I have a pressure gauge on the Commando and a piece of clear tube on the Norvin and the Comet special as on Eglis so I can see oil circulating as soon as the engine is started.
Actually the valve itself can hardly fail as this is only a ball and a spring.
Some grit can be trapped between the ball and its seat and no consequences to the engine in this case.
BUT, if the connection (pipe) between the valve and the pump isn't absolutely air tight the oil will eventually drain and next time you start your engine the valve won't open because there is no oil between valve and pump so no suction.
I think there is no valve failure only badly fitted one.
Marcus idea is great though.
Actually the valve itself can hardly fail as this is only a ball and a spring.
Some grit can be trapped between the ball and its seat and no consequences to the engine in this case.
BUT, if the connection (pipe) between the valve and the pump isn't absolutely air tight the oil will eventually drain and next time you start your engine the valve won't open because there is no oil between valve and pump so no suction.
I think there is no valve failure only badly fitted one.
Marcus idea is great though.