Source: Thermal Controller
Shut-off valves
The globe valve is a forced seal valve, so when the valve is closed, pressure must be applied to the disc to force it.
No leakage of the sealing surface. When the medium enters the valve from the bottom of the valve disc, the resistance that needs to be overcome by the operating force is the friction between the valve column and the packing and the thrust generated by the pressure of the medium, and the force of closing the valve is greater than the force of opening the valve, so the diameter of the valve stem should be larger, otherwise the failure of the top bend of the valve stem will occur.
Gate valve
The opening and closing parts of the gate valve (gate valve) are the gate plate, the direction of movement of the gate plate is perpendicular to the direction of the fluid, and the gate valve can only be fully opened and closed, and cannot be adjusted and throttled.
When the gate valve is closed
The sealing surface can only rely on the medium pressure to seal, that is, rely on the medium pressure to press the sealing surface of the ram to the valve seat on the other side to ensure the sealing of the sealing surface, which is self-sealing. Most gate valves are forcibly sealed, that is, when the valve is closed, the ram should be forced to the valve seat by external force to ensure the tightness of the sealing surface.
When the valve is opened
When the ram lift height is equal to 1:1 times the valve diameter, the passage of the fluid is completely unobstructed, but this position cannot be monitored during operation. In actual use, it is marked by the vertex of the stem, that is, the position that cannot be opened, as its fully open position. In order to account for the lock-up phenomenon due to temperature changes, it is usually rewound 1/2-1 turn back to the apex position as the position of the fully open valve. Therefore, the fully open position of the valve is determined by the position of the ram (i.e. the stroke).
relief valve
The safety valve is a kind of safety protection valve, its opening and closing parts are in a normally closed state under the action of external force, when the medium pressure in the equipment or pipeline rises, it will be automatically opened when it exceeds the specified value, and the medium pressure in the pipeline or equipment will be prevented from exceeding the specified value by discharging the medium to the outside of the system. Safety valves belong to the automatic valve category, which are mainly used in boilers, pressure vessels and pipelines, and the control pressure does not exceed the specified value, which plays an important role in protecting personal safety and equipment operation.
Adjustment of the opening pressure of the safety valve
(1) Before the safety valve leaves the factory, its opening pressure should be adjusted to the setting value required by the user one by one. If the user proposes the working pressure level of the spring, it should be adjusted according to the lower limit of the pressure level in general.
(2) Before installing the safety valve on the protected equipment or before installation, the user must re-adjust it at the installation site to ensure that the setting pressure value of the safety valve meets the requirements.
(3) Within the range of the spring working pressure level indicated on the nameplate, the opening pressure can be adjusted by changing the spring compression amount by rotating the adjustment screw.
(4) Before rotating the adjusting screw, the inlet pressure of the valve should be reduced to less than 90% of the opening pressure to prevent the valve disc from being driven to rotate when rotating the adjusting screw, resulting in damage to the sealing surface.
(5) In order to ensure the accuracy of the opening pressure value, the medium conditions at the time of adjustment, such as the type and temperature of the medium, should be as close as possible to the actual operating conditions. The opening pressure often varies depending on the type of medium, especially when the aggregate state of the medium is different (e.g. from liquid to gaseous phase). As the operating temperature increases, the opening pressure generally decreases. Therefore, when adjusted at room temperature and used at high temperature, the setting pressure value at room temperature should be slightly higher than the required opening pressure value. The degree of high is related to the valve structure and material selection, and should be based on the manufacturer's instructions.
(6) When the conventional safety valve is used to fix the additional back pressure, when the opening pressure is adjusted after the inspection (the back pressure is atmospheric pressure at this time), its setting value should be the required opening pressure value minus the additional back pressure value.
Ball valves
Ball valve It has the action of rotating 90 degrees, and the body is a sphere, with a circular through hole or channel through its axis. The ball valve is mainly used in the pipeline to cut off, distribute and change the flow direction of the medium, it only needs to rotate 90 degrees and a small torque to close tightly. Ball valves are best suited for on/off and shut-off valves, but recent developments have designed ball valves to allow them to throttle and control flow.
Key features:
The main characteristics of the ball valve are its compact structure, reliable sealing, simple structure, easy maintenance, sealing surface and spherical surface are often in a closed state, not easy to be eroded by the medium, easy to operate and maintain, suitable for water, solvent, acid and natural gas and other general working media, but also suitable for media with poor working conditions, such as oxygen, hydrogen peroxide, methane and ethylene, etc., which are widely used in various industries. The ball valve body can be monolithic or combined.
Check valves
One-way valve: Check valve, also known as check valve or check valve, is used to prevent the backflow of media in the pipeline. The foot valve of the suction off of the water pump also belongs to the category of check valves.
The opening and closing parts rely on the flow and force of the medium to open or close by themselves, so as to prevent the medium from flowing backwards. Check valves belong to the automatic valve category, which are mainly used on pipelines where the medium flows in one direction, and only allow the medium to flow in one direction to prevent accidents.
Principle:
Check valve refers to the valve that automatically opens and closes the valve disc by relying on the flow of the medium itself to prevent the backflow of the medium, also known as check valve, check valve, reverse flow valve, and back pressure valve. The check valve is an automatic valve, and its main function is to prevent the backflow of the medium, prevent the pump and the drive motor from reversing, and the discharge of the container medium. Check valves can also be used to supply lines to auxiliary systems where pressure may rise above the system pressure. Check valves can be mainly divided into swing-type check valves (rotating according to the center of gravity) and lifting check valves (moving along the axis).
The function of a check valve is to allow the medium to flow in only one direction and to prevent it from flowing in the opposite direction. Usually this kind of valve works automatically, and the disc opens under the action of fluid pressure flowing in one direction; When the fluid flows in the opposite direction, the fluid pressure and the self-closing disc of the disc act on the valve seat, thus cutting off the flow.
Butterfly valves
Butterfly valve, also known as flap valve, is a simple structure of the regulating valve, but also can be used for low-pressure pipeline medium on/off control.
Disadvantages of butterfly valves
1. The range of operating pressure and working temperature is small.
2. Poor sealing.
According to the structural form, butterfly valves can be divided into offset plate type, vertical plate type, inclined plate type and lever type. According to the sealing form, it can be divided into two types: soft seal type and hard seal type. The soft seal type is generally sealed with a rubber ring, and the hard seal type is usually sealed with a metal ring.
According to the connection type, it can be divided into flange connection and clamp connection; According to the transmission mode, it can be divided into manual, gear transmission, pneumatic, hydraulic and electric.
Advantages of butterfly valves
1. It is convenient and fast to open and close, labor-saving, and has low fluid resistance, and can be operated frequently.
2. Simple structure, small size and light weight.
3. It can transport mud and accumulate the least liquid at the mouth of the pipeline.
4. Under low pressure, good sealing can be achieved.
5. Good adjustment performance.