Function of extraction check valve
is quite singular. However, extraction check valve is indispensable for turbine.
Closing extraction check valve: when extraction check valve receives closing signal, air compressing three-way magnetic valve is opened. Compressed air connects with upper chamber of piston on extraction check valve. Depend on compressed air to overcome the functions of spring force and vapor pressure, making joy stick move downward, forcibly closing extraction check valve.
Opening extraction check valve: when extraction check valve receives opening signal, air compressing three-way magnetic valve makes compressed air inside upper chamber of piston on check valve connect with exhaust port, draining off compressed air inside air chamber. Spring force makes joy stick move upward to free position. When steam passes through valve disc, check valve is jack by applied force of steam.
Extraction check valve on extraction steam pipe line of turbine is very important. When turbine is throwing off loads, extraction check valve prevents turbine from overspeeding due to backflow of steam and stops heater and pipeline from bringing water into turbine.
Structure of extraction check valve
The structure of extraction check valve is classified into two types:
1. Check valve on regenerative extraction steam;
2. Flap extraction check valve on cylinder extraction pipeline where high pressure having large flow rate passes through.
The two kinds of check valve are using pressure water as controlling power. To realize long distance automatic closing, pipeline is equipped with a water control system, which is called as check valve pressure transmission device.
1. Standard of design, manufacturing and acceptance adopts ANSI B16.34. Strength and sealing completely meet requirements of standard. Vacuum test of valve is carried out under state of vacuum. Service life of whole machine meets customers' requirements.
2. The disc is designed to connect with stem through rocker, which can automatically center with sealing face of valve, ensuring sealing face coinciding.
3. For different temperatures, materials of body mainly adopt carbon steel or high temperature steel. Sealing face is bead welded with carbide alloy.
4. Valve is equipped with damping heavy hammer, which can balance kinetic moment of closure member in case of water hammer.
5. Sealing face of seat inclines in a definite angle, reducing closing time and impact, protecting equipment and pipeline.
6. Lumen of body is designed as streamline, having high flow capacity which reduces valve resistance.
7. Actuator is spring returning cylinder or hydraulic cylinder, which is independent with closure member. The obstacle on actuator has no impacts on actions of closure member.
8. Opening of closure member is equipped with stop gear which is used to protect closure member from being damaged due to over opening.
9. Inwall of hydraulic cylinder is coated with wear and corrosive layer which can extend service life and reducing action resistance, making valve more flexible and reliable.