Tale of THREE BRods - .25, .30 and .357 Completed, Page 19 !

[rsterne]

Oh, I was able to turn the probe no problem, it was the OD of the .30 cal section that had so little to remove it wasn't worth trying to get it to run true in my 3-jaw.... easier to just file and sand it to fit the chamber.... The length of the cocking slot is not the problem, the position where the cocking lug on the hammer stops is already set, and the front edge of that governs how far back the bolt can withdraw.... I checked it today before assembly, and I only had to remove another 0.020" to make it operational.... I have to hold the bolt back to remove the magazine, but next time I pull it apart I will see where the pellets load relative to the barrel port, I only need to remove another 0.020" and I won't have to hold the bolt back against the hammer spring to swap the mag....

I assembled the .30 cal version today, using the tube with the Cothran valve and the MDS hammer, and did some test shots tethered at 1900 psi and also at 2900 psi.... After about 20 shots at 2900 I started to get some blowby, and within 3 shots, it was severe, with a 200 fps velocity drop.... I pulled the gun apart to find this....



Yep, that's whats left of the Teflon Transfer Port.... Looking at the damage, I think the bottom edge which was thinned out to clear the O-ring in the Cothran valve failed, which let HPA out between the valve and the OD of the port, which then collapsed the port.... Interesting failure, anyway, and the first time I have had a Teflon TP do anything strange.... If there was no O-ring in the Cothran valve, and the TP tube was full thickness to the bottom, I think it would have been fine, as I have used them at much higher FPE and pressure levels.... Anyway, I'll have to come up with a solution, maybe just use PEEK?....

I was quite pleased with the numbers I achieved.... I tested both the 45 gr. and 50 gr. JSB pellets at 1900 psi, and then tested some NOE 67 gr. BBTs and also some Accurate 71 gr. BBTs at both pressures.... Here are the results, with the SSG gap adjusted so that the valve is operating just above the cliff....  NOTE - I EDITED THE TABLE BELOW AFTER MAKING A BRASS TRANSFER PORT - I GUESS THE TEFLON ONE WAS FAILING, BECAUSE I GAINED 50 FPS ON THE 2900 PSI SHOTS....




These represent some pretty impressive power at those pressures.... I now have to make the same tests on the other tube assembly, with the steel hammer and my modded valve.... I got my new NOE .253 cal 51 gr. BBT mould today, so once I get some cast up I will be able to see what these guns will do with those at 2900 psi.... I also need to try the 41 gr. BBTs as well.... so lots of testing ahead yet....

Bob

[oldpro]

 I had same failure 3 times today with Cothran valve blowing out delrin so I made and alloy Tport and the awesomeness of his valve just shined like gold bullion. I used and over travel limiter and MDS hammer and all I can say is WOW!!!!! 

[Motorhead]

Lol .... Not really laughing, just acknowledgment of the why I have been painstakingly fitting PEEK transfer tubes for a few years now in those applications where BIG and THIN WALL have been used together.

[Buldawg76]

I see that you made a brass Transfer port to replace the Teflon one that imploded from the HPA blast but was just wondering if you could have just done away with the o ring in the Cothran valve and made the Teflon the same thickness for its full length instead of thinning it for the o ring at the valve end. I don't really see the need for the o ring with a Teflon TR or any other material that is used as a crush type of seal for the TP.

That failure really shows the power of HPA in a confined area and how it will find a path of least resistance to escape to the atmosphere.

Mike

[rsterne]

The Cothran valve has a 3/8" ID hole to hold the transfer port, but right at the bottom of that hole, it has a half-depth O-ring groove to retain a # 011 O-ring, that is nominally 5/16" ID x 7/16" OD.... This requires that the bottom 1/16" of the transfer port (it is intended that it be made from brass) is turned down to 5/16" OD.... I did that with my Teflon port, which for that bottom 1/16" left the wall thickness only 1/32", and it looks like that is what failed.... I thought about doing as you suggested, and leaving the Teflon 3/8" OD right to the bottom, but then the bottom 1/16" (maybe 0.070") would be unsupported because that area in the valve port recess has been removed to form the groove in the valve for the O-ring.... I was concerned that the TP would fail in that area, blowing outwards, or at the very least expand, locking the TP into the groove in the valve.... After examining the alternatives, I decided to use brass, and seal it at the top, against the barrel, with an 8mm x 10mm x 1mm Metric O-ring located in a shoulder in the top of the Transfer Port.... I made the brass transfer port with a 0.060" long shoulder (5/16" diam.) at the bottom, and a few thou long at the top, and then machined the length down until I could just push the receiver down against the main tube, by compressing the O-ring in the valve.... Being brass, the length is, of course, critical.... I then machined a shoulder 0.035" smaller in OD, and 0.035" deep, into the top end of the transfer port.... This puts the 1mm O-ring into significant compression.... I only tried a few shots, but it sealed perfectly, and I picked up 50 fps.... That makes me quite certain that the Teflon port started to fail almost as soon as I began testing at 2900 psi, which caused the velocity loss.... It is possible that it may have even affected the 1900 psi tests, that will be determined another day....

In the meantime, I am pretty stoked to break 150 FPE at 2900 psi.... 

Bob

[lloyd-ss]

Very nice power from your combination, Bob.  The thin wall at the input end of the soft T-port can definitely cause problems once the air gets behind it.  I am glad you got the brass port sorted out.

[oldpro]

 I couldn't get what I would call a commercial seal on Dons Valve with that oring gland at the bottom so I bored it out and made a compression oring seal like on the Flex. I think it's the only part of the valve design that needs to be re done. I put his valve with a oring over travel buffer in and I'm having awesome results. I know have tons of adjustments with pressure and hammer striker and spring tension. Super Happy!!!!

[rsterne]

I ran all the tests again, with more bullet weights, and determined the position of the cliff.... As expected, it is a bit different with pellets than with bullets.... The lighter pellets need 1/2 turn less SSG Gap (ie slightly more hammer energy) to stay above the cliff.... Here are those results....



It only takes 1 flat (1/6 turn) on the SSG to go from operating properly to being intermittent, and another flat to see the velocity in the basement.... For the velocity tests with the different bullets I adjusted the SSG so that it was solidly on the plateau.... I added the 62 gr. NOE HollowPoints to the testing today, and also I had some .308 cal 80 gr. BBTs from Accurate that I sized down in 2 step) so that I could try them in this barrel.... All the bullets shot today were sized to 0.300".... Here is the expanded table of results at 1900 and 2900 psi with all bullet weights tested....



Note that the Cothran valve pushes bullets faster at 2900 psi than pellets at 1900.... I didn't do any efficiency testing yet, I'm going to test my modded valve first, putting it through the same tests as I did today with the Cothran....

Bob

[grand-galop]

That is huge power!! May i ask why the heaviest bullet has a different curve or dramatic change in the turns you have with the SSG??
The fps is so constant troughout the settings that i Wonder if you maximized the efficiency right before the cliff..

[rsterne]

Alain, the black line on the graph above is at 2900 psi, the red and blue are at 1900 psi.... It is the extra pressure that requires a drastic reduction in the SSG gap to increase hammer energy.... The blue and black lines are the same bullet weight, just different pressures....

I started testing my valve today, and got some data at 1900 psi, but when I changed to 2900 the valve started to leak air out the barrel.... I took a bit more data, figuring it would probably be OK, but the leak got worse so I had to degas the gun and pull it apart.... I lapped the seat and poppet and reassembled, and it still leaked.... I put some soapy water in the exhaust port, and it looked like it was bubbling from the right side, where I had plugged the velocity adjuster hole with epoxy when I inserted the larger, longer seat into the valve when I modded it.... I stripped it apart again, cleaned it thoroughly, and put on some penetrating Loctite, the thin green kind that wicks into threads, hoping it would wick into the cracks and seal them.... I will try it out tomorrow, if it still leaks, I may need to make another valve....

I made an interesting discovery down at my bullet trap this afternoon.... It has several sacrificial layers of particle board, backed by a steel plate, and with all the shooting, it had carved a hole through the layers of wood, down to the steel.... I found these two flattened BBT's laying on the floor, just in front of the trap....



Pretty KEWL, what 150 FPE can do.... *grin*....

Bob

[Hobbyman2007]

The picture reminds me of the fly joke. " what's the last thing to go through a flys mind as he hits a windshield ? ............... his @@@. " . Too bad about the valve leak Bob. I'm sure you'll have it sorted out soon enough .

[Buldawg76]

The Cothran valve has a 3/8" ID hole to hold the transfer port, but right at the bottom of that hole, it has a half-depth O-ring groove to retain a # 011 O-ring, that is nominally 5/16" ID x 7/16" OD.... This requires that the bottom 1/16" of the transfer port (it is intended that it be made from brass) is turned down to 5/16" OD.... I did that with my Teflon port, which for that bottom 1/16" left the wall thickness only 1/32", and it looks like that is what failed.... I thought about doing as you suggested, and leaving the Teflon 3/8" OD right to the bottom, but then the bottom 1/16" (maybe 0.070") would be unsupported because that area in the valve port recess has been removed to form the groove in the valve for the O-ring.... I was concerned that the TP would fail in that area, blowing outwards, or at the very least expand, locking the TP into the groove in the valve.... After examining the alternatives, I decided to use brass, and seal it at the top, against the barrel, with an 8mm x 10mm x 1mm Metric O-ring located in a shoulder in the top of the Transfer Port.... I made the brass transfer port with a 0.060" long shoulder (5/16" diam.) at the bottom, and a few thou long at the top, and then machined the length down until I could just push the receiver down against the main tube, by compressing the O-ring in the valve.... Being brass, the length is, of course, critical.... I then machined a shoulder 0.035" smaller in OD, and 0.035" deep, into the top end of the transfer port.... This puts the 1mm O-ring into significant compression.... I only tried a few shots, but it sealed perfectly, and I picked up 50 fps.... That makes me quite certain that the Teflon port started to fail almost as soon as I began testing at 2900 psi, which caused the velocity loss.... It is possible that it may have even affected the 1900 psi tests, that will be determined another day....

In the meantime, I am pretty stoked to break 150 FPE at 2900 psi.... 

Bob

Bob
I wondered about the Teflon TP sealing without the o ring there and no relief cut into the Teflon TP as well. That as you said it may likely fail like the one you had did only in the opposite direction with the pressure expanding it into the o ring groove in the valve ports seat. I am glad you got the brass TP to seal and used captured o rings at each end that hopefully will hold up to the volume of air that the valve is capable of flowing thru it.

A gain of 50 fps is quite a bit and indeed shows the Teflon TP was leaking from the start and progressively got worse until it failed. It has me wondering if I need to use the steel TP that Don supplied me with the valve even though I am having issue getting the TP to seat properly in the valves port. It has the o ring that yours has for the reducing bushing and then the bushing has a groove cut in the bottom of it the same as the valve to capture a o ring between it and the lower end of the TP and is where I am having trouble keeping the o ring in place without it moving under the thin lip on the TP that should capture it.

The testing is going very good for sure and making 150 fpe is some real power in the 30 cal so just hope both guns group as well as they make power. I am very confident that they will group excellent also.

Mike 

[rsterne]

The leak around the insert I made persisted.... so it was time to remake my valve.... I talked to Travis at W.A.R. and he suggested I bore the valve out 1/2" straight through and make a new insert and seal it with O-rings.... Here is what I came up with....



This is a pretty radical repair job, but it gave me the opportunity to do some neat things.... I made the insert a bit longer, to make room for the front O-ring ahead of the port, and enlarged the exhaust port to 1/4" at a 20* angle (same as the 7/32" port was before).... I drilled the throat out to 9/32" to handle the flow of the larger port, and made a PEEK poppet to handle the loads of the larger seat.... This makes the exhaust port basically the same size as the Cothran valve, and as the transfer and barrel ports....

The details of this mod are pretty much explained in the photo above.... The insert is 1/2" OD, sealed with two # 012, 90D O-rings.... There is another hole in the valve for a 10-32 setscrew, in the same plane as the three valve mounting screws, and a dimple in the top of the insert for that to tighten into.... That holds the insert securely in the valve while you machine the port and the three holes for the valve mounting screws.... They are blind holes in the insert, tapped 1/8" deep, using the threads in the valve as a guide, which requires slightly longer valve screws, as the same screws hold the valve and insert in place against the 3000 psi reservoir pressure.... The poppet is made from PEEK, with the stem from 1/8" drill rod, threaded 5-40 into the PEEK.... The stem is 0.070" longer than stock (for my shortened valve).... in a stock length valve it would be even longer....

I assembled the valve and installed it into the tube and it held pressure beautifully.... I then set about testing the .30 cal setup with this new valve.... I had hoped that the PEEK would make up for the larger throat, and not require more hammer strike, but alas that was not the case.... I had to use significant preload at 2900 psi, and a bit of preload at 1900 with bullets.... At 1900 psi with pellets, I had to use preload to max. out the velocity, but the knee of the curve is right about at zero gap on the SSG.... Here is how the gun responds the hammer preload, using the same pressures and pellets as I did for the Cothran valve above.... 6.8 turns out from max. is "zero" gap for the SSG, so at 7 turns and out the SSG is operating, at less than 7 turns there is preload on the valve stem....



When the hammer strike was on the plateau, here are the velocities I achieved with the various pellets and bullets at 1900 and 2900 psi....



Comparing these maximum numbers to the Cothran valve, at 1900 psi there is virtually no difference in fps or FPE.... At 2900 psi, with pellets my valve is almost there with the Cothran, but with bullets I am losing just a bit with the 62-71 gr. bullets and about 10% less FPE with the 80 gr.... I think I may be running out of hammer strike with the heavier bullets, and the difference between the two valves is now insignificant (as you would expect, with equal ports) except for one thing.... My valve is a LOT harder to open, compared to the Cothran.... I'm using a steel hammer that weighs 104 grams, and a lot of preload on the spring, compared to the Cothran, where I'm using an MDS hammer that weighs 51 grams, and lots of gap in the SSG, in fact I could reduce the preload, or fit a lighter spring.... Don's Powerhouse valve sure is EASY to open.... On the other hand, I can tune my valve down onto the knee of the curve, which should make it more efficient.... I think it's time to start trying to work on improving the efficiency of the Cothran valve by making an adjustable lift arrangement so that I can lower the velocity when using the Cothran valve without lowering the pressure....

Bob

[oldpro]

 Well look at you go!!! That looks fantastic and now you can change valve seats and ports at will!!!! Pretty nice work there my friend! I did my seat a little bigger but same idea as I wanted more threads in the insert. Now just pop it out anytime you need to adjust throats or T port area. This guy had a 450 Throat and 300 T-port ! Kaboom!!!

[rsterne]

Yeah, with a 1/2" OD insert you have to use longer screws, the stock ones are too short to give it enough support.... Of course with a larger OD insert, the loads are higher, so the longer screws are probably still a good idea anyway.... You can certainly hog everything out this way.... and you have the added benefit of being able to guarantee that the seat is at 90* to the valve stem hole, 'cause you're not working down inside the valve.... I see you didn't bother with a rear O-ring, no problem with air escaping into the hammer space during a shot?.... That's why I put one there, plenty of room aft of the screws, even in my shortened valve, tons of room in a stocker....

Certainly eliminates the problem of a stock MRod valve not having enough room for a big exhaust port.... Thanks again for the idea, Travis.... much appreciated.... 

Bob

[oldpro]

I like your rear oring idea Bob and the other thing we can do is use epoxy to build a smooth ramp up to tport now that it's easy to get to.

[Motorhead]

Another trick ( design you can use now ) is that of keeping the poppet head diameter smaller for easier opening by going to a tapered seat like an automotive head valve.

All my personal PCP's with Peek poppet heads have been done this way for a few years now.
Seat / Head on an @ 15* angle having the sealing margin very near the O.D. edge of poppet.

Here is what I use in my M-rods based on a .250 throat valve. Poppet O.D. is @ .300" having sealing margins of .020" just .005" from the O.D. diameter.
* Being the seal between the two is across a flat the peek has not shown but minor extrusion into the throat at @ 2K working pressures ( regulated actions )

[oldpro]

 Or go exotic and use two stage poppet with big throat!

[rsterne]

I went back to the tube with the Cothran valve today, looking to experiment with varying the lift at 1900 psi.... First I had to make a hammer with an adjustable striker position.... This is the second MDS Nylon hammer I have made, and this time I decided to make it even lighter, with an aluminum core.... They are pretty simple to make, actually.... I started with a piece of 3/4" aluminum, faced it off and drilled it through with a #3 drill (the tap size for 1/4"-28 threads) and then used a 1/2" end mill to create the spring cavity 3/4" deep.... I then knurled the outside longer than the hammer, but leaving a smooth area I could hold in the lathe chuck.... I bored a piece of MDS to a few thou over 3/4", but about 0.010" smaller than the OD of the knurling, faced both ends square to a length of 1.25", and pressed them together to form this....



I then turned the OD to finished diameter to slide smoothly in the tube, and holding the stub of aluminum in a collet I drilled and tapped two 8-32 holes, one for the cocking pin and one for a "brake" to prevent the adjusting screw from adjusting itself.... I then faced off the length at the nose, added the taper for the sear, and tapped the nose through to 1/4"-28, ground the cup point off a 1/2" long setscrew, and installed it with the allen key hole on the inside.... I then dropped a 1/8" long piece of 1/8" diam. Delrin in the front hole, against the side of the adjuster, and topped that off with a 1/4" long 8-32 setscrew, tightened against the Delrin, pressing it into the threads of the adjuster.... Now I can adjust the striker from flush 3 turns in either direction, which is greater than the length of the valve stem on the Cothran valve, so I can go from full lift to no lift in (just under) 6 turns.... Here is the finished hammer, which weighs 28.4 grams (exactly 1 oz.)....



I had a small scrap of energy absorbing polymer sheet about 3/32" thick from Lloyd, which he used in his Cothran valve experimenting, and cut a washer from it with a 3/8" hole (for the striker to clear) and the OD a snug fit in the tube, and installed it hard up against the back of the Powerhouse valve as a bumper to stop the hammer and absorb it's energy.... I removed the spring guide from my SSG, so that I could access the lift adjuster from the back with a long 1/8" allen key, and using the same hammer spring as before, reassembled the gun.... I set the preload on the spring to zero (with the striker just touching the valve stem) with the striker set flush with the face of the hammer.... Assuming the hammer hits the bumper, the valve stem will be driven open about 0.108", and at 0.036" travel per turn of the adjuster, that means that 3 turns out (proud of the hammer face), the striker will push the valve fully open, and backed out about 2.5 turns below flush, it won't open the valve at all.... That was the theory, anyways....

I reassembled everything, tethered the gun at 1900 psi, loaded up a mag. with 45 gr. JSBs, and took a shot.... I had no idea if the valve would cycle properly at these settings or not, and smiled as the shot went through the Chrony at 978 fps, exactly the same as the plateau velocity I had before.... I checked the velocity with more spring preload and it stayed the same, as expected, then reduced the preload, no change at 1 turn of gap, a few fps less at 2 turns, but at 3 turns of gap it dropped to 284 fps.... OK, so there is the normal "Cliff" for the Cothran valve.... I set the preload at 1 turn negative (ie 1 turn of gap), and started adjusting the lift by moving the striker in and out.... When I increased the lift (striker extended), the velocity stayed the same, as expected.... Then I started backing it out, below flush, to reduce the lift on the valve, while leaving the valve cycling properly by virtue of having lots of hammer strike.... I was hoping to be able to have much finer control over the velocity, to give me the ability to control the velocity on the Powerhouse valve without having to change the pressure.... Unfortunately, I was disappointed....

As I recessed the striker into the valve, at 1 turn below flush the velocity held steady at 978 fps.... I figured, "OK, this valve doesn't need much lift".... At 2 turns below flush, I got 321 fps.... much like I did when changing the preload a turn, the valve either cycled or it didn't.... At 2.5 turns out, or further, the valve didn't open, exactly as I had hoped, no shot at all occurred.... I tried various combinations with more preload on the spring, to make sure that I had LOTS of hammer strike, and could not get away from that annoying cliff.... If I was just 1/6 turn (one flat on the allen key) more recessed than where the velocity was steady at 978 fps, the velocity was unstable, it could  be anything from under 600 to over 800 fps.... As I recessed it more, the velocity range dropped, but it was still not stable, fluctuating 100 fps or more, shot to shot.... If anything, I think the velocity was more stable with the valve lift greater, and reducing the preload.... I'm pretty frustrated at this point.... Travis suggested I try a heavier valve spring, but I don't have anything suitable, unfortunately.... At this point, I still have no way to reduce the velocity when using a Cothran valve, other than by dropping the pressure....

Bob

[oldpro]

 Take the spring out and stretch it and shim it. Theres plenty of room and once you have more spring rate the valve adjustments can be made but not in small amounts but you will be able to get some adjustment and not just have and on off switch. But like you said its all about matching the pressure to the valve not about dwell and lift.