Hydraulic Fluid Level Detection.

[ndzied1]

There's a lot of guesswork being done in these posts.

Here's another possibility. I have seen oil lubrication systems that pump out oil to lubricate large rotating tables and slides.

When the system starts, a large amount of oil is pumped out of the reservoir filling lines and bearing surfaces and then a steady state flow ensues as oil flows out and gravity feeds back.

When the system stops, all the oil slowly returns to tank.

Pressure is relatively low the entire time.

Maybe the OP will eventually get back and let us know what this system really is.

 

[wolverine1981]

WOW!!! THANK YOU ALL FOR THE OVERWHELMING RESPONSE.

There is sure a lot of good information here, I really do appreciate your support.