GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: Airsnipe on December 22, 2015, 12:52:45 AM
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I'm working on a .25cal build and am trying to figure out the poppet dia, valve throat dia, and TP dia. I'm looking for 45-60ft/lb. I'm using a smooth twist barrel and will probably be shooting JSB 25.39gr or 33.95gr (around 900fps if accuracy allows) depending on which one is most accurate. I will be using a regulator and I'm of course looking for the most efficient setup I can accomplish.
I have an idea of where these specs should be but I would like to hear from the guys here that have built guns in this cal. and what they have found to be efficient. Any other specs regarding regulator pressure, valve spring weight, hammer spring weight, hammer weight and travel are of course welcome. Not trying to get you to design my gun for me but I am looking for some help in making some decisions. ;D I'm super exited about this build but I'm starting to be overwhelmed with spec details :o and I'm having a hard time pulling the trigger on building certain parts as I just can't decide what to do LOL.
And of course, as soon as I'm done, I will post pics and results. I will likely do a build thread as well.
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I would use a barrel port that is 3/16" (75% boresize), and work my way back from there, at that diameter, for the transfer port and exhaust port.... The valve throat will have to be larger, to allow for the area of the valve stem, and I find that having about 10% more area to make up for losses around the seat and stem helps the efficiency.... A 1/4" throat works OK for a 1/8" stem.... If the stem is 5/32", you need a 17/64" throat.... I have found that a regulator setpoint of 1800-2000 psi will produce the power you are looking for with that porting.... You can use a hammer spring similar to that found in a QB 7X, and a hammer between 60-80 grams.... The valve spring is relatively unimportant, as long as it doesn't go coil bind and choke the flow, I find about 7 lbs. force on the seat about right for many PCPs.... All of these specs can be done by modding a Disco valve, BTW....
You can go up one size on everything, making the transfer and exhaust ports 7/32", but you will have to make the barrel port oblong or it may damage the pellet.... It will be the right area at 3/16" wide x 1/4" long.... The throat should be 17/64", but with a 1/8" stem to have enough area.... Going larger than that diameter on the throat may cause problems in getting the valve to open at higher pressures, requiring a heavier hammer and stronger spring.... This size porting will pretty much give you any power you want in .25 cal, depending on the pressure you run....
Bob
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+1 on that advice. What platform are you working from, or is it a ground up build? the marauder valve will reach the fpe you want with a TP and barrel port increase to .156". Hammer is ~79grams and a 10lb spring. Can't remember the throw off the top of my head.
Bill
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Thanks Bob, I was planning on going with 75%-80% of bore based on some of your other posts I have read. This was exactly the confirmation and push I needed to get some stuff done. :D
Bill, it's a ground up build. I'm using a 1.5"OD titanium tube so a Marauder valve is not going to work out. I also don't think I'm going to pin the valve. I don't like the design requirements to pin @ 1.5"OD forces. I know its doable but threading sounds much easier to accomplish all the safety factors I want and the design I want. That and I have a lathe that has a through hole that will fit the tube. The valve and end cap/fill adapter will be 7075.
One thing I'm stuck on is how I'm going to make the Ti tube black. Doesn't seem like you can anodize Ti black so maybe powder coating.
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I'm not so sure you can reach 60 FPE with an MRod valve at 1800-2000 psi, although you can at 3000.... Since you are starting from scratch, I would use the larger sizes, there is no disadvantage other than the heavier hammer strike required.... and you can push upward to about 100 FPE shooting 50 gr. slugs at 3000 psi.... Here are the sizes I used in the valve for the Millenium Pumper, and for my .30 cal Grizzly (FD-PCP based) gun....
Barrel port - 3/16" x 1/4" for .25 cal (7/32" hole for .30 cal)
Transfer port - 7/32" (0.219")
Exhaust port - 7/32" (0.219")
Valve throat - 17/64" (0.266")
Valve stem - 1/8" - giving the equivalvent area of a hole 0.235" diameter
This size is capable of 60 FPE at 2000 psi in .25 cal.... and 100 FPE at 2200 psi in .30 cal.... with reasonable efficiency (over 1.0 FPE/CI) and using pellets.... You can achieve higher power levels (at reduced efficiency) of course.... particularly if you use heavier bullets.... As a rough guide, a hammer weighing 100 gr. with an inch of travel, powered by a QB 7X hammer spring or similar, should put you in the ballpark.... If you can use one, the poppet from an MRod will work perfectly with the above sizes, up to 3000 psi.... no need to use PEEK, Delrin is just fine....
Bob
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Airsnipe, I like the idea of threading the tube to retain the valve also. It will certainly make a stronger assembly. Are you going to have a different tube for the hammer threaded on behind the valve, so that the valve retention threads don't become an issue for the hammer? Or maybe a sleeve in the rear of the tube for the hammer to slide in?
Lloyd
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Bob, a question for you, please. Normally (I think) you use barrel ports of 75% of the bore dia. Do you only use oblong ports when you want to push the upper limit of FPE for the caliber? Any other advantage to using oblong ports considering the extra effort that they take to construct?
Thanks, Lloyd
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The valve will thread into a block of aluminum that will be the hammer tube and breech. The way a lot of FX guns (as well as others) are made. The issue I have been trying to figure out with this design is that it's probably not naturally as light weight as using the air tube for the hammer tube and just bolting a smaller block for the breech. But the idea of threading another tube for the hammer tube onto the valve would be pretty light. I could use a fairly thin wall tube of aluminum and use a transfer port tube with o-rings on each end to connect air flow to the barrel like an Mrod. This would allow a small block of material for the breach and bolt. But the way I'm thinking, I'm not sure how I would attach the breech block? I have an idea though, that would still probably be less weight than my original design. So many things to consider... :o
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Lloyd.... That is correct, any time I need to exceed 75-80% of the caliber (for maximum FPE) I make the barrel port oblong to get the needed area.... If you are going for bore-sized porting, a typical port would be approximately 75% x 125% of caliber.... The barrel port in my new Monocoque .257 PCP is just over 3/16" x 5/16", and the rest of the ports are just over 1/4".... The valve throat is 5/16" with a 1/8" stem, and a 3/8" OD poppet made from PEEK to withstand 3800 psi on that large an area.... It actually isn't that difficult to make an oblong barrel port, you use the appropriate width mill (to match the width of the port ~ 75% bore).... plunge in at 90* flush with the rear of the transfer port, then tilt the mill about 20-30* forward (depending on barrel wall thickness), and plunge in again, still flush with the back of the previous hole.... The length of the port at the transfer port face will about match the port diameter, while at the edge of the bore, it will be longer.... A slight tapering of that up to meet the round transfer port, staying within the thickness of the barrel wall, and you usually get what you need....
Bob
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Gonna follow this one for sure. Good luck with the build.
Joe
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Missed the 2000psi for 60fpe. Nope wont get it with 2000. Maaaybe 2300 iirc.
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Bob, might be a stupid question but what is the difference between the exhaust port and transfer port?
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The exhaust port is machined into the valve (as is the throat).... the transfer port connects the valve to the barrel....
Bob
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How much valve travel should I expect?
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The lift, when operating efficiently, is surprisingly small.... about 1/4 the throat diameter, or about 1/16".... That can double at the bottom of a shot string in an unregulated gun.... but if the lift is more than 50% of the throat, you can almost guarantee the gun is being pushed beyond reasonable FPE, in the attempt to just get one shot for bragging rights.... In a regulated PCP, operating on the knee of the curve, 1/4 - 1/3 of the throat diameter is all you will need....
You should never try and artificially limit the lift, give yourself lots, and let the self-regulating action of the valve do what it does best.... If you allow about 3/16"-1/4" of lift you will have plenty available.... My new .257 Monocoque, with a 5/16" valve throat only has the stem protruding 1/4" behind the valve, and I plan on inserting a 1/16" energy absorbing bumper there, although it will be removable (just in case)....
Bob
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Good luck with the build!!
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I'm not so sure you can reach 60 FPE with an MRod valve at 1800-2000 psi, although you can at 3000.... Since you are starting from scratch, I would use the larger sizes, there is no disadvantage other than the heavier hammer strike required.... and you can push upward to about 100 FPE shooting 50 gr. slugs at 3000 psi.... Here are the sizes I used in the valve for the Millenium Pumper, and for my .30 cal Grizzly (FD-PCP based) gun....
Barrel port - 3/16" x 1/4" for .25 cal (7/32" hole for .30 cal)
Transfer port - 7/32" (0.219")
Exhaust port - 7/32" (0.219")
Valve throat - 17/64" (0.266")
Valve stem - 1/8" - giving the equivalvent area of a hole 0.235" diameter
This size is capable of 60 FPE at 2000 psi in .25 cal.... and 100 FPE at 2200 psi in .30 cal.... with reasonable efficiency (over 1.0 FPE/CI) and using pellets.... You can achieve higher power levels (at reduced efficiency) of course.... particularly if you use heavier bullets.... As a rough guide, a hammer weighing 100 gr. with an inch of travel, powered by a QB 7X hammer spring or similar, should put you in the ballpark.... If you can use one, the poppet from an MRod will work perfectly with the above sizes, up to 3000 psi.... no need to use PEEK, Delrin is just fine....
Bob
This is very close to the specs that I used on my mrod .25 build and was able to produce 110 fpe but very inefficient at this power level. Using 58g slugs. I was able to get 1.0 efficiency around 88-85 fpe. This was shooting from 3000-2000.
My exit port and transfer ports:. .206
barrel port was oval: cant remember the specs:
Through/poppet sit: .256
here is link http://www.gatewaytoairguns.org/GTA/index.php?topic=90710.50. (http://www.gatewaytoairguns.org/GTA/index.php?topic=90710.50.)
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I'm getting about 132% bore volume for the regulated air volume available to the valve with my current dimensions. That is not counting the volume of the space between the valve and barrel. Does that sound adequate? Seems like I should increase that. What is a good number to shoot for?
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I recommend 1 cc of plenum (post regulator volume) per FPE you want the gun to produce.... That way you won't have to bump the setpoint up to compensate for a lack of volume.... If the plenum is too small, you get a larger pressure drop during the shot cycle (because the regulator can't top up the pressure in the 1-2 mSec that the valve is open)....
You are talking .25 cal, but don't specify a barrel length.... If I assume 24", your barrel volume is 19.3 cc, and 132% of that would be just over 25cc.... That is about 1/2 cc per FPE, and while that will work, you can count on having to increase your regulator setpoint maybe 200 psi above what the gun would need to shoot at 50 FPE.... I will use my 2560 as an example.... I get 52 FPE (with 25 gr. pellets) at 1900 psi, and the plenum volume is 65 cc.... With a 25 cc plenum, I would expect to have to increase the setpoint to about 2100 psi to get the same FPE and efficiency....
Since you will be installing the regulator in the reservoir tube, you have to trade off plenum with reservoir volume.... In that case, somewhere around 1/2 cc per FPE may be a better choice for optimum shot count.... Just be aware that you will need a higher setpoint to get the FPE you want....
Bob
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Thanks Bob, I was planning on going with 75%-80% of bore based on some of your other posts I have read. This was exactly the confirmation and push I needed to get some stuff done. :D
Bill, it's a ground up build. I'm using a 1.5"OD titanium tube so a Marauder valve is not going to work out. I also don't think I'm going to pin the valve. I don't like the design requirements to pin @ 1.5"OD forces. I know its doable but threading sounds much easier to accomplish all the safety factors I want and the design I want. That and I have a lathe that has a through hole that will fit the tube. The valve and end cap/fill adapter will be 7075.
One thing I'm stuck on is how I'm going to make the Ti tube black. Doesn't seem like you can anodize Ti black so maybe powder coating.
You can have your Titanium tube Cerakoted.....
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You can have your Titanium tube Cerakoted.....
Ya, I have been looking into cerekote, duracoat, aluma-hyde... Seems like Cerekote is the way to go. Anyone have experience with any of these and would like to share opinions?
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Thanks Bob, I was planning on going with 75%-80% of bore based on some of your other posts I have read. This was exactly the confirmation and push I needed to get some stuff done. :D
Bill, it's a ground up build. I'm using a 1.5"OD titanium tube so a Marauder valve is not going to work out. I also don't think I'm going to pin the valve. I don't like the design requirements to pin @ 1.5"OD forces. I know its doable but threading sounds much easier to accomplish all the safety factors I want and the design I want. That and I have a lathe that has a through hole that will fit the tube. The valve and end cap/fill adapter will be 7075.
One thing I'm stuck on is how I'm going to make the Ti tube black. Doesn't seem like you can anodize Ti black so maybe powder coating.
What are your specs for the Ti tube? Are you going to thread it or use the screw/pinned method?
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I am using 3al-2.5v (105k yield) 1.5 OD .087 wall. Both ends will be threaded.
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I personally like the cerakote.... Both my Extreme rifles have all the parts cerakoted and I am very pleased with the durability..
Also, here is something about the tube you are using that you may find useful..http://www.airgunadvice.net/viewtopic.php?t=16452&highlight=pressure+test (http://www.airgunadvice.net/viewtopic.php?t=16452&highlight=pressure+test)
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You guys always have bright ideas which is pretty cool for sure
Cheers
Jay
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Interesting test of the TI tube.... looks like the ultimate failure was a tensile failure of the tube wall where the thread stopped, an area that is only subject to pressure once the O-ring lest go.... up until then it is in pure tension.... Judging by the big bulge in the wall of the tube, I would say that area is NOT an area of concern, however, and here is why.... JMO of course....
It seems obvious to me that the first thing that happened is that the tube wall started to expand, because the hoop stress exceeded the yield strength of the tube wall.... Once that expansion reached the O-ring, which may have happened rather rapidly, the O-ring ceased to seal, and the pressure was then allowed to reach the end of the thread root.... That area was strong enough to resist the end force on the plug (pure tensile), but once the hoop stress was added, it failed immediately and catastrophically.... The good news here is that the tube bulged before it failed.... If it hadn't bulged, the O-ring would have still sealed, and the thinned area at the thread root would likely not have failed.... With 1" of thread engagement, I am not surprised that neither end plug had a problem, in fact you could probably remove them by hand after the test and they would have looked perfect....
Bob
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This is a great test.
Now I wonder how this failure would have happened if there would have been some holes in the tube between the o-ring and the threaded section like Bob had suggested earlier? As long as the holes where large enough the vent the pressure quick enough and did not cause the weak link by weakening the tube, I would guess the tube would have dumped the pressure without such a catastrophic failure (tube separation).
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I personally like the cerakote.... Both my Extreme rifles have all the parts cerakoted and I am very pleased with the durability..
Also, here is something about the tube you are using that you may find useful..http://www.airgunadvice.net/viewtopic.php?t=16452&highlight=pressure+test (http://www.airgunadvice.net/viewtopic.php?t=16452&highlight=pressure+test)
Did you do the cerakote yourself or have it done?
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This is a great test.
Now I wonder how this failure would have happened if there would have been some holes in the tube between the o-ring and the threaded section like Bob had suggested earlier? As long as the holes where large enough the vent the pressure quick enough and did not cause the weak link by weakening the tube, I would guess the tube would have dumped the pressure without such a catastrophic failure (tube separation).
Chip Smith (who made the tube and commissioned the test) makes lots of Ti tubes and has the knowledge and experience that go along with that. Designing a weak link into your system that will give you a soft failure is a good idea, especially if there is the potential of over-pressurizing a particular part in the system.
Lloyd
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For the Cerakote finish, I like it ok, but I have a local source that does a very nice job with polyester powder coat, which I really love. The particular product he uses for my stuff is VERY tough and you can drill and machine a finished part without chipping or separation. Using proper care, I can even chuck parts in a lathe right on the powder coat with no marring of the finish. One thing to be aware of is the buildup of the powdercoat (and Cerakote, too) onto the surfaces. Like if you are making a close slip-fit band around a tube and both parts get powdercoated all over and you have .003 buildup per surface, that means you need a total clearance of .012 so that the parts will fit back together. And different shops will have different thicknesses.
Another thing about powder coat is that it builds up a little extra on SHARP outside corners. So you need to give all outside corners a noticable edge break or radius to avoid assembly or appearance problems. Lessons learned, LOL. ;)
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You can anodize ti. I have some of the same tubing, and my plan is to use 7075 threaded ends, but one end will be similar to a Hatsan, with the valve being made using an end cap. As long as you're using a block for the hammer it would be the easiest and safest way that I can think of to do it.
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You can anodize ti. I have some of the same tubing, and my plan is to use 7075 threaded ends, but one end will be similar to a Hatsan, with the valve being made using an end cap. As long as you're using a block for the hammer it would be the easiest and safest way that I can think of to do it.
I don't think you can anodize it black.
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You're right, it's more of a very dark purple.