It appear to be a small orifice maybe? - Don't know what item 1 is - which allows a small amount of reverse flow (the arrow indicates reverse flow). No idea why this would be a good thing, but presumably whoever drew it up thinks it is was required. It's not specific to a dual plate or any typ of check valve and is quite unusual to promote reverse flow through a pump. The isolation valve doesn't say NO or NC or give any indication of why it is needed.

This is quite small pipes here (3/4").

BTW it's much better to try and post things as an image with the camera button. Then people don't have to down load it.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

If the rest of the pump discharge line is vertical or otherwise at a higher elevation than the check this small bypass could be to allow the liquid sitting on the check valve to be drained back into the suction piping when the pump is shut off. Drainage would occur either manually via operating the ball valve or if (1) is an orifice plate with a small bore and the ball valve is left open it would allow drainage back across the check valve automatically without any real impact to the pump during operation.

That's what it looks like to me function wise. As to the why and when, that's tougher to answer without a lot more information.

So how about it BZLAM21? You've logged in since the replies were posted, but your history shows you started 18threads and only replied to 8 of them.

That's not how this site works - we expect a bit of a response and interaction not just "thanks for the replies"...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.