Valve common small problem solving method Typical valve performance introduction and working principle

Valve common small problem solving method Typical valve performance introduction and working principle

Why is the two-seat valve easy to oscillate when working with a small opening? For a single core, when the medium is flow open type, the valve stability is good; When the medium is flow closed, the stability of the valve is poor. The double seat valve has two spool, the lower spool is in the flow closed, the upper spool is in the flow open, so, in the small opening work, the flow closed type spool is easy to cause the vibration of the valve, this is the reason why the double seat valve can not be used for the small opening work. Its valve stem is 2 ~ 3 times thicker than the straight stroke valve stem, and the choice of long-life graphite packing, stem stiffness is good, packing life is long, the friction torque is small, small return difference.
How to solve the valve common small problems
1. Why is it easy to oscillate when the two-seat valve is small open? For a single core, when the medium is flow open type, the valve stability is good; When the medium is flow closed, the stability of the valve is poor. The double seat valve has two spool, the lower spool is in the flow closed, the upper spool is in the flow open, so, in the small opening work, the flow closed type spool is easy to cause the vibration of the valve, this is the reason why the double seat valve can not be used for the small opening work.
2. Why can’t the double seal valve be used as a cut-off valve? The advantage of the two-seat valve spool is that the force balance structure allows the pressure difference to be large, while its outstanding disadvantage is that the two sealing surfaces can not be in good contact at the same time, resulting in large leakage. If it is artificially and forcibly used to cut off the occasion, obviously the effect is not good, even if it has made many improvements (such as double seal sleeve valve), it is not desirable.
3, what straight stroke regulating valve blocking performance is poor, Angle stroke valve blocking performance is good? Straight stroke valve spool is vertical throttling, and the medium is horizontal flow into and out of the valve chamber flow channel must turn back, so that the valve flow path becomes quite complex (shape such as inverted “S” type). In this way, there are many dead zones, which provide space for the precipitation of the medium, and in the long run, cause blockage. The direction of the Angle stroke valve throttling is the horizontal direction, the medium flows in and out horizontally, and it is easy to take away the unclean medium. At the same time, the flow path is simple, and the medium precipitation space is very little, so the Angle stroke valve has good blocking performance.
4. Why is the stem of the straight stroke regulating valve thinner? It involves a simple mechanical principle: large sliding friction and small rolling friction. Straight stroke valve stem up and down movement, packing slightly pressed a little, it will put the valve stem wrapped very tight, produce a large back difference. For this reason, the valve stem is designed to be very small, and the packing is commonly used with a small coefficient of friction PTFE packing, in order to reduce the backdifference, but the problem is that the valve stem is thin, easy to bend, and the packing life is short. To solve this problem, a better way is to use the travel valve stem, namely the Angle stroke type of regulating valve, its valve stem is 2 ~ 3 times thicker than the straight stroke valve stem, and the choice of long-life graphite filler, stem stiffness is good, packing life is long, the friction torque is small, small return difference.
The ball valve is evolved from the plug valve. It has the same 90 degree rotation action, except that the plug body is a sphere with circular through holes or channels through its axis. When the ball is rotated 90 degrees, the spherical surface should appear at both the inlet and outlet to cut off the flow. Ball valves require only a 90 degree rotation and a small rotational moment to close tightly. Completely equal valve body cavity for the medium provides little resistance, straight through the flow channel. Ball valves are suitable for direct opening and closing, but can also be used for throttling and flow control.
A typical valve
1 gate valves
The gate valve is used as a cut-off medium, the whole flow is straight through when it is fully open, and the pressure loss of the medium running is ** * small. Gate valves are usually suitable for operating conditions that do not require frequent opening and closing, and keep the gate fully open or fully closed. Not intended for use as a regulator or throttling. For THE HIGH speed flow MEDIUM, THE gate CAN cause the gate vibration in the condition of local opening, and the vibration may damage the sealing surface of the gate and seat, and the throttle will cause the gate to suffer from the erosion of the medium.
From the structural form, the main difference is the form of the sealing element used. According to the form of sealing elements, gate valves are often divided into several different types, such as wedge gate valves, parallel gate valves, parallel double gate valves, wedge double gate gates, etc. ** Commonly used forms are wedge gate valves and parallel gate valves.
Open stem wedge type single gate valve
2 stop valve
Globe valve is used to cut off the flow of the medium, the axis of the stem of the globe valve is perpendicular to the sealing surface of the seat, and it is broken by driving the up and down of the spool. Once stop valve is fully open, it will no longer have a contact between the seat and clapper sealing surfaces, and have a very reliable cutting action, thus its sealing surface mechanical wear and tear is small, because most of the cut-off valve seat and valve disc is easy to repair or replace the whole valve sealing components without removed from the pipeline, This is suitable for applications where the valve and line are welded together.
The flow direction of the medium through the valve has changed, so the flow resistance of the globe valve is higher. The fluid introduced into the globe valve from the lower part of the spool is called formal assembly, from the upper part of the spool is called reverse assembly. When the valve is formal assembly, the opening of the valve is labor-saving and the closing is laborious. When the valve is reverse assembly, the valve is closed tightly and the opening is laborious.
Electric flat seal globe valve
3 check valve
The purpose of the check valve is to allow medium to flow in only one direction and to prevent directional flow. Usually the valve is automatically operated, under the action of a flow of fluid pressure in one direction, the disc opens; When the fluid flows in the opposite direction, the fluid pressure and the self-overlapping valve disc of the valve disc act on the seat to cut off the flow. Including swing check valve and lift check valve.
Swing check valve
4 butterfly valve
The butterfly plate of the butterfly valve is installed in the diameter direction of the pipe. In the cylindrical channel of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis, and the rotation Angle is between 0° and 90°. When the valve is rotated to 90°, the valve is fully open. Butterfly valve simple structure, small volume, light weight, only a few parts. And only need to rotate 90° can quickly open and close, simple operation. When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the resistance when the medium flows through the valve body, so the resistance generated by the valve is very small, so it has better flow control characteristics, can be used for adjustment.
Butterfly valve has two types of elastic seal and metal seal. Elastic seal valve, sealing ring can be mounted on the body or attached to the butterfly plate around. The valve with metal seal is generally longer than the valve with elastic seal, but it is difficult to achieve complete sealing. The metal seal can adapt to higher working temperature, and the elastic seal has the disadvantage of being limited by temperature.
5 ball valve
Ball valve is evolved from the plug valve. It has the same 90 degree rotation action, except that the plug body is a sphere with circular through holes or channels through its axis. When the ball is rotated 90 degrees, the spherical surface should appear at both the inlet and outlet to cut off the flow.
Ball valves require only a 90 degree rotation and a small rotational moment to close tightly. Completely equal valve body cavity for the medium provides little resistance, straight through the flow channel. Ball valves are suitable for direct opening and closing, but can also be used for throttling and flow control. The main feature of ball valve is its compact structure, easy to operate and maintain, suitable for water, solvents, acids and natural gas and other general working media, but also suitable for poor working conditions of media, such as oxygen, hydrogen peroxide, methane, ethylene, resin, etc. Ball valve body can be integral, can also be combined.
6 diaphragm valve
Diaphragm valve is connected with an elastic diaphragm on the compression part, the compression part is moved up and down by the stem operation, when the compression part rises, the diaphragm is held high, forming a pathway, when the compression part falls, the diaphragm is pressed on the body, the valve is closed. This valve is suitable for opening and throttling. Diaphragm valve is especially suitable for the transport of corrosive, viscous fluid, and the valve operating mechanism is not exposed to the transport of fluid, so it will not be contaminated, do not need packing, the stem packing part will not leak.
7 the relief valve
The PRINCIPLE OF ACTION OF THE RELIEF VALVE IS BASED ON FORCE BALANCE, ONCE THE PRESSURE ON THE DISC IS GREATER THAN THE SPRING SET PRESSURE, THE DISC WILL BE PUSHED AWAY BY THIS PRESSURE, AND THE GAS (LIQUID) IN THE PRESSURE VESSEL WILL BE DISCHARGED TO REDUCE THE PRESSURE IN THE PRESSURE VESSEL.
8 the regulator
Regulating valve main working principle, is to change the flow area between the valve disc and seat, to adjust the pressure, flow and other parameters of the purpose.
This section mainly introduces the main structure of the valve body and the valve core, the flow characteristics of the valve and the solution to the cavitation noise problem of the valve core.