My .257 Condor Build

[rsterne]

Thanks for that, Marko, that would be a good way to do it.... Suppporting the back of the bottle so you don't put a side force on it, only twisting it, would be the thing to watch.... I guess you could make a cradle to support the butt of the tank in the tailstock, but that would be a lot of work....

I managed to get the valve out with a close fitting 5/16" steel pin in a vise, and warming the tank / valve joint with a heat gun.... Once cracked loose it unscrewed easily....

Bob

[rsterne]

I managed to get the valve off with some heat from a heat gun.... Once it softened the glue and it moved, after that it spun off no problem.... I had a bit of trouble figuring out how to remove the top hat and stem.... The top hat threads onto the stem from the back (bottom side, against the valve), so can't be removed without pulling the stem out of the valve.... You do that by unscrewing the brass collar with the two slots in it to remove the valve assembly from the valve body.... Remove the bottom brass part first, to remove the spring, as that reduces the load on the front collar and it spins out easily....

Once I had the inner valve assembly out of the valve body, I turned the top hat in towards the valve until it touched the 1mm O-ring I had there.... I then used a screwdriver between the top hat and the brass collar to pry upwards a bit, which starts the other end of the stem pulling out of the Delrin poppet head.... Once it moved a bit, I turned the top hat down again, to reduce the gap the screwdriver was in (to keep it working easily) and repeated this operation until the stem pulled out of the poppet.... There were no splines or grooves in my stem, so it wasn't too hard to remove....

Once I had the valve all apart, I had a good look at the air passage in the stem.... The front part is drilled out 0.215", and the rear is crossdrilled with a 5/32" drill from each side to meet almost in the middle.... The air has to make two nearly 90 deg. turns, plus the back edge of the cross holes is shrouded by the conical part of the stem, and the brass valve body when the valve opens.... It is those two holes that feed the inside of the stem I wanted to work on.... I had seen some stems where the 1/4" OD part of the stem was simply milled away on each side, but I had also been warned that if you weaken the stem too much in that area, it will bend or break.... I decided I would use a 5/32" mill on an angle to ease the flow but leave as much metal as possible where the conical part of the stem meets the small diameter area behind that....

The trick was trying to figure out how to hold the stem.... The front part of is it threaded for the top hat, and is larger than 1/4".... so the plan I had of holding that in a 1/4" 5C collet wouldn't work.... I tried to slide a drill stem inside, thinking I could clamp onto that, and found out that the two setscrews in the top hat had dented the inside of the stem ever so slightly.... just enough that it wouldn't slide over a #3 drill, which was the correct size.... I used a fine 3/16" chainsaw file to carefully remove the bumps from the setscrews until the valve stem would slide easily over the stem of the #3 drill.... I screwed the top hat back into place, located it so the dents in the stem were centered in the setscrew holes, and with the stem of the #3 drill in place, tightened the screws.... I positioned the end of the drill so that it was about 1/8" forward of the cross holes... As I thought, the valve stem collapsed just a bit, gripping the stem of the drill to support it.... That allowed me to tighten the setscrews fairly snug without damaging the valve stem.... I then mounted the front part of the top hat in a 5/16" collet, which I installed in a square 5C collet holder, and turned the stem so that a drill placed through the cross holes was at 90 deg. to the faces of the holder.... It looked like this....



I mounted the square collet holder in the milling attachment in my lathe, with the cross holes horizontal.... and with the C/L of the stem on the vertical C/L of the chuck.... I then rotated the milling attachment about the vertical axis until the stem was at a 30 deg. angle to the chuck bore, and mounted a 5/32" end mill in the chuck.... I carefully milled away some material on one side of the stem to change the cross hole from 90 deg. to the stem C/L to just 30 deg.... I went gradually closer to the C/L of the stem until I could feed the mill through into the 0.215" hole in the center of the stem.... At that point, with one side done, it looked like this.... In this end view, looking in the direction of the airflow, you can see how much straighter the flow path is on the right.... In the original setup on the left, you can barely look into the main hole in the stem....



I then mounted the square collet holder on the other side and repeated the procedure.... ending up with the two cross holes penetrating the sides of the stem at a 30 deg. angle.... That basically straightens the airflow from two 90 deg. bends to just a shallow "S".... hopefully reducing the resistance to flow and the turbulence at that point.... The area of the two 5/32" holes is 7% greater than the area of the main hole through the center of the stem.... Here is what the stem looks like after changing the angle of the holes....



There is still quite a bit of metal between the cross holes and the stem to support it.... I'm hoping that is enough strength to survive the rigors of valve operation.... Incidently, once this machining is done, you end up with virtually bore-size passages for a .22 cal Condor.... However, in this .257 cal version the porting is only 84% of the caliber, and 70% of the bore area.... I think I will get an improvement in performance, but don't expect to approach what Doug Nobel gets with his valves.... Fortunately, I have one of those coming to fit a 250 bar (3625 psi) 500 cc aluminum bottle I just happen to have on the shelf.... When I built my .457 Hayabusa, I bought two.... 

Bob

[Back_Roads]

 Nice deal with the degasser, I was just thinking something like that would be nice, when I discovered a leaky air gauge on my Escape UL 

[rsterne]

This evening I did some testing with the new angled ports in the stem.... First I tried all the Power Wheel settings at 3000 psi, with 2 different bullet weights....



I still have the 1 mm Oring in place on the stem, and the top hat was in exactly the same place as before.... The valve acts completely differently.... It is much like a Cothran valve, it either cycles or it doesn't....  …. Once the valve is shooting at almost full power, all that increasing the PW setting does is use more air, as you would expect.... With light slugs, there is only 2 turns on the PW to go from 500 fps to over 900, and with the heavy slugs it is even worse, just one turn from 400 fps to over 800.... I shot some strings with the lighter slugs at three different power wheel settings.... I used a 3000 psi fill, as before....



At PW = 5 or 6, it was a declining shot string, with only 6 or 7 shots within a 4% ES.... Yes, the power was increased significantly, but tuning for a decent number of shots just didn't happen.... When I tried PW = 4, the first 4 shots were under 750 fps, then it jumped up to 934 when the pressure dropped to about 2900 psi.... The next shot was faster at 943 fps, and then it started to decline again, with only 7 shots within a 4% ES....

Interestingly, the gun wasn't using much air, the pressure at the end of the strings was between 2670-2760 psi.... That meant that the efficiency was astounding (for a Condor), averaging about 1.4 FPE/CI, compared to 1.1 FPE/CI in stock form (with the O-ring)…. Those strings are shown in the dotted lines above, for comparison.... The longer strings with the stock valve stem are because I could shoot down to about 2400-2440 psi before the ES exceeded 4%....

With 82.5 gr. slugs I got over 138 FPE on the first shot (868 fps) but the velocity dropped about 10 fps per shot, and when I backed the power wheel off to try and get a bell-curve then the velocity suddenly dropped by half.... I never got anything but a declinging string of 4-6 shots within a 4% ES.... 

So, I am in a bit of a pickle.... I gained a decent amount of power, but now have a gun that can really only be shot tethered.... At 3000 psi it still won't launch the 66 gr. 257420 HPs I have at 950 fps, which is what I get with my Hayabusa…. It has slightly less air (460 cc instead of 500), and a 2" longer barrel (28" instead of 26")…. but the Hayabusa got a nice bell-curve of 10 shots of 935-948-928 (a 2% ES) with the original valve, and with the new balanced valve I have increased the efficiency about 20% with a slight gain in fps as well.... I was hoping that the axial flow valve in the Condor would make up for the 2" shorter barrel.... but with this valve, that is not the case.... It certainly shows the importance of full bore-area porting, which the Hayabusa has and the Condor does not....

I don't know if a change in hammer weight (lighter or heavier, likely lighter) might make a difference in getting a bell-curve or not.... If anyone has any ideas, or has run into a similar problem with a "high-flow" valve in a Condor, please give me a hint.... 

Bob

[T3PRanch]

I use this for degassing: An AirForce Charging adapter from before spin lock and an aluminum standoff which measures 8mm od by 5mm id by 6.4mm tall.


The standoff is placed on top of the Top Hat and the adapter screwed down till contact is made. A slight twist at that point will vent the bottle.

[MJP]

The airforce valve is a tricky bugger to tune sometimes.
And when you get it just right the valve stem collapses between the holes and you are back to square one.

It's not even strong enough for moderate hammer mass increase, let alone with porting it out.
 
As for shot string, I have never been after that as I mostly shoot tethered.
It does respond well to bigger than bore size ports, you'll get amazing results with very short barrels.

Marko

[rsterne]

Well I can't imagine needing more hammer mass, the velocity plateaus at about PW = 6.... so no need to go heavier, unless there is something I totally don't understand.... which is always possible, I guess....

Bob

[rsterne]

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....

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.... 

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

[rsterne]

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.... 

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.... 

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%).... 

Bob

[MJP]

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....

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.... 

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

Oh, someone actually has built one. Have the plans downloaded from a russian forum some 5 years ago.

[rsterne]

That's cool.... I just haven't seen it before....  …. Forums are a great way to share things, which is why I posted it here....

One thing I thought about, though.... Most regulators vent the center (Belleville) section to atmosphere so that there is a constant reference pressure for the regulator.... I wonder how such a constant reference is achieved, when the regulator is immersed in a tank with variable pressure.... 

Bob

[MJP]

There is a vent hole if my memory serves me right. I'll try to dig up the plans from my old hard drive.

Marko

[gabi.nechita]

Bob
You can also put the bottle under the barrel and use what ever plenum you want, bottle or cilinder.
The hardest part is when you will make the link beetwen bottle and plenum .
Please take a look on this link.

[rsterne]

Cool, but Bullpups are illegal in Canada....

Bob

[MJP]

Here is the in bottle reg pictures.
There was one detail pic of the regulator from the bottom of the tube but unfortunately I cant find it.




Marko

[rsterne]

Tiny plenum, only 14 cc.... I don't see any way to vent the regulator to atmosphere, and I don't know any other reliable way, do you?....

Bob

[calinb]

Here is the in bottle reg pictures.
There was one detail pic of the regulator from the bottom of the tube but unfortunately I cant find it.
<snip>
Marko

I downloaded the exact same three pics from the links in post #25 here, Marko:
https://www.airrifle.co.za/threads/39263-Regulator-for-Airforce-Condor/page2

There was no forth pic but, if you can remember the name / URL of your Russian forum source, it might still be available there or on webarchive.org
-Cal

[MJP]

This is something like 5+ years old stuff. I have some design on some old hard drive that was derived from that, I'll try to look it up.
I think thats the one I remember to be vented out to atmosphere.

Marko

[rsterne]

I don't see a vent on the drawing from the bottom, where the regulator must be, up to the top, which is the only place you can reference to atmospheric pressure....

Maybe that's why it never developed, and disappeared?....

Bob

[Gippeto]

Some stuff here; https://popgun.ru/viewtopic.php?f=23&t=124956&start=2220

Remember some regulator stuff on the TAG (years back) as well. Noticed a link in the popgun.ru post, but of course it's dead now.

Seem to recall a couple folks trying regs that were not vented over the years...orings eventually leak and cause problems...venting required.

Al