Solenoid Valve versus Sprinkler Valve

So first of all i have no clue whether or not i chose the correct category but here we go. Our team has been working on an off season T-shirt cannon and it’s both gone well and gone horrible. We’ve solves all electrical issues and it drives and launches fine. The main issue is the distance we fire. At 120psi with our current solenoid valve we fire in the region of 40 ish yards. This is a major problem because to fire on our football field we need to at least fire 70 yards or more. This is what I believe is the closest match to what our current solenoid valve is
U.S. Solid Electric Solenoid Valve- 1" 24V DC Solenoid Valve Brass Body Normally Closed, VITON SEAL - U.S. Solid. I did some research and attributed it maybe to flow rate but i also decided to compare our new robot cannon to the old one which used a sprinkler valve. I don’t know if they modified it in any way because I was not on the team when they built it but I do know that they were able to fire over 100 yards at around 70psi. Does anyone might know what the issue is between the two and maybe have a solution to the issue. Also if anyone knows a better category to post this in just direct me there if you can. Thanks.

A couple of questions:

  1. How big is the volume of the “low pressure” tank feeding 120 psi air into the barrel? (assuming you have one, and you aren’t trying to get all of the shot air through the regulator from your high pressure tank)
  2. What kind of restrictions are between the tank and the low pressure tank?
  3. What is the CV rating of the valve? A Cv of 12 (from your link) should be plenty.
  4. How tight a fit is the T-shirt in the barrel? (tighter = further)
  5. How long is the barrel (longer = further)
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Not knowing the specifics, I can only speculate.

Flow rate is important. Try to compare the flow rates of both valves to see if it is significantly different.

Also important is launch seal. The shirt must MUST seal tightly to the barrel. Use a wadded plastic shopping bag as a sabot to guarantee that seal.

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We have a three tank system setup but the main tank that the barrel feeds off of is I believe 2.5 gallons i would have to go to our workshop to get its exact measurements and i would also have to do the same for the barrel as we are off season. I also think the inner diameter of the pipe is 3 inches and our t shirts fit tightly in them i would also have to go out to our shop to get the exact circumference of the barrel and the shirts. I will reply back in around 30seconds minutes
Thank you

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the Cv is 12 yes

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A photo would help. Assuming your barrel is ~24" or more long, a 2.5 gallon low-pressure tank should hold 3 or 4 times as much volume as the barrel, which is plenty. A 12 Cv valve should be plenty too (that’s about how much ours is iirc). So I’m not hearing anything obviously wrong from your description.

Our barrel is 48 inches long with an outer diameter of 3.5 inches and an inner diameter of three inches while on average our t- shirts diameter is 3.25 inches. Our two smaller tanks that feed to the main tank connect to it through tubing that has an inner diameter of 2/8ths of an inch. The older t shirt cannon has a 72 inch barrel with the same diameter but we tested it and it gave us worse results.

we have 2 of the smaller tanks I only took a picture of one because they are exactly the same this is a photo of the sprinkler valve setup of the original t shirt cannon.

From what you have described my best guess is that your valve is not the issue. Will you record a slow motion “Side view” of the bot firing and post it to this thread? I had almost the exact same experience last year whilst designing a similar bot. I also would suggest that you feed the cannon with 2 1/2 inch hoses rather than 2 1/8th in hoses. The diameter of your tubing is critical to achieving a good flow rate. I would guess that your valve is seeing nowhere near its max flow because the tubing is restricting it severely.

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Valve opening speed is also very important. Sprinkler valves (modified for air cannons) open very quickly - pressure in the barrel starts building as soon as the valve cracks open but if it opens too slow, it becomes an obstruction to the flow a @nuclearnerd mentioned in his post.

The shirt starts moving as soon pressure builds i the barrel - as it moves, the volume behind it in the barrel increases and the pressure drops unless the incoming flow is sufficient to maintain (and even increase the pressure as the valve continues to open).

Enough stored volume, at a sufficient pressure, controlled by a fast opening valve, going into a barrel that is reasonably sealed by the T-shirt (or using a sabot as the seal as mentioned @DonRotolo - I like them because they take the beating and not the T-shirt) are the secret for good range.

What do people use to regulate the high pressure (scuba tank) air down to about 120 or so to feed the shooting tank? Our solution for this is a regulator valve specified to do this from a paintball gun, but it keeps freezing up on us after one or two shots.

You could use the low pressure port on the first stage of a scuba regulator. I believe that is 120 psi. Some are specially designed to resist freezing if it becomes a problem.

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The smaller tanks are feeding into our main tank through the 2/8th inner diameter inch hose. Our actual cannon is being fed by a 1inch pipe from our main tank that runs to the solenoid and then the barrel. We thought that a larger opening would help and it did but it hasn’t gotten the same results as previous years.

This is your friendly neighborhood CDer reminding you to never, ever, everevereverever use PVC with anything that might maybe end up acting as a pressure vessel.

PVC becomes brittle with age and UV exposure, and small shards of it embedded in flesh don’t show up on X-ray imaging. ABS would be a safer route, or more ideally, metal tube.

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Nuff said

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Exactly why we dont use the old cannon anymore

This is the barrel btw

What happens if it gets clogged for some reason?

Moving away from PVC is absurdly cheap insurance compared to the potential risk in a few years.

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I’ve posted the math before, and I’ll likely do it again.
Consider two cylindrical tanks, 24" long and 3" in diameter, both pressurized to 100 psig (.7 MPa g), one with air, one with water. In both cases, the volume is about 85 cubic inches, or 1.4 liters. The comprehensibility of water is about 5x 10^{-10}/Pa, meaning it wants to expand by about a tenth of a mL to reach atmospheric pressure. The air, on the other hand, wants to expand by a factor of seven, meaning more than 8L of expansion. Thanks to the non-linearity of the expansion, it isn’t quite that bad, but there is still significantly more than 1000x the energy stored in the air than in the water. Air rated pipes and tanks tend to tear rather than shatter when they fail, reducing shrapnel; materials which may shatter (e.g. PVC pipe) are likely to be rated for water but not air.

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Well I am trying to focus on the issue that we are shooting at half the distance of what we need so my main post is looking for decent solenoid valves or a different option that will get us to around 100yards at 80-100psi because at 120psi our current distance we get around 40 or more. We do plan on changing to maybe an aluminum barrel or ABS

Do more than plan. PVC is dangerous, much more than you think.

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