless of the power wheel setting after that....  8)

It appears that the O-ring, by slowing the reversal of the valve stem, increases the dwell and reduces the bouncing closed of the stem, which is limiting the velocity to 800 fps in this case, instead of 870.... This is a rather strange case of an O-ring buffer actually increasing the peak power of a PCP (by nearly 20%)....  :o

Bob

  • Coalmont, BC

Alan

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Re: My .257 Condor Build
« Reply #17 on: January 31, 2020, 12:23:39 PM »
Makes me wonder if the o-ring "size" is specific? As in thicker or thinner?
  • 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.

rsterne

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Re: My .257 Condor Build
« Reply #18 on: January 31, 2020, 02:36:38 PM »
It absolutely would be.... I tried a 0.070" thick one before I tried this one (0.039"), and the gun at that time lost a LOT of power.... See previous page, Reply #10....

Bob
  • Coalmont, BC