2 ms·

This is sort of a general issue. Compressed air is much more dangerous than water under similar pressure, because air is far more compressible. If you pressuriz

by amluto 3y ago

This is sort of a general issue. Compressed air is much more dangerous than water under similar pressure, because air is far more compressible. If you pressurize water to, say, 100 psi, you’re compressing the water a tiny bit (water is not very compressible) and stretching the container a bit. The stored energy is roughly 100 psi * (change in volume) / 2, and the change in volume is small. If you hit a water pipe. with a shovel and break it, and your pipe has a rather high 100 psi of water in it, you will regret it: you will get wet, you’ll have a muddy hole, and you will be sad because you have to repair it. If you compress air to 100 psi, you are compressing it to a rather small fraction of its original volume. So the change in volume is greater than the entire volume of compressed air and is almost as large as the uncompressed volume, so 100 psi * (change in volume) / 2. 1 cubic foot of air compressed to 100 psi is something like 10 kJ. Beware! If you winterize your irrigation system with compressed air to 100 psi (terrible idea), and you hit a pipe with a shove while it’s still at 100 psi and break it, you will release a lot of energy.

Certified 3y ago
Generally you are not compressing water though if dealing with compressed fluids (unless you are trying to simulate deep ocean depths for pressure testing.) You are compressing Hydraulic Fluid which can cause Hydraulic Injection Injury which can lead to loss of limb [1]. [1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2532970/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2532970/
- amluto 3y ago
  You’re generally not compressing water or hydraulic fluid because they’re not very compressible. (Although I think many hydraulic fluids are actually more compressible than water, but still barely compressible. They’re used for other reasons. The ideal hydraulic fluid for most applications is entirely incompressible.) But systems using hydraulic fluid to carry power have something that keeps it pressurized as it moves: that is, something that can supply power. Often very large amounts of power. (So do water pipes that have some form of supply, of course, but the pressures are much lower.) So if you pressurize fluid in a pipe, you are storing some energy in the compressed fluid. You may also have a lot of energy stored or power available in some other component of the system. In any event, the type of injury you’re describing seems like more of a velocity issue. When you allow fluid to escape from a high pressure environment to a low pressure environment through an opening that doesn’t have a whole lot of friction, the stored energy converts to kinetic energy. Some basic physics says that a small volume V of fluid has potential energy PV and mass rho * V. Conservation of energy says that, when that potential energy is gone (the fluid escapes), it has the same energy, but now it’s 1/2 m v^2. You can solve for velocity, which scales like sqrt(P). (The real story is more complicated. Pressure in fast-moving things is a bit messy due to Bernoulli’s Law, and different disciplines use annoyingly different terminology. Static pressure, total pressure, stagnation pressure, just plain old pressure, oh my!) Water (or air) jetting out of a hose through a tiny hole at even 100 psi is not likely to inject itself into a person.

by amluto 3y ago

Certified 3y ago

Generally you are not compressing water though if dealing with compressed fluids (unless you are trying to simulate deep ocean depths for pressure testing.) You are compressing Hydraulic Fluid which can cause Hydraulic Injection Injury which can lead to loss of limb [1]. [1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2532970/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2532970/

amluto 3y ago
You’re generally not compressing water or hydraulic fluid because they’re not very compressible. (Although I think many hydraulic fluids are actually more compressible than water, but still barely compressible. They’re used for other reasons. The ideal hydraulic fluid for most applications is entirely incompressible.) But systems using hydraulic fluid to carry power have something that keeps it pressurized as it moves: that is, something that can supply power. Often very large amounts of power. (So do water pipes that have some form of supply, of course, but the pressures are much lower.) So if you pressurize fluid in a pipe, you are storing some energy in the compressed fluid. You may also have a lot of energy stored or power available in some other component of the system. In any event, the type of injury you’re describing seems like more of a velocity issue. When you allow fluid to escape from a high pressure environment to a low pressure environment through an opening that doesn’t have a whole lot of friction, the stored energy converts to kinetic energy. Some basic physics says that a small volume V of fluid has potential energy PV and mass rho * V. Conservation of energy says that, when that potential energy is gone (the fluid escapes), it has the same energy, but now it’s 1/2 m v^2. You can solve for velocity, which scales like sqrt(P). (The real story is more complicated. Pressure in fast-moving things is a bit messy due to Bernoulli’s Law, and different disciplines use annoyingly different terminology. Static pressure, total pressure, stagnation pressure, just plain old pressure, oh my!) Water (or air) jetting out of a hose through a tiny hole at even 100 psi is not likely to inject itself into a person.