# Calculate hydraulic pump speed

1. Jun 12, 2007

### robhlee

About those hydraulic devices that are used for lifting cars and such; how can you calculate the maximum speed at which those will operate?

2. Jun 12, 2007

### Danger

I've never seen that mentioned anywhere, but it must be based upon how much volume the system can flow per second. That probably comes down to what the regulator and valve are rated at.

3. Jun 14, 2007

### robhlee

I think the focus of the issue is the hydraulic fluid; I just wanna know an approximation of how the fluid would move (i'm just talking about some noncompressible oil; would it differ a lot between types of oils?). Would a hydraulic system be able to work instantaneously/ rapidly in response to some force? Do all hydraulic machines work very slowly or what?

Just to clarify, the system i am referring to is just your simple textbook model on hydraulics and forces applied. Two platforms of varying surface areas connected by a tube of hydraulic fluid.

Last edited: Jun 14, 2007
4. Jun 14, 2007

### Danger

All fluids will act the same way as far as compressibility goes. The differences between them stem from such things as operating temperature range, reactivity with materials such as seals, and other chemical properties. You could run a bulldozer on water if you had to.
The limit to reaction time is partly a matter of inertia of the involved mechanical components vs. the power of the pump, but is ultimately restricted to the speed of sound in the fluid. It can never be 'instantaneous'.
Others here such as Brewnog and Fred know far more about it, though.

edit: I'm not sure, but you might have better luck if you ask to have this moved to the Engineering section.

Last edited: Jun 14, 2007
5. Jun 15, 2007

### FredGarvin

The speed of the actuation is going to be a function of the flow rate of the main hydraulic pump in the system (assuming other technicalities are avoided). We could get into a real discussion of valve and hydraulic system components that would regulate that flow rate though.

In the very simple layout that you mention, the effect of input would be immediately felt as output on the other side. In reality, there may be a slight delay due to a very small amount of compressibility in the working fluid. A typical hydraulic fluid has, on the order of 1% compressibility over a very wide range of temperatures IIRC.