Installation Precautions
Safety valves are important safety accessories on special equipment, and their installation also has corresponding requirements. Here are some common items:
1. For boilers with rated evaporation greater than 0.5t/h, install at least two safety valves: boilers with a rated evaporation of less than or equal to 0.5t/h, at least one safety valve. Safety valves must be installed at the outlet of the separable economizer and at the outlet of the steam superheater.
2. The safety valve should be installed vertically at the highest position of the potter and the header. Between the safety valve and the drum or header, the outlet pipe and valve for steam should not be installed.
3. The lever type safety valve shall have a device for preventing the weight from moving by itself and a guide frame for restricting the deviance of the lever. The spring type safety valve shall have a device for lifting the handle and preventing the adjustment screw from being twisted.
4. For boilers with rated steam pressure less than or equal to 3.82 MPa, the safety valve throat diameter should not be less than 25 mm: For boilers with rated steam pressure greater than 3.82 MPa, the safety valve throat diameter should not be less than 20 mm.
5. The connecting pipe of the safety valve and the boiler shall have a cross-sectional area not less than the inlet cross-sectional area of ​​the safety valve. If several safety valves are installed together on a short pipe directly connected to the drum, the cross-sectional area of ​​the short pipe should not be 1.25 times that of all safety valves.
6. Safety valves should generally be equipped with exhaust pipes. The exhaust pipes should be straight to a safe place and have sufficient cross-sectional area to ensure unobstructed exhaust. The bottom of the safety valve exhaust pipe should be filled with a drain pipe that is connected to a safe place, and no valve is allowed on the exhaust pipe and the drain pipe.
Classification method of safety valve
Our common safety valves generally have the following types:
1. According to the overall structure and the loading structure, it can be divided into three types: heavy hammer lever type safety valve, spring type and control type;
2. According to the ratio of the valve opening height to the valve circulation diameter, it can be divided into two types: micro-open type and full-open type safety valve;
3. According to the way of gas discharge, it can be divided into three types: fully enclosed, semi-closed and open.
The so-called safety valve generally refers to the more common spring-type safety valve.
What should be the contents of the safety valve factory data
The safety valve must be shipped with the product quality certificate and a strong metal nameplate on the product. The following contents should be stated on the nameplate:
(1) Manufacturing unit name, manufacturing license number;
(2) product number;
(3) Model, type, specification;
(4) Nominal pressure, MPa;
(5) valve seat diameter, mm;
(6) Emission coefficient;
(7) Year of manufacture;
(8) Inspection mark.
The applicable media and temperature should also be indicated on the nameplate of some safety valves.
Safety valve selection
The selection of safety valves should be considered from the following aspects:
1. The structural form depends mainly on the process conditions of the equipment as well as the working medium and characteristics. Generally, spring type safety valves are used for boilers and pressure vessels. If the equipment medium is toxic, flammable and explosive, a closed safety valve should be selected.
2. Fully open safety valves should be used for boilers, high-pressure vessels, medium and low-pressure vessels with large safety discharge and small wall thickness corrosion allowance.
3, pressure range, each safety valve has a certain working pressure range. When selecting, the appropriate safety valve should be selected according to the maximum allowable working pressure of the equipment.
4. The discharge amount must be greater than the safety discharge amount of the equipment. In this way, when the overpressure is exceeded, the safety valve is opened to discharge part of the medium in time to prevent the pressure from continuing to rise. For boilers, the total displacement of the safety valve must be greater than the maximum continuous evaporation. For pressure vessels, the displacement of the safety valve must be greater than or equal to the safety relief of the pressure vessel.
Safety valve common fault
When the safety valve is used normally and verified, various failures are often occurred and the main cause of the failure is caused by improper design, manufacture, selection or use. If these faults are not eliminated in time, it will affect the efficacy and life of the valve, and even fail to provide safety protection. Common faults and elimination methods are as follows:
1. Leakage. Under the normal working pressure of the equipment, leakage exceeding the allowable degree occurs between the valve flap and the seat sealing surface. The reason is that there is dirt between the valve flap and the sealing surface of the valve seat. The valve can be opened several times with a lift wrench to flush the dirt; the sealing surface is damaged. It should be repaired by grinding or grinding after grinding according to the degree of damage; the stem is bent, tilted or the lever and the fulcrum are skewed, so that the valve core and the valve disc are misaligned. Should be reassembled or replaced; the spring elasticity is reduced or loses its elasticity. Measures such as replacing the spring and re-adjusting the opening pressure should be taken.
2. It does not open when the pressure is specified. The reason for this is that the pressure is not accurate. The amount of compression of the spring or the position of the weight should be readjusted; the disc is stuck to the seat. The safety valve should be manually deflated or drained periodically; the lever of the lever safety valve is stuck or the weight is moved. The weight position should be re-adjusted and the lever moved freely.
3. Open below the specified pressure. Mainly the fixed pressure is not allowed; the spring aging elasticity decreases. The adjusting screw or the spring should be properly tightened.
4. The pressure continues to rise after exhaust. This is mainly because the safety relief valve of the selected safety valve displacement device should be re-selected with a suitable safety valve; the center line of the valve stem is not correct or the spring is rusted, so that the valve flap cannot be opened to the proper height, and the valve stem should be reassembled. Or replace the spring; if the exhaust pipe is not enough, take the exhaust pipe that meets the safe discharge area.
5. The valve flap jumps or vibrates. Mainly due to the spring stiffness is too large. Should use the appropriate stiffness of the spring; improper adjustment of the adjustment ring, so that the return pressure is too high. The position of the adjustment ring should be readjusted; the resistance of the discharge pipe is too large, causing excessive discharge back pressure. The discharge pipe resistance should be reduced.
6. The valve flap will not return to the seat after discharge. This is mainly caused by the spring-bending valve stem, the valve flap is not installed properly, or is stuck. Should be reassembled.
Safety valve is different from other valves
The safety valve is an important accessory for safety protection of pressure limiting and pressure relief on special equipment (boilers, pressure vessels, pressure pipes, etc.). The reliability and performance of its actions are directly related to the safety of equipment and people, and are closely related to energy conservation and environmental protection. However, safety valves are sometimes confused with other valves that can perform similar functions, so the following points should be clarified:
1. The safety valve is directly installed on special equipment, and its management and performance must meet the requirements of the relevant departments of quality and technical supervision departments and special equipment. It is an automatic pressure relief device driven by static pressure of the pre-valve medium. It is characterized by a full opening action with a sudden opening. For gas or steam applications.
2. The structure and performance of the relief valve are similar to those of the safety valve. They automatically discharge the internal medium when the opening pressure is exceeded to ensure the safety of the equipment. The relief valve, also known as the relief valve, is an automatic pressure relief device that is driven by the static pressure of the medium in front of the valve. It opens proportionally as the pressure exceeds the increase in opening force. Mainly used for fluid applications.
3. Safety relief valve, also known as safety relief valve, is an automatic pressure relief device driven by medium pressure. It is suitable for both safety valves and bleed valves depending on the application.
4. The discharge of the safety valve is required, and there is no clear requirement for the relief valve. In general, safety valves should be more reliable than bleed valves.
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