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Compressed or pressurised ?

Compressed or pressurised ?

Compressed or pressurised ?

Anybody prepared to explain the difference between compressed and pressurised?
'Cos as everybody is keen to point out to me, you can't compress a liquid (well you can but not very much). But if we can't compress a liquid, how do we do hydraulic tests on boilers?
And please do not be afraid to state the obvious, as there appears to be a fundamental hole in my understanding.


RE: Compressed or pressurised ?

"Pressurized" means to increase the presssure above atmospheric.  Typically the term is used when the fluid is largely incompressible (i.e., the change in fluid volume is a small percentage of the total system volume).

"Compressed" is used when significant mass must be added to a system to increase pressure.

They are just words.  I do work on a non-return hydraulic pump that the 0.4% compressibility of the hydraulic fluid is the controlling factor in the pump capacity.  So what?  When you are doing a hydrostatic test, of course the test liquid compresses some, but you use a large-volume fill pump and a small volume pressurization pump to make up the fluid compression and the pipe expansion.  Again, so what?  Just because both the fabrication being tested and the test fluid have some small amount of elastisticity, does not mean that a test can't be performed.

David Simpson, PE
MuleShoe Engineering
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RE: Compressed or pressurised ?

I tend to agree with David. This is sort of like the "engine" vs "motor" debate.


RE: Compressed or pressurised ?

So it's purely down to semantics then ?

RE: Compressed or pressurised ?

With due respect to my colleagues that think the two terms are identical, here is the real truth:

"Pressurized" means under pressure.  

"Compressed" means a change (reduction) in volume DUE (normally) to pressurization.

RE: Compressed or pressurised ?

Jr Hoss - So what you are saying is that you can be pressurized without being compressed? I don't know of any absolutely non-compressible materials, though I don't claim to be a materials expert.


RE: Compressed or pressurised ?

So basically, what you are saying is pressurised is under pressure and compressed is pressurised,ie  under pressure.


Nope sorry..........you have got me there.



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