Introduction and Application of Safety Valve

Safety valve in the pipeline, when the medium pressure exceeds the specified value, the valve will automatically open, discharging excess media;

When the working pressure is restored to the prescribed value, it is automatically closed.

I. Terminology commonly used in safety valves

1. Opening pressure: When the medium pressure rises to the prescribed pressure value, the valve disc opens automatically and the medium sprays out rapidly.

The pressure at the valve inlet is called the opening pressure.

2. Discharge pressure; After disc opening, if medium pressure in equipment pipeline continues to rise, disc should be fully opened, discharge rating

Medium discharge, the pressure at the valve inlet is called discharge pressure.

3. Closing pressure: When the safety valve is opened and some medium is discharged, the pressure in the equipment pipeline gradually decreases, and when it is reduced to

When the working pressure is less than the predetermined value, the disc closes, the opening height is zero, and the medium stops flowing out. Pressure at the inlet of the valve

Force is called closing pressure, also known as return pressure.

4. Work pressure; The medium pressure in the normal work of equipment is called work pressure. At this time, the safety valve is in a sealed state.

5. Discharge: When the disc of discharging medium is in full open state, the discharging of medium measured from the outlet of the valve in unit time

Output, known as valve displacement.

Types of Safety Valves

1. According to the structure of safety valve.

(1) Heavy hammer (lever) relief valve: Use lever and weight to balance disc pressure. Hammer relief valve by moving the hammer

Position or change the weight of the hammer to adjust the pressure. Its advantages lie in its simple structure, while its disadvantages lie in its bulky and low recoil force. this

Safety valves of various structures can only be used on fixed equipment.  (2) Spring relief valve: The pressure of the compression spring is used to balance the pressure of the valve disc and seal it. Spring relief valve relies on regulation

Spring compression to adjust the pressure. It has the advantages of small size, light weight, high sensitivity and installation position.

The position is not strictly limited; the disadvantage is that the force acting on the stem varies with the spring deformation. At the same time, we must pay attention to the heat insulation and heat dissipation of the spring. Spring force of spring type safety valve should not exceed 2000 kg. Because the spring is too big and too hard

Not suitable for accurate work.

(3) Pulse relief valve: Pulse relief valve consists of main valve and auxiliary valve. The main valve is connected with the auxiliary valve through the pulse of the auxiliary valve.

The impulse action drives the action of the main valve.

Pulse relief valves are usually used in large caliber pipelines. Because large caliber safety valves such as heavy hammer or spring type are not used.

Adapt. Pulse relief valve consists of main valve and auxiliary valve.  When the medium in the pipeline exceeds the rated value, the auxiliary valve first acts.

Drive the main valve action, discharging excess media.

2. According to the ratio of the maximum opening height of the relief valve disc to the diameter of the seat, it can be divided into two parts:

_Micro-opening: The opening height of the disc is 1/20-1/10 of the seat diameter. Because of the small opening height, the structure and geometry of the valve are not as strict as that of the all-open type. It is convenient to design, manufacture, repair and test, but its efficiency is low.

(2) Full-open: The opening height of the disc is 1/4-1/3 of the seat diameter.

Full-open safety valve relies on the expansion impulse of the gas medium to make the valve disc rise sufficiently and discharge capacity. It makes use of the upper and lower control rings of the disc and seat to form a pressure zone between the disc and the upper and lower throttle rings, so that the disc rises to the required opening height and the prescribed return pressure. This kind of structure has high sensitivity and many uses, but it is difficult to adjust the position of the upper and lower adjusting rings, so it should be carefully used.

3. According to the structure of the relief valve body, it can be divided into two parts.

(1) Fully enclosed type: when discharging medium, it does not leak out, but all is discharged through the discharge pipe.

(2) Semi-closed: When discharging medium, one part is discharged through the discharge pipe, and the other part leaks out from the valve cover and stem.

(3) Open type: When discharging medium, it will not lead outside, but will be discharged directly by petition of valve disc.