How can I make a piston?

By that, I mean how can I make that disc that goes in the tube? I need it to be airtight (I'm planning  on using it in a homemade watergun). And if I can't make one, is there a non-online shop from which I can buy it?

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Sandisk1duo8 years ago
what if you use a piece of stretchable rubber?
like form a balloon?

it should act the same way...
Shagglepuff (author)  Sandisk1duo8 years ago
Do you mean like I should use it like a diaphragm or use it on the piston? And if you do mean use it like a diaphragm, I don't think it could stretch far enough. 
yeah, like a diaphragm!

it would work, if you used a whole balloon

Shagglepuff (author)  Sandisk1duo8 years ago
Great idea, but a ballon will probobly break.


I f you used, let's say, a big sheet of rubber, it would effectively seal off the air from the water.
the balloon wouldn't burst, all it would be doing is separating the air from the water, it would transfer all the energy
Shagglepuff (author)  Sandisk1duo8 years ago
But I'm planning on making the cannon two feet long...
weather balloons
Shagglepuff (author)  Sandisk1duo8 years ago
Shagglepuff (author) 8 years ago
Here's a bit more info-
The piston is NOT for the pump, it's actually made to build a watergun that uses a piston to seperate the water from the air (like this one: However, I don't really have spare pistons lying around, so this is why I want to make one. Also, because of this, it needs to be  fairly large (hopefully 4 inches) in diameter.
Shagglepuff (author)  Shagglepuff8 years ago
Oh, and I want it to be airtight so that I can pressurize it and then keep it pressurized for the rest of the (watergun) fight. Then I can just take advantage of the water pressure from a garden hose to fill and pressurize it.
seandogue8 years ago
Several ways, but for the flex disk that is used as the cylinder seal, you need to make a punch of slightly larger diameter than the internal diameter of the cylinder bore.

For a small cylinder, say 2" or less, you can use a piece of metal pipe as the punch by grinding the end to form a blade
Re-design8 years ago
A circle of rubber the same size as the opening, clamped between two washers that are slightly less than the opening.  The rubber will squeeze out and make it a tight fit.

Make the rod out of a long bolt..
Burf8 years ago
For a water gun, it doesn't necessarily have to be air tight.  A snug, slip fit will work nicely.
Depending on the diameter of the tube, you could make piston out of a piece of hardwood; carve a groove around the edge and roll a rubber O-ring into the groove, or even make your own O-ring out of a piece of leather.
Think of how a medical syringe works and try to make something similar.
lemonie8 years ago
You'll be using PVC tube I guess? Got any PVC bits that would do? You'd want a rubber O-ring and some silicone grease too I should think.