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How to speed up a ball valve.
I have been out in my garage shop making a wood lever extension for my 1/2 ball valve.
I cut off the stop on the valve and it can rotate 360*.
I was rotating the valve with the rough plywood extension and an idea struck me.
It occurred to me to use 2 springs instead of 1?
Not 2 springs in parallel, but 1 ea at the 180* position.
One at the top pulling towards the muzzle.
The other one at the bottom pulling towards my shoulder.
The sear would engage on the bottom of the lever.
i made a spring operated ball valve. it wasnt even a spring, it was just a bunch of rubber bands. i had to hold the tension with my hand, then when i let go it opened. it wasnt very safe... at all, but it worked well.
"physics, gravity, and law enforcement are the only things that prevent me from operating at my full potential" - not sure, but i like the quote
you know you are not an engineer if you have to remind yourself "left loosy righty tighty"
Here one example:
Ondskehems All metall Springloaded ballvalve-rifle.
The trigger mechanism is the most "difficult" part of it... And I agree with Hi... it wasnt safe...
Any idea how fast it opens? Try making an audio recording of the valve opening.
To be effective the valve needs to open in less time than the ammo's transit time in the barrel. That transit time tends to be pretty fast.
For example, a 5' barrel that you want to fire at 500 FPS. Rough estimate puts the average speed in the barrel at 250 FPS. Time to go 5' at 250 FPS is 20mS. You want the valve to open faster than that. WAG that at two or three times faster you are doing pretty well (and further increases in speed of the valve will have less and less affect on the performance). So you want the valve to open in less than 5~10mS.
Standard video frame rate is 33mS/frame. In a video of the valve opening there shouldn't be any frames of the valve actually opening. It should go from one frame with the valve fully closed to the next frame with the valve fully opened. In an audio recording you can get much higher time resolution but you need something distinct in the recording to mark the start of opening and the fully opened time points.
Well done on understanding and stating the limitations of a ball valve. Especially on higher pressure and shorter barrels and lighter projectiles.
Transit time vs opening time. If you use GGDT, most barrels have most acceleration in the first 1/3 of the transit time. Getting the valve open in this first 1/3 makes a lot of difference. This is the primary reason our team did not use a ball valve for the t shirt launcher competition.
Our design goal was for a valve with under 5 ms. We appear to have faster than 2 ms.
Last edited by Technician1002 on Sat Jul 04, 2009 6:47 pm, edited 2 times in total.
I feel like an ant running into DDT.
I gotta turn around!
Your valve design is awesome at 2 msec!
Please estimate the opening time for the following:
In addition to opening time and dwell, how do they compare in CV?
I am working on a valveless gun design.
Thanks for your valuable input.
Commercial QEV's are very fast. Speed is Dependant on pressure. Due to the extremely low mass of the moving part, these can't be beat by anything but a burst disk.. They are well below 1ms. The disadvantages is the flow path and valve seat sizes. When open the square edge of the valve seat and plumbing into and out of the orifice limits the flow so the COF is limited.
Barrel sealing piston speed has many factors. In general, ones with a large valve seat in relation to the overall OD of the piston operate quicker because the pilot pressure has to be very low before they unseat. The Mauler Valve is of this configuration. The sudden pressure rise on the face of the piston slams them open. With a low mass, these are very fast.
With too narrow of a ratio of sizes of valve seat to piston OD, the force to get them started is very low, so too much eq port flow, too small of a pilot, or too much friction can cause these temperamental valves to fail to fire. When they work right, they are very hard to beat. Speed is dependent on piston mass and pressures used as well as the valve seat to OD ratio which affects the pilot pressure where it operates. These can be very fast and don't always require a fast pilot to pop open.
The chamber sealer has lots of force on the face of the piston. They are noted for their reliability. They just work. The supah valve is of this style. When they open, they are noted for increased force when they crack open due to the larger area exposed to chamber pressure. How much depends on the ratio of the valve seat to the OD. These valves are noted for requiring a large fast pilot. Pressure in the pilot if not vented very quickly will re close the valve or prevent full opening as the chamber pressure quickly drops. On the down side, they have a larger dead space. An advantage over a barrel sealer is they open with much less force into the bumper, so they are less prone to breakage. Their speed is highly dependent on the pilot speed. These are generally slightly slower than a barrel sealer due to higher pilot pressure when it cracks open. COF is about the same as a barrel sealer of the same dimensions.
A sprinkler valve in the chamber sealer configuration (center of the diaphragm has chamber pressure) are notorious for this honking with small pilots.
Coaxial is simply the barrel is inside the chamber. Most coaxial designs are barrel sealers. The advantage is huge ports from the chamber into the valve can be made for a very high COF. With high speed and high flow, this configuration is used in some of the most powerful air cannons made.
If I made errors or missed something, please feel to add your input.
Thanks for your responses.
A few questions:
T Shirt launch test data, position and time. Blips are 1 foot of shirt travel in the barrel."
Did you measure the blips and the positions?
What caused the blips at 12" intervals?
"Commercial QEV's are very fast. Speed is Dependant on pressure. Due to the extremely low mass of the moving part, these can't be beat by anything but a burst disk.. They are well below 1ms. The disadvantages is the flow path and valve seat sizes. When open the square edge of the valve seat and plumbing into and out of the orifice limits the flow so the COF is limited."
If the "pop" is dependent on the opening time and a commercial QEV opens in less than 1 msec, it would appear to me that the 4 msec head start would make up for the limited CV. In addition, would "porting and relieving" to remove square edges and roughness improve the CV to more competitive numbers?
I have done a little research on the web an I have not seen any QEV's rated above 150 psi. Are there higher pressure QEV's?
Most of the info including pictures of the setup are posted on the official contest website. The blips are generated by passing a magnet though a coil of wire. The barrel has coils of wire carefully spaced 1 foot apart starting at the muzzle. The first coil is near the initial position but is not at the zero position. Working backwards, each foot of travel can be measured for time. The curve as the magnet passes through is an S shape. The middle of the S where the voltage crosses zero is the precise point where the magnet is neither entering or leaving the coil and is a tight indicator of the precise center of the coil.
Taking time measurements for each foot and working backwards we can create an acceleration graph using the change in velocity as acceleration. Using that we were able to tell at what length we were no longer accelerating much and gave us the optimum barrel length to match the COF of our valve and volume of our tank. Looking at the early acceleration of light objects (4 inch foam ball) we got a good indication that the valve opening time is under 2 ms. Acceleration drops after the first foot and not still increasing from a valve still opening. Acceleration in the first measured foot is the highest and only possible with a fast valve.
We used this data to find the best length and decide between a 2.5 or 3 inch barrel. Even with a 2 inch valve the 3 inch barrel was a better choice for speed. We predicted higher speed from the 2.5 inch.
COF is how well a flow passes through a valve when it is open. Big flow when open counts. A fast QEV for example may only be able to supply enough flow to get the foam ball up to 250FPS, even though it can open faster than a piston. A fast enough piston and high COF is a winning combination.
Attached is the 60 PSI shot of the 4 inch foam ball. Note the high acceleration early in the shot. Remember, this is a 2 inch valve feeding a 4 inch barrel. Plug in the values into GGDT. This graph is the one we used to find the COF is high. Lower COF valves simply won't achieve this speed. At the end it is still accelerating, but at a slower rate. Only a high COF can reach these launch speeds with a 4 inch barrel. 454 FPS and rising isn't bad on a 4 inch bore at only 60 PSI.
Link to the official site.. http://inteltrailblazerschallenge.wikispaces.com/Barrel+length+trim+method
"A fast enough piston and high COF is a winning combination."
F=ma is the universal relationship.
That is the bottom line. Period!
Projectile performance is analogous to a drag race; usually won by the fasted reaction time after green.
Slow valves = low F. The rest is elementary Dr. Watson.
Excellent methodology and implementation.
You took spud guns into the laboratory and accurately measured the acceleration inside the barrel in real time.
My definition of Science: "Humankind's attempt to measure Nature".
You unconfused me with the facts.
True if the race cars are pretty well matched in horsepower. A low COF valve even though faster is like racing a Geo Metro with a fast driver against a slow reacting driver in a race car. The Geo will be quicker off the line but the 1/4 mile is won with the higher horsepower.
F=ma is the universal relationship.
A valve with a low COF provides low F when open. Top speed is limited.
A slow valve provides low F until open. A fast valve with high COF provides high F for most of the quick trip out the barrel.
Slow valves = low F while opening. The rest is elementary Dr. Watson. Fixed it Holmes. The longer a valve takes opening the longer the force is low. A low COF valve has low force when open, even if the valve opens faster.
For some people, this is easily done.
For the competition, both COF for high Force, and Valve Speed for early high Force, were design goals to achieve high Acceleration.
It's what engineers do. Find the limitations and seek improvements.
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