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Due to the simple structure, easy processing, low manufacturing cost and convenient installation of the multi-stage flow restricting orifice plate, under the premise of meeting the process requirements, the flow restriction or pressure reduction can be achieved by replacing the regulating valve, which greatly reduces the investment and operation and maintenance costs. It has been widely used in foreign process equipment and played an important role in the safe operation of the equipment.

In general, the regulating valve needs to be equipped with a multi-stage restrictor orifice in the following cases. When the pressure drop on the regulating valve is large, and the allowable pressure drop of the regulating valve does not meet the requirements, a multi-stage flow restricting orifice plate can be set to absorb part of the pressure to reduce the pressure drop on the valve. When the bypass pressure drop of the regulating valve is large, a multi-stage flow restricting orifice can be installed at the bypass to prevent the danger of overpressure or liquid level emptying caused by manual operation of the bypass valve.

When it is necessary to reduce the noise of the regulating valve, the multi-stage restrictor orifice plate is installed on the rear of the valve, the front of the valve and the bypass. It can be directly clamped between the regulating valve flange and the pipe flange, or between the pipe flanges.

There are two types of multi-stage restrictor orifice plates: single-hole single-hole and single-hole single-hole. We will mainly discuss single-board and multi-board options.

1. For gas and steam

In order to avoid blocking the flow at the outlet of the pipeline with a multi-stage flow restricting orifice plate, the pressure P2 behind the orifice plate cannot be less than 55% of the pressure P1 before the plate. Note: Flow resistance means that when the gas phase medium is discharged from high pressure to low pressure, within a certain range, the flow rate will increase as the pressure on the low pressure side decreases. However, when the low pressure side pressure drops to a certain value, even if the low pressure side pressure continues to decrease, the flow rate will not increase. This phenomenon is called blocked flow. At this point, the gas reaches a critical flow state, in which the flow velocity reaches the speed of sound. The excess pressure energy is no longer converted into the kinetic energy of the medium, but into the energy dissipated by the gas molecules.

2. For liquid

When the liquid pressure drop is less than or equal to 2.5MPa, a single-plate orifice plate is selected. When the liquid pressure drop is greater than 2.5MPa, multi-stage flow restricting orifice plates are selected so that the pressure drop of each orifice plate is less than 2.5MPa.

A multi-stage restrictor orifice is equivalent to a constriction in a pipeline. When liquid flows through a constriction, the flow becomes thin or constricted, and the cross-section appears downstream of the actual constriction, known as a constriction. Consequently, the local flow velocity of the liquid on the constricting surface increases.