The specific working principle of the flow control orifice plate

This post was last edited by shanxg on 2011-1-5 21:39. 1. Working principle of the flow control orifice plate: The orifice plate can be used as a flow measurement element to determine flow rates, or it can function as a throttling element to regulate flow rates and reduce pressure. When there is a certain pressure difference before and after the orifice plate, as the fluid flows through it, for a given orifice size, the flow rate through the orifice plate increases as the pressure difference increases. However, when the pressure difference exceeds a certain value (known as the critical pressure difference), the flow velocity of the fluid through the constriction in the orifice plate reaches the speed of sound. At this point, no matter how much the pressure difference increases, the flow rate through the orifice plate remains constant and does not increase any further. A flow control orifice plate functions on the basis of this principle to regulate the flow rate of the fluid and reduce pressure. 2. Application of flow control orifice plates in process installations: Firstly, they are used to control the minimum flow rate of centrifugal pumps, thereby ensuring their safe startup and proper operation. When starting a centrifugal pump, in order to achieve a certain outlet pressure and reduce the starting current of the motor, it is necessary to start the pump with the outlet valve closed or partially closed. However, for certain centrifugal pumps, such as high-head centrifugal pumps and those used to transport volatile liquids, the gap between the impeller inside the pump and the pump casing is very small, which makes it easy for the fluid to vaporize. Therefore, these types of centrifugal pumps require a certain flow rate during startup and operation. If such centrifugal pumps operate without any liquid flow (i.e., in a closed condition), vortices will form within the pump, causing the liquid to heat up and vaporize, which leads to cavitation or pressure buildup and can easily damage the pump. To ensure the safe start-up and proper operation of such centrifugal pumps, it is required that the pump have a minimum discharge flow rate; this value is known as the minimum flow rate of the centrifugal pump. Typically, the minimum flow rate is specified by the pump manufacturer. To ensure a minimum flow rate, a return line is added to the outlet pipeline of the centrifugal pump, known as the minimum flow line. By using a flow-limiting orifice plate on the minimum flow line, it is possible to ensure the safe operation of the centrifugal pump, even in the event that the pump’s outlet valve is closed due to an error, thereby preventing damage to the pump. Second, use a flow control valve to limit the maximum flow rate. In process operations, where flow rate does not need to be adjusted and only a maximum flow rate needs to be specified, a flow-limiting orifice plate can be used in place of a flow control circuit to prevent excessive flow and thus save on investment. This is also one of the most common uses of flow restriction orifice plates. Third, prevent bypass flow in each branch pipe. In some cases, the process requires that the flow rates in each branch pipe be equal. However, since it is difficult for the pressure drops across each branch pipe to be exactly equal, there are differences in their flow rates. By using flow control orifice plates, the pressure drop in each branch can be adjusted to maintain a consistent flow rate in all of them.

Throttle orifice plate I. Overview The throttle orifice plate is installed in pipelines to limit the flow rate of a fluid or reduce its pressure. The LG-XLB type flow-limiting orifice plate is designed and manufactured in accordance with standards such as GB2624, HG/T 20570, GD2000, and GD87. II. Measurement principle: When a fluid passes through an orifice plate, a pressure drop is generated, and the flow rate through the orifice plate increases as this pressure drop increases. However, when the pressure drop exceeds a certain value, that is, beyond the critical pressure drop, regardless of how much the outlet pressure decreases, the flow rate will remain constant and will not increase any further. A flow control orifice plate is used based on this principle to limit the flow rate of a fluid or reduce its pressure. Throttling orifice plates are classified into single-orifice plates and multi-orifice plates based on the number of openings on the plate ； Based on the number of orifice plates, they can be classified as single-stage and multi-stage. III. Applications 1. Situations where process materials require pressure reduction. 2. When a large pressure drop is required upstream and downstream of a valve in a pipeline, in order to reduce fluid erosion on the valve, an orifice plate can be connected in series upstream of the valve, provided that throttling through the orifice plate does not result in the formation of a gas phase. 3. Places where the fluid needs to flow in small quantities and continuously, such as the flushing pipes of pumps, the bypass pipes of hot standby pumps (low-flow protection pipes), analysis sampling pipes, etc. 4. Areas where pressure reduction is needed to reduce noise or wear, such as vent systems. IV. Main Technical Parameters 1. Nominal diameter: 10mm ≤ DN ≤ 500mm 2. Nominal pressure: PN ≤ 42 Mpa 3. Operating temperature: -50℃ ≤ t ≤ 550℃ 4. Stage type: Single-stage, multi-stage 5. Number of ports: Single port, multiple ports 6. Precision grades: Grade 1, Grade 1.5, Grade 2 7. Connection methods: Welding, flange connection 8. Referenced standards: GB2624, HG/T 20570, GD2000, GD87 Key selection considerations: (1) For gases and steam, in order to avoid flow blockage in pipelines using flow control orifice plates, the pressure behind the orifice plate (P2) must not be less than 55% of the pressure before the plate (P1), that is, P2 ≥ 0.55P1; therefore, when P2