A Restriction Orifice Plate is similar to an orifice plate but is much thicker. It is used to drop upstream pressure of a system. While passing the fluid through thick plate energy is lost in friction and heat resulting considerable pressure drop. Normally single Orifice Plate having larger Thickness is used. However when the Flow velocities crosses the limit of critical flow and are subjected to sonic velocities to avoid noise vibration and cavitations in the liquid the Restriction Orifice Plates are designed in multistage form. For Viscous fluids and low Reynolds number the upstream side of the Restriction Orifice plate is beveled. The discharge coefficient of the restriction orifice plate is, also as per the orifice plate, approximately 0.6 according to ISO 5167. The bore is designed as per ISO 5167 and thickness as per R.W Miller/Ward-Smith. When the noise through single hole is beyond the acceptable limit sometimes Multi Hole plates are used as restriction orifice plates .The process condition defines the no of holes. Multistage with multi holes restriction is also a possible combination.
In case of restriction orifice, the size of the orifice is chosen in order to have desired pressure drop across the restriction orifice. This effect is known as choked flow across the orifice. As the name suggests, function of a restriction orifice is to restrict the flow and kill pressure downstream of the orifice.