GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: happymecanic on June 04, 2021, 05:56:24 PM
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Hi guys,
Is there a way to determine the number, dimensions and disposition - ()()()()( - or - (())(())(( - etc of the Belleville washers (spring discs) in the internal regulator of a PCP air rifle? If for example you have one that’s messed up from the start (not by me). Assuming I know the specs of some spring washers I have bought – 10 mm x 5,2 mm x 0,5 mm - ( https://spaenaur.com/wp-content/uploads/2018/02/Disc-Spring-Washers-D39-D64.pdf ) , the dimensions of the regulator and the high/low pressure I have/want (3000/850 psi), would it be feasible to calculate the quantity and strength of necessary spring washers? What about preload, if necessary, how much? Thanks in advance.
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If you have all the dimensions, including the assembled height of the Bellevilles, the specifications on them, and the space available when the regulator is closed, plus the diameter of both ends of the piston, then it can be calculated to some approximate value.... However I don't know of any simple formula that is readily available to do the job, it would be a matter of figuring out the force on the piston at 850 psi, and then coming up with a Belleville stack where the force equals that when the stack is compressed to the installed height with the seat just closed....
Bob
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If you have all the dimensions, including the assembled height of the Bellevilles, the specifications on them, and the space available when the regulator is closed, plus the diameter of both ends of the piston, then it can be calculated to some approximate value.... However I don't know of any simple formula that is readily available to do the job, it would be a matter of figuring out the force on the piston at 850 psi, and then coming up with a Belleville stack where the force equals that when the stack is compressed to the installed height with the seat just closed....
Bob
Thank you Bob, I was so hoping you'd chime in :D. I guess I need to calculate the surface area of the piston head (regged pressure) and of the piston stem tip (high pressure) to be able to determine the difference of pressure between the two, which will therefore be useful to determine the force of the spring washers pack? I made this prehistoric hand-drawing ;D, hope it can be of some help:
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It would help if you can measure the height of the washer when decompressed, that way you can get a more accurate "h" dimension which is roughly "overall height - thickness of the washer". Knowing "h" would help to calculate the load at max deflection and find the correct constant to use for calculating load at different compressions. Measuring some similar belleville washers I have from a different regulator I got an "h" value of 0.011 inches so that's the distance the washer has to compress to be completely flat. Using that number along with the dimensions of your washers and the properties given in the document, I found the max load to be 135 pounds and an h/t of 0.56. Table 1 in the document has the constants you multiply against the max load to find load at different compressions based on the h/t value, 0.56 falls right between 0.5 and 0.6 in the table so I don't know which would be best to use. Again this is where having a more accurate overall height measurement would help.
As for finding a layout that will work in this application the document more or less says "idk figure it out yourself", they give formulas for parallel and series configurations but in a regulator you most likely need a hybrid set up which they don't give any formula for. I think Bob is right that there is no good way to calculate this in one formula, it's basically just trial and error based on height of the stack, required deflection, and the spring rate needed. It seems like a parallel stack of washers can be treated like one thick washer but I think that will change the h/t. Sources are conflicted as to whether or not thick washers require more complex calculations to find "h" but it seems like most think it's ok to use the "overall height - thickness" equation.
OK so here is where my own analysis begins and where I'm not entirely sure I'm correct so ideally if someone more knowledgeable comes along and reads this they can give their input as well. The main thing to remember here is that IF this is correct, it's only correct for linear spring stacks where the "layers" are all the same. As in ((()))((())) and not progressive stacks like ((()))(())() where the spring rate increases with compression. I think it will mostly come down to trial and error to get exactly the results you are looking for, calculations can only get you in the ball park.
I would start by finding the required height of the stack by measuring the distance from the face of the piston to the face of the regulator where the small piston enters. Figure out how much deflection you need in the stack by determining the number of adjustment wheel turns you you want between max and minimum settings. Divide the adjustment distance by the height of the stack to find the percent change in deflection. Calculate the force on each side of the piston when the reg is open by subtracting the area of the small end from the area of the large end and multiplying that by 850 to find the spring rate needed at the lowest setting. Find the constant in table 1 that corresponds to the amount of deflection you want, then divide 850 by the constant and see if it gets you to 3000, if it doesn't then find a new arrangement and repeat.
To calculate the spring rate of a given arrangement you have two options. In a parallel arrangement you can just multiply the number of washers against the spring rate of one washer to get the total force required to flatten that stack, a series arrangement will have the same spring rate as a single washer with more deflection. In combination you would multiply the max deflection load of one washer by the number of washers in a parallel stack to get the max load, and multiply the distance of deflection by the number of parallel stacks to get max deflection.
Hopefully this is useful, it got way longer than I initially planned on it being but the first half is really just a summation of the document you linked plus me plugging those numbers into a belleville calculator. The second half is my own ideation on the matter and may or may not be right, YMMV, good luck.
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That regulator is difficult to assess, because the force on the piston from the HP air would appear to change significantly, depending on the input pressure.... unless I am not understanding the operation.... When the reg. is seated, it would appear that the HP air is pushing against an area of (0.196^2xPI/4) - (0.118^2xPI/4) = (0.0302) - (0.0109) = 0.0193 sq.in.... At 3000 psi, that would be 58 lbs., but at 850 psi only 16 lbs.... If the output pressure is 850 psi, the force trying to collapse the Bellevilles would change, because on the large end we have (0.411^2xPI/4) = 0.133 x 850 = 113 lbs.... so it would swing from (113 - 58) = 55 lbs. when the tank is full to (113 - 16) = 97 lbs. at setpoint.... :o
Bob
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That regulator is difficult to assess, because the force on the piston from the HP air would appear to change significantly, depending on the input pressure.... unless I am not understanding the operation.... When the reg. is seated, it would appear that the HP air is pushing against an area of (0.196^2xPI/4) - (0.118^2xPI/4) = (0.0302) - (0.0109) = 0.0193 sq.in.... At 3000 psi, that would be 58 lbs., but at 850 psi only 16 lbs.... If the output pressure is 850 psi, the force trying to collapse the Bellevilles would change, because on the large end we have (0.411^2xPI/4) = 0.133 x 850 = 113 lbs.... so it would swing from (113 - 58) = 55 lbs. when the tank is full to (113 - 16) = 97 lbs. at setpoint.... :o
Bob
I'm glad I'm not the only person confused about that. The drawing was posted while I was in the process of writing the response so I didn't get to see it until after I posted. The original picture was confusing but I assumed that there was just something I wasn't seeing and approached it like it was a normal reg. Like if the small end of the spool went in and out of an o-ringed chamber that would work despite being a weird design. As it stands from the drawing it does look like you'd have a wild variation over the range of tank pressure. What gun is this reg for?
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Well there IS an O-ring on the small end of the piston, it's inside the chamber instead of on the spool (which slides through it).... I think it would work fine without the step down in diameter to the knife-edge seal on the end.... I have NO idea why it has that feature.... ???
Bob
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I think that one at the end of the spool is there to seal the spring chamber and the knifes edge seals against a flat seat that threads into the end. The way I understood the drawing was that it was the housing and the internals side by side.
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Gents I forgot to include the high-pressure-side Oring locking ring in my drawing, my bad :-[. You can see it in the picture of the parts. This regulator goes in a Listone Industry Taichi-X .22 pcp rifle.
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Does the small end of the spool piston fit through the brass ring to press against the white delrin?
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Does the small end of the spool piston fit through the brass ring to press against the white delrin?
Yes it does. The Oring goes in first and abute on the bottom of the threaded hole, then the brass lock-ring screws in, then the white delrin piece.
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That regulator is difficult to assess, because the force on the piston from the HP air would appear to change significantly, depending on the input pressure.... unless I am not understanding the operation.... When the reg. is seated, it would appear that the HP air is pushing against an area of (0.196^2xPI/4) - (0.118^2xPI/4) = (0.0302) - (0.0109) = 0.0193 sq.in.... At 3000 psi, that would be 58 lbs., but at 850 psi only 16 lbs.... If the output pressure is 850 psi, the force trying to collapse the Bellevilles would change, because on the large end we have (0.411^2xPI/4) = 0.133 x 850 = 113 lbs.... so it would swing from (113 - 58) = 55 lbs. when the tank is full to (113 - 16) = 97 lbs. at setpoint.... :o
Bob
I hear you loud and clear on that, Bob. This is something that's bugging me too; if we had a constant high pressure input I understand my reg would work as expected and deliver a constant low-pressure set-point. But as a pcp rifle tank loose pressure, this cause an imbalance in the reg, in my case anyway ???. How do other pcp regulators work to compensate for that imbalance? Or am I missing something? :(
Here's a diagram of the pressure tube/regulator/receiver adapter from my owner's manual:
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Most regulators have the seat on the adjustment knob not the piston so when it seals no air can get through to the small end, when it opens the air pressure is allowed to pass through the the piston freely so the pressures equalize on each side. That way the springs are the only thing holding it open since the pressure on each side of the piston cancels out the force on the small end. That's why I said originally to subtract the area of the small side from the large side, since that difference is the force trying to close the piston. Once it closes again there is no longer any air trying to push the piston open except for whatever surface area is exposed to the seat which is usually a virtual pin hole so the force only changes by five or six pounds over the course of a 3000 psi fill.
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I agree with Bob and CS, unless I’m missing something, as designed, that reg would have a remarkably wide swing.
I may have missed it in the body of the thread but you must have been experiencing issues to have brought you into this rabbit hole. ??
According to the parts diagram vs your piece, they have added another oring and switched to a single atm vent hole instead of two. Neither changes anything. The extra oring probably was because they were getting leakage caused by the single oring passing by the vent hole in tube (just guessing).
Dave
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I agree with Bob and CS, unless I’m missing something, as designed, that reg would have a remarkably wide swing.
I may have missed it in the body of the thread but you must have been experiencing issues to have brought you into this rabbit hole. ??
According to the parts diagram vs your piece, they have added another oring and switched to a single atm vent hole instead of two. Neither changes anything. The extra oring probably was because they were getting leakage caused by the single oring passing by the vent hole in tube (just guessing).
Dave
Yes I had quite a few issues with this rifle, the regulator being the last one I found. I don't know the original configuration of the spring washers, and I just found another major quirk: the regulator body is about 0.031'' smaller than the part of the tube it goes in. No more wonder why the Orings were extruding after a very short period >:( . And I thought it was due to cheap OEM orings ::). Now I need to make a new regulator body before I can seriously hope to do some testing. Will update as soon as I can.
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If you are going to make a new reg body, a redesign might be in order.
Dave
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If you are going to make a new reg body, a redesign might be in order.
Dave
I'm all in for suggestions dear fellow :D.
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Surely we can come up with a better design than they have done.
What is the od and id of the small end of piston? It needs to be plugged with ball or wafer and then the shaft cross drilled.
Then the hp end of body needs to be designed to allow for existing oring seal to function on piston but only allow hp air to enter through the center of an adjustable plug.
I can draw this out but it might be a couple days.
Dave
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Open source regulators courteousy of GTA, I like it.
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Can you measure the overall height of the washers you have? I can't accurately find a washer arrangement without knowing that measurement. Also by 3000/850 do you mean a reg that adjusts from 850 to 3000 PSI or do you want it fixed at 850?
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Can you measure the overall height of the washers you have? I can't accurately find a washer arrangement without knowing that measurement. Also by 3000/850 do you mean a reg that adjusts from 850 to 3000 PSI or do you want it fixed at 850?
15 stacked spring washers like so: )()()()()()()() , measures 0.430''. This would give me about 0.020'' of preload.
3000 psi is the max fill pressure in my rifle's tank, 850-900 psi is the fixed, non-adjustable regulated pressure I'd like to get. This regulator is not originally meant to be adjustable. If that could be relatively easy to re-design the reg to be adjustable that would be nice, since I have to make a new body anyway. Thanks for the help Tom, very appreciated!
Surely we can come up with a better design than they have done.
What is the od and id of the small end of piston? It needs to be plugged with ball or wafer and then the shaft cross drilled.
Then the hp end of body needs to be designed to allow for existing oring seal to function on piston but only allow hp air to enter through the center of an adjustable plug.
I can draw this out but it might be a couple days.
Dave
Thanks a lot for the help Dave! You have the dimensions you need in my drawing, hope it's clear enough :-[ . Here's another pic of the internals if that can help:
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I have never built a "knife edge seat" style regulator that is fed from the side.... but if I was going to, I would make the diameter of the knife edge on the end of the piston the same diameter as the small end (shaft) of the piston, like the Lane Mk.9's.... That should eliminate and change in the output pressure as the tank pressure drops.... JMO....
Bob
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I have done an initial mark up of your sketch to throw out some changes that need to be made to get this to a more conventional reg design.
Also, CS had a question that you need to answer.
Do you have the a lathe available for this?
Dave
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Also, if Bob and CS could chime in on the proposed changes, it would be appreciated.
I’m sure I’ve probably missed something.
Thanks gents,
Dave
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Your changes would probably work, but I would recommend doing this....
(https://hosting.photobucket.com/images/oo221/rsterne/Regulator.JPG?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/ec7c3593-4578-4151-a54b-04e884d967df/p/691898f8-d94b-4fa8-aa49-7f2500de697e)
Simply move the knife edge out to the full diameter by boring the taper out larger, and then adjust the seat in further.... This should eliminate any pressure change as the tank empties.... and no new parts required....
Bob
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What does changing diameter of sealing surface change?
Dave
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The change in output pressure when you change input pressure is BECAUSE the sealing surface is smaller than the shaft of the piston, which is where it seals into the reg. body.... I explained that in Reply #4.... If the seat OD and the O-ring ID is the same (which it would be if there was no step in the end of the piston), then there would be nowhere on the end of the piston shaft for the HPA to push on when the reg. is seated.... Therefore, it wouldn't matter what the input pressure was, the setpoint would remain constant.... That is how the Lane Mk.9 regs. work....
Bob
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I understand that dynamic. Do not refute it works. But it only has that dynamic AFTER the piston is seated. Not WHILE reg is cycling or in other words REGULATING.
Again, I’m not saying it doesn’t work, just haven’t messed with the Lane style.
And I definitely agree it would be an easier change than I laid out. Would definitely be worth trying before making a bunch of new parts.
Dave
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While there may be a TINY time lag during the cycling of the reg., once the seat is open the pressure between the end of the stem and the seat will be nearly the same as that inside the stem, and on the regulated side of the piston.... If you add up all the plus and minus forces, you will find that if that pressure is indeed equal, there would be no net force on the piston.... Regulators only open a very small distance, and the chamber in the regulator around the stem must fill through the small vent hole in the side of the regulator, and if the stem lifts more than a small distance, the primary pressure drop will be across the vent hole.... The area under the knife edge seat (for a 0.196" diameter) would equal the area of a 1/16" vent hole (0.003 sq.in.) when open only 0.005".... After that, there would be a greater pressure drop across the vent hole than across the regulator seat....
As I said previously, I have never had a Lane regulator, but they do work, quite well in fact, and that is the way they are built.... I would think there is probably a small difference in the output pressure as the tank pressure falls.... but in practice it does not appear to be any worse than a regulator such as a Ninja which fills through a tiny hole in the end.... For sure there is a difference in the force on the piston due to changing pressure in the tank with that design.... If the hole is 1mm (0.040"), the area is 0.00126 sq.in. and the force would be 3.8 lbs. at 3000 psi and only 1.1 lbs. at 850 psi.... That is a change of 2.7 lbs.... The effective piston area (big - small) on a Ninja is 0.1577 sq.in., so the closing force on the piston (that must be balanced by the Bellevilles) is (0.1577 x 850) = 134 lbs. at 850 psi.... That means a pressure swing of (2.7 / 134) = 2.0%, that you can do nothing about....
Bob
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Thanks for that Bob. I was not taking into account the pressure drop at the side entrance.
Dave
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Wasn't he also experiencing o-ring extrusion because the regulator housing was too small? You could try switching to more durable o-rings but that may just be a bandaid. If you need to make a new housing anyway it opens up a lot more design options, I don't know if you could modify it to be adjustable using the stock Delrin piece. I had been envisioning a design like Dave posted but Bob definitely has a good idea, especially if you were keeping the stock housing it would need much less fabrication.
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Wasn't he also experiencing o-ring extrusion because the regulator housing was too small? You could try switching to more durable o-rings but that may just be a bandaid. If you need to make a new housing anyway it opens up a lot more design options, I don't know if you could modify it to be adjustable using the stock Delrin piece. I had been envisioning a design like Dave posted but Bob definitely has a good idea, especially if you were keeping the stock housing it would need much less fabrication.
I actually enjoy machining airgun parts, it's half of the fun! I also find Bob's idea the easiest to start with, should come up with a prototype spool and reg body real soon. I have some free time ahead this week-end, and some 304 SS available. Let the chips fly!
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Hmm, not sure why they put a step into the piston as stated by others...remove the step in your next iteration without question...as that just causes variation on the high pressure side during pressure swings as already noted by others.
If they did that by design, I can only imagine where else they burgered things up. Sheesh.
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I have done an initial mark up of your sketch to throw out some changes that need to be made to get this to a more conventional reg design.
Also, CS had a question that you need to answer.
Do you have the a lathe available for this?
Dave
I may have missed that question???
Yes I do! It's a King Industrial KC1022-ML (Canadian model), a clone of the Grizzly G0602.
I'm finishing my coffee and I'll start the spool.
Good day all :D
Francois
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Great!
You can make ANY type of reg you want.
Odd coincidence, the first reg I designed and made was for a Listone Victor. They had a large check valve where the reg should be.
Dave
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Hmm, not sure why they put a step into the piston as stated by others...remove the step in your next iteration without question...as that just causes variation on the high pressure side during pressure swings as already noted by others.
If they did that by design, I can only imagine where else they burgered things up. Sheesh.
LOL! You don't wanna know ;D.
I already have quite a few hours of repair work in that rifle, but so far it's worth it as it doesn't cost me much money to improve it, and it gives good results. I also like to see it as a learning platform in PCPs for me, as it was my very first PCP airgun.
Cheers!
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I think Dave might have meant me asking about overall height, I just divided the total height of the stack by 15 given that they were all evenly arranged in your answer. That got me 0.0286" which when you subtract the 0.0197" thickness leaves 0.009" of deflection per washer. Using that info it seems like your washers should take 112 lb of force to deflect completely. The actual arrangement depends on how much space you end up with in your final design and how much travel you want in the adjuster. I'm not sure that you can effectively get a full swing from 850 to 3000 in one regulator, 850-1700 is probably more reasonable, again it depends on how much adjustment travel you want/have. Also I don't think I'd preload the washers in an unpressurized state just for ease of assembly. Hope you have fun with it, I can hardly keep one working gun in my collection because I'm always taking them apart and "improving" them.
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So I just finished the new spool, it's dimensionally identical to the original one. Only differences are it's made of 304 SS and the seat tip no longer has a step, based on the suggestions made by Bob Sterne.
The edge is about 0.005'' wide, and rounded and polished. I made the Oring groove with radiused corners insead of square, had good results in the past with this design. The through-hole is 1.5 mm ID like the original, took about 15 min to drill that small size hole :o. I used a Dremel 37.5° (included angle) HSS cone bit to cut the inlet cone. I was even able to make these tiny M3-0.5 threads for the puller I use to extract the reg from the tube, not easy to thread that smal in SS :P. I polished the stem, where it rides in the Oring, with up to #1000 grit wet/dry sandpaper, then finished with #0000 steel wool. Surface finish is very nice, the Oring shouldn't have difficulties sealing on that. I made the stem of the spool 0.010'' longer and shaved 0.010'' off the face of the delrin screw to a new smooth finish. So far, so good :D.
The next frontier, the regulator body ;D.
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Very nice work, SS is a pain in the butt.
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I think Dave might have meant me asking about overall height, I just divided the total height of the stack by 15 given that they were all evenly arranged in your answer. That got me 0.0286" which when you subtract the 0.0197" thickness leaves 0.009" of deflection per washer. Using that info it seems like your washers should take 112 lb of force to deflect completely. The actual arrangement depends on how much space you end up with in your final design and how much travel you want in the adjuster. I'm not sure that you can effectively get a full swing from 850 to 3000 in one regulator, 850-1700 is probably more reasonable, again it depends on how much adjustment travel you want/have. Also I don't think I'd preload the washers in an unpressurized state just for ease of assembly. Hope you have fun with it, I can hardly keep one working gun in my collection because I'm always taking them apart and "improving" them.
As designed, the total spool travel is 0.063'' with the lock ring installed, let's say 0.065'' to allow for a little ''crush'' of the delrin seat. That is 48% of total possible deflection of 0.135'' (15 x 0.009''). If I'd remove one washer, I'd have no preload and 0.126'' of possible total deflection. 0.063'' of travel equals to exactly 50% of that. If I refer to the Spaenaur spec sheet, that would mean 54 lb of force @ 50% of deflection, correct? Bob calculated that @ 850 psi, there would be 113 lb of force on the spool head, couter-balancing the spring washers force. As I'm seeing it, I could make a threaded adjustable delrin seat, similar in function to what Dave kindly posted, and have enough adjustment range to find the ''sweet spot''. Does my reasonning seems logical?
Very nice work, SS is a pain in the butt.
And thank you!
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Yes, that sounds reasonable to ‘build in’ adjustability.
Very nice machine work!
Dave
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Thank you Dave!
So here I go, the new regulator body is done :D. I made it in 6061-T6 Al, almost exactly the same as the original. The differences are it's now sized correctly for the tube, and I re-positionned and drilled the atmospheric vent hole bigger (1.5 mm vs 1 mm). I still have to check the fit in the tube with the Orings installed, and if the internals all fit good, but I made the new reg with all dimensions (except the OD) within 0.001'' of the original, so I'm pretty confident 8). I had to make some special micro-tools to cut the bores and retaining ring groove. I used broken taps from where I work, excellent steel! New reg body on the left in pics. Will update soon.
Edit: Forgot to mention, I machined the spring/spool bore 0.015'' deeper to remove preload on the 15 spring washers pack.
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This morning I lapped the edges of the spring washers on a #2000 wet/dry sandpaper, then cleaned them and installed them on the spool. Then put the spool in the reg body to check the height of the spool's head vs the retaining ring groove. It's about perfect, the top of the spool's head is flush with the lower edge of the groove, my calculations and machining are good. So when the retaining ring is installed, there's zero preload on the spring. I'll use that as a starting point, some variables are still to be worked on, like shimming or not, different washer configuration, hammer strike and port size (I probably forget a lot right now). Another factor to consider is that I decided to convert the rifle to .177 caliber. I have a 24'' LW choked barrel doing nothing these days ;D, and in the beginning I wanted this rifle in .177, so the decision is not hard to take.
I had an interesting read yesterday night:
https://hardairmagazine.com/ham-columns/introduction-to-the-pcp-regulator-dont-ignore-the-plenum/
https://hardairmagazine.com/ham-columns/tuning-regulated-pcp-airguns/
So before putting the rifle all back together I'm very tempted to make a tube extension. It would be between the pressure tube and receiver, and would have provision for a pressure gauge, so I could see the regulated pressure I get. That would certainly help for tuning the reg I'm sure. Another small benefit is that it would also act as a plenum, maybe that would be helpful for consistency of the shots? I know that for a low power target rifle one don't need that much valve/plenum volume, but it can't hurt to have a few more CC's of regulated pressure I guess?
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Excellent work.
Dave
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Excellent work.
Dave
Thank you again Dave! I also work in parallel on building an adjustable regulator based on your design. Now that ''the ice is broken'', I'm pretty confident at going at it.
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Very first Chrony result, with the stock 18'' .22 cal barrel, shooting a CPUM 14.3 grains domed pellet, with the reg setup like I described earlier: 440 fps. :D :D :D Exactly my goal! (Yes I'm Canadian, yes I know!).
Still need to do a string of shots, to see about consistency and number of shots I get from this 90 CC tank. Also very curious to see tomorrow if there's any leaks. I filled to 3000 psi, according to my main tank gauge. The gauge on my rifle only shows 1.75 MPa (2575 psi), may have to replace it :P. More to come.
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Good job and on your first attempt as well. That should be a big improvement.
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Good job and on your first attempt as well. That should be a big improvement.
Thank you Tom!
I discovered there's a slow leak coming from the atm. vent hole, the rifle is loosing about 400 psi a day. That means the two front most Orings still have a problem sealing :(. Dunno yet why it's still leaking, but the way the tube is machined may well be the cause. I noticed there's a small step just before the regulator is completely seated, I need to de-gas the gun and carefully check how it's made, me thinks there may be a sharp corner somewhere harming the Orings. At the very worst I have another reg. body ''blank'', but I guess re-machining the pressure tube a bit may help more. The way I see it, the step in the tube is not necessary so it may be a good move to machine it off. More on that later.
I tried to calculate at what regulated pressure the gun now operates:
Input pressure: 3000 psi
Spring washers pack height: 0.430'' (no preload when installed). According to the chart, the total possible deflection for each spring washer is 0.0099'', let's say 0.0095'' in the real world, since I lapped them. So total possible deflection for the entire spring pack should be 0.1425'' (15 x 0.0095'').
Spool (piston) stroke is a real 0.065'' from ''open'' to ''closed'' position, that is 45.6% of total possible deflection, 0.065''/15 = 0.0043'' of deflection per washer.
According to the chart, @ 50% of deflection (0.005'') the spring washers each have 54 lb of force on them, I'll use a value of 46.8 lb for 0.0043'' of deflection. So 46.8 lb x 15 washers= 702 lb needed to collapse them 0.065''? If I use Bob's calculations to determine the force applied on the spool's head @ 850 psi: (0.411^2xPI/4) = 0.133 x 850 = 113 lbs. I no longer take into account the counterbalancing force applied on the new spool's tip (HPA side), since it no longer has this step it had on the original one. Do these numbers seem right?
Starting here I'm a bit confused. I'm no math genius, and I still have a hard time wrapping my head around all these numbers so they make sense :-[. I haven't made the new plenum yet (with provision for a pressure gauge), so I don't know the real pressure at which the reg is actually set. How can the smallish pressure on the spool's head ''combat'' the force of the spring washers, which is much greater? Again I'm sure I'm missing something important, please guys I need your lights!
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I think I'm onto something, I just found this in a google search: https://www.airgunforum.ca/forums/topic30074.html (https://www.airgunforum.ca/forums/topic30074.html)
I knew spring washer disposition had a role to play, just didn't see the correlation so far. So my reasonning was totally wrong, the force of the springs doesn't add up like I did :-[.
I calculated the spring rate of one washer:
Force to flatten: 99 lbs, divided by total travel of 0.0099'' gives a 10000 lbs/inch of spring rate.
I have 15 washers, so I multiplied 10000 by a factor of 0.06666666, which gives a rate for the spring pack of 666.6 lbs/inch. That value multiplied by the actual travel of 0.065'' gives 43.3 lbs of ''opening force'' applied by the springs washers when the chamber is pressurized. @ 850 psi of regulated pressure there would be 113 lbs of force on the spool's head, so no problems closing the spool when set pressure is reached. If I ''retro-calculate'' the necessary pressure needed to close the spool, using the calculated force of 43.3 lbs, that gives 43.3 / 0.133 = 325 psi to close the spool? I also know that spring washers has a non-linear sping rate ???.
Is it possible that the regulator has such a low set point?
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Belleville Springs has information on their site about stacking and calculations for rates.
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Happy,
Try plugging in some different distances to close fully and you will see how much a few thou of extra compression on the springs effects output pressure.
Also, take into consideration the force needed to seal at the small end. Once the piston makes contact, the ‘spring rate’ of the sealing material comes into play.
As you can see, being a little ‘off’ on measuring can throw your data off. Even the better reg manufacturers have ways to adjust final output. Too many variables.
Dave
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Happy,
Try plugging in some different distances to close fully and you will see how much a few thou of extra compression on the springs effects output pressure.
Also, take into consideration the force needed to seal at the small end. Once the piston makes contact, the ‘spring rate’ of the sealing material comes into play.
As you can see, being a little ‘off’ on measuring can throw your data off. Even the better reg manufacturers have ways to adjust final output. Too many variables.
Dave
These variables are quite annoying ;D ;D ;D.
I wonder how many more thou the tip has to travel to fully seal. If I use a spool travel 0.005'' longer, for 0.070'' of travel, that gives 46.67 lbs of opening force, that would gives a set point pressure of 350 lbs. If I use a travel of 0.075'' that gives a 375 lbs set point. I suppose I'd also have to take into account the friction of all parts, and also the force applied on the inlet cone in the spool, I know it's possible to calculate it but I'm at a loss here :o. If someone is willing to try and calculate it, here's the dimensions of the inlet cone:
big diameter: 0.185''
small diameter: 0.063''
included angle: 37.5°
I don't remember how to calculate the height, I know one need to use the sine or cosine function??? And how to calculate the linear force applied to the canted cone walls is out of my reach...
Just can't wait to have a regulated pressure gauge installed!
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Sorry, but if Belleville washers are stacked in series (single stack), the force to deflect the washers does NOT increase, only the travel distance needed.... Conversely, if they are in parallel, the force increases but the travel does not....
) = 54 lbs. for 0.005" .... spring rate = 10800 lbs/in.
)( = 54 lbs. for 0.010".... spring rate = (10800 / 2) = 5400 lbs/in.
)) = 108 lbs. for 0.005".... spring rate = (10800 x 2) = 21600 lbs/in.
Using your numbers, 15 washers stacked up in series )()()()()()()() where it takes 54 lbs. to compress one 0.005" would have a combined spring rate of (10800 / 15) = 720 lbs/in.... If the load on them is 113 lbs. at 850 psi, they should compress (113 / 720) = 0.157".... That works out to (0.157 / 15) = 0.0105" per washer.... If your washers cannot collapse that far, they will go "coil bound" and stop compressing before 850 psi is reached....
If you installed them in pairs, like this.... )) (( )) (( )) (( )) ( .... you would have a situation where the single washer at the right end would collapse fully when the others were compressed half way.... That is why, if I can't use them as singles, I ALWAYS use them all in pairs, with no singles or triples.... So, let's look at 14 washers instead, arranged in 7 pairs.... Each pair would have a spring rate of 21,600 lbs/in.... However, you have 7 pairs, so the spring rate would be (21600 / 7) = 3086 lbs/in.... With a load of 113 lbs. at 850 psi, they should compress (113 / 3086) = 0.037".... That, for sure, would be within the capabilities of the washers to handle without going "flat"....
If that stack doesn't work for you because is it too short, you can add more pairs of washers, or you can add flat shims.... In fact, the single washer on the end, in the paired stack of 15, will pretty much act like a shim equal to just over the thickness of the metal in the disc, once it is collapsed.... Let's say that when assembled your setpoint pressure was 500 psi instead of the 850 you want.... From the areas of the piston, we know that there is 113 lbs. available at 850 psi, so that means we would have (500 / 850) x 113 = 66 lbs. available at 500 psi.... The difference is (113 - 66) = 47 lbs.... Since the spring rate of our stack of 7 pairs of Bellevilles is 3086 lbs/in. then you would require a shim of (47 / 3086) = 0.015" in thickness to increase the setpoint from 500 psi to 850 psi.... Each thou of shim will increase the setpoint pressure about 23 psi....
Bellevilles are reasonably linear in operation through the middle of their range.... but even so, these calculations are only an approximation.... Some experimentation will be required to fine tune the setpoint pressure....One other word of caution.... If the Belleville washers collapse flat before the piston seals the inlet side, the regulator will stay "open", and bypass the inlet pressure through to the outlet.... This can happen if you are shimming a regulator, and it can cause you to blow a burst disc, or overpressure the gun, in a heartbeat.... :o
Bob
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If I understand this correctly you're having issues with leaks out the vent hole which would suggest a problem with o-rings not a problem with the belleville stack. If the stack had an issue you'd get creep or outright failure of the regulator, a leaking vent hole would be caused by one of the o-rings on either side of the spool. A belleville is a linear spring so if you need 100 lb to flatten is and you preload it to 90 lb then you only need 10 more pounds to flatten it.
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Sorry, but if Belleville washers are stacked in series (single stack), the force to deflect the washers does NOT increase, only the travel distance needed.... Conversely, if they are in parallel, the force increases but the travel does not....
) = 54 lbs. for 0.005" .... spring rate = 10800 lbs/in.
)( = 54 lbs. for 0.010".... spring rate = (10800 / 2) = 5400 lbs/in.
)) = 108 lbs. for 0.005".... spring rate = (10800 x 2) = 21600 lbs/in.
Using your numbers, 15 washers stacked up in series )()()()()()()() where it takes 54 lbs. to compress one 0.005" would have a combined spring rate of (10800 / 15) = 720 lbs/in.... If the load on them is 113 lbs. at 850 psi, they should compress (113 / 720) = 0.157".... That works out to (0.157 / 15) = 0.0105" per washer.... If your washers cannot collapse that far, they will go "coil bound" and stop compressing before 850 psi is reached....
If you installed them in pairs, like this.... )) (( )) (( )) (( )) ( .... you would have a situation where the single washer at the right end would collapse fully when the others were compressed half way.... That is why, if I can't use them as singles, I ALWAYS use them all in pairs, with no singles or triples.... So, let's look at 14 washers instead, arranged in 7 pairs.... Each pair would have a spring rate of 21,600 lbs/in.... However, you have 7 pairs, so the spring rate would be (21600 / 7) = 3086 lbs/in.... With a load of 113 lbs. at 850 psi, they should compress (113 / 3086) = 0.037".... That, for sure, would be within the capabilities of the washers to handle without going "flat"....
If that stack doesn't work for you because is it too short, you can add more pairs of washers, or you can add flat shims.... In fact, the single washer on the end, in the paired stack of 15, will pretty much act like a shim equal to just over the thickness of the metal in the disc, once it is collapsed.... Let's say that when assembled your setpoint pressure was 500 psi instead of the 850 you want.... From the areas of the piston, we know that there is 113 lbs. available at 850 psi, so that means we would have (500 / 850) x 113 = 66 lbs. available at 500 psi.... The difference is (113 - 66) = 47 lbs.... Since the spring rate of our stack of 7 pairs of Bellevilles is 3086 lbs/in. then you would require a shim of (47 / 3086) = 0.015" in thickness to increase the setpoint from 500 psi to 850 psi.... Each thou of shim will increase the setpoint pressure about 23 psi....
Bellevilles are reasonably linear in operation through the middle of their range.... but even so, these calculations are only an approximation.... Some experimentation will be required to fine tune the setpoint pressure....One other word of caution.... If the Belleville washers collapse flat before the piston seals the inlet side, the regulator will stay "open", and bypass the inlet pressure through to the outlet.... This can happen if you are shimming a regulator, and it can cause you to blow a burst disc, or overpressure the gun, in a heartbeat.... :o
Bob
Thanks so much Bob!
If I understand this correctly you're having issues with leaks out the vent hole which would suggest a problem with o-rings not a problem with the belleville stack. If the stack had an issue you'd get creep or outright failure of the regulator, a leaking vent hole would be caused by one of the o-rings on either side of the spool. A belleville is a linear spring so if you need 100 lb to flatten is and you preload it to 90 lb then you only need 10 more pounds to flatten it.
You understand perfectly Tom. There's a small leak that doesn't seem to affect the functionnality of the regulator, and I think I found the issue. I took the rifle apart today and found out the middle Oring has a small rough spot on its OD, like it abraded on something sharp. Other than that I'm glad to report that the Orings no longer extrude, except for the small abraded spot they're in excellent condition.
Yes the Belleville stack has no preload (and no loose either) when installed (with no pressure), and the piston (spool) only travels 0.065'' before contacting the delrin seal face (let's say 0.070'' to allow for some ''crush''). Total maximum travel for this washers stack is 0.1425'', the spool only use roughly 50% of that available travel to close and seal.
After some searches I found it's plausible to have the velocity I got using set pressure between 4 and 500 psi in .22 calibre. I saw velocities in the high 400s with a set pressure of 450 psi, I now believe I was very lucky and fell on the ''sweet spot'' right at the beginning regarding the Belleville stack. I'm really impatient to install a gauge and see the true set pressure, that'll help tremendously to find out WHY it shoot so well ;D.
Tomorrow I plan to start machining the new plenum, will update on that as soon as I can.
Cheers!
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I would guess your setpoint is a bit less than 400 psi.... based on your measurements....
Bob
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A few rough calculations suggest to me that you're reg pressure is around 390 PSI right now. Basically going off the numbers which have been posted previously, 850 PSI = 112lb of pressure on the spool, each washer requires 113lb to flatten completely. Since washers added in series increase the amount of travel for a given applied pressure, we can assume 850 PSI would completely flatten the stack. So if you have 0.1425" total travel in the stack and 0.065" between the seat and spool then 0.065 / 0.1425 = 0.4561 and 0.4561 x 850 PSI = 387 PSI.
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A few rough calculations suggest to me that you're reg pressure is around 390 PSI right now. Basically going off the numbers which have been posted previously, 850 PSI = 112lb of pressure on the spool, each washer requires 113lb to flatten completely. Since washers added in series increase the amount of travel for a given applied pressure, we can assume 850 PSI would completely flatten the stack. So if you have 0.1425" total travel in the stack and 0.065" between the seat and spool then 0.065 / 0.1425 = 0.4561 and 0.4561 x 850 PSI = 387 PSI.
I believe you and Bob are right, but I'll know for sure real soon, I just finished the new plenum/tube extension :D.
I used 316L SS to make it, corrosion will never be a problem. It has a 1/8'' NPT port for a gauge, and the plenum chamber has a volume of 4.5 cc (not counting the gauge hole, and gauge itself). That was a heck of a job cutting the OD threads, and even harder cutting the ID threads, but now both sides of the new part has tighter tolerances than the original fitment.
I installed an old gauge I had, didn't know if was good or not, after filling the rifle I saw it's no good gauge anymore, need to replace it. I can't tell yet the real-life pressure there is after the regulator, and I need to take the gun apart again, as there's still a leak through the atm. vent hole (I suspect the HPA side small Oring). More to come.
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If the gauge works (and doesn't leak) but the pressure reading is incorrect, you can calibrate it by popping the lense off (easier said than done), connect it to a known pressure at about midscale and then rotate the scale underneath the needle until it reads correctly.... A tiny drop of glue to hold the scale in place, and then pop the lense back in....
Bob
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If the gauge works (and doesn't leak) but the pressure reading is incorrect, you can calibrate it by popping the lense off (easier said than done), connect it to a known pressure at about midscale and then rotate the scale underneath the needle until it reads correctly.... A tiny drop of glue to hold the scale in place, and then pop the lense back in....
Bob
:D I remember doing this quite a few years ago, but this little fellow is dead I think ;D. The needle didn't even moved when I rapidly de-gased the rifle. Doesn't matter too much, I had another (good) one, in megaPascal though. One megaPascal (mPa) equals 147 psi IIRC. I installed it and re-filled the tank. The HP gauge reads 15 mPa (2205 psi), and the regulated pressure gauge reads around 3 mPa (441 psi), as far as I can tell, by using this gauge before. The needle was exactly on ''zero'' at no pressure, and climbed quickly to its current value when I filled the tank. 441 psi is pretty close to calculations, considering friction and seal crush, maybe some other factors too. This is an excellent base for tuning work to come, so far pretty satisfied of the results 8). Now to get rid of that pesky leak... ;D.
Edit: I dry fired the rifle a few times, I kept my eyes on the regulated pressure gauge and there were no visibles variations. Regulated pressure seems to be very consistant, pretty encouraging for accuracy!
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Excellent work! The best part is that your output is consistent.
Dave
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Thanks Dave, this is the goal ;).
Update:
The leaks is more severe than i thought, but it also shows me how the regulator reacts. The rifle now has 4MPa (588psi) on the HP gauge, and the regulated pressure gauge shows something like 2.75 to 3 MPa (404 to 441 psi). Not too bad as a spread or?
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Plenty good enough, I think.... It is almost impossible to read a gauge like that to within 40 psi, IMO....
Bob
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Finally had the time to shoot a string, only to notice my Chrony's battery wasn't too good anymore. I was only able to get 15 ''good'' shots before the battery died and gave me error after error, but the result is useful anyways. Also I located the leak the gun had, was exactly what I thought: I haven't tightened the brass locking ring enough, so the small HPA-side Oring wasn't sealing well and leaked air into the atmospheric chamber.
I used CPUM 14.3 grains domed pellets for testing. Starting tank pressure is 19.5 MPa (2825 psi), reg pressure is 3.5 MPa (500 psi), on the last shot fired the tank was @ 13 MPa (1885 psi), and the regulated pressure stabilized after the third shot @3 MPa (435 psi) and stayed there. There's a VERY short delay between the moment the shot is fired and the moment the reg has ''rebuilt'' the pressure, I'd say less than a second. After the first 3 shots, the regulated pressure always returned to the very same point on the gauge 8). Here's the string:
1- 475.1 fps @ 19.5 MPa (2825 psi)
2- 460.1
3- Error
4- 448.3 fps @ 18 MPa (2610 psi)
5- 432.2
6- Error
7- 438.6 fps @ 17 MPa (2465 psi)
8- 445.2
9- Error
10- 439.2
11- Error
12- 434.4
13- 436.4
14- 431.9 fps @ 15 MPa (2175 psi)
15- Error
16- 428.5
17- 433.7
18- 436.9
19- Error
20- Error
21- 429.8
22- Error
23- 436.2 fps @ 13 MPa (1885 psi)
24- Error
25- Error
26- ...
Starting there my Chrony would only give ''Error'' readings :P. The regulated pressure seems to stabilize at around 2600 psi of tank pressure, and it seemed to maintain itself pretty well down to where I got. Also I'm guessing the regulator has to somewhat ''break-in'' to give its full potential. Just too bad I couldn't shoot down to reg set point to see exactly how many good shots I get but, oh well, this is part of the game ain't it?
I want to test further, to see if I can get less spread between shots, just by means of pressure regulation. I'll build a second ''modular'' regulator as I want to see the results of a twin-regulated setup. I'm guessing that regulating the ''first stage'' to around 1800-2000 psi could help to get a more consistent shot string right from the start. Also I still haven't ''played'' with hammer strike and valve setting, so some more improvements may show eventually.
So far my journey into the PCP ''Dark Side'', despite all the hitches I met, is pretty rewarding. I'd like to thank again y'all that helped me, was almost like getting back to school :D.