In industrial automation, it is critical to select the right valve and operate it correctly. The following is some practical information about double-seated control valves, straight stroke control valves and angle stroke valves, designed to help U.S. users better understand and apply these devices.
- Small Opening Oscillation Problems with Double Seated Control Valves
Double-seated control valves are uniquely designed with two spools, one in the direction of fluid inflow (upper spool) and the other in the direction of outflow (lower spool). When the spool is in the small opening condition close to closing, the fluid flow near the lower spool becomes unstable, which can cause the spool to oscillate. This is because the spool is less stable when it is near the flow closed state. Therefore, in the selection, should avoid the double-seat adjustment valve for frequent small openings need to be adjusted occasions. - double seat control valve should not be used as a cut-off valve
Double seat adjustment valve spool design with force balance structure, can withstand a large front and rear pressure difference. However, because its two sealing surfaces can not be close contact at the same time, the leakage is relatively large, so it is not suitable for use as a cut-off valve. This structural limitation cannot be completely overcome even with improved designs such as the addition of sleeves. - Comparison of anti-blocking performance of straight stroke and angle stroke valves
The spool of the straight stroke control valve moves vertically, and the fluid flows horizontally. The flow path in the valve cavity is usually S-shaped, which is easy to form blind zones, and the medium in these areas is easy to precipitate, resulting in blockage. In contrast, the spool of the angle stroke valve rotates horizontally, the medium also flows horizontally, it is not easy to form a dead zone, and the precipitate is easily taken away by the fluid. Therefore, from the point of view of anti-blocking performance, the angle travel valve is superior to the straight travel valve. - The reason why the stem of the direct travel control valve is thin
The valve stem of the straight stroke valve slides up and down, generating a large friction force. In order to reduce the friction, the valve stem is designed into a slender shape and adopts PTFE packing with a small friction coefficient. However, this also brings about problems such as easy bending of the valve stem and short packing life. Therefore, attention needs to be paid to these potential problems when using straight stroke control valves. - High cut-off differential pressure for angle travel valves
The spool design of the angle stroke valve makes the combined force of the medium acting on the spool produce a very small torque on the spool, so it can withstand a large differential pressure. This gives angle travel valves a significant advantage where high differential shutoff pressure is required. - Cut-off valve why choose hard sealing
Soft-sealed valves are usually superior to hard-sealed valves in terms of shutoff effectiveness. However, in terms of wear resistance and reliability, soft-sealed valves are far inferior to hard-sealed valves. Comprehensive consideration of leakage and reliability, hard seal shut-off valve is more ideal. Modern cut-off valves often use surfacing wear-resistant alloy technology, which greatly improves the sealing performance, fully able to meet the use of cut-off valve requirements.
