What causes pressure in an noncompressible fluid?

I think you now know why they say there are those that teach and those that can do. Fluidics is my profession, strong emphasis on hydraulic systems.

When you look at the micro instead of the macro, you limit your horizon. There is only ONE answer for pressure in a system: Resistance to flow. What happens to the molecules, I could care less. I know, but it serves no purpose in day to day design and troubleshooting issues, which is 99.999% of all applications. The remaining percent is for dreamers.

Every time I get a novice to ride herd on in my profession, I always have to "undue" what was taught in school. A prime example is that it is believed that a pressure wand delivers 5000 PSI force to the object being cleaned. Not in this life. The pressure, once it leaves the containment of the hose or tubing is atmospheric. You are then dealing with velocity. to quantify the issue, take a sledge hammer and use 5000 lbs force to hit the side of your car. Force is force, water, steel, whatever. If you hit the side of your car with 5000 lbs force, I'll guarantee you it will dent the hell out of it.

So, what causes pressure in a "non-compressable" Fluid? First of all, fluid is compressable. You are putting a mechanical load on fluid, and limiting its flow path to achieve pressure. Any other answer is just blowing smoke up somebodies ass.

How the blazes can you name yourself as curious? In any case, the question should first be answered - politely - as has been done, that there is no such thing as an incompressible fluid. Then, although it should certainly not be micro at the expense of macro, understanding what is going on at the micro level can be helpful, particulately (sic) when it comes to momentum (so-called pressure) washers. By your statement here, I think you are applying "undue pressure" to be ignorant.

And it is more than possible to apply a 5000 pound force to the side of your car without making a dent - in fact, the the typical force on the side of a car is in the order of 2000 pounds/sq.ft.

And it is more than possible to apply a 5000 pound force to the side of your car without making a dent

I can verify what you are saying. I've just finished constructing a proof-of-concept prototype of a small vehicle, and I've subjected at least one side of that vehicle to an incredible 50,000 pounds of force! The vehicle is still under test, and has been subjected to this force for a long time... but still, not a scratch.*

To put that into perspective, consider that a solid aluminum bar of aircraft grade 6061 T6 aluminum has a tensile strength of just 45,000 psi!

* You may ask: "Why such brutal test conditions?" Well, think of the occupants. What if this 50,000 pound force were applied directly to them?

Hi Curious,

Have a look at # 67 and you'll see why I titled this the way I did . . . . . . guess it didn't work. Ha.

Fluidics? Cool. Interesting stuff. I'd like to pick your brain for a year or three.

OK, back to practical and non-practical discussions. The purpose of this post was to learn if my answer, and graphic depiction, to the question of "What causes pressure in a liquid pipeline" needed tuning for the intended purpose as well as to educate me, a full time project of Steve S., Ken, Del, Physicist, Europium and others.

How would you have answered, simply, in layman terms, where the person asking (who is a mechanical engineer and boss of a technology group) would not have replied "Yes I know that, but I want to know what is occurring at molecular levels."

Answers of:

* Resistance to flow

* The head capacity of a centrifugal pump converting velocity energy to pressure energy

* The specific gravity of the fluid compared with the available head capacity of the pump

* Elastic containment vessel

. . . bla bla bla

would not have answered his question. Ask 6 people and you'll get 8 answers.

Ah ha . . . you are the vendor. As a former vendor myself linking miles of pipe all over the shop floor to test, we NEVER passed up an opportunity to jack with the inspectors. And heaven help the ego toting pump inspectors (like me) when we did a pump case hydro. Some proven silliness:

1.0 -- Go get a busted gauge with no needle and paint one on the face and tell them "Welcome, we got 'er pumped up and she's been holding for 6 hours before ya got here . . . come look". Of course, you need one end of the pipe open for extra fun.

2.0 -- If it leaks, tell 'em you are now checking the outside of the pipe where flow it greatest . . . you know . . to give 'em a fair test inside and outside the pipe.

3.0 -- Lastly, pour several puddles near the flanges before they arrive and have empty tubes of Bar's leak scattered about.

For pump case hydros:

4.0 -- Go to Sam's Club and buy 3 of those little kid swimming pool snorkel kits and when the gurus show up, hand 'em out.

5.0 -- Here is a slide below from my high energy pump class. Show up dressed like this soaking wet when you greet them.

Petro, In addition to your slides you may show an alcohol-in-glass thermometer. The "system" is closed and if energy is added by heating the bulb the vapor pressure of the fluid exerts pressure and the fluid rises in the stem to indicate a rise in temperature.

Likewise, if a simple bourdon tube measuring PSIG is capped off at sea level when the atmospheric pressue is 14.7 PSIA the gauge reads 0.0 If the barometer falls the gauge reads below zero, etc.

If you put some alcohol in the base of the gauge and cap it off you just made a thermometer, which looks an awful lot like your 1st slide, at no flow.

Although simple training aids, everyone will at least see the effects if not the reason for your question.

Hey . . I have one of those curly cue colored alcohol glass bulbs heated by my hand sitting on my desk. Good conversation piece. I tell people I boil the fluid with my sexy personality and hot hand !