As I was doing my forks the other day, I had a thought . . . and this might be a fun place to ask it. So if fluid is incompressible, let’s say you have a thick steel container of 10 cu.ft. that does not flex or expand under pressure, and you fill it with fork fluid at 1,000 PSI fluid pressure and then sealed. There is no air or vapor of any sort in the container, just the hydraulic fluid, and no further pressure is being applied in any way. What would happen if you flipped a valve open on the tank real quick? Does the fluid just instantly go to ambient pressure since there is no force behind it? Or is there some stored energy there somewhere even though the fluid cannot be compressed? Any fluid dynamics whizzes here? Beeeuuulllerrr . . . .?
While liquid (suspension fluid in this case) is considered incompressible, it is very slightly compressible. So it will compress some tiny, largely insignificant, amount. Your container will also expand slightly, no matter how thick it is, but it will also be a small amount.
So if you were to create this scenario, the lid would move very slightly due to the tiny amount of compressibility in the system as it got up to 1,000 psi. If you were to suddenly remove all pressure somehow, the lid would quickly move that same distance it compressed earlier plus some more until the inertia was overcome by gravity (assuming the lid was on top). How crazy of a reaction this is would be dependent on the size and weight of the lid.
If you had a balanced aspect ratio on the container, like 10 x 10 x 10 dimensions, the end result wouldn't be terribly exciting. If you had a much narrower container, 0.1 x 0.1 x 1,000 tall, it would be much more exciting as the lid would have moved more getting up to pressure and would and be a lot lighter, leading to a more dramatic movement as the energy was released.
Thanks! That's kinda interesting to think about.
As @Luxon MX said, everything deforms under pressure...
Imagine you cut a hole with an area of 1/1000th of a square inch in the tank then put a piston in the hole with a 1 pound weight on it. The tank will be at 1000 PSI from that. Basically, since it's incompressible it takes no energy to raise it to any pressure you want.
This is why they test steam boilers with water instead of air. You get high pressure with low energy so nothing explodes if the boiler fails.
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Not exactly the same, but be careful with your bike drink bottles when shuttling downhill mountain bike runs. 😆 When you fill a bottle at the bottom of the mountain and then open it at the top, you might get a drink volcano up your nose.
Nice! I had not considered that and that is really awesome to think about as well. Thank you for that!
They don't test pressure vessels of any kind with air because it's a big spring. If it lets go it'll keep going until the volume of air which was in the container returns to it's original volume. Water does not compress, so the only spring effect is from the distortion of the vessel returning to it's unpressurized state.
Water doesn't compress?
No, water and other liquids are not compressible for practical purposes. From a pure physics standpoint, liquids can be compressed...the amount is insignificant though.
Assuming no stresses/compression...the ram will just continue the force it has from applying the 1000psi pressure when the valve opens. It all depends on the size of the cylinder and ram and valve.
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