A brief introduction to the valve regulating mechanism

A brief introduction to the valve regulating mechanism

Valve terms 1-01 Automatic valve Self-acting valve A valve that acts on its own by the ability of the medium (liquid, air, steam, etc.) 1-02 Actuated valve A valve operated by manual, electric, hydraulic, or pneumatic operation 2-01 gate valve Gate Valve, SL > Valve terminology
1-01 Automatic valve Self-acting valve A valve that acts on its own by the ability of the medium (liquid, air, steam, etc.) 1-02 Actuated valve Actuated valves are operated by manual, electric, hydraulic, or air pressure The opening and closing parts (disc) are driven by the valve stem and move up and down along the tight surface of the seat. Par-allel slide valve gate valves with parallel sealing faces 2-03 Wedge gate valve gate valves with parallel sealing faces 2-04 allel slide valve Outside stem rising through Handwheel type gate valve stem for lifting movement, the transmission thread in the body cavity outside the gate valve 2-05 Inside screw nonrising stem type gate valve stem for rotating movement, The transmission thread is inside the body cavity of the gate valve 2-06 Quick open-and-close gate valve the stem of which rotates as well as moves up and down cavity gate valve 2-07 cavity gate valve the diameter of the passage in the body is different. Flat gate valves 2-08 Flat gate valves with and without diversion holes are available for gate valves with and without diversion holes. Flat gate valves with diversion holes can pass through the ball pigging, The plate gate valve without diversion hole can only be used as the opening and closing device on the pipeline 3-01 Butterfly valve whose opening and closing member (Butterfly plate) rotates around a fixed axis 3-02 Center line-type Butterfly valve the Center of rotation (that is, the Center of the valve shaft) of the Butterfly plate The center of rotation of the butterfly plate (i.e., the center of the valve shaft) was located at the center line of the valve body and sealed with the butterfly section The center of rotation (i.e., the center of the valve shaft) of the butterfly plate and the sealed section of the butterfly plate formed a dimensional eccentric; The rotary center of the butterfly plate (i.e., the center of the valve shaft) formed a dimensional bias with the sealing surface of the butterfly plate, and another dimensional bias with the center line of the valve body. The center line of the valve body sealing surface and the center line of the valve seat (i.e., the center line of the valve body) form an Angle offset valve. 4-01 Rotary valve The valve with the opening and closing parts rotating relative to the center of the surface of the valve seat sealing surface 03 Floating ball valve Float ball valve Ball valve with no Fixed shaft 4-04 Fixed ball valve Fixed ball valve Ball valve with Fixed shaft 4-05 Flexible ball valve Flexible ball 4-06 Ball valve with an elastic slot on the ball 4-06 Cock, plug A valve with a plug rotating about its axis 4-07 Clampyte plug valve without packing inside the body, The sealing of the plug and the sealing surface of the plug body can be realized by tightening the nut under the plug valve. Gland packing Plug valve 4-08 packing type plug valve Gland packing plug valve 4-09 self-sealins plug valve packing type plug valve self-sealins plug Valve plug seal between plug and rely mainly on the pressure of the medium itself to implement oil seal cock valve 4 to 10 of plug valve Lubricated plug-in valve adopts oil seal cock valve regulating mechanism
Brief introduction of valve regulating mechanism, brief introduction of valve regulating mechanism
The adjusting mechanism is a device that converts the output displacement change of the actuator into the change of the flow area between the valve spool and the valve seat. Usually called the regulating mechanism for the valve, such as straight through single seat valve, Angle valve, etc. Its structural characteristics can be analyzed from the following aspects. Brief introduction of valve regulating mechanism

From the displacement of the valve core, the regulating mechanism is divided into linear displacement valve and angular displacement valve. They are used with linear displacement actuator and angular displacement actuator respectively. Straight through valve, Angle valve, sleeve valve and so on belong to linear displacement valve, also known as sliding stem valve (Sl> from the spool guide, can be divided into top guide, top and bottom guide, · sleeve guide, stem guide and seat guide and other types. For fluid control and closure, the spool guide is very important. The spool guide is used for the alignment of the spool and the seat. The top guide is guided by a guide sleeve or packing structure in the valve cover or valve body; Top and bottom guide using the valve cover and the guide sleeve of the lower valve cover to achieve the guide, the double seat valve and the need to guide the regulating mechanism need to use the top and bottom guide; The sleeve guide is guided by the outer surface of the valve core and the inner surface of the sleeve. This guide mode has self-centering performance and can realize the alignment of the valve core and the valve seat. The valve stem is guided by the guide sleeve on the valve cover and the valve seat ring, and the shaft sleeve and the valve stem are guided; Seat guides are used in small flow control valves that align directly with the seat. Brief introduction of valve regulating mechanism
From the unbalanced force of the valve core, the valve core of the regulating mechanism has unbalanced and balanced two types. Balanced spool is a spool with a balance hole opened on the spool. When the spool moves, the upper and lower part of the spool are connected because of a balance hole, so most of the pressure difference between the two sides is offset to reduce the effect of unbalanced force on the spool. The balanced spool needs to balance the chamber, so it is necessary to seal the device. According to the flow direction, the pressure of the balance spool can be the pressure before the valve (the center to the outflow) or the pressure after the valve (the outside to the center). Balance spool can be used for sleeve structure spool, also can be used for plunger structure spool. Both sides of the unbalanced spool are the pressure before and after the valve of the control valve. Therefore, the unbalanced force of the spool is large, and the control valve of the same caliber needs an actuator with greater thrust to operate. Brief introduction of valve regulating mechanism
From the valve core pressure relief, the valve core structure has single stage pressure relief and multistage pressure relief. Because of the large pressure difference between two ends, the single-stage step-down structure is suitable for the occasions with small noise and no serious cavitation. In the high noise reduction requirements, cavitation serious occasions.
In the multistage step-down structure, the pressure difference between the two ends of the control valve is decomposed into several pressure differences, so that the pressure difference in each grade is small, will not occur cavitation and flash phenomenon, so as to prevent cavitation and flash, but also reduce the noise. Brief introduction of valve regulating mechanism
From the view of flow characteristics, according to the different changes of flow area, it can be divided into linear characteristics, equal percentage characteristics, fast opening characteristics, parabola characteristics, hyperbolic characteristics and some correction characteristics. Flow rate, J Bi, indicates the relationship between stem displacement and flow rate. Usually, the flow characteristics are used to compensate the nonlinear characteristics of the controlled object. The shape of the spool or the shape of the sleeve hole determines the flow characteristics of the control valve. Straight, process spool can be divided into plate type (for quick opening), plunger type, window type and sleeve type. Due to the change of the opening area, the flow area is different when the spool moves, so as to achieve the required flow characteristics. Plunger and window valves are also available in different shapes depending on the desired flow characteristics. The spool of Angle stroke valve also has different shapes, for example, traditional valve plate for butterfly valve, dynamic profile valve plate; For ball valve O – hole, V – hole and modified – hole structure. Brief introduction of valve regulating mechanism
From the interchangeability of valve inner parts, some regulating mechanisms of the valve inner parts can be easily replaced and maintained, for example, sleeve valve can be easily replaced to achieve different flow characteristics; The top and bottom oriented valve inner parts can easily turn the spool and seat to realize the replacement of the positive body valve and the reverse body valve, so as to realize the replacement of the air opening and gas closing mode; Body separation valves can be easily removed for seat replacement and cleaning. Brief introduction of valve regulating mechanism
From the valve cover structure, according to different application requirements, can use ordinary valve cover, can also use a long neck type valve cover or with heat dissipation or heat absorption plate long neck type valve cover, in addition to bellows seal type valve cover. Long NECK COVERS ARE USED FOR HIGH AND LOW TEMPERATURE APPLICATIONS TO PROTECT STEM PACKING FROM MEDIUM TEMPERATURE AND PREVENT ADHESION, SNAGGING, LEAKAGE OR REDUCED LUBRICATION. In addition to the extension of the valve cover, the packing temperature away from the medium working temperature of the long neck valve cover, can also increase heat dissipation or heat absorption sheet, made with heat dissipation or heat absorption sheet of the long neck valve cover, so that the medium temperature is reduced or increased. Generally, the cast long neck valve cover has better heat dissipation and high temperature adaptability, is used in high temperature applications; The LONG-NECKED STAINLESS STEEL BONNET PROVIDES LOW THERMAL CONDUCTIVITY AND GOOD LOW TEMPERATURE ADAPTABILITY FOR USE IN LOW TEMPERATURE APPLICATIONS. When THE CONTROLLED MEDIUM IS NOT ALLOWED to leak, the upper COVER OF the USUAL PACKING structure cannot be used, and the upper cover with bellows seal must be used. This construction USES a bellows seal to seal the controlled medium in the valve body, out of contact with the packing, preventing fluid leakage. The influence of pressure and temperature of bellows should be considered when selecting.
From the connection of regulating mechanism and pipeline, there are several kinds of screw pipe connection, flange connection, flanged clamp connection and welding connection. Small control valve often use rotary pipe thread connection, the valve body connection end is the taper pipe thread, pipe connection end for the taper pipe thread. This CONNECTION IS SUITABLE FOR PIPE CONNECTIONS FOR CONTROL VALVE BODIES LESS THAN 2 “. No, FOR HIGH TEMPERATURE SERVICE. Due to the difficulty of maintenance and disassembly, it is necessary to install live connectors upstream and downstream of the control valve. The flange connection is made of the flange matching with the control valve, connected with bolts and gaskets, and the matching flange is welded on the pipeline. According to the different control valve connection flange, there are different matching flanges, such as flat flange, convex flange, annular joint surface flange, etc. The flange used should be compatible with the rated working pressure and temperature of the control valve. Flat flange connection, gasket can be installed between the two flange faces, suitable for low pressure, cast iron and copper control valve installation connection. Convex flange processing has a tightening line, it is a small groove concentric with the flange, when the gasket installed between the two flanges under the action of the bolt pressing, gasket will enter the groove of the tightening line, make the connection of the seal closer, convex flange connection is suitable for most applications used in cast steel, alloy steel control valve. The annular joint surface flange is used to connect the high pressure control valve. The lens gasket is used. When the gasket is pressed, the gasket is pressed into the U-shaped slot on the convex surface of the flange to form a tight seal. Clamp connection is suitable for connecting low pressure and large diameter control valves such as gate valve and butterfly valve. External flange is used to clamp the control valve, and gaskets are placed on the connecting surface. Bolt is used to press the flange to complete the connection between valve and pipeline. Weld connections Weld the control valve directly to the pipe using either socket or butt welding. The advantage of welded connection is that strict sealing can be achieved, the disadvantage is that the welded connection requires the body material to be welded, and is not easy to remove from the pipeline, therefore, generally do not use welding connection. A brief introduction of valve regulating mechanism A Brief introduction of valve regulating mechanism