evening….

mrs vader says that you cant compress a liquid, hence their use in hydraulics, i say you can… who is right (and yes i know i am in the wrong just for being a bloke 😉 )

cheers

MrsVader is – you can’t compress liquid…

You’re wrong 🙂

Liquids are generally regarded as incompressible but they do compress a ‘tiny’ little bit. So you’re both right…

she’s right

you’re correct, technically, but even without bringing gender and marital politics into it, you’re wrong

You can, but no where near as much as a gas. It’s much harder to compress a liquid, which is why it is used in hydraulics.

Both of you are right.
From a scientific perspective you can compress just about anything.
But it’s easier when talking hydraulics to ignore the compression as it’s a very small amount.

Technically yes (that’s how sound and pressure waves exist) but you need so much force to compress liquid by even a tiny amount that they’re effectively considered as incompressible.

some liquids are more compressable than others.

otherwise we’d use water in our hydraulic disc brakes rather than (relatively) expensive brake fluid

If you want to be pedantic, then yes it does compress (as will a solid). Nothing like as much as a gas and for things like hydraulic brakes etc, it’s as near incompressible as makes no difference. But you could force the point and win the argument.

I can’t compress liquid but i can turn eight pints of ale into eleven pints of piss.So it seems you can expand a liquid even if you can’t
compress it.

we’d use water in our hydraulic disc brakes

and when youve gone 20 secs DH you can stop and make a brew with the boiling water

http://www.newton.dep.anl.gov/askasci/eng99/eng99607.htm

Yes you can compress a liquid, it’s just not very compressible.
It’s also slightly confused by it’s ‘compressibility’ being somewhat dependent on the context. So for instance in fluid mechanics it’s a reasonable assertion to say that it’s incompressible but not so in say physics.

If you want to mess with her mind though – rubber with a poisson’s ratio of 0.5 is also incompressible.

The compressibility(?) of water is not really what makes it not suitable for brake fluid, more its other properties such as its boiling point.

Having your fluid turn to steam under heavy braking would not be particularly desirable.

she has agreed that i am right…… i am so in trouble now…..

😀

Start an argument about how much gravity there is in the space station – that’s always good for some physics confusion in my house 🙂

now it comes to light… mrs vader studied fluid mechanics as part of her MEng….and not physics… so we are both right…

Having your fluid turn to steam under heavy braking would not be particularly desirable

fair point & perhaps water was a bad example, but you get the idea

Put some water in her brake fluid and ask her again.

Having your fluid turn to steam under heavy braking would not be particularly desirable.

How would it turn to steam in a sealed system ?

I used to run water in my Magura HS33’s back in my trials days. Made for a much lighter lever pull, but with trials,not need to worry about speed and boiling fluid. Didn’t feel any more compressible than the oil it replaced!

What about diesel, when it compresses doesn’t it turn into a gas?

How would it turn to steam in a sealed system ?

It would get hot! At some point it could well be hot enough to turn to steam… The temperature this happens at depends on pressure but you could well get bubbles of steam in your brakes.

woody21 – Member
What about diesel, when it compresses doesn’t it turn into a gas?

If you’re talking about in an engine, then it atomises into small liquid droplets

I was – never sure exactly what happens in the engine

It doesn’t need to be a vented system to create steam. It’s how a steam engine works. It’s steam, but at a tremendously high pressure.

i boiled some C2s once. They worked fine until i let off the lever pressure slightly (as the made steep descent got less mad steep) and both wheels locked. Had to wait a 15 mins before i could turn the wheels.

compression of any gas creates heat, in diesel it is enough heat to ignite the fuel mix.

Pour some brake fluid into a black hole and it will compress very nicely by a ratio of a few million or more…

cheekyboy – Member

How would it turn to steam in a sealed system ?

If its a sealed system, why does everyone on stw seem to be periodically bleeding their brakes?

You’re correct.

What about diesel, when it compresses doesn’t it turn into a gas?

No. Compress it enough and it turns into solid. (given a constant temprature)

If its a sealed system, why does everyone on stw
seem to be periodically bleeding their brakes?

It’s only really sealed when the brake is on…

Diesel is atomised before the compression bit in a engine.

The diesel is not compressed. The air around it is compressed, heats up and burns the fuel.