I never thought I would find myself in this discussion, but here I am. Life has been busy, and I have only been able to turn out one project a year or so. Last year was the LRC-425 Tennis Ball Gun. I have grown bored with combustions, and now I feel the urge to shoot a golf ball at Mach 1. Hybrids have always been fascinating to me, but usually it was just fine to admire them from a distance. Now with the advancement of piston valves and manometric metering, I figure its time to take it up a notch.
This design has been in the works since June. I have brainstormed several different designs, arrangements, and methods; as well as drawn inspiration from many designs here on Spudfiles. Don't worry, I will give credit where it is due.
Here are the current specs:
-Shoots golf balls
-manometric metering
-Custom EPDM Inline Piston Valve
-2" Galvanized Steel Pipe fittings
-Ignition circuit to be built by JBK Enterprises, LLC.
That is all I have for now. Right now, I have started tinkering with the piston valve design. I am basically cutting out round discs of EPDM rubber and compressing them on 5/16" threaded rod between two large washers.
I have attached a concept drawing for your amusement. Like most of my projects, this is a Design-Build project. Basically it means figuring stuff out as I go. My reason for posting is so you all can provide me with suggestions, concerns, and encouragement if you will. Please give me any feedback.
My first question though is, can someone either explain to me or link me to a page about Manometric metering and how it works? Thank you.
Update: Golf Ball Piston-Valved Hybrid (LRCH-200)
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Last edited by Binder17 on Sun Aug 16, 2015 9:53 am, edited 1 time in total.
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Juggernaut12121
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Hiya, it's kind of funny but I'm about in the same boat as you. I've been planning a piston valve hybrid similar in scale since August or so, although I think I've got everything pretty much figured out.
Anyhow, idk if you've heard of HGDT but it's very helpful for designing hybrids (it's a computer program that's free to download made by one of the members on this site, I beileve he goes by D_Hall). You may also want to move the ball valve going to the pilot, once the piston flies back it's going to compress the air behind it momentarily to a higher pressure, meaning that the tubing could be ruptured if not strong enough. That and it adds extra space to the pilot volume (you want to avoid that). And you'll want to place your ignition point as close to the middle of the chamber as you can, this makes it so that the gases ignited move about the chamber in two waves going opposite one another, rather than one wave having to travel the whole chamber (this makes ignition happen more quickly, and hence you get more efficiency out of the cannon).
Other members may be able to explain this much better, but I feel that's the gist. Good luck!
Anyhow, idk if you've heard of HGDT but it's very helpful for designing hybrids (it's a computer program that's free to download made by one of the members on this site, I beileve he goes by D_Hall). You may also want to move the ball valve going to the pilot, once the piston flies back it's going to compress the air behind it momentarily to a higher pressure, meaning that the tubing could be ruptured if not strong enough. That and it adds extra space to the pilot volume (you want to avoid that). And you'll want to place your ignition point as close to the middle of the chamber as you can, this makes it so that the gases ignited move about the chamber in two waves going opposite one another, rather than one wave having to travel the whole chamber (this makes ignition happen more quickly, and hence you get more efficiency out of the cannon).
Other members may be able to explain this much better, but I feel that's the gist. Good luck!
Whatever the mind can conceive and believe, it can achieve
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mark.f
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Overall good setup, tried and testing too, lol.
Good luck with the manometric metering... if you need any help getting a transducer working give me a ring/message, as well if your backup meter needs encouraging...
Hope to see this thing at Christmas.
Good luck with the manometric metering... if you need any help getting a transducer working give me a ring/message, as well if your backup meter needs encouraging...
Hope to see this thing at Christmas.
Juggernaut:
Thank you for the suggestions. For now I will focus on the efficiency of the piston, and I will likely add a spark strip later. I have been debating over that air line running to the pilot. I am planning on using copper tubing, but like you said, I am not sure if can handle the burst pressure. I am hoping that since the tubing is 1/4", that the pressures will not reach critical. Trial and error time.
Mark:
I will likely need help with the transducer. I am not sure what to order off of ebay. For testing, I will use a standard volumetric setup. This year, I have off Christmas Eve through January 4th, so I will likely finish it off at home. You are welcome to join the party. Also, any suggestions for a metal golf ball barrel? I have looked far and wide in the DFW area and cannot find the right size aluminum or steel pipe I want.
Thank you for the suggestions. For now I will focus on the efficiency of the piston, and I will likely add a spark strip later. I have been debating over that air line running to the pilot. I am planning on using copper tubing, but like you said, I am not sure if can handle the burst pressure. I am hoping that since the tubing is 1/4", that the pressures will not reach critical. Trial and error time.
Mark:
I will likely need help with the transducer. I am not sure what to order off of ebay. For testing, I will use a standard volumetric setup. This year, I have off Christmas Eve through January 4th, so I will likely finish it off at home. You are welcome to join the party. Also, any suggestions for a metal golf ball barrel? I have looked far and wide in the DFW area and cannot find the right size aluminum or steel pipe I want.
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mark.f
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IMC conduit if you can find it... you can order DOM or hydraulic tubing if you can't, but it'll be expensive.
As for the transducer, it's a piece of cake... just order one with a suitable full-scale accuracy and pressure range... you'll want to consider a isolation valve as well.
As for the transducer, it's a piece of cake... just order one with a suitable full-scale accuracy and pressure range... you'll want to consider a isolation valve as well.
So the assembly is going well so far. It has been difficult to put a lot of work into it lately. Another complication has been the fact that I have just bought a house with a garage, but I have limited tools. All the materials except for the barrel have been bought out, however, I am still lacking an air compressor. So I am not in a hurry to fully assemble this thing yet, because then I would have to wait to test it. I am tempted to purchase a bicycle pump, but that is money that could go towards an air compressor. It is the holi.ay season and my wife wants me to invest in other things for now. Testing may have to wait until Christmas when I go back to Louisiana.
Anyway, on to technical issues. The main problems I am foreseeing are getting the piston to seal properly, and procuring a suitable golf ball barrel. I am sure other issues will come up.
My plan for the piston is to make it work. My goal is to have an O-Ringless piston, but I will resort to it if it is the only way.
My plan for the barrel may be to sleeve some SDR-21 pvc with thin wall aluminum tubing. This will keep the cost down and also produce a lighter barrel. My only concern is the burst pressure. I will need to consult my charts to see if it can handle it. Otherwise, I will get thicker walled aluminum pipe.
Some other updates. The ignition system will be a spark plug and BBQ igniter for now. This will be for testing purposes. Later, it will be upgraded with a spark rod and and ignition coil circuit from a gas heater. The fuel system will be a modified volumetric system from the LRC-425 (Last year's project). Later, it will be upgraded to Manometric.
I will post pictures soon.
Again, questions and concerns are encouraged. Thanks.
Anyway, on to technical issues. The main problems I am foreseeing are getting the piston to seal properly, and procuring a suitable golf ball barrel. I am sure other issues will come up.
My plan for the piston is to make it work. My goal is to have an O-Ringless piston, but I will resort to it if it is the only way.
My plan for the barrel may be to sleeve some SDR-21 pvc with thin wall aluminum tubing. This will keep the cost down and also produce a lighter barrel. My only concern is the burst pressure. I will need to consult my charts to see if it can handle it. Otherwise, I will get thicker walled aluminum pipe.
Some other updates. The ignition system will be a spark plug and BBQ igniter for now. This will be for testing purposes. Later, it will be upgraded with a spark rod and and ignition coil circuit from a gas heater. The fuel system will be a modified volumetric system from the LRC-425 (Last year's project). Later, it will be upgraded to Manometric.
I will post pictures soon.
Again, questions and concerns are encouraged. Thanks.
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I am hoping to slide the piston into the pilot chamber, and then you can tighten lock nut until it is snug against the metal wall. With the proper lubrication, it might work.
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Juggernaut12121
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Very nice, looks like it's coming quite well. I have to say I quite like what you did with the piston.
A few questions if I may, what does the inside of your piston housing look like? I can't a length of pipe that isn't welded.
And I think you may want to use some thicker washers, depending on how high you go mix wise.
A few questions if I may, what does the inside of your piston housing look like? I can't a length of pipe that isn't welded.
And I think you may want to use some thicker washers, depending on how high you go mix wise.
Whatever the mind can conceive and believe, it can achieve
I had that problem with the weld. If I am assuming right, you are talking about the welded seam in the pipe nipple. I got home from Ace Hardware and opened the package to find a big nasty weld inside that made putting a piston through it impossible. My solution was to go with Black Steel on that fitting. The weld is almost perfectly flush on the inside because it does not have the build up of zinc from the galvanization process.
I have labored immensely over reducing the shock of the piston against the back of the piston chamber. I know that without proper shock absorption, it will bend the crap out of the washers and maybe the rod as well. This would compress the rubber and likely lodge it inside the chamber. I have considered springs and rubber pads, but I think I have an idea that will work well to protect the piston. I plan on constructing a dampener that will take the brunt of the force, and redistribute the shock away from the piston. It will be designed to get bent up. The only downside will be having to replace it after a while.
I have labored immensely over reducing the shock of the piston against the back of the piston chamber. I know that without proper shock absorption, it will bend the crap out of the washers and maybe the rod as well. This would compress the rubber and likely lodge it inside the chamber. I have considered springs and rubber pads, but I think I have an idea that will work well to protect the piston. I plan on constructing a dampener that will take the brunt of the force, and redistribute the shock away from the piston. It will be designed to get bent up. The only downside will be having to replace it after a while.
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MrCrowley
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As suggested above, you'll definitely need thicker washes (in my experience). Feel free to give it a go first. I think mine are about 3-4mm thick for the body and about 4-5mm thick for the washer behind the sealing face. I'd also say that you need a thicker and harder sealing face. My original sealing face was probably about 10mm thicker, if not more, and made of fairly hard rubber but it would deteriorate from both the seat cutting in to it and the heat disfiguring the rubber.
I ended up going for a 16mm thick sealing face made out of rubber that could not be compressed at all by hand. You have to remember that you'll have quite a lot of force behind the piston (200-300PSI compared to only ~120PSI in most pneumatic piston valves) and the seat is metal and can easily seal against the rubber (unlike a thicker and blunter seat made from PVC). So even though a hard rubber sealing face may not seem like it would seal, it probably will.
As for your idea, it might work. Worth a shot. I think to get the seal you need you'll have to tighten it so much that it will be extremely difficult to move inside the valve. I think it will wear down quickly or perhaps loosen up after awhile. I'm not sure if it would be a long term solution. That being said, you may be able to find a 'goldilocks' zone where the piston has been tightened enough that it creates a partial seal but is still moveable within the valve and then when pressure is applied behind the valve it compresses it more and creates a full seal.
I ended up going for a 16mm thick sealing face made out of rubber that could not be compressed at all by hand. You have to remember that you'll have quite a lot of force behind the piston (200-300PSI compared to only ~120PSI in most pneumatic piston valves) and the seat is metal and can easily seal against the rubber (unlike a thicker and blunter seat made from PVC). So even though a hard rubber sealing face may not seem like it would seal, it probably will.
As for your idea, it might work. Worth a shot. I think to get the seal you need you'll have to tighten it so much that it will be extremely difficult to move inside the valve. I think it will wear down quickly or perhaps loosen up after awhile. I'm not sure if it would be a long term solution. That being said, you may be able to find a 'goldilocks' zone where the piston has been tightened enough that it creates a partial seal but is still moveable within the valve and then when pressure is applied behind the valve it compresses it more and creates a full seal.
I couldn't either. Grab a dremel or a file and get to work! If you create 'pits' by filing too deep, just use some JB-Weld or other epoxy to fill it in.I can't a length of pipe that isn't welded.
MrCrowley,
What kind of rubber have you used? I went with EPDM specifically since it has high abrasion resistance and heat resistance.
What kind of rubber have you used? I went with EPDM specifically since it has high abrasion resistance and heat resistance.
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Juggernaut12121
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I've been thinking of using a hockey puck for the sealing face (or at least part of one) 
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MrCrowley
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I didn't select a particular type of rubber, just visited a few places and got what looked good. The stuff I used was from a boat trailer roller. Apparently 'heavy duty rubber', whatever that means.Binder17 wrote:MrCrowley,
What kind of rubber have you used? I went with EPDM specifically since it has high abrasion resistance and heat resistance.
Like this: http://www.etrailer.com/comparison.aspx ... 2=YR5213-5