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PostPosted: Mon Nov 07, 2016 12:27 pm 
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Location: Coalmont BC
A couple of years ago I built a Disco Double.... It had a home-made breech that allowed me to interchange between .25, .30 and .357 cal TJ barrels.... It uses a Boyd's Blaster stock in Forest Camo and a Gen1 MRod trigger.... This is what it looks like currently....

Image

The .25 and .30 cal barrels are 25" and can be fitted with the CF shroud and Hatsan Air Stripper as shown.... The .357 barrel is 28" and was never fitted with the shroud.... The current valve is a modded Disco valve with 0.219" exhaust and transfer ports, a 0.266" throat, and a PEEK poppet with a 0.112" stem, which means the area is larger than the ports.... The .25 cal barrel has a 0.188" x 0.250" barrel port, while the .30 and .357 cal barrels have round 0.219" ports.... After a lot of testing and development work, here are the "best" tunes I established for this gun, using pellets and bullets in each caliber....

Image

You will notice that the gun is a rear cocker.... This was necessary because with the large valve throat, running at 3000 psi, a heavy hammer and stiff spring was needed to provide enough hammer strike to achieve maximum power, and cocking it using the bolt just wouldn't work any more.... This always annoyed me about this gun, because the breech uses MRod magazines, and as a repeater, having to cock the gun separately was counter-productive.... When a friend of Don Cothran's offered to send me a Powerhouse valve, I jumped at the chance (thank you, Todd).... Having a valve with even larger ports, that would be much easier to cock, seems like the perfect fit for this gun.... I'm really looking forward to getting to work on it over the next few days to see what happens....

Bob

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PostPosted: Mon Nov 07, 2016 12:31 pm 
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that's great stuff Bob thanks for sharing
and that's a sweet looking Disco.... 8)

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PostPosted: Mon Nov 07, 2016 1:51 pm 
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First order of business is a comparison between the Cothran Powerhouse Valve and a stock Disco valve and one of my modded ones.... Out of respect for Don, I will not photograph or disclose the details of the internals of his valve.... Suffice it to say that he spent years developing it, and being a balanced design, it's key feature is being easy to knock open even though it has huge ports.... Here are photos of the three valves, showing the exhaust ports....

Image

The stock Disco exhaust port is 0.152" diameter, at 90* to the throat.... The valve in the center is nearly identical to the one in my Disco Double, it has the same port sizes, but uses an MRod poppet, which has a smaller OD and stem, instead of the PEEK poppet I made.... The valve exhaust port is 0.219" diameter, and slants towards the throat at a 20* angle to improve the flow.... The brass valve is Don's Powerhouse Valve.... It has a deep 3/8" diameter recess for the transfer port, and the very short port on my valve measures 0.258" diameter.... Both my modded valve, and Don's, use 10-32 mounting screws to allow safe use of higher pressures, compared to the 8-32 screws used in a stock Disco valve.... My screws were shortened to 3/16" because the holes in the valve are blind (they do not penetrate the throat of the valve).... The tapped holes in Don's valve are right through into the throat area, which makes them easier to manufacture, and you can use the full 1/4" length screws without a problem.... However, I noted that the end of the screws stick through about 1/32" into the throat, so I will be grinding the ends off, just to make sure they do not protrude and disturb the flow.... The front of the valve is very different as well....

Image

The stock valve (on the right) has a 1/4" hole and uses a straight valve spring of that ID.... My modded valve is quite a bit larger, and the spring is slightly tapered to allow more flow.... Don's valve is pretty much wide open at the front, so there is very little restriction on flow into the valve.... The SHCS you see in the center mounts his "Force Reduction Piston" which is past of the pressure balancing mechanism of the valve.... In simple terms, it reduces the area of the piston under pressure to reduce the force holding the valve closed.... This reduces the hammer strike required to open it, and allows MUCH larger ports and therefore greater flow.... I have not measured the ports, but Todd supplied me with the dimensions, and he said the throat is 0.335" diameter with a 0.175" stem, giving an area equivalent to a 0.284" hole.... This means that the smallest restriction to flow is the exhaust port itself, which is just over 1/4".... Since that will allow bore-size porting on a .25 cal, and is large enough on a .30 cal to require an oval barrel port, I will not be changing or modifying the valve in any way....

If you were using the Powerhouse Valve exclusively on a .357 cal, it may be worth increasing the exhaust port to 9/32", which is as large as you can go with a drilled barrel port on that caliber without loading problems being a possibility.... Lloyd did this in his test of the MRod Powerhouse Valve.... However, with the limited reservoir capacity of my Disco Double (250 cc), using that much air would be for "bragging rights" only, and while it might be fun to see what the maximum power I could get out of the Powerhouse Valve by modifying it, that isn't the point of this test, and my gun will inevitably end up back at .25 or .30 cal in the end.... On a single tube Disco, hogging out the port for a full house .357 would make even less sense, IMO.... Therefore, this test will be of a "drop-in" Powerhouse valve....

Bob

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PostPosted: Mon Nov 07, 2016 9:09 pm 
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Well, I spent the afternoon in the shop, and the gun is already back together.... It went more quickly than I expected, with no glitches.... The first step was to drain the gun of air and completely strip it apart.... While I had the lower reservoir off, I blued it, something I never got around to originally.... I drilled the hole in the main tube where the transfer port goes to 3/8" to match the recess in the Cothran valve, shortened the 10-32 low-profile high-tensile screws about 0.030" so that they were flush with the inside of the throat, lubed the O-ring and installed the valve.... I then installed a PRod gauge port and reinstalled the gauge and reassembled the two reservoirs, slid on the barrel band that holds them parallel, checked the alignment in the stock, tightened the barrel band and then filled the reservoir, in 3 stages of 1000 psi, letting the gun cool and checking for any drop in pressure each time.... There was no indication of a leak, so after cooling for a while I topped the gun up to 3000 psi and left it sit while I worked on the breech and barrel....

I decided to start with my .357 barrel, I figured I may as well push the gun all out to start with.... Since the barrel OD is only 1/2", enlarging the flat for the transfer port to seal against is tricky, because if you machine the flat full width, the center will break into the bore.... I lined up the barrel carefully in my milling attachment, taking great care to get the existing 5/16" diameter flat (which was full width) square with the tip of the end mill, and then carefully increased the diameter, using a 3/8" end mill, until I just touched the bottom of the existing pocket.... I then used a 1/4" end mill to increase the size of the port, and although the seat margin was a bit narrower on the sides than on the front and back, I figured it would probably seal up fine with the Telfon transfer port I was going to use.... I deburred the port, set the breech up in the mill and redrilled the transfer port through hole to 3/8" as well.... I then used a piece of 3/8" OD Teflon rod to make the transfer port.... I drilled it out to 1/4", and then ran a size "F" drill though it to match the exhaust port in the valve and the barrel port.... I then cut it slightly over length, and gradually shortened it until I judged it to be about 0.010" too long, which is the amount of "crush" I like to see in a Teflon port, and reinstalled the barrel and breech.... So far, so good....

I know that the Cothran valve is very easy to knock open, but of course I had no idea where to start with the hammer spring.... I plan to make an SSG for this gun, but being impatient I wanted to find out A. if the gun still worked, and B. a rough idea of what I would need for a spring.... Todd sent me three springs with the valve, one from a 22XX, one from a 13XX, and one labelled "Disco", but it is a lot longer than the Disco springs I have here, so I can only assume it is from the newer Discos.... So that I didn't have to rebuild the RVA into an SSG just yet (impatient, remember) I tried to slide the springs onto my existing rear-cocking rod.... Well, the 22XX and 13XX springs would slide on, but the Disco spring was a bit too small on the ID.... I decided to try the 13XX spring, slid it onto the rear-cocking rod, reassembled the back of the gun, and checked to see if I could get to coil bind on the spring.... The answer was "I think so", it's very close, but the RVA adjustment screw hit the back of the hammer first.... In any case, at least I could see if the gun would fire.... I installed the .35 cal single shot tray, slid a 77.8 gr. JSB Exact pellet into the breech, and pulled back the cocking knob....

WOW!!!.... Was that ever EASY to cock.... So easy, I actually grabbed the knob, pulled the trigger and lowered the hammer back down onto the valve stem and did it again, just to make sure it really cocked.... The spring I had been using was made from 0.059" wire, and this one is only 0.033".... No way is this going to open that huge valve against 3000 psi was my first thought.... Anyway, I aimed though the Chrony and squeezed the trigger.... MAN IS THIS THING LOUD !!!.... 1002 fps, which is 173 FPE.... with a PELLET !!!.... After I recovered my composure I decide to tether the gun and take a few more shots, backing off the preload a turn at a time to see if I was on the plateau, the downslope, or somewhere near the knee.... I tethered it to my Great White, using a 2900 psi Ninja regulator, confirmed that I was at maximum available preload and fired again.... 1002 fps again.... I backed it off a turn and got 995.... Another turn, and I got a mouse fart.... well not quite, but by comparison it was, and the velocity was only 693 fps.... I fiddled with it for a few more shots, using smaller adjustment on the preload, and I'm faced with what is basically a switch.... Either the valve opens with gusto, or it doesn't.... Just 1/4 turn on the preload drops the velocity from in the 990s down into the 800s.... With this combination of spring, it's either all or (nearly) nothing....

Anyway, I was running out of air, but I wanted to take a few shots with bullets before I top up my tank tonight.... I had two weights of bullets sized to 0.357" to fit the barrel, both from Lee moulds.... a 132 gr. and a 154 gr.... I set the preload back to maximum, and shot a couple of each.... The 132 gr. averaged 849 fps (211 FPE) and the 154 gr. averaged 796 fps (217 FPE).... These were tethered at 2900 psi.... I have no idea if there is any more available or not, I will need a stronger hammer spring to tell.... That will have to wait for tomorrow.... As it sits right now, I have never seen this much power from a Disco before.... about 10 X the FPE of a stock one....

Bob

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Airsonal;
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PostPosted: Tue Nov 08, 2016 6:45 pm 
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I didn't have a chance to try a different hammer spring today, but I did try three strings, from 3000 psi, with the 78 gr. JSB pellets and two bullet weights, 127 & 154 gr.... I set the 13XX hammer spring to maximum preload, and shot 3 shots with each bullet, and the last shot was at, or just under 96% of the first.... Here are the results....

Image

As you can see, the first shot was the fastest, so adding hammer spring, while if might give a higher peak velocity, would not help create a usable shot string.... The efficiency at this power level, considering the gun is tuned for "first shot fastest" is a bit better than I expected.... With the pellets, averaging 164 FPE it was 0.69 FPE/CI, with the 127 gr. averaging 198 FPE it was 0.86 FPE/CI, and with the 154 gr. averaging 211 FPE it was 0.94 FPE/CI....

I'm in a little bit of a quandary here about what to do to eliminate the fussiness of this setup to preload.... I would like to tune it for either 2 shots of equal velocity, or as flat a 3 shot string as possible.... but even small changes in preload drop the velocity a ton.... Perhaps this is a function of the heavier than normal hammer I have.... With the rear cocking rod and handle it weighs 82 grams, as opposed to 60 grams for a stock Disco hammer.... I will ponder this overnight....

Bob

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Airsonal;
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PostPosted: Wed Nov 09, 2016 8:00 pm 
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Well today I was supposed to prune our fruit trees, but it rained so I got a reprieve.... and another day in the shop.... I had never drilled a hole for a cocking pin in my .357 cal bolt for the Disco Double, as I had always used it in that caliber with the rear cocking hammer.... So, I drilled an tapped a hole in the correct place and orientation for the 4-40 SHCS I use for a cocking pin, installed that, and then replaced the rear cocking hammer with a stock Disco hammer and spring, and fitted a Challenger RVA to the back.... I installed a very light indicator rod with O-ring through the spring so that I could measure the lift.... It looks like this....

Image

The gap between the O-ring and the RVA screw is how far the valve opened.... I cranked the preload to coil bound, and as expected got almost identical velocities to yesterday's tests.... I then reduced the preload a turn at a time, firing one of each bullet and recording the velocities, lift, and pressure drop, always starting from 2900 psi (my regulator setpoint).... Here is what happened to the velocities as I reduced the preload....

Image

There was absolutely NO velocity change for the first 3-4 turns reduction in preload, proof positive that I am getting the absolute maximum possible velocity for each bullet at 2900 psi.... Even at 6 turns out from coil bound, the velocity had only dropped about 10 fps.... However at 7 turns out, all that changed, and in a hurry.... Basically, the velocity fell off a cliff, accompanied by a huge reduction in the noise, pressure drop, and lift.... When I plotted the valve lift and the efficiency, here is the results.... These were for the 127 gr. bullet, but the other curves are similar....

Image

It would appear that the Cothran valve can only open physically about 1/8", although I didn't confirm that by measurement on the valve itself.... However, the actual amount the valve opened certainly plateaued at that value, regardless of increasing preload.... It would appear than any valve opening greater than 0.090" only wastes air, without producing any additional velocity.... What happens over just 1 turn of preload adjustment, however, below that lift value, is exceptional.... As the lift initially starts to decline, at about 6 turns out from coil bind, the amount of air used drops, likely because the dwell is being reduced along with the lift.... Since the amount of air used drops faster than the power, the efficiency climbs, until the valve hits the "cliff".... I don't know what else I can call it.... There is no "knee" in velocity as you reduce the preload, the valve suddenly stops opening fully, and the velocity plummets.... The FPE drops to 1/4 or 1/3 of full power over about 1 turn reduction in preload, and then by a similar factor again over the next turn.... Just 2 turns of preload separate nearly full power from barely opening at all.... In fact it can go from nearly full power to very little with just 1/4 turn of adjustment.... or a pressure change of just 100 psi....

The amount the valve opens is influenced to some extent by the bullet weight.... with heavier bullets causing more lift and dwell at the same preload.... At full power and low power the difference in lift is nearly unmeasurable, but in the transition zone it is significant.... At 6 turns out, the lift was about 0.052" with the pellet, 0.065" with the 127 gr. bullet, and 0.072" with the 154 gr. bullet.... This places the exact location of the "cliff" at a slightly different preload when you change bullet weight.... The decrease from 0.060" lift to just 0.020" occurs with as little as 1/4 turn change in preload.... I find this makes it difficult to find the exact point where that occurs, but the fortunate thing is that doesn't matter much, because you will always want the valve opening properly, and an extra 1/2 turn of preload doesn't waste much air.... This characteristic is undoubtedly why Don says that the valve is intended to make big power, not sip air.... My experience so far would definitely confirm that....

Once I determined a setting that made sure that the valve was opening properly but not wasting excessive air, I shot three strings, one with each bullet, starting from 2900 psi.... The results were nearly identical to yesterday....

Image

I was able to get three shots with a 4% ES or less, and the pressure drop was 520 - 540 psi, with the heavier bullets using slightly less air than the pellet to produce more FPE.... I tried many settings, and was unable to achieve even the first two shots at equal velocity, let alone a normal bell-curve.... When I tried, once I got the first shot to drop in velocity, it dropped several hundred fps, and until the pressure dropped 100-200 psi the valve wouldn't return to operating at full power.... At the moment, I can see no way to get what I consider a "normal" tune that peaks in velocity below the starting pressure....

The efficiency of this valve, when operating properly, is very good.... With the 78 gr. pellet at an average of 166 FPE I got 0.88 FPE/CI.... with the 127 gr. bullet averaging 199 FPE it was 1.07 FPE/CI.... and with the 154 gr. bullet the 3-shot string averaged 208 FPE at an efficiency of 1.15 FPE/CI.... While the strings are great for hunting because they are at near maximum power.... getting two shots of the same velocity has so far eluded me....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
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PostPosted: Thu Nov 10, 2016 6:28 am 
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If the preload is not getting the small changes in valve opening you need then this might be a good time to try the Bstaley mod.

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PostPosted: Thu Nov 10, 2016 8:29 am 
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Another way to control how far the valve can open is like the setup on the BT65. The aluminum disc threaded on at the very front of the valve stem takes the impact from the hammer. If the valve stem were threaded all the way to the valve body you can limit the valve opening to what ever you like. An o ring between the disc and the valve body would be a good idea.
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PostPosted: Thu Nov 10, 2016 11:24 am 
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I have considered whether the bstaley mod would be useful in this situation.... but I have used it before, and while it is great for increasing the shot string while reducing the power, it does so by REDUCING the lift in the latter part of the shot string.... ie by limiting the self-regulating capabilities of the valve.... In effect it works like a stiff, progressive valve spring, where the rate increases drastically with compression distance.... Since the Cothran valve is LACKING in self-regulation, this would seem to be exactly the wrong direction to go....

Artificially limiting the valve stem travel, while allowing you to easily set the exact power level at a given pressure, will guarantee that a valve can no longer self-regulate.... Once you fix the lift, the velocity will directly follow the pressure, dropping as the pressure drops.... That is the problem we have already.... What we need is the opposite to occur, for the lift to increase as the pressure drops.... as happens in any unregulated PCP operating on the bell-curve....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Nov 10, 2016 4:06 pm 
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I installed an SSG this morning, using a new Disco spring (at least I think that is what it is) and set the preload to give about 5 lbs. of force and then adjusted for a slight gap.... No joy, about 200 fps.... I adjusted the gap to zero, about the same.... but as soon as I set "negative" gap (ie some preload on the valve stem when uncocked) the velocity jumped to nearly 1000 fps.... I pulled it apart and adjusted the preload to 7 lbs. and at that setting I could barely get any gap without the spring going coil bound, which takes about 12 lbs. of force, making the gun about as hard to cock as I find acceptable using the bolt handle.... At 3000 psi I still had only about 500 fps, so I drained the reservoir down to 2500 and it shot over 900, so I thought "finally, I will get a curve".... I filled the reservoir 100 psi at a time, and the velocity suddenly dropped at about 2800 psi.... I then filled to 3000 and shot a string with the following results.... I was using the 78 gr. JSBs, and later added the data for the bullets.... The pressure curve only applies to the pellets, of course....

Image

It's pretty clear what is going on here.... When the pressure is over about 2800 psi, the valve is not opening properly.... It is only using about 40 psi per shot, and the velocity is varying all over the place between 570 and 680 fps.... As soon as the pressure drops below the magic number, the valve opens the way it should, and the velocity jumps way up into a stable operating zone.... It uses about 150 psi per shot from then on, with the velocity dropping as the pressure drops....

I was hoping to see a further improvement in the efficiency using the SSG, and indeed that did occur.... Previously I was getting 0.88 FPE/CI with the pellets, and now it was 1.03 FPE/CI.... although the average power was down slightly from 166 FPE to 160 FPE over the first 3 "proper" shots.... What continues to disappoint me is that I still have been unable to get anything that resembles a bell-curve.... When I dial the hammer strike down below a critical point, the velocity drops like a stone because the valve is outside its proper operating range.... When the valve IS inside its proper operating range, then all I can get is a "first shot fastest" shot string....

Without changing anything on the gun I tried 3-shot strings with each bullet, starting at 3000 psi.... The starting velocities were as before, and actually the drop per shot was slightly less, because the gun was using less air per shot with the SSG.... It only used 440 psi for 3 shots, so obviously it's working.... The efficiencies increased to 1.30 FPE/CI with the 127 gr. and 1.38 FPE/CI with the 154 gr, with slightly increased power, up from a 3-shot average of 208 FPE to 213 FPE.... There was only a 21-26 fps drop over the 3 shots (3% ES), which means a very usable 3 shots for hunting with either bullet.... The combination of the Cothran Powerhouse Valve and an SSG produces a great setup for my Disco Double in .357 cal, capable of over 200 FPE for 3 shots within less than a 3% ES.... Of course in a single tube Disco, with half the air, you would only get two, with a greater loss in velocity between the shots (maybe 2 within a 4% ES?).... A third shot would be at significantly lower velocity, although OK for a follow-up if required....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


Last edited by rsterne on Thu Nov 10, 2016 4:13 pm, edited 1 time in total.

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PostPosted: Thu Nov 10, 2016 4:12 pm 
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Tried a smaller transfer port diameter?

Al


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PostPosted: Thu Nov 10, 2016 4:18 pm 
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I can try that, Al, in this gun I can restrict the barrel port with the simple twist of a screw that keeps the probeless bolt from retracting clear of the barrel port.... My previous experience in doing that, on a conventional valve, is that it drops the velocity without any significant change to the bell-curve....

Image

My frustration is that I can't even achieve two shots of the same velocity.... As near as I can tell, this valve simply does not self-regulate....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Nov 10, 2016 4:39 pm 
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Just wondering if the virtually unrestricted high speed flow is creating some low or low-er pressure spots in the valve. Choking up the tp a little should raise back pressure a little and possibly increase self regulation.

Al


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PostPosted: Thu Nov 10, 2016 5:02 pm 
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I just tried your suggestion.... No joy.... I screwed the adjuster in 4 turns, which blocks off about half the barrel port.... 3000 psi fill, 78 gr. JSBs....

635 - 931 - 916 - 905 fps.... pressure remaining 2540 psi.... 3 "good" shots avg. 917 fps (145 FPE) at 1.03 FPE/CI.... First proper shot at about 2940 psi....

I then screwed it in another turn, same fill and pellets....

877 - 867 - 860 - 852 - 840 fps.... pressure remaining 2340 psi.... 5 shots avg. 859 fps (127 FPE) at 0.92 FPE/CI.... starting at 3000 psi (like the bullets)....

As you can see, the increased backpressure caused the valve to open properly at a higher pressure, just like a heavier bullet does.... However, there is still no sign of self-regulation.... The flatter strings are due to less pressure drop per shot as the FPE goes down.... but they are still first shot fastest.... I see no point in going further, I was getting more power, better efficiency, and a proper curve with my original valve.... I can get 10 shots inside a 4% ES bell-curve at 126 FPE average with the same pellets on a 3000 psi fill.... 834-867-842 fps at 0.98 FPE/CI, and that was without an SSG.... or 9 shots at over 130 FPE, or 7 shots at 135 FPE....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Fri Nov 11, 2016 10:06 pm 
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Before I get sidetracked, or try modifying anything, I wanted to find out how changing pressure affected the velocity with the Powerhouse valve.... I filled my Disco Double to 3000 psi and shot a string all the way down to 1000 psi using the 78 gr. JSB pellets, which took 22 shots.... I did not alter the SSG during the string, it had just a tiny gap to start with.... I recorded the velocity of each shot, along with the pressure.... and then graphed the results.... The velocity declined in virtually a straight line over the entire pressure range.... I then normalized the data, and calculated the velocity, FPE, pressure drop per shot, and FPE/CI for each 500 psi step, and the data is presented in the table below....

Image

You will note that the efficiency increased as the pressure dropped, something I did not expect, and this is quite different to what happens with a conventional valve, when you don't change the preload.... With a normal self-regulating valve, there is more air released with each shot (that's why it self-regulates), and the pressure drop increases the more you shoot, with the gun getting louder with each shot.... Since the velocity and FPE drops with pressure and the air use goes up, the efficiency drops.... This valve did the opposite.... As the pressure dropped, the valve released less air per shot, ie the pressure drop decreased as the string progressed, up until the pressure dropped to about 1300 psi.... After that, down to 1000 psi, it lost just 60 psi per shot, and as the velocity and FPE were still decreasing, the efficiency started to drop below 1300 psi.... The efficiency peaked at 1300 psi, at 1.53 FPE/CI, at 772 fps (102 FPE).... That is a staggering amount of power at just 1300 psi, along with stellar efficiency.... It took 9 shots to go from 3000 psi down to 2000.... but another 13 shots to get down to 1000....

This suggests some very interesting things to ponder.... First, to put this in perspective, 102 FPE with a .357 is the equivalent of 50 FPE in .25 cal, at just 1300 psi, with the same barrel length.... Now I'm not saying this is possible, but it sure makes me want to find out.... Also, I still had the SSG set to fire the valve at 3000 psi, what will happen to the efficiency if I increase the SSG gap until the velocity just starts to drop at 1300.... ie is there even more efficiency available if I tune the Cothran valve closer to the "cliff" ?.... Obviously, I'm going to have to find out.... I have a 1900 psi regulator here, so I will tether the gun at that pressure, and see if I can improve on the 1.30 FPE/CI efficiency I saw today.... If that occurs, then I will shoot another string down to 1000 psi, and compare those results to todays.... If the efficiency shows a similar peak, then I will try retuning the gun for minimum air use at that velocity and see what happens....

There could be some pretty interesting results from all of this.... data that could point the way for regulated use on a .25 cal version of my Disco Double.... I guess time will tell....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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