Key selection points for flow restriction orifice plate

(1) Considerations for gas and steam selection
When using restriction orifice plates for gases and vapors, it is important to consider avoiding choked flow. When the pressure behind the restriction orifice plate (P2) cannot be less than 55% of the pressure in front of the plate (P1), that is, when P2 ≥ 0.55P1, a single plate restriction orifice plate can be selected; Once P2<0.55P1 occurs, a single plate cannot be used and multiple plate flow restriction orifice plates must be selected, ensuring that the pressure behind each plate is greater than 55% of the pressure in front of the plate.
For example, in some steam transmission pipelines, if the ratio of pressure behind the plate to pressure before the plate is found to be less than 55% through calculation or actual monitoring, multi plate flow restriction orifice plates should be selected according to this rule to ensure stable, safe, and smooth flow of steam in the pipeline, avoid various operational problems caused by choked flow, and ensure the normal operation of the entire process system.

(2) Liquid selection considerations
For liquids, their selection is mainly based on the pressure drop of the liquid. When the pressure drop of the liquid is less than or equal to 2.5 MPa, a single plate orifice plate is usually selected to meet the process requirements. In scenarios such as ordinary domestic water transportation pipelines and some simple water circulation cooling systems, due to the small pressure drop generated by the liquid in the pipeline, a single plate orifice plate is sufficient to control the flow rate and achieve the corresponding pressure reduction function.
When the liquid pressure drop is greater than 2.5 MPa, multiple orifice plates need to be selected, while ensuring that the pressure drop of each orifice plate is less than 2.5 MPa.
For example, in large-scale chemical liquid material transportation pipelines or some high-pressure liquid process flows, the pressure drop generated by the liquid flowing through the pipeline is relatively high. In this case, it is necessary to select multi plate orifice plates according to requirements and allocate the pressure drop of each plate reasonably to ensure the smooth operation of the entire liquid transportation and related process links, and prevent damage to pipelines and equipment due to improper pressure drop control.
(3) Method for determining the number of holes

When determining the number of holes in the flow restriction orifice plate, the selection is generally based on the nominal diameter of the pipeline. When the nominal diameter of the pipeline is less than or equal to 150mm, a single orifice plate is usually used; When it is greater than 150mm, a porous plate is used. The aperture (do) of porous orifice plates can generally be selected in specifications such as 12.5mm, 20mm, 25mm, and 40mm. When calculating the number of pores (N) in a porous plate, the first step is to calculate the pore size (d) based on a single pore plate, and then use the formula to determine the number of pores in the selected porous plate.
For example, in a large industrial pipeline with a nominal diameter greater than 150mm, the aperture of the single hole orifice plate is calculated based on relevant parameters such as flow rate in the early stage. Combined with the actual aperture specification of the selected porous orifice plate, the required number of holes can be accurately calculated using the above formula, and the appropriate porous orifice plate can be determined for installation and use to ensure effective control of fluid flow.