Head of water

[Richard C]

The initial static head is measured from the water line in the tank & this is the one that should be used in every case, as the water level decreases so does the pressure; it’s dynamic but the effective pressure on any device will also be affected by anything other than a vertical feed.

As far as it’s relative to pumps; manufacturers have to make certain assumptions when giving installation advice & some are more cautious than others.

 

[Agile]

A column of water 10m high ( 9.81 m actually) produces a pressure at the bottom 1bar higher than atmospheric, and pro rata.

Starts to get more complicated when you start comparing with atmospheric.

Seal your column of water at the top so its becomes a sealed system.

Watch the pressure gauge at the base showing 1 Bar as you pump out all the air from the room until its at zero.

What does the gauge read now?

 

[cantaloup63]

Starts to get more complicated when you start comparing with atmospheric.

Seal your column of water at the top so its becomes a sealed system.

Watch the pressure gauge at the base showing 1 Bar as you pump out all the air from the room until its at zero.

What does the gauge read now?

Good question indeed. I'm tempted to say 0

 

[monoxide62]

What does the gauge read now?

Maybe you're looking for an answer.

 

[cantaloup63]

On the one hand, since the system is sealed then the water cannot "escape" since it needs an opening at the top to allow air to replace the volume as it leaves. On the other hand, the water has got mass and therefore gravity pulling it down "through the gauge". On the third hand the vacuum will be triny to "suck" the water out. Therefore, after careful consideration of these three parameters, I , er, dunno

 

[hansthebear]

you are talking about the difference between guage pressure and absolute pressure, you cannot defeat gravity......

 

[cantaloup63]

you are talking about the difference between guage pressure and absolute pressure, you cannot defeat gravity......

And so the answer is....

 

[hansthebear]

the hydrostatic pressure would be the same as before as atmospheric pressure is not a factor in the equation.

i think thegauge would read the same

 

[echoes]

A column of water 10m high ( 9.81 m actually) produces a pressure at the bottom 1bar higher than atmospheric, and pro rata.

Starts to get more complicated when you start comparing with atmospheric.

Seal your column of water at the top so its becomes a sealed system.

Watch the pressure gauge at the base showing 1 Bar as you pump out all the air from the room until its at zero.

What does the gauge read now?

2 bar

 

[dotto]

Imagine you have a 20m tank full of water. You drill a hole 1m below the shut off level and another hole 1m above the base of the tank. You will certainly have a greater jet of water coming out of the hole 1m above the base of the tank than coming out of the hole 1m below the shut off level which proves that you do calculate pressure from the shut off level....i think

 

[DeltaT2]

Imagine you have a 20m tank full of water. You drill a hole 1m below the shut off level and another hole 1m above the base of the tank. You will certainly have a greater jet of water coming out of the hole 1m above the base of the tank than coming out of the hole 1m below the shut off level which proves that you do calculate pressure from the shut off level....i think

Yes indeed, but you don't get the pressure or head my learned friends think you do!! It's all very 'black & white' in theory, but in practice??!!!

Thanks to everyone, even the hard of thinking.

 

[DeltaT2]

The initial static head is measured from the water line in the tank & this is the one that should be used in every case, as the water level decreases so does the pressure; it’s dynamic but the effective pressure on any device will also be affected by anything other than a vertical feed.

As far as it’s relative to pumps; manufacturers have to make certain assumptions when giving installation advice & some are more cautious than others.

Many. many state that the 'Head' is measured from the base of the tank Richard, as the document in my link details!! Are you right or are they right..........Conflict my auld china, conflict!!

 

[sooey]

It doesn't matter what anyone says dick it should be measured from the waterline. That's not me saying that, it's the laws of science.

 

[Nige F]

Meanwhile - back on the conveyor or in this case the flying boat on the endless pool

 

[DeltaT2]

Meanwhile - back on the conveyor or in this case the flying boat on the endless pool

Profound??!!!!................