Lube Oil sight flow indicator position (w.r.t bearing)

[JBC2008]

API 614 6.3.9.1 requires Lube oil sight flow indicators to be mounted on the drain line, rather than a supply line to a bearing.
Can anyone please explain to me why this is stipulated by the code and the disadvantages associated with having the flow indicator on the supply line? (In this case, the context is the radial bearings of an HV drive).


Many Thanks

 

[smckennz]

By having the indicator on the drain line, there is a higher probability that a healthy indication means oil has actually passed through the bearing. A healthy feed line indication means oil is heading towards the bearing but may not get there. Also many supply line indicators have an integral regulating valve. An accidentally closed valve on a supply line means no oil to the bearing.
There is sense in the requirement.

Cheers

Steve