SSP 001
Select Gate
READ GTA FORUM RULES BEFORE POSTING
GTA Forum Help Desk
GTA Announcement Gate
Dealer Area
GRIP
AirgunWeb Airgun Videos
Airgun Repository of Knowledge
Vendors and Vendor Videos
AirGun Expo 2021
Airgun Expo 2022
Contests and Giveaways!!!
Welcome New Members
In Memoriam
GTA Contributing Members
Shot Show Videos
Hajimoto Productions
Airgun Detectives
Air Gun Gate
BB Guns and Such
"Bob and Lloyds Workshop"
American/U.S. Air Gun Gates
European/Asian Air Gun Gates
PCP/CO2/HPA Air Gun Gates "The Darkside"
Air Archery
Vintage Air Gun Gate
Air Guns And Related Accessories Review Gates
Hunting Gate
Machine Shop Talk & AG Parts Machining
3D printing and files
Buyer's, Seller's & Trader's Comments
Bargain Gate
Back Room
Target Shooting Discussion Gate
Target Match Rules
Shooting Match Gates
Field Target Gates
The Long Range Club
100 Yard Match
Discussions By States
Welcome,
Guest
. Please
login
or
register
.
Did you miss your
activation email
?
1 Hour
1 Day
1 Week
1 Month
Forever
Login with username, password and session length
Home
About
Help
Old GTA
Gallery
Search
Stats
Login
Register
Advertise Here
GTA
»
All Springer/NP/PCP Air Gun Discussion General
»
Machine Shop Talk & AG Parts Machining
»
Engineering- Research & Development
(Moderators:
Rocker1
,
Wayne52
) »
SSP 001
« previous
next »
Print
Pages: [
1
]
Go Down
Share This!
Author
Topic: SSP 001 (Read 1161 times))
LaCombreKnives
Shooter
Posts: 11
yes
Real Name: Timothy
SSP 001
«
on:
September 16, 2017, 02:27:05 PM »
Hi All
New to the forum but not new to air rifles. Well, springers at least
I am hoping someone will be able to check my math on a build I am currently losing my mind on. Now bear in mind I barely finished school, am not a machinist and make pocket knives for a living so this is all head ache stuff for me LOL. The design is not my own and I do have permission to use some parts of it IE - the two arm lever. Valve design is mine and everything else is based on any pump out there.
The vid shows current progress
newbielink:https://youtu.be/iXDYNsolErE
[nonactive]
]
I tested today on a friends chrono and I am currently getting 430 FPS with one pump. My aim is 700 plus FPS with 15.5 gr pellets.
So here is the math:
My pump chamber is 289615 cubic mm or 289.615 cc and this is fixed/static and is volume at state 1
Using Boyle's law I worked out that I need a volume at state 2 of 1934 cubic mm (or 1.93 cc) to get the required 2200 psi (150 bar)
My current valve has a internal volume of 500 cubic mm (0.5cc) and this is giving me a constant of 430 FPS with 15.5 gr pellets and I couldn't understand why because common sense says smaller area = higher pressure and that's good - right? Well actually not. According to Boyle's law my current set up was giving me up to 8000 PSI. This didn't sound right so I went and re-did the maths and no matter how many times I put in the figures I was getting 8000 PSI in my valve. Now I know that what is on paper is not always reality and if any one is wondering if it is impossible I have a 5mm wall honed pipe around the valve and the valve has a 8.5mm wall around the chamber. The formula says 8000 psi so why am I not blowing myself up or shooting at the speed of light?
With a few hundred hours of surfing my friend google and getting more confused I found two comments on Airgun nation:
"The +/- 630 cc of air per shot for the Vulcan example is the volume of air that would expand from the
pressurized air reservoir to the atmosphere with each shot.
If you want to do the calculation for your own PCP, the equations can be simplified:
cc of air used per shot @ atmospheric conditions= (Bar used per shot)*(actual air reservoir volume cc)
**bar used per shot=(initial air reservoir fill pressure-ending pressure)/# shots fired
to convert volume from atmospheric conditions to air reservoir pressure of 150 bar:
cc of air used per shot @ 150 bar=(cc of air per shot @ atmospheric)/150
And:
"I just checked my 22 Evanix and used 50 bar in 22 shots or 2.27 bar/shot. The Evanix has a 290 cc air cylinder so the cc used per shot is 2.27*290=658 cc per shot @ atmospheric pressure
Converting 658 cc to 150 bar, 4.4 cc per shot. The Evanix shoots 18.1 grain at 980 fps. Pretty sure these numbers are in the ball park for our PCP’s
using the numbers from your Wildcat I calculate 525 cc per shot atmospheric or 3.5 cc per shot at 150 bar."
So I double checked his math using Boyle's law:
P1 = 1 Atmosphere
V1 = 658 cc
P2 = 150 bar
and the output was 4.4 cc per shot
This made me realize that the volume of my valve chamber was a quarter of the size it should be. Doesn't matter how high the pressure is if the volumes of the ports and the barrel are far higher - what should be a crack becomes a fizzle fart as the pressure is drastically reduced entering a larger volumetric area. My ports are 4.8mm just for interest sake.
So it all clicked. I checked the math again. If the above formula is right for the Evanix then I would need:
P1 = 1 Atmosphere
V1 = 289 cc (my pump volume)
P2= 150 bar
= 1.95 cc of air required in my valve chamber
And this all agrees with my original calculation a year ago when I started of a valve chamber of 1934 cubic mm
Yes - it took a year for it to make sense LOL but I would appreciate it if someone/anyone could point out any errors in my calculations - saves me a whole lot of money.
The irony is I didn't want to spend any money on a PCP - I am way past that point now
Logged
South Africa, Natal
rsterne
Member 2000+fps Club
Bob and Lloyd
GTA Senior Contributor
Posts: 26957
GTA Forums Person of the Year 2017
Real Name: Bob
Re: SSP 001
«
Reply #1 on:
September 17, 2017, 02:02:04 PM »
Yes, your valve volume of 0.5 cc is way too small, because of the reason quoted.... Once that air expands into the barrel, the pressure drops drastically.... In theory, with a pumper, all that SHOULD matter is the swept volume of the pump, so you should have 289 cc available for the shot.... That works out to (289 / 16.4) = 17.6 std. CI, and if you reached an efficiency of 1.0 FPE/CI, that would be 17.6 FPE, which is a 15.5 gr. pellet at 715 fps.... However, there are several losses the occur during pumping.... you lose energy from heat, and although your valve may be 0.5 cc, there are wasted volumes that we call "headspace" between the valve and the top of the piston, which you must add to the valve volume when calculating your pressure.... In addition, the higher the compression ratio the lower the pumping efficiency.... The result is that you are not reaching anywhere close to 8000 psi....
You don't state the dimensions of your pump, but assuming it is a single stage, they might be 1" ID x 22.4" stroke.... If that is the case, the force on the piston to reach 8000 psi would be 6280 lbs., or over 3 tons.... That in itself tells me there is a serious error in the calculations somewhere....
Bob
Logged
Coalmont, BC, Canada
🇺🇦
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).
LaCombreKnives
Shooter
Posts: 11
yes
Real Name: Timothy
Re: SSP 001
«
Reply #2 on:
September 17, 2017, 02:20:38 PM »
Thanks Bob, much appreciated. I thought the 8000 psi was way out.
Pump Bore is 0.98 inches ID (25mm)
Pump stroke is 22.83 inches (580mm)
Internal valve chamber is now 0.649 inches (ID bore) (16.5mm) and 0.708 inches (18mm)long - about 3.85 CC. With my head space being 1.4 CC so a total of 4.85 CC if I subtract the working parts in the valve. Does this sound close to about right?
Really appreciate the help. Having great fun with this build but it's been a big learning curve and test of my machining skills.
Logged
South Africa, Natal
rsterne
Member 2000+fps Club
Bob and Lloyd
GTA Senior Contributor
Posts: 26957
GTA Forums Person of the Year 2017
Real Name: Bob
Re: SSP 001
«
Reply #3 on:
September 17, 2017, 03:00:49 PM »
With a 4.85 cc high pressure volume, and 289 cc on the swept volume, you can in theory reach (289 / 4.85) = 60 bar, or about 865 psi.... That drops the load on the piston to a much more reasonable 678 lbs.... If your barrel is 24" long, the volume is 15 cc, so your valve is about 1/3rd of that volume, which is a good number for reasonable power with a dump valve as in a pumper.... If the 1.4 cc of headspace is not "usable" volume for the shot, your valve is only (3.85 / 15) = 1/4 of the barrel volume, still a reasonable volume....
If your headspace was 1.4 cc is your original setup with the 0.5 cc valve, your actual HP volume was 1.9 cc, so the pressure was only reaching 152 bar (2200 psi), not 8000.... Whether or not that 1.4 cc of headspace was/is useful in producing FPE will depend on how it can flow through the valve to the exhaust port.... If the inlet into the valve is tiny, that 1.4 cc is simply wasted volume, and you should do everything you can to eliminate it....
Since an SSP doesn't need a check valve on the inlet side, perhaps you can simply drill out the inlet side to, say 1/2", so that the 1.4 cc of headspace becomes usable HPA?....
Bob
Logged
Coalmont, BC, Canada
🇺🇦
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).
LaCombreKnives
Shooter
Posts: 11
yes
Real Name: Timothy
Re: SSP 001
«
Reply #4 on:
September 18, 2017, 12:08:41 AM »
Thanks, Appreciate it.
I did. My actual pump volume is 17.97 cu in, so all head space and parts in the valve have been deducted. I assumed Boyle's law might be a bit out. Theory and practical don't always agree I have learned. Also, never took into account barrel length etc so with:
295 cc swept volume and 3.85 cc high pressure volume I am looking at about (295/3.85) = 76 bar?
Less head space 2.54 cc (292.46 / 3.85) = 75 bar
My barrel is 12 cc so my valve is about a third of the volume
My aim was 150 bar with an original valve volume of 1.9 cc (292/1.9) = 153 bar but I am not getting the FPS I want so am doing something wrong somewhere. I realized my valve volume was actually 0.5 cc and that was not enough volume of air for a 12 cc barrel volume. Made a new valve yesterday with a 2.5 cc volume that I will try today and see what results I get.
Am I on the right track? Would shortening the barrel make a difference?
Thanks
Tim
Logged
South Africa, Natal
LaCombreKnives
Shooter
Posts: 11
yes
Real Name: Timothy
Re: SSP 001
«
Reply #5 on:
September 18, 2017, 06:57:04 AM »
On Saturday I tested with a friends chrono and my high pressure volume in the valve was 0.5cc and I was shooting at 436 fps. I got my chrono today and my valve is now at 3.85cc and I am shooting at 420fps. Something is seriously wrong here.
Logged
South Africa, Natal
rsterne
Member 2000+fps Club
Bob and Lloyd
GTA Senior Contributor
Posts: 26957
GTA Forums Person of the Year 2017
Real Name: Bob
Re: SSP 001
«
Reply #6 on:
September 18, 2017, 06:47:35 PM »
The head space has to be included in the volume AFTER compression takes place.... The compression ratio is "swept volume" divided by "final volume".... The "final volume" is the valve volume, PLUS the headspace, which is any and all volume between the piston and the valve....
Generally, shortening the barrel will decrease the velocity....
It makes sense that your velocity has decreased.... In an SSP, the volume of air you are compressing is the same, regardless of valve volume.... Larger valve = lower pressure.... I think the headspace is what is causing your problems....
Bob
Logged
Coalmont, BC, Canada
🇺🇦
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).
LaCombreKnives
Shooter
Posts: 11
yes
Real Name: Timothy
Re: SSP 001
«
Reply #7 on:
September 19, 2017, 12:27:22 PM »
Thanks Bob, really appreciate all the info. Getting the feeling that anything over 750 FPS on a SSP with anything over 15 grains is pipe dreams. But I have learned a lot and will continue with the project and my other air rifle builds as time permits.
Logged
South Africa, Natal
Print
Pages: [
1
]
Go Up
« previous
next »
GTA
»
All Springer/NP/PCP Air Gun Discussion General
»
Machine Shop Talk & AG Parts Machining
»
Engineering- Research & Development
(Moderators:
Rocker1
,
Wayne52
) »
SSP 001