weirplate

noun2

1. •
   A metal plate that forms an obstruction to adjust the flow of a weir.

   • Why a difference in temperature between the water and the weirplate should cause the water to spring clear at low heads cannot very well be explained. — 1927
2. •
   An adjustable plate that controls the amount of liquid held in a chamber of a machine.

   • The weirplate at the bottom, inside the drum at F, serves the same purpose as in the machine you have seen — namely, to provide an inner wall of water of the desired thickness within the drum. — 1912