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Compressor size needed - who is good at math?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Compressor size needed - who is good at math?

Unread postAuthor: morphious » Fri Mar 09, 2012 8:09 pm

I have a cannon on the way to me that I need to figure out what size compressor would be needed to run it.

Here are the details. This is an industrial machine that we built to test golf balls.

2 position/2 way valve 1" NPt 0-300 PSIg recommended.

Filter/regulator 1/2". Figure 1/2 flow rate.

Can use 1/4 inch to 1/2 inch adapter on it form the compressor hose. but it seems like most tank / compressors I can get online have 1/4 inch.

The goal is to figure out what size / type compressor I need to run this at 100 PSI shots about every 3 seconds. Obviously do not want the tank to run out, or run all the time.

Will a shorter hose be better too?

Please let me know your thoughts.

-M
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Unread postAuthor: Mr.Tallahassee » Fri Mar 09, 2012 8:47 pm

Depends on the size of the chamber and how many shots you want. A high pressure tank regulated to 100PSI is your best bet. Maybe a Scuba tank would do the trick. That would give you countless shots with a small chamber.
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Petitlu wrote:My balls are made of lead and weigh 22g but I can make heavier or lighter ...
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Unread postAuthor: morphious » Fri Mar 09, 2012 8:51 pm

Hi, it has no chamber, it will just be run off of the compressor. The cannon already has a regulator to shoot at 100 PSI.
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Unread postAuthor: Mr.Tallahassee » Fri Mar 09, 2012 8:57 pm

If that's the case then with 1/4'' hose you wont get a golf ball more than 20 feet. That's a lot of restriction on flow. I suggest adding a small (few cubic inches) chamber to get the range to test them. It may work but I just can't see it going far at all. :?
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Unread postAuthor: morphious » Fri Mar 09, 2012 9:05 pm

This is for testing the durability of golf balls, see my other ports here:

http://www.spudfiles.com/forums/buildin ... 23679.html

the company that helped me build this is getting:

100 PSI = 114.3 MPH 167.6 ft/sec

It fires about once every 3 seconds. It has a PLC and HDMI interface to count the shots and it gets average of 130 shots on one type of ball before the ball casing cracks.

He has a big 120 gallon shop system width 1/2 hoes and said he it does come on once every 20-30 shots.

but that is a little large for my use...
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Unread postAuthor: Fnord » Fri Mar 09, 2012 9:39 pm

You could possibly get that type of performance with a 1/2 hose, directly connected. 1/4" is probably a no-go.

The amount of air you're using will greatly depend on how long you keep the valve open, so figuring air consumption will not be as straightforward as a normal cannon. For a ballpark estimate you'd need to calculate the muzzle energy of a golf ball traveling at your desired velocity, then divide by your rough efficiency (usually only around %10 at most). That's the energy you're actually using.
Then you'll have to figure what volume of air stores that energy at 100psi.
There's an old thread where this was discussed.

Lastly you'll need to compare this volume to the cubic feet/minute ratings on the compressor you're looking at. Account for at least a 30% margin of error.
You'll see now why it's often a better idea to just buy locally and return it/buy the next bigger one if it doesn't work.
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Unread postAuthor: Technician1002 » Sat Mar 10, 2012 8:16 am

To use LESS compressor air, it is highly recommended to use a small chamber as a local surge tank. Because of the flow restriction as already mentioned, the surge tank can provide much higher flow in the duty cycle of the repeating launch. This permits reducing the pressure used for the same launch parameters and lower air use per shot.

For example if you make an air chamber 1/7th the volume of the barrel, and charged it to 7 bar, it would expand (not counting cooling effects) to just enough volume to void the barrel for each shot. This would be with a much higher force on the ball with a larger valve between the chamber and barrel (sprinkler valve) resulting in much higher energy efficiency. If you doubled the chamber volume and reduced the pressure to 1/2, your air use would be the same but at lower efficiency for a slower shot.

If you made the chamber 1/2 size and simply shortened the barrel by 1/2, you cut your air consumption in half, but do not cut your velocity in 1/2 raising efficiency.

Google the math onlne to find the amount of air stored in a tank at a given pressure. You can model your compressor size requirement from that based on how many charges you need per minute to get SCFM used per minute. Use GGDT to model how fast you can launch your ball using various valve, chamber, and barrel sizes. With the combination of the two, you can match a compressor size to meet your requirement. An exact match = compressor running constantly but keeping up with demand. Larger than needed will cycle. Smaller than needed will not keep up pressure.
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