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Physics FAQ

Last updated on 2008-01-17


Can a water gun explode?

Hypothetically speaking, yes, a water gun can explode. However, most stock guns have pressure relief valves which would release any extra pressure to prevent damage to the gun. Some homemades also feature pressure relief valves. PVC pipe can handle much higher pressures than those in stock guns though. Explosions are possible in all pneumatic systems.

Can CO2 be used to pressurize a gun?

Yes. A student named Andrew Mommsen built a CO2 powered water gun several years ago. A member of a spud gun forum also built a CO2 powered water gun.

Can electrolysis power a water gun?

No. It would take too long in battle, and access to electricity or a battery is required. Performance would be much worse than with an electrically-powered pump.

How bad is dropoff in air pressure water guns?

For the first quarter or third of a shot, dropoff is quite minimal. Because output varies as the square root of pressure, a small change in pressure will make even less of a difference in terms of performance. However, dropoff intensifies greatly for the rest of the shot.

How can I achieve a certain pressure in a certain number of pumps in an APH?

Consult the APH design tool to help design to your own specifications.

How can I increase range without increasing the pressure?

Consider changing the nozzle and interior flow.

How do pneumatic launchers work?

Pneumatic launchers use pressurized air to propel a projectile. The air is stored in tank, and a valve is opened to let the air out through a barrel.

How do water guns work?

Water guns use a system to generate pressure and propel the water. Air pressure water guns use pressurize, compressed air to push water; constant pressure systems use rubber bladders; spring systems use springs; and piston pump systems use force directly from pumping. For more information, see our article about how water guns work.

How does a ball valve work?

Ball valves use a ball of plastic or metal to seal a hollow, spherical enclosure. The ball has a wide, cylindrical hole through the middle. The ball can rotate on an axis perpendicular to the flow of water so that the hole is either aligned with or hidden from two openings in the valve. Rotating the ball by turning a torque arm turns the flow on or off as the seal opens and closes. For more information, see our trigger valves article.

How does a pump work?

Pumps have plungers attached to long rods that can be slid through a tube. Check valves, also known as one-way valves, make sure water can only enter from the reservoir and exit to the pressure chamber and nozzle. When the plunger is pulled out, water is sucked in from the reservoir. When the plunger is pushed in, the water is forced into the pressure chamber or through the nozzle. For more information, see out pumps article.

How does the nozzle size affect range?

We provide a detailed description in the nozzle and interior flow article.

How well would baking soda and vinegar power a water gun?

We do not know; but we do know the mess it would make and the hassle it would be to clean up and deal with. Stick with conventional metohds.

How well would Diet Coke and Mentos power a water gun?

We do not know; but we do know the mess it would make and the hassle it would be to clean up and deal with. Stick with conventional metohds.

In a gun with multiple pressure chambers, when does each one kick in?

They don't; they kick in all at the same time, emptying at the same rate. For more information, check out this article on the subject.

What are the straws in the nozzle for?

The straws improve laminar flow. The are also called linear guidance walls since they guide the stream linearly. They improve laminar flow by decreasing the diameter of the pipe while maintaining flow. This lets the stream more easily follow a line and be less turbulent.

What is CPS technology?

CPS technology is a rubber bladder. Water expands it from the inside out; it inflates like a balloon. This effect powers the gun and makes the flow and pressure more constant.

What is negative pressure?

Negative pressures are pressures below atmospheric pressures. Negative pressures suck instead of push. Pumps create negative pressures to bring water into themselves.

What is the maximum range CPS could achieve?

The maximum anyone has achieved in a CPS system is about 65 feet in both homemades and modified guns. It is very difficult to get range past this.

What is the pressure inside my gun?

There are two ways to get this: using a pressure gauge or using a calculation. Pressure gauges will give accurate, gauge pressures. But for guns without pressure gauges, calculations can be done. Boyle's Law is usually sufficient if you know the volume of the pressure chamber and the amount of water in it. However, for true accuracy, use Van der Waals equation.

Which has higher pressures: air pressure or CPS?

For the most part, the pressures depend on the individual water guns. However, air pressure water guns can usually provide higher pressures because the pressure continually increases as you pump. With CPS water guns, the pressure increase is insignificant, although pressure at the end of the shot will be higher.

Would filling the space of the casing outside of a CPS bladder with pressurized air give the gun extra power?

Assuming you have sealed off the CPS chamber, yes, the maximum possible pressure will be increased. However, the technique defeats the purpose of the CPS (constant pressure system), as it causes the pressure to change depending on how full a the bladder is, as with an air pressure water gun. Pressurized air may also contribute to excessive rubber bladder wear.


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