【2025 Control Valves】Flow direction and installation orientation of control valves”
Thread Content
I. Flow direction: The mystery of the direction in which the medium flows. The flow direction of a control valve is intuitively indicated by the arrow on the valve body, which shows the path taken by the medium within the control valve. The flow direction can be divided into two main types: Flow-out type: The flow direction of the medium is the same as the direction in which the valve core opens, that is, the medium flows in the direction in which the valve is opened. Flow-blocking type: The flow direction of the medium is the same as the direction in which the valve core closes, that is, the medium flows in the direction opposite to that of valve closure.
The choice of flow direction directly affects the performance and operating characteristics of the control valve. In practical applications, selecting the appropriate flow direction based on the process conditions can solve many problems in production.
II. Installation orientation: The proper and reverse installation of control valves refers to the positioning of the valve spool in straight-through double-seat control valves and straight-through single-seat control valves. It’s like changing the position of the valve core, thereby altering its regulating properties. Characteristics of different valve body mounting orientations: 1. Straight-through double-seat control valve: It has two valve cores and seats, as well as a dual-guidance structure, which allows the valve core to be easily switched from an upright position to an inverted position. All that is needed is to invert the valve core, connect the valve stem to the lower end of the valve core, and swap the upper and lower valve seats. 2. Direct-acting single-seat control valve (diameter > DN25mm): The valve core also features a dual-guidance structure; by simply changing the connection position between the valve stem and the valve core, it is possible to operate the valve in either forward or reverse orientation.
Effect of direction change: In the normal position, the valve core moves downward, reducing the flow area between the valve core and the valve seat. Reverse installation: The valve core moves downward, increasing the flow area between the valve core and the valve seat. This feature allows control valves to exist in two \"product forms\": normal orientation and reverse orientation; by changing the installation position of the valve core, the flow capacity of the valve can be adjusted flexibly.
III. Flow direction versus installation direction: a fundamental difference 1. Flow direction: It concerns the direction in which the medium flows, determining whether the valve is of the \"flow-open\" type or the \"flow-close\" type, and it affects the performance of the control valve. 2. Installation orientation: Pay attention to the installation position of the valve core; by changing the flow capacity of the control valve, it is possible to achieve different effects – a reduced flow area when installed in the correct orientation, and an increased flow area when installed in the reverse orientation.
When a control valve is used in conjunction with a pneumatic actuator, the combination of direct/indirect action and correct/reverse installation determines the final air-shut/air-open characteristic. This combination is like a carefully choreographed duet that requires perfect coordination to perform at its best. A proper understanding and clever application of these combinations can provide flexible and diverse solutions for the design of automated control systems.
Flow direction selection: 1. Ball valves and ordinary butterfly valves have no requirements regarding flow direction, and any flow direction can be chosen. 2. Three-way valves, Venturi angle valves, and sleeve valves with double seals and balance holes have a specified flow direction, which generally cannot be changed. 3. For single-seat valves, angle valves, high-pressure valves, single-seal sleeve valves without balance holes, and low-flow control valves, the flow direction of the control valve should be selected based on different operating conditions.
1) For high-pressure valves with DN≤20, due to the high static pressure, large pressure difference, and severe cavitation erosion, a flow-blocking type should be selected； When DN＞20, good stability should be used as a criterion to determine the flow direction.
2) For angular valves used with high-viscosity media containing solid particles where good \"self-cleaning\" properties are required, a flow-blocking type should be selected.
3) For single-seat valves and low-flow control valves, a flow-open type is generally selected; when scouring is severe, a flow-close type can be used.