[gricha]

Hi all

Quick question
We have a hardinge SR 200 m lathe
Why is there a return pipe for the hydraulic oil?

[Jim Dawson]

It's called a case drain. It routes any internal leakage back to the tank. If you look at it when running you will most likely see a small stream of oil in the tube.

[Kelsang-Lungta]

Why is there a return pipe for the hydraulic oil?

Within every hydraulic “circuit”... you must have a return side.
Like the blood in your body. Veins are the return lines, the heart is the pump, Arteries are the supply.
Hydraulic systems are sealed and meant to operate without contamination. (Filters)
Embrace your inner Pascal. Learn his laws on hydraulics.
(Without a return line... it won’t work and something will likely fail if that flow is precluded. Hydraulic force is like liquid steel. You cannot compress a liquid, so it must go somewhere. Most often it goes safely back to the hydraulic reservoir via the “return line”.)

[Kelsang-Lungta]

The use of terms “Hydraulic” lines, shouldn’t be confused with lines of “lubrication“.
Lubrication is a different environment for oil use and application.
It’s open to ambient pressure and typically less than 50psi in a feed line.