GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: Monkeydad1969 on July 06, 2015, 01:25:57 AM
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Got a new TP in for my Cothran PowerHouse vavle. So here are pics of the Cothran valve compared to a stock Disco valve, and the TP (thanks to member miksatx for the TP):
(http://i1302.photobucket.com/albums/ag124/josephb1969/IMAG2268_zpsxjcw1zul.jpg)
(http://i1302.photobucket.com/albums/ag124/josephb1969/IMAG2269_zpsyotrmmmv.jpg)
(http://i1302.photobucket.com/albums/ag124/josephb1969/IMAG2271_zpsghuz7vqr.jpg)
(http://i1302.photobucket.com/albums/ag124/josephb1969/IMAG2272_zps4i4ncexb.jpg)
(http://i1302.photobucket.com/albums/ag124/josephb1969/IMAG2273_zpstdswkcwb.jpg)
(http://i1302.photobucket.com/albums/ag124/josephb1969/IMAG2284_zpsleujwn2u.jpg)
(http://i1302.photobucket.com/albums/ag124/josephb1969/IMAG2285_zps1tunug0e.jpg)
(http://i1302.photobucket.com/albums/ag124/josephb1969/IMAG2286_zps5bo2t7i5.jpg)
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Nice.... How big is the exhaust port in the valve?....
Bob
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Very nice Joe.
Look forward to reading about the gun your building with the valve.
Dave
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The lip is 3/8" and the exhaust is 1/4" ID (I believe). I will have to measure it later when I take it apart.
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That TP looks massive!!!!
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Right now I am getting 50fpe with a 13XX spring cut down about 3 coils less than a Disco spring. With no preload. On a 2400psi fill I have gotten 850fps/69fpe shooting a Eunjin 43.2 with a cut down heavy hammer spring. The valve is a beast.
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geeez I wish my .30 pellets would hurry and get here. Good work Joe that ought to knock the heck out those pdawgs.
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I think, after talking with my bud Dave, I am going to order a .30 from TJ, then later a .357.
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Can't go wrong!! I still need to order my TJ .357 as well!
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Can't go wrong!! I still need to order my TJ .357 as well!
Did you get pricing per inch? Wonder if it has changed.
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yep pricing per inch- I think it goes up a bit when you go over a certain length- maybe over 30"? I could be wrong about the length. I got a 24" .30 barrel for $118... $133 with shipping. He packages the barrels really really well!
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Is that the .300 with 1 in 10 twist?
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Nice valve & TP Monkeydad!
Have you been over at the 54 airgun forum and seen this post about a 357 cal w/cothran valve used in a 2260 tube...gracious
http://www.network54.com/Forum/581291/message/1432337130/2260+pcp+.357+My+1st+big+bore+project%21%21%21 (http://www.network54.com/Forum/581291/message/1432337130/2260+pcp+.357+My+1st+big+bore+project%21%21%21)
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Nice valve & TP Monkeydad!
Have you been over at the 54 airgun forum and seen this post about a 357 cal w/cothran valve used in a 2260 tube...gracious
http://www.network54.com/Forum/581291/message/1432337130/2260+pcp+.357+My+1st+big+bore+project%21%21%21 (http://www.network54.com/Forum/581291/message/1432337130/2260+pcp+.357+My+1st+big+bore+project%21%21%21)
Not yet, until now. That guy is on here already. I think he can get better fpe, though.
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Look forward to seeing your results Sir.
Dave
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The one I ordered was the one Sean and Bob came up with: 1:26 twist, .590" O.D.
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Tom are you going to prep the barrel or have someone else do that?
Joe
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Someone else- I don't have the skill nor the machines to do the work. I have the drive though! The .357 TJ will be going on a QB build.
D.C. needs to start making Prod PowerHouse valves too! Much more secure build in my mind... Then I'll do a Crosman .25 Katana, Ver. 2 build!!
I wonder how much Oommpf this valve will have with .25 cal 70 gr slugs... Hmmmmm
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49 grain slugs are doing pretty good. Need to chrony. But in my little 12' fun range (pathetic, I know), I have some Bob's BT's 49gr and they are going 2.25" into 2 2x8's put together---thru the first and about halfway into the 2nd. I know the distance isn't impressive, but I have high hopes. RVA turned in 4 turns on 2200psi fill.
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Curious how that valve is supposed to open easier? IMO it will not. Lots of closing forces but I cannot for the life of me see how it would open any easier than any other popped valve.
Walter.....
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Curious how that valve is supposed to open easier? IMO it will not. Lots of closing forces but I cannot for the life of me see how it would open any easier than any other popped valve.
Walter.....
I own 3 cothran tubes all have powerhouse valves. I know for a fact they open easier than a p rod valve with out pressure against it. If you don't own one you don't have a informed opinion about it.
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Walter, you need to talk to Al (Gippeto).... Here is what he wrote about it, referencing the photo on the Cothran website.... http://www.cothranmachine.com/PowerHouse%20Valve%20from%20October%202013.pdf (http://www.cothranmachine.com/PowerHouse%20Valve%20from%20October%202013.pdf)
Very small hole in the valve stem is a vent...(can just be seen below and to the left of center of the o-ring) stem is partially hollow. Small piece of rod slides inside of valve stem.
Piston assembly on the right is secured to the body by the screw.
Valve "hat" is hollow...slides over top of piston assembly...uses the urethane seal shown...lower force holding valve closed requires softer material to seal.
The piston area being vented to atmosphere, the net effect is a reduction in surface area for pressure within the valve to push on...resulting in lower opening force.
During the shot cycle, pressure bleeds through the hole in the valve stem, past the rod to the piston assembly and adds a considerable amount of closing force. Once shot cycle is completed, this would then vent back to atmosphere...rod would slow the venting, helping hold the valve closed during early (higher force) hammer bounce events. Rod diameter could be tweaked to adjust fill rate/closing force, but would also effect on the venting end....
I admit that without Al's description of how it operates, I had no clue.... :-[
Bob
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Curious how that valve is supposed to open easier? IMO it will not. Lots of closing forces but I cannot for the life of me see how it would open any easier than any other popped valve.
Walter.....
I own 3 cothran tubes all have powerhouse valves. I know for a fact they open easier than a p rod valve with out pressure against it. If you don't own one you don't have a informed opinion about it.
The PowerHouse valve is a GOD among valves :) ...it is very nice. Yes it is very easy to crack open. It does amazing power.
Joe
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I'm still hoping he does one for a Prod!!!
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I'm still hoping he does one for a Prod!!!
That would be sweet. Have you asked him yet? Can you imagine one for a M-Rod? Can you say .30 M-Rod conversion?
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The piston inside the stem is a closing force best I can determine.
Respectfully beg to differ with Al on this one.
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Curious how that valve is supposed to open easier? IMO it will not. Lots of closing forces but I cannot for the life of me see how it would open any easier than any other popped valve.
Walter.....
I own 3 cothran tubes all have powerhouse valves. I know for a fact they open easier than a p rod valve with out pressure against it. If you don't own one you don't have a informed opinion about it.
Held one in my hands fully dissassembled. Made a full sketch of the unit. Does that count for an informed opinion?
What pray tell does no pressure forces have to do with the discussion?
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Piston is bolted to the front of the valve, so the area of the piston (smallest black O-ring) is subtracted from the area of the sealing surface of the poppet seat (somewhere on the white O-ring), since the inside of the "top hat" shaped poppet is vented to atmosphere when the valve is closed.... I've never had one in my hands, but Al's description makes sense to me when I look at the photos.... Since it is a known fact that the valve is MUCH easier to open at a given pressure, perhaps you have another explanation?.... The small rod inside the valve stem works like a "leaky check valve" in combination with the tiny bleed hole in the stem, helping the valve to not open during hammer bounce.... but allowing the inside of the poppet to return to atmospheric pressure before the next shot....
If you have a sketch that shows otherwise, I'd love to see it.... scan it and post it?....
Bob
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High pressure on piston seal will push on the sleeve closing the valve
On firing the small rod becomes active assisting the popped return to closed.
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High pressure on piston seal will push on the sleeve closing the valve
Sorry, I don't understand.... The piston, carrying the small O-ring, is bolted to the front of the valve and doesn't move, correct?....
The vent hole in the valve stem is inside the exhaust port of the valve, and hence is at port pressure.... high during firing, atmospheric between shots....
The small rod inside the stem rattles around with a small clearance, delaying pressure change immediately after a shot.... to avoid bounce....
After the shot, the inside of the valve stem, and hence inside the poppet sleeve, is at atmospheric pressure.... therefore the closing pressure acts only on the seat area MINUS the piston area....
What did I miss?....
Bob
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Pressure inside pushes towards low pressure. In this case the piston is stationary and force acts on move able sleeve to push it off the piston. A closing force
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Curious how that valve is supposed to open easier? IMO it will not. Lots of closing forces but I cannot for the life of me see how it would open any easier than any other popped valve.
Walter.....
I own 3 cothran tubes all have powerhouse valves. I know for a fact they open easier than a p rod valve with out pressure against it. If you don't own one you don't have a informed opinion about it.
Held one in my hands fully dissassembled. Made a full sketch of the unit. Does that count for an informed opinion?
What pray tell does no pressure forces have to do with the discussion?
Well maybe ya should have put it together and pushed the valve stem in and out with your thumb. Instead of drawing pictures of it.
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Valve spring force is about 5 percent of the issue.
To run a weak valve spring the closing forces come from other parts.
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What pray tell does no pressure forces have to do with the discussion?
Stop praying maybe that will help. I made a simple statement that the valve opened easier. I made this obeservence by doing this test I held a cothran valve in one fist and a p rod valve in the other and pushed down on the valve stems. the cothran pushed in easier.
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Here is a drawing of the valve, as I understand it, without the small rod inside the stem.... It is shown in the closed position.... Since the rod is a loose fit in the stem, and only acts as a "leaky check valve", when the valve is closed the pressure inside the head of the poppet is at atmospheric pressure.... I have also omitted the spring for clarity.... The stem (blue) and the poppet head (red) are threaded together and move as one unit.... Everything shown in black is fixed, the piston is bolted to the front of the valve....
(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/Cothran%20Valve_zpsnxpfzcj1.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/Cothran%20Valve_zpsnxpfzcj1.jpg.html)
The force holding the valve closed would be the air pressure of the HPA, acting on the area of the seat minus the area of the fixed piston.... If the piston area is half what the area of the OD of the seat is, the force holding the valve closed would be reduced by 50%.... Therefore, only half the force would be required to open the valve....
Please note the above drawing is not to scale, and is not intended to violate Mr. Cothran's rights.... it is intended to simply explain how the "Force Reduction System" he has invented works....
Back to you, Walter.... ;)
Bob
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Michael.... Your test is static and has nothing to do with the air pressure in the valve (because there wasn't any).... All you were measuring was the spring force.... That was Walter's point....
Bob
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Michael.... Your test is static and has nothing to do with the air pressure in the valve (because there wasn't any).... All you were measuring was the spring force.... That was Walter's point....
Bob
And your drawing is wrong Bob you left out the stabilizer piston that fits in the stem.
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and you didn't read my post.... I bolded where I covered that....
Bob
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Piston pushs tophat/stem away from it closing valve
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Seriously, Walter?.... How does it do that?.... It's bolted to the front of the valve and doesn't move?.... Only the red and blue parts in that drawing move, and they move as one unit as they are threaded together.... The "top hat" slides on the O-ring on the piston, therefore the piston can apply no force to it....
Bob
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Closing force does not require movement
The pressure tries to push the red part off the piston hence closing force
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and you didn't read my post.... I bolded where I covered that....
Bob
Sure I read it. thats why I mentioned the drawing is wrong. Not real sure what respecting his invention is supposed to mean in explaing how the system works. There's a link to a airguns mag that has a article on some of the valve design. the valve is tore apart and each part named. Mr Cothran don't seem to worried about his invention that I can tell. But leaving out that stabilizer piston in the valve stem in real life the valve doesn't work right.
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Michael.... Since you seem to know exactly how the valve works, I suggest you draw it "properly", with all the parts, in several positions; closed, just open, and closing, and show the position of the rod (stabilizer piston) in each, and the airflow that occurs.... It only took me an hour to "whip up" that drawing, and I feel that it 100% represents the situation when the valve is CLOSED, since the stabilizer piston is a loose fit inside the valve stem, with atmospheric air pressure surround it, which is why I omitted it from the drawing.... because it makes NO difference to the valve when closed....
Walter.... Yes, the air pressure tries to push the red part off the piston.... but can only act on the area OUTSIDE the diameter of the piston.... Thank you for making my point.... If the piston diameter equalled the seat diameter, the only force holding the valve close would be the spring.... Draw it out and see....
Bob
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http://www.cothranmachine.com/WhatNew.HTML (http://www.cothranmachine.com/WhatNew.HTML)
Hey all, just go to this link and you can find the link to actual story in Airgun Hobbyist Magazine.
And lets all just relax. It's just a valve, even though it is BAD @R$E!
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because it makes NO difference to the valve when closed
Bob
if the gun is charged with air and you have left the stabilizer piston out of the valve stem. Tell me Bob what keeps the air from leaking out the hole in the valve stem?
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Last attempt.... Here is a drawing with the piston diameter equal to the seat diameter....
(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/Cothran%20Valve2_zpstthec9ux.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/Cothran%20Valve2_zpstthec9ux.jpg.html)
With the valve closed, as shown, there is NO force holding the valve closed except the spring.... Have a nice day !!!
Michael.... The hole in the stem and the pocket in the head of the poppet are on the OUTSIDE of the valve seat, and are at atmospheric pressure when the valve is closed.... there is no pressure there to leak.... I repeat, the rod (stabilizer piston) is a LOOSE FIT and rattles around inside the valve stem and does NOT seal anything.... It simply slows down the pressure changes during the firing cycle to prevent valve bounce.... I would imagine it was added later because the valve opened TOO easily and became a machine-gun from hammer bounce.... It was, I must admit, a VERY clever way to deal with that problem.... but it has NOTHING to do with the "Force Reduction System" which is the key to why the Cothran valve opens so easily.... Like I said, take the time to draw it out and show me where I am wrong.... Same thing goes for anyone....
Bob
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Michael.... Since you seem to know exactly how the valve works, I suggest you draw it "properly", with all the parts, in several positions; closed, just open, and closing, and show the position of the rod (stabilizer piston) in each, and the airflow that occurs.... It only took me an hour to "whip up" that drawing, and I feel that it 100% represents the situation when the valve is CLOSED, since the stabilizer piston is a loose fit inside the valve stem, with atmospheric air pressure surround it, which is why I omitted it from the drawing.... because it makes NO difference to the valve when closed....
Walter.... Yes, the air pressure tries to push the red part off the piston.... but can only act on the area OUTSIDE the diameter of the piston.... Thank you for making my point.... If the piston diameter equalled the seat diameter, the only force holding the valve close would be the spring.... Draw it out and see....
Bob
Sorry Bob I dont follow the outside the piston
I see it as closing forces being the sum of the areas with pressure differential in the same direction
The valve seal force is leftward in the sketch
The piston tophat force is leftward as well.
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OK, Walter, maybe one more try.... If you have a sleeve sliding on a rod, and surround it by HPA, is there an end force on it?.... Rhetorical question, so I'll answer it.... NO of course not.... On the second drawing I just posted, where the piston diameter is the same as the seat diameter.... there are two shoulders on the ends of that red part exposed to the HPA.... one on the right (where the HPA will push to the left) and one on the left, just above the seat (where the HPA will push to the right).... Those forces will completely cancel out, leaving no net force on the red part, just as if it was a sleeve surrounded by HPA....
In the case of the Cothran valve, the piston PREVENTS the HPA from pushing on the end of the red part over its whole diameter.... Only the DIFFERENCE in area between the piston and the valve seat can cause a force to hold the valve closed once it is on the seat....
Bob
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Kind of a hard one to put in simple terms, but will take a swing at it...
Force generated is pressure multiplied by the area upon which it acts, think we can all agree on that.
For an example, lets say seal diameter of the "hat" part of stem is .300", and the piston diameter is .250"...works out to areas of .071sqin and .049sqin respectively.
No disagreement about valve stem diameter generating closing force during the shot cycle, so we'll call that part a given.
Will break the valve stem into a few parts...the shaft, what I'm going to refer to as the "hat"...usually a piece of delrin, the soft seal, and the little rod which moves inside the stem of the Cothran valve. Common terminology is important when trying to share an idea.
In our case, to generate force with a direction, one side of a contained object is exposed to a higher pressure than the other.
In the case of a "conventional" poppet valve, the throat side of the "hat" is at atmospheric pressure, while the other side is exposed to reservoir pressure. This generates a force holding the valve closed. If we take our example of .300" dia....that's 213 lbs force at 3000psi holding the valve closed.
With the Cothran valve, we have the added factor of the piston assembly...which, being vented to the valve throat is at atmospheric pressure before the shot cycle begins. This area, with atmospheric pressure on both sides, generates a net zero force.
Before shot cycle begins, effective area upon which pressure in the reservoir can act is .071sqin - .049 sqin.... .022sqin...@ 3000psi, that's 66 lbs force holding valve closed.
If it helps, think of the "hat" in a Cothran valve as a doughnut without a center (riding on a tube and all mounted within a larger tube) ...having no center, it has less surface area than if it were solid the full diameter.
Once things get pressurized by the shot cycle (pressure from the throat area enters via the small hole in the side of the shaft), the area of the piston does generate closing force...the little rod within the shaft helps to maintain that closing force after throat pressure has fallen to atmospheric...and helps keep the valve closed while the hammer is bouncing.
Hope that makes some sense...
Al
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I see it as pressure across seat = closing force
Plus pressure across piston tophat seal = more closing force
Inside valve is hp and atm on other side of piston seal
That produces a closing force
I think we need to determine the seal barrier locations and then assign the force direction
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Thanks, Gippeto.
Joe
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I have one a part right now seems that the little rod got stuck in the valve stem. Velocity dropped 250 ft per sec. Waiting on replacement parts. Didn't leave it aired up when I was waiting on a new breech.
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Thanks, Al.... I guess Walter is going to need a demonstration....
Bob
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Not sure what you mean by that Bob.. ???
Al
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Just that he doesn't agree, so perhaps showing him that the valve does, in fact, require less force to open than a conventional valve might change his mind.... That is, after all, the whole point behind the "Force Reduction System"....
Bob
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Yup, a demo is definitely overdue. My brain is hurting real bad.
Will be making a test fixture to sort this out. Cannot get my head around d this one lol
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Darn it, you guys have made more work for me, I bought a used Cothran .357 about a month ago. It does shoot hard. Now I have to disassemble it to satisfy my curiosity about what valve is in it. I know, relieve the air pressure first. Regards, Tom
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Don't feel bad, Walter, I know what you mean about brain burn.... I looked at the photo forever with no joy until Al explained it.... then I went DUH!.... *lol*....
Bob
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my valve. i'll try to get a pix of the hole in the valve stem when the valve is together. As it's not visible while the valve is closed.
(http://i160.photobucket.com/albums/t190/miksatx/DSC00095_1.jpg) (http://s160.photobucket.com/user/miksatx/media/DSC00095_1.jpg.html)
Not a real clear pix but you can make out the hole in the stem this is valve wide open.
(http://i160.photobucket.com/albums/t190/miksatx/DSC00097_1.jpg) (http://s160.photobucket.com/user/miksatx/media/DSC00097_1.jpg.html)
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if you take the valve a part be sure the hole is facing up in the exhaust port. i have had this valve stem hole rotate out of the exhaust port and lose performance. I use long slim needle nose to grab the stem push in and line the hole back center in the exhaust port.
Leaks I've had them on both sides caused by debris under the valve seal and a nick in the o ring on the piston leaked right out the vent hole in the valve stem. I believe I'll be changing out my fill valve with a disco one since it has a metal filter.
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Started on a test fixture last night. While redrawing the parts I had an epiphany lol
Reduced to simplest elements it is a chamber with a central guide rod. Then a piston with an internal and external sealing oring fits into fitting
It now is easy to understand that the force generated will be due to the EFFECTIVE area! Man I missed that somehow!
So my apologies for my pigheadedness :-)
The valve as made by Cothran is pure genius!
Will finish the test fixture and perhaps Bob will help me post pics on here.
Brain is starting to calm down now!
Cheers
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Cheers.... ;D
Email me the pic and I'll put it in my photobucket account.... bob at mozey-on-inn dot com
Bob
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Here is the sketch of Walter's test rig....
(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/IMG_4780_zpsnnlb5i7s.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/IMG_4780_zpsnnlb5i7s.jpg.html)
Bob
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Thank you Bob
Built the test rig. Made the large piston 0.650" and the small 0.460"
With the full diameter pumped to 150 psi the scale read 40 pounds.
With the annulus sensing the 150 psi the scale read 19 pounds.
So fun was had and the brain is able to relax a bit :-)
Now to discover more ways to use this neat idea.............
Walter
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Walter's Test Rig....
(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/IMG_4795_zpsbsrc1jrz.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/IMG_4795_zpsbsrc1jrz.jpg.html)
(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/IMG_4796_zpsnoi3mcgr.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/IMG_4796_zpsnoi3mcgr.jpg.html)
(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/IMG_4797_zpsa9d9jqzf.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/IMG_4797_zpsa9d9jqzf.jpg.html)
(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/IMG_4798_zpstuwt2ozx.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/IMG_4798_zpstuwt2ozx.jpg.html)
Bob
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Thank you Bob. Thinking of uses for this biased valve idear :-)