Check valves for turbo oil feed lines?

We've had some discussion here at the shop about putting check valves in the oil feed side of the turbo on low mount turbos to prevent gravity feeding when the engine is off. I've seen a few sources saying this is a must and have had discussion with some people that say they've never head of needing that and isn't necessary. What is your take on the matter. Thanks.

NOTE, my thoughts as discussion points - I'm NOT an expert!

If you mean oil from the sump draining back through the turbo's return line, I can't see it being a problem as long as the turbo's and the return in the sump are above the maximum oil level and there's sufficient drop on them with a large bore to ensure drainage.

If the turbo's are mounted low enough that the return line(s) are higher than the turbo's then any oil in the return may be expected to drain back, but if they're mounted that low I'd expect there to be drain sumps, with breathers, mounted under them with electrical scavenge pumps returning the oil anyway, so running them with a short delay on shut-down, and maybe an initial prime (with fuel pumps?) should avoid any issues.

A check valve installed the wrong way will be way worse that no check valve. I would double check (pun intended) you are doing it correctly if you choose to install one.

If the turbo is mounted below the resting oil level of the engine system, a check valve on the feed side will not avoid oil pushing out the seals at rest, since oil can back fill from the return side. You wouldn't want a check valve on the return side as that could impede return flow during engine operation.

If the turbo is mounted above the resting oil level of the engine system, but not high enough to gravity drain, you'll need a scavenge solution. Like Gord said you could run an electric scavenge pump on the turbo drain hose during engine operation, and for a few seconds after engine shut down.

I have a car with a dry sump and when a certain brand turbo is on the car, it smokes on startup from oil seeping into the turbine housing while engine off, but this doesn't happen with another brand turbo. I've seen a mini sump below the turbo to help reduce this, but that still only helps if the turbo is below the resting oil level of the system.