Introduction of marine seawater safety valve

Safety valves are the most widely used safety devices on pressure vessels and pressure pipes. In marine power plant seawater systems, in order to prevent the system pressure from exceeding the permissible limit and to ensure the safe operation of the system, a spring-acting safety valve is provided. In the course of use, such safety valves have problems such as leakage, corrosion, and reliability, and they cannot meet the requirements for use, so they have been improved.

Marine water safety valve body materials generally use ZCu16Si14I or ZCuAl10Fe3, these materials are relatively poor in the ability to resist corrosion in the actual use of environmental conditions. When the outer surface of the valve is in contact with a medium such as bilge water and sewage, it is susceptible to corrosion. The setting value of the spring direct-acting safety valve and the re-seating pressure adjustment are inconvenient. When the re-seating pressure is lower than the normal working pressure of the system, the reliability and safety of the system work are adversely affected.

According to the existing problems of the valve, it is determined to improve the material and structure of the valve:

1. Material selection (1) Valve body material The cast copper alloy used for the safety valve body is poor in corrosion resistance, causing leakage of the medium along the sealing boundary. As a result, all parts of the safety valve (except gaskets, fasteners, and springs) were replaced with HDR (a duplex stainless steel). HDR has excellent resistance to chloride ion corrosion and stress corrosion resistance, good seawater erosion resistance (tube flow rate up to 7m/s or more) and strong sand erosion resistance, and good welding, cold bending and other comprehensive processing Performance is the material of choice for ship seawater piping systems.

(2) Sealing surface material In order to improve the sealing performance of the valve, the valve plate and the valve seat sealing surface are made of cobalt-based hard alloy (Figure 1). The sealing surface has sufficient rigidity and strength, and when the system has no medium pressure, it can withstand the great specific pressure generated by the spring. Moreover, cobalt-based hard alloys have good mechanical properties and grinding and grinding properties. And the elastic deformation ability is also good, can withstand the impact of the valve seat back.

(3) Spring material Seawater safety valve springs need to meet the requirements of stability, strength and seawater corrosion resistance. Therefore, in improving the design, In2 conel is selected as the spring material for the seawater medium micro-lift safety valve. In the production of springs, through aging treatment and strong pressure treatment, it has a stable elasticity and strength, to ensure the repetitive operation of the safety valve.

2. Structural Improvements The seawater safety valve for marine use has a poor working environment and therefore requires high sealing and vibration resistance. In order to ensure that the safety valve is strictly isolated from the outside world, a gasket is provided at the joint of the valve body and the valve cover, the valve cover and the protective cover, and the valve cover and the protective cover are closed at the positions other than the connection site. This allows the entire safety valve to have no part of the medium to be leaked except for the inlet and discharge ports.

In order to improve the anti-vibration performance of the safety valve, in addition to the necessary springs and spring seats for the safety valve, a reasonable sealing surface positioning system is also provided. That is, the entire valve stem is used to penetrate the entire interior of the spring, and both ends of the spring are clamped by the spring seat. The upper end of the valve stem adjusts the screw, and the adjustment screw has a pre-compression amount of the adjustment spring to assist the spring and other components to keep the valve closed when the valve is lower than the setting pressure. Moreover, through the clearance between the inner cylindrical surface and the upper end of the valve stem, the upper end of the valve stem has a good guiding effect. The bottom of the valve stem is a spherical hardfacing layer that matches with the cone (or spherical surface) of the valve disc. This not only ensures that the upper end of the valve stem can smoothly move inside the cylindrical surface of the adjusting screw, but also when the valve body is inclined or subjected to vibration. When the centerline of the valve stem deviates from the centerline of the sealing surface, it can be automatically corrected through the contact between the spherical surface and the conical surface (spherical surface) so that the centerline of the valve stem and the centerline of the sealing surface are re-coincided. Ensure that the force of the valve stem on the sealing surface is always in the center position, so that the stress on the sealing surface is more uniform. A guide sleeve is provided around the disc so that the flap can only move in a cylindrical plane perpendicular to the sealing surface.

Under the mutual restraint and effect of multiple parts, the safety valve can still achieve better sealing effect under the condition of vibration and tilt. At the same time, it is also conducive to the accurate opening of the valve, stable discharge and timely return seat, so that the safety valve has a good anti-vibration capability. In addition, an adjustment ring is provided on the valve seat of the safety valve so that it can better adjust the return seat pressure.

The improved seawater safety valve adopts a new structural form, replacing the valve body, the spring and the sealing surface material. After the cold and hot state tests, its performance meets the requirements for use and solves the problems existing in the use of the original safety valve.