# Pressure difference in a hydraulic system?

1. Mar 17, 2005

### hectorbvo

Is there any difference in pressure in a pressurized tank/piston filled with a liquid between the bottom of the tank/piston and the top of the tank? My problem is that Pascal’s law states that the pressure exerted on an enclosed fluid is transmitted undiminished throughout the fluid and acts equally in all directions. But this law is not taking in account the pressure exerted by the fluid itself (density * Gravity * Height) (Bernoulli). I believe that the pressure exerted in the bottom of the fluid should be grater than the pressure exerted at the top. Maybe the difference is negligible, but the fact is that it is there. Can someone help me with this.

Hector

2. Mar 17, 2005

### FredGarvin

You are correct. That being said, you are correct that in most cases that difference is negligible, especially in hydraulic systems. If we are talking hydraulic systems, then another thing to consider is that the reservoirs in a hydraulic system are usually, relatively small. That would give you a tank size that would result in a pressure variation from top to bottom due solely to $$\rho gh$$ that is extremely small. Consider that with the fact that usually an operating system pressure is in the range of 1000-3000 psi and you can see that the number truly is not worth considering.

3. Mar 17, 2005

### hectorbvo

In my opinion all the theories used to justify the use of this product are wrong. Please read it and comment.

As I see it, it doesn't matter if the return from the muffler is at the bottom or at the top of the tank, the pressure of the fuel exiting the tank will be the pressure supplied by the muffler + the pressure exerted by the fluid itself. I'm planning to write to these guys end tell them how wrong they are but I need a second, expert opinion.