1. Basic types and structures of stop valves
Stop valves can be divided into several main types according to different structural designs and working principles:
1. Straight-through stop valve
Straight-through stop valve is the most common type of stop valve. The fluid channel in its valve body is in a straight line with the valve seat and valve disc. When the fluid passes through, the movement of the valve disc is perpendicular to the valve seat, which can effectively control the flow. This type of stop valve has lower fluid resistance and better sealing performance, and is suitable for medium and low pressure pipeline systems.
2. Angle stop valve
The fluid channel in the valve body of the angle stop valve is at a 90-degree angle. This design changes the direction of the fluid path. It is usually installed at the angle bend of the pipeline and is suitable for occasions where the flow direction needs to be changed.
3. Y-type stop valve
The valve body of the Y-type stop valve is in the shape of a "Y". When the fluid passes through, the flow path is at a certain angle. This type of stop valve has lower fluid resistance and is suitable for occasions that require high flow and have high requirements for the flow rate of the fluid. The design of the Y-type stop valve also helps to reduce the scouring of the medium and extend the service life of the valve.
4. Forged steel stop valve
Forged steel stop valves are made of forged steel and have stronger mechanical properties. They are suitable for high-pressure and ultra-high-pressure occasions. They are commonly found in the oil, natural gas, chemical and other industries. Forged steel stop valves have good sealing and strong corrosion resistance, and are suitable for high-strength, high-temperature and high-pressure working environments.
2. Key factors in choosing stop valves
When choosing stop valves, the following factors need special attention:
1. Media type
The selection of stop valves needs to select appropriate materials and sealing methods according to the type of media to be controlled. Common media include:
- Water: Generally use valves made of cast iron, carbon steel, cast steel, etc.
- Oil: Use stainless steel or alloy steel materials to prevent oil leakage.
- Gas: Generally use carbon steel or stainless steel, and choose high temperature resistant and corrosion resistant materials.
- Chemicals: It is necessary to consider the corrosiveness of the medium and choose materials with strong corrosion resistance, such as stainless steel, alloy steel, polytetrafluoroethylene (PTFE), etc.
2. Working pressure and temperature
The pressure and temperature resistance of the stop valve directly determine its applicable occasions. When purchasing, make sure that the working pressure and temperature range of the valve are suitable for the working conditions. For example:
- Normal temperature and pressure: Stop valves made of carbon steel or cast iron can meet the requirements.
- High temperature and high pressure: alloy steel, stainless steel and other high-strength and high-temperature resistant materials need to be selected.
- Low temperature: For low-temperature media such as liquefied gas, low-temperature stop valves such as low-temperature steel or alloy steel need to be selected.
3. Sealing performance
The sealing performance of the stop valve is very important, which directly affects the control effect of the fluid. Common sealing methods are:
- Soft seal: Suitable for low-temperature and normal temperature fluids, good sealing, suitable for low pressure occasions.
- Hard seal: Metal materials are used as sealing surfaces, suitable for high temperature, high pressure, corrosive fluids, and more reliable sealing performance.
4. Fluid control accuracy
The accuracy of the stop valve depends on the design of the valve and the movement of the valve disc. In situations where precise flow control is required, special attention should be paid to the movement of the valve disc when selecting the stop valve:
- Low flow rate, precise control: Selecting straight-through or Y-type stop valves can provide more precise flow control.
- Large flow, high-speed fluid: Forged steel or large-diameter stop valves can meet the needs of high flow.
5. Valve material and corrosion resistance
Depending on the use environment, the corrosion resistance of the valve material is very important. For example:
- Water pipe system: You can choose stop valves made of carbon steel, cast iron and other materials, which usually do not require too high corrosion resistance.
- Seawater or chemical pipeline: You need to choose stainless steel, alloy steel or materials with better corrosion resistance.
- High temperature and high pressure environment: You need to choose alloy steel or stainless steel, which has better oxidation resistance and corrosion resistance.
6. Installation method and size
There are three common installation methods for stop valves: flange connection, threaded connection and welding connection. When installing, you need to ensure that the size, interface and pipe specifications of the valve match:
- Flange connection: Suitable for medium and large diameter pipes, easy installation and good sealing.
- Threaded connection: Suitable for small diameter pipes, easy installation and often used in low pressure occasions.
- Welding connection: Suitable for high temperature, high pressure or dangerous environment, with firm connection.
7. Operation mode
The operation mode of the stop valve usually includes manual, pneumatic, electric and other different forms. When choosing, you need to consider the convenience of operation and the degree of automation:
- Manual: Suitable for small and medium-sized systems, simple operation and low cost.
- Pneumatic: Suitable for automatic control occasions, quick operation, and suitable for large-scale fluid control.
- Electric: Suitable for occasions that require remote control or precise adjustment.
8. Valve size and flow requirements
The size of the stop valve should be selected according to the actual pipeline diameter and flow requirements. When the flow is too large, the sealing surface of the valve will be greatly impacted, which may affect its service life. Therefore, the appropriate valve specifications should be selected according to the flow of the pipeline system.
3. Common applications of stop valves
Stop valves are widely used in various pipeline systems that require interception or flow regulation. Common application areas include:
1. Water treatment: Used in urban water supply systems, sewage treatment systems, etc. to control the inflow and outflow of water.
2. Petroleum and natural gas: In oil and gas pipelines, it plays the role of cutting off and regulating flow.
3. Chemical industry: used for chemical medium delivery pipelines to prevent chemical backflow or leakage.
4. Power industry: in power plants, control the flow of media such as steam and cooling water.
5. HVAC: used for water flow regulation in air conditioning, heating and other systems to ensure the operation of the system.
6. Food and beverage: used for precise control of liquids or gases in the production process to ensure stable flow.
4. Selection case
Suppose a chemical plant needs to purchase a stop valve for a pipeline system for conveying acidic chemicals. It requires good corrosion resistance, sealing and flow control functions, and can withstand high temperature and high pressure. The following selections can be considered:
- Material selection: stainless steel or alloy steel is selected to ensure good corrosion resistance.
- Type selection: select straight-through or Y-type stop valves to ensure good flow control accuracy.
- Sealing method: select hard sealing method to ensure sealing under high temperature and high pressure environment.
- Installation method: select flange connection to ensure stable and reliable connection in high-pressure pipeline system.
5. Conclusion
When purchasing a stop valve, you need to consider multiple factors such as the medium type, working pressure, temperature, sealing performance, flow requirements, etc. By choosing the appropriate stop valve type, material and size, you can effectively control the flow of fluids and protect the safe operation of pipeline systems and other equipment.