Hello to all the wise people out there
Can any one reply me why is it a standard that the Fluid Speed In Pressure , Suction And Return Lines are 7 meter/ sec, 4 meters / sec and 1.5 meters / sec respectively
Is there any formula behind it or it is an imperical outcome
Waiting for a prompt reply
With kind Regards
Muhammad Umair Nazar

I was told it has to do with Pressure Drop.
In a typical Suction Line application the only Pressure available to move the fluid is One Atmosphere wherever you happen to be located. It is why the hydraulic system on the Space Shuttles Robotic Arm has a pressurized Reservoir that forces fluid to the pump.
A Suction Line will start cavitating around 3-4 PSI if velocity is too high so that is the reason for the 2-4 FPS figure most give.
I always heard Return Lines should not be higher than 10-15 FPS so back pressure on actuators is reduced, allowing them to attain the working force required at the lowest possible working pressure.
On Working Flow Lines the figure I grew up with is 15-20 FPS to reduce line size. These lines have full system pressure available so they can stand a higher pressure drop.
Having said all that, ANY PRESSURE DROP IN ANY HYDRAULIC CIRCUIT ia WASTED ENERGY and I have seen hydraulic circuits that over heat just because the lines were under sized. Save a few dollars on Valves and Plumbing and sepnd a lot on energy for the life of the circuit.
It's in the basic Ebook here:
http://www.hydraulicspneumatics.com/200/eBooks/

All speed numbers are incorrect as they don't take into account
all flow and fluid conditions. Have a look at the attached file.

EQUATIONS.pdf (106 Kb, 49 downloads)

Thanks Nahum for the Formula and explanation. It is a Keeper and will be put in my files.

Like most 'rules of thumb' they don't include all variables, but are simplified for 'most' conditions, petroleum oil, operating temperatures moderate, fairly short lines not pressure drop limited, etc. etc.
Because of my operating environment, I tend to the low end, oversizing lines etc, but it is not worth it to do the reynolds numbers etc calcs in most applications.

thus, the 'rules' are just normal guidelines, and it is the engineers job to know when apppropriate to use them, and when to go deeper.

In many ways, similar to the issues peter brings up to simulate everything. In the generic everyday 95% applications the modeling and simulation and calcs are unecessary. In the 5% applications, simulation is necessary. It is the good engineer that can separate the two situations and apply the right tools.

.02
kcj