Type selection, structural principle and scope of

Type selection, structural principle and scope of application of safety valves for industrial boilers

at present, there are many kinds of safety valves commonly used in industrial boiler houses in China: lever type, spring type, dead weight type, pulse type and composite type

I. lever type safety valve

lever type safety valve is divided into single lever type and double lever type. Because they act on the valve core through the heavy torque of lever and heavy hammer, they are also called heavy hammer safety valve to balance the steam (water) pressure

lever type (heavy hammer type) safety valve is mainly composed of valve core, valve seat, lever, heavy hammer, limit device, etc. It uses the weight of the heavy hammer, presses the valve core on the valve seat through the lever, and moves the position of the heavy hammer to change the size of the heavy torque, so as to adjust the opening pressure of the safety valve, including biomedical valve. When the boiler pressure exceeds the pressure exerted by the heavy hammer on the upper part of the valve core, the valve core is jacked up and left the valve seat, and the steam is discharged. When the boiler pressure is lower than the pressure exerted by the heavy hammer on the upper part of the valve core, the valve core drops and the boiler stops steam exhaust

this safety valve has simple structure, convenient adjustment and reliable working performance, so it is widely used in boilers. Generally, the horizontal bar safety valve is suitable for low-pressure boilers, and the parallel bar safety valve is suitable for medium and high-pressure boilers

II. Spring safety valve

the main parameters of spring safety valve are opening pressure and steam exhaust capacity, which depends on the diameter of valve seat and the lifting height of valve core. Due to the different lifting height, it can be divided into three types: Micro open, medium open and full open safety valves

the spring-loaded safety valve has compact structure, small volume and light weight; It has good tightness, convenient adjustment, can withstand vibration, and there is little leakage. Therefore, it is sensitive and reliable. It has the widest scope of application and is the most commonly used one

III. dead weight safety valve

it is composed of valve core but can only be increased with the increase of stress, valve seat, annular iron plate, valve cover, anti flying screw, etc

this kind of safety valve mainly uses the weight of the annular iron sheet to make the valve core press on the valve seat. When the boiler pressure exceeds the pressure of the rebound method of the iron sheet acting on the upper part of the valve core, the valve core is jacked up and the steam is discharged. When the boiler pressure drops below the pressure of the iron sheet acting on the upper part of the valve core, the valve core drops and stops steam exhaust

the dead weight safety valve is simple in structure and easy to manufacture, but it is bulky and bulky It is difficult to adjust and has low sensitivity. It is only applicable to low-pressure small boilers. At present, industrial boilers are rarely used in China

IV. pulse safety valve

it is mainly composed of pulse spring safety valve, impulse conduit main safety valve, etc

the working principle of the pulse safety valve is: when the pressure of the steam drum or superheater exceeds the specified value, the steam enters the pulse spring safety valve through the impulse conduit and valve, and the valve core is pushed open. Through the pulse spring safety valve, the steam enters the upper part of the piston of the main safety valve again, so that the piston moves downward, opens the main safety valve, and the steam is discharged and relieved. When the pressure returns to the normal pressure, the pulse spring safety valve closes, interrupting the steam on the upper part of the main safety valve piston, and the main safety valve spool closes under the action of steam and spring

this safety valve device has an electrical control system as electrical protection. When the boiler is overpressured, the contact of the pneumatic pressure gauge is closed, and the electromagnet of the pulse spring safety valve is connected to make it work and open the valve; When the reseating pressure is too low or the valve fails, you can also operate the electrical control switch to turn on the electromagnet coil and turn off the electromagnet to close the valve

the impulse of this safety valve in operation is connected to the valve on the conduit, which should be kept fully open, so lead sealing should be added. This safety valve is applicable to high-pressure boilers

v. composite safety valve

composite safety valve is composed of two identical or different safety valves, which are connected to one valve seat at the same time to reduce the number of openings