Pascal's barrel.

Pressure in fluids and gasses is dependant of the density of the fluid/gas and the height.
So a small tube at 10m high has the same pressure on the bottom as a 10m deep pool filled with water. So you don't need alot of water to get tremendous pressure, think of pascal's barrel... He made a barrel explode by using a tube of 10m high or something of only a millimeter wide and adding one drop of water to make the barrel explode.
I was just thinking, I recall that people sometimes run pumps in series because the second pump gets more head pressure supplied by the first pump.
Now if you put a very high column acting as a reservoir right over the intake of the pump, would that give a similar result, or does the added pressure get nullified because the pressure is also increased inside the loop?
Something like this:

I I
I I
I I
I I
I I
I I
I I
I I
I I
I I
I I
PUMP
INTAKE


But very high, like a few metres.
If it does work, some sort of passive pressurizer could also be used, like a column of a high density fluid like mercury...
Is this free pump performance or am I thinking wrong?

I thought Pascal's law was dependant on gravity. In a closed-loop pressurised WC loop, isn't gravity mostly defied?

gravity still exists in there, but the movement of the pump just negates most of it's effects, but I think pascal's law still exists... gravity is everywhere
But pascal's law is indeed dependant on gravity as the weight constant (translation?) is in the formula, density multiplied by height mulitplied by the constant of weight.
so for a watercooling loop of pure water and half a meter high, the formula is
1000 kg/m³ . 0.5m . 9.811N/kg plus the atmospheric pressure, wich is 101300 pa, so the pressure at the lowest point on the bottom of the loop would be 106 205 Pa.
The constant of weight I used is for belgium, it's different dependant on location.

Ok. I had to bone up on this stuff. This is Pascal's law summarized: In a body of equally dense fluid at rest, the pressure is the same for all points in the fluid so long as those points are at the same depth below the fluid's surface.

According to the wording, seems that this rules out these laws when applied to the moving water in a loop.

A closed loop is not affected by gravity; think of a theoretical situation where one hooks the inlet and outlet of a pump up to either end of a line of tubing of irrelevant length. No matter how the tubing is positioned, the elevation of the pump in relation to the TE and IE of the tubing becomes irrelevant. No matter where the pump is, the water will still have to travel an equal distance up and down the tubing. In our theoretical tube-pump setup, what goes up must go down an equal height, and what goes down must go up an equal height which pretty much means there is no change in pressure due to gravity. Water isn't compressable, so without an inflow or outflow in a closed loop, the pressure remains constant. Obviously, this changes a bit when we start adding flow reducing components and bends, but the impact of gravity will still be minimized, and the only differentials in pressure and velocity come as a result of the physical aspects of your watercooling loop.
I say "all but" because gravity will still have an impact directly related to the ID of the tubing, which for a 1/2" ID would be 0.0013 atmospheres.
In an open setup, the impact of gravity will be roughly .42psi per foot. Sure, you could make a rez that is a few feet tall to get some "free psi" in an open setup, but you are going to have to get that water into the rez somehow, and those same "free psi" you got going down are going to be working against you trying to pump water back into your rez.

a closed loop can be effected by gravity in VERY LARGE loops. if you look at my res designs and comments you will notice i use the same basic design method .

vertical rad narrow and tall feeding directly into the pump and have excelent results

futura2001 said:

...snip...

Click to expand...

You can compress water, it just takes a huge amount of pressure.

And pressure isnt constant throught the loop. There is negative pressure at the inlet of the pump and positive pressure after the outlet.

Dont remember where it was but there have been threads on pressurizing the loop. Pretty sure the consensus was that it has no gains and tons of negatives...

number 1 negative is rating of parts in the loop cant take the pressure. you wont see many rads that can stand more than 48psi

thorilan said:

a closed loop can be effected by gravity in VERY LARGE loops. if you look at my res designs and comments you will notice i use the same basic design method .

vertical rad narrow and tall feeding directly into the pump and have excelent results

Click to expand...

In a very large closed loop, yes. However, for our practical purposes it is a non issue because the resistance of the sheer volume of water will become an issue before gravity does.
From what I've seen of your loops, you generally prefer a long, tall rez feeding into the pump, which feeds into a vertical single core rad, then out to the first block, right? My understanding is that the gains from the rez would be mostly negated by the rad and upward travel to the block. There certainly would be some measurement of gain as you place the top of the rez above the block, but I would not think it would be a measurable gain unless you are using some really tall cases. In fact, while my experience with water systems comes from designing drainage, sewer, and water systems for civil projects and in no way consider myself an expert on watercooling systems, I would think that the reduction in tubing and unnecessary bends in your setups would have a far greater impact than those few inches higher your rez is above the rest of your setup.

And yes, while I didn't directly mention the pump as I should have, I did mention that the physical aspects of your loop are going to have an impact on pressure.
You are right, water is compressable on a very microdynamic scale. In the biz, we generally use 0.0003% per psi, however I am not enough of an egghead to hold an argument as to whether it is the water itself compressing, or the air within the water compressing. whatever the case, water generally can be described as incompressable unless the water pressure is into the thousands of PSI or your data requires an extremely precise measurement.

the reduction in tubing and unnecessary bends in your setups would have a far greater impact than those few inches higher your rez is above the rest of your setup.

Click to expand...

this is true. i just like to cover all bases in my design because every bit adds up.
if i ever get enough money and time i have a t1 velocity pump i want to use to make a 2 meter tall bong with using sewage pvc .

A tall filler tube for your T or res will increase the pressure in the loop, and this will help keep the pump from cavitating. But the column of water will increase the pressure in the entire loop equally. That means that, except of the benefit to your pump, the pressure differential across your block won't change.