GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: ray1377 on October 04, 2020, 05:38:46 PM
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Is there an easy formula for figuring the final PSI when compressing a know size or volume of air? And how much effect would altitude have on the answer? Like say 5000 ft ASL vs. 400 ft ASL?
And I totally guessed on the valve volume size so pay little attention to the actual number. I was trying to find the volume size of say a Daisy 853 SSP valve or at least that's my thoughts. Something tiny to build up quite a bit of pressure. Just wondering how much pressure is possible out of a certain size or volume of air when it is compressed. And at this point for the sake of argument lets say that I can pump this regardless of the final outcome or pressure. More interested in final valve available pressure when its compressed more than anything else.
Thanks
Ray
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The formula is
PV=pv
Where
P= pressure of before volume (1 atm)
V= volume of tube
Volume of tube = i.d.^2 x 0.7854 x length
p=pressure of valve (what your solving for)
v=volume of valve
That’s the basic formula for 100% efficient pump
Dave
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so 15 inches stroke on a 1 inch piston into a valve
.5 times .5 times 3.14 is .785 .. THEN .785 times 15 =11.78 cubic inches swept volume .. the compression ratio is based on the valve volume. you mentioned 1/2 a cubic inch . ( thaats way too large for an SSP )
so the fnal pressure would be 348 psi , give or take. keep in mind 1/2 cu inch is 8.19 ccs// I think most SSPS have about 1/4 that ..( whch wwould give 1392 psi
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so 15 inches stroke on a 1 inch piston into a valve
.5 times .5 times 3.14 is .785 .. THEN .785 times 15 =11.78 cubic inches swept volume .. the compression ratio is based on the valve volume. you mentioned 1/2 a cubic inch . ( thaats way too large for an SSP )
so the fnal pressure would be 348 psi , give or take. keep in mind 1/2 cu inch is 8.19 ccs// I think most SSPS have about 1/4 that ..( whch wwould give 1392 psi
LOL, yea I warned you I was guessing at the valve size :)
So what is the volume of a stock 1377 valve just for reference?
What I was wanting was to compress that 15 inch x 1 inch down to nearly nothing, sorta like a Daisy 853 does.
Then what would the pressure be :)
Thanks
Ray
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so 15 inches stroke on a 1 inch piston into a valve
.5 times .5 times 3.14 is .785 .. THEN .785 times 15 =11.78 cubic inches swept volume .. the compression ratio is based on the valve volume. you mentioned 1/2 a cubic inch . ( thaats way too large for an SSP )
so the fnal pressure would be 348 psi , give or take. keep in mind 1/2 cu inch is 8.19 ccs// I think most SSPS have about 1/4 that ..( whch wwould give 1392 psi
LOL, yea I warned you I was guessing at the valve size :)
So what is the volume of a stock 1377 valve just for reference?
What I was wanting was to compress that 15 inch x 1 inch down to nearly nothing, sorta like a Daisy 853 does.
Then what would the pressure be :)
Thanks
Ray
normally an SSP doesnt have a " holding chamber " type valve like we see on a 1377.. the piston stops at the end of the stroke , and whatever space is left before the valve is the valve volume.. With a long sidelver, you can push a 1 inch piston to about 1800psi.. With a 392 configuration , a normal man can push the piston ( .775inch ) to about 2000 ..
SO leverage is key.. Think BIG lever, big piston, big compression ratio , thats kinda the ideal scenario
1377 valve volume is probably 1.5cc , im guessing.
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i lookeed it up , itts .1 cubic inches so 1.69cc for a 1377
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i lookeed it up , itts .1 cubic inches so 1.69cc for a 1377
Dang, where did you find that?
I looked last night for like an hour trying to find the volume of the Daisy 853 and the 1377 and come up short on both of them.
So if I use the smallest space for my 15 x 1 inch stroke instead of the wild guess of half a cubic inch what would the pressure be?
And by smallest space I mean feasible within the design of a SSP, which you stated has no actual valve, since the compression chamber at the end
of the stroke becomes the valve.
Wow, that's a mouthful
Ray
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I thought about that last reply and its confusing to me, and maybe you as well.
Let's say for argument that you took a 853 and increased the available stroke (available compression area) to twice it's normal length thereby compressing twice as much air into the same size valve with the same pump. Would it be possible to get twice the FPS output if your doubling the charge? Or does air not work that way? And I say length because it would be harder to go larger dia. because you'd have to design bigger everything. Seems like making it longer would be a little easier. Maybe not.
Ray
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longer stroke is harder, becasue ur pump linkage still needs a slot to travel in.. anyway , the pressure would be about 1550 psi , i didnt do the exact math , just basing that on my 1392psi quote earler. If you have the volume , you can move pellets at high speed with only about 1200 psi .. So dont always think peak pressure. Remember its a combination.. ( you could NOT pump a larger piston into the thousands, unless your sidelever is 3feet long and the entire structure is solid steel.)
as i mentioned earler , for a 1 inch piston youd be very lucky even with a surplus of MA to reach 1800
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theres been a lot of smart people looking at these issues for many years.. But the immutable laws never go away , and thats the horsepower to air compression relationship,, and how best to do it.. Were i to build one now , id go simple.. Use a crosman topend like Phil and others have, build the sidelever like it was made for lifting a car, build the main tube to be rigid and perhaps use a crosman trigger to save work,prob go 1.5 inch piston where the piston isnt engaged by the sidelever till middle of the arc.. the list goes on
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Well for sake of not having to reinvent the wheel. If I try anything in the way of design I would probably use either a factory discovery pressure tube or something similar like a cothran stainless version. Or something like that. So that would drop the 1 inch down to at least 7/8's.
Man I really want this to work in a bad way. I been thinking about Dr. Bob's Millenium pump gun only without a valve, just set up like a Daisy 853 SSP.
The search continues
Ray
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you wouldnt have the swept volume with either arangement to make an effectivee ssp.. Maybe a marauder with an extended tube
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The potential FPE of any pneumatic is related to the barrel volume and the average pressure.... Smaller valve volumes (as a percent of barrel volume) are more efficient, but larger ones deliver a higher average pressure.... For an SSP, you have a choice to make between a higher pressure and more valve volume.... For a given barrel volume (caliber and length), and a given pump effort, there will end up being an optimum valve volume....
MSPs store air in the valve, enabling you to divide the pumping effort (energy input) over several strokes, making each one possible, while increasing the amount of air compressed and available for the shot.... Not only that, but you can decide how many pumps to take, based on your FPE requirements at the time....
A Retained Air Pumper (sometimes called an Air Conserving Pumper or ACP) uses a precharge pressure, and a larger valve designed to only dump a portion of the air on each shot.... This reduces the number of pumps required to replace that air, but since you are working against the precharge pressure, each pump requires more effort.... although not more than the effort on the last pump with the MSP version to reach the same pressure....
Bob
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The potential FPE of any pneumatic is related to the barrel volume and the average pressure.... Smaller valve volumes (as a percent of barrel volume) are more efficient, but larger ones deliver a higher average pressure.... For an SSP, you have a choice to make between a higher pressure and more valve volume.... For a given barrel volume (caliber and length), and a given pump effort, there will end up being an optimum valve volume....
Bob
So not putting you on the spot Mr. Bob but what do you think might have been possible "FPE" wise if you could have built your Millennium pumper as a SSP with a much smaller valve while using the discovery based air tube? And also, what would be the difference between using a discovery tube and a marauder tube? And for the sake of argument let's say we're going to be using 8.4 gr pellets in .177 caliber. Or do you believe a .22 caliber SSP would be better than a .177 caliber? 12 ft/lbs in .177 would be ideal and suit me to a T. :)
Thanks
Ray
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Long time ago knew a guy that had a Titan Mohawk it was the U.S. version multi pump .22...Very cool rifle but heavy and more expensive... about 350$ iirc...a very nice accurate rifle... but at the time wanted a lighter rifle for my backpacking/camping and instead used a Benji .22 modded to about 18 fpe...had a modded Crosman 2200 also... was very impressed with the Mohawk tho...
There was a single stroke version .177 also...being a bit big the cocking effort of the .22 did not bother me but not everybody felt that way... and most said the SSP .177 was about 9-10 fpe...
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https://youtu.be/OnSVFusWuiQ (https://youtu.be/OnSVFusWuiQ)
Found this on youtube.
I would love to have a gun like this if I could get close to 12 ft/lbs in .177
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I don't have a clue what the Millennium Pumper could do as an SSP.... I wouldn't want to use a larger diameter tube than a Disco one, that was a beast to pump at 2000 psi.... I know as an SSP that force would only be right at the end of the pump stroke, but I would sooner be able to hit 2000 psi with a Disco tube than 1000 with an MRod tube at the same pumping difficulty (yes, it has twice the area)....
The MP used a pump linkage from the 392 Steroid, with the same swept volume.... so there is no reason it should not perform the equal of a Benji converted to an SSP....
Bob
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Hi Ray, The ssp I built has a 1.031" piston diameter and a swept volume of 7 cubic inches, and a firing chamber/valve volume about the same size as the eraser on a number 2 pencil, that same space also contains the valve head/seal. The pressure is close to 3000psi. The gun made 11.2 fpe. in .177 and 12.1 fpe. in .22 with the same length barrel. James
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Hi Ray, The ssp I built has a 1.031" piston diameter and a swept volume of 7 cubic inches, and a firing chamber/valve volume about the same size as the eraser on a number 2 pencil, that same space also contains the valve head/seal. The pressure is close to 3000psi. The gun made 11.2 fpe. in .177 and 12.1 fpe. in .22 with the same length barrel. James
Thanks Mr. James
Was it a bear to cock?
Did you custom build your pump linkage or use one from
a factory built design?
And what did you use for the pump tube?
And lastly, what length barrel for .177?
Only problem I can't wrap my head around is when stuffing a valve or making the volume area less, how do you know how much area or room to leave for the exhaust poppet to be able to "lift" enough to get your charge of air out without constricting flow too much but still have the valve "stuffed" as much as possible?
Thanks
Ray
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Hi Ray, Everything on the gun is custom made except the barrels which are 2260 and 1760 barrels cut down to 19.250". The pump lever is 19.250" long from the pivot pin to the end of the lever. It takes 64 pounds of force to close the lever. The valve being opened faced with the piston closing off the front of the valve I allowed .070 for the valve head travel, there's nothing to prevent the valve head from striking the piston on opening other than the pressure, so I don't know if the valve head contacts the piston or not. Since the piston diameter and stroke length are fixed, I had to make six valves before I had the firing chamber volume small enough to make the most power I could out of the gun. The firing chamber volume with the valve stem and head in place, is only .028 cubic inches/twenty eight thousands of a cubic inch,if my math is correct. The valve is the same diameter as the piston, it's a knock open valve with a 1/16" valve stem, the head of the valve is .223 in diameter x .170 long. The valve is 1.031" in diameter and the firing chamber is placed up near the top edge of the valve to keep the transfer port short, the valve throat is off set in the firing chamber high enough so that the 1/16" valve stem almost touches the inside wall of the compression tube. It's all very nit picky , but that's what it took to get it done. James
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Hi Ray, Everything on the gun is custom made except the barrels which are 2260 and 1760 barrels cut down to 19.250". The pump lever is 19.250" long from the pivot pin to the end of the lever. It takes 64 pounds of force to close the lever. The valve being opened faced with the piston closing off the front of the valve I allowed .070 for the valve head travel, there's nothing to prevent the valve head from striking the piston on opening other than the pressure, so I don't know if the valve head contacts the piston or not. Since the piston diameter and stroke length are fixed, I had to make six valves before I had the firing chamber volume small enough to make the most power I could out of the gun. The firing chamber volume with the valve stem and head in place, is only .028 cubic inches/twenty eight thousands of a cubic inch,if my math is correct. The valve is the same diameter as the piston, it's a knock open valve with a 1/16" valve stem, the head of the valve is .223 in diameter x .170 long. The valve is 1.031" in diameter and the firing chamber is placed up near the top edge of the valve to keep the transfer port short, the valve throat is off set in the firing chamber high enough so that the 1/16" valve stem almost touches the inside wall of the compression tube. It's all very nit picky , but that's what it took to get it done. James
Fantastic work Mr. James.
Thank you so much for the information :)
Thanks
Ray
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I wonder if it would be beneficial to use a spring on the outside of the valve stem with a keeper to close the valve instead of an internal spring pushing against it to close it? It would make building a smaller volume valve more simple I would think. Thoughts guys??
Thanks
Ray
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Check out the crosman a.i.r.177. It’s a ssp valve is open to piston and is plastic.. Fortitude valve opens to gauge and could be a good donor for a disco tube sized ssp if you wanted to use oem parts for simplicity.
Bobs millennium pumper is the reason I joined gta! I spent/spend a lot of time thinking about a acp once reading bobs work showed me the inefficiency of a dump valve.
There were others that have attached co2 cartridges into the valve on 1377 to make a acp with relative ease? It’s a option with caveman tools and skills.