Diffuser/Orifice Plates is basically a thin plate with holes. It is usually placed in a pipe in which fluid flows. As fluid flows through the pipe, it has a certain velocity a certain pressure. When the fluid reaches the orifice plate with holes, the fluid is forced to converge to go through the small hole; the point of maximum convergence actually occurs shortly downstream of the physical orifice, at the so-called vena contracts. As it does so, the velocity and the pressure changes. Beyond the vena contracts, the fluid expands and the velocity and pressure change once again
The orifice plates are also available as a tab handled plate that can be located between flanges.