# Hydraulic energy

Del8
Hi,

I would like to understand what is the difference between the case when w=0 and the wase when w>0 in this device:

http://imageshack.com/a/img540/3493/Ntztkk.png [Broken]

The arm is turning clockwise at w. The hydraulic pump is fixed to the arm. A disk at the end of the arm can turn around itself and it turns at start at w too. The shape of the disk is like a turbine. The hydraulic fluid gives a force F1 to the disk. F1 is transmitted to the arm: F3, and the reaction of the arm is F2 to the disk. The disk receives a torque Fr with 'r' the radius of the disk. |F1|=|F2|=|F3|=|F|. The arm receives the torque FR. The fluid is recovered by the pump, the fluid is in closed circuit.

An external device not drawn recover energy from the arm for keep constant the rotationnal velocity of the arm. So I guess w constant for the arm (not for the disk).

I can understand the sum of energy when w=0 but when w>0 and especially if 'w' is very high it seems te arm receives the torque FR and the work from the arm is FRwt. So the pump must give more energy when w>0 than w=0 but how and why ?

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Gold Member
Hi. This is probably just because we're not used to the same systems of expression, but I simply cannot make heads nor tails of your diagram. You seem to have mechanical linkages and fluid flows and who-knows-what all cobbled together. Is there some other way that you can draw it with maybe more descriptive labelling?

Del8
Ok, without the pump:

http://imageshack.com/a/img540/74/Q8GqFT.png [Broken]
A black arm is turning around a fixed axis (red color) clockwise at w. A grey disk can turn around itself, at start the disk is turning at w too.

I drawn a blue arrow for show the direction of the fluid. The fluid gives the force F1 to the disk. The pump is fixed to the black arm. The fluid is in a closed circuit.

Can you understand like that ?

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Mentor
You haven't drawn-in the pipe that brings the water back to the pump. If the circuit is closed, the rotation doesn't help overall: the rotation adds some energy as the water goes out to the turbine and costs you the same energy to bring it back to the pump.

Del8
There is a pipe for brings the fluid back to the pump. All turns at w at start.

http://imageshack.com/a/img537/2590/zZlkS0.png [Broken]

I think my forces F1, F2 and F3 are correct, true ? So there is a torque FR to the arm ? This torque works at FRwt. Like the pump and the fluid are turning at w too (with the rotationnal velocity of the arm constant because I recover energy for have w constant), why it is more difficult for the pump to give pressure ?

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Gold Member
I am leaving this in Russ' care; he knows a lot more about it than I do.

Del8
I think it's easier to understand if the pump and the pipe are at the same radius, like that the fluid is always at the same velocity:

http://imageshack.com/a/img537/9614/OsR6v5.png [Broken]

The pump is fixed to the black arm. I think I forgot the force on the fluid: F4 ?

But now, the arm has a negative torque, so I need to give energy for keep constant w (I want w constant), but in this case it's easier for the pump to give pressure ?

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Mentor
Oh, you're interested in the rotations, not the energy of the water. Ok, well if you extract energy at the wheel, you can make the whole apparatus rotate, which will reduce the amount of energy extracted at the wheel by reducing its rotation rate relative to the arm.

Is this an attempt at a perpetual motion machine? Please be aware, we don't do perpetual motion discussion here.

Del8
Is this an attempt at a perpetual motion machine? Please be aware, we don't do perpetual motion discussion here.
with an hydraulic device ! it's a joke ?

I have questions:

1/ my forces are correct ?
2/ There is a counterclowise torque to the black arm ?
3/ I would like to understand the difference with the case w=0 and the case w>0. With w=0, all is ok but with w>0 (the rotationnal velocity of the arm is constant by an external device), the device need to add energy but why it is easier for the pump to give pressure if I compare with the case w=0 ?

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Mentor
with an hydraulic device ! it's a joke ?
What's a joke? This thread? My response? Yes, hydraulic devices are among the most popular for attempted perpetual motion machines.

Could you please explain why we are here? What is the point of this device/thread?
1/ my forces are correct ?
You haven't indicated any forces, just locations for forces. And it looks like you are missing some. In particular, it is not clear if anything is opposing the rotation of the turbine.
2/ There is a counterclowise torque to the black arm ?
I believe there is, but am unsure due to the vagueness of your description.
3/ I would like to understand the difference with the case w=0 and the case w>0. With w=0, all is ok but with w>0 (w is constant by external device), the device need to add energy but why it is easier for the pump to give pressure if I compare with the case w=0 ?
I don't see that the operation of the pump will change. Can you explain what you mean?