The safety valve is a kind of safety guarantee for the equipment and the staff. The safety valve of the air compressor can use hot water, steam boiler, high pressure water and other methods to play the effect of protective measures. In order to ensure that the performance of the air compressor safety valve does not change, the air compressor safety valve must be regularly maintained and cleaned to prevent dust, water vapor, stains, etc. from entering the valve body and affecting the performance of the valve body.
What aspects of the work need to be done in cleaning and maintenance?
1. Monthly maintenance items
It is necessary to maintain the safety valve of the air compressor every month, and the maintenance personnel must be professional personnel. Otherwise, the valve body will have problems during the maintenance process. Monthly maintenance content The organic oil filter and the oil and gas separator are cleaned, and the air filter also needs to be cleaned. The cooling equipment also needs to be lubricated, and check all parts of the pump body to eliminate potential safety hazards, and clean the valve body.
2. Annual maintenance items
The annual maintenance item is that z* of the air compressor safety valve needs to be maintained. This is different from the monthly, and the inspection is more extensive. Regarding the annual maintenance items, the oil and water lines need to be cleaned, and the oil and steam lines need to be cleaned, and the various parts of the valve body should be adjusted to check whether there are problems. If there are problem parts, they need to be replaced in time.
Further reading
Classification and characteristics of safety valves
Divided according to the overall structure and loading mechanism
According to the overall structure and loading mechanism, the safety valve can be divided into three types: heavy hammer lever type, spring type and pulse type.
Among the three types of safety valves, spring-loaded safety valves are more commonly used.
1. Heavy hammer lever safety valve
The heavy hammer lever safety valve uses a heavy hammer and a lever to balance the force acting on the disc.
According to the principle of lever, it can use a heavy hammer with a smaller mass to obtain a larger force through the increase of the lever, and adjust the opening pressure of the safety valve by moving the position of the heavy hammer (or changing the mass of the heavy hammer).
2. Spring-loaded safety valve
The spring-loaded safety valve uses the force of a compression spring to balance the force acting on the disc.
The compression amount of the coil spring can be adjusted by turning the adjusting nut on it, and the opening (setting) pressure of the safety valve can be corrected according to the need by using this structure.
3. Pulse safety valve
The impulse safety valve consists of a main valve and an auxiliary valve. The main valve is driven by the impulse action of the auxiliary valve. Its structure is complicated, and it is usually only suitable for boilers and pressure vessels with a large amount of safety relief.
Divided by different media discharge methods
According to different media discharge methods, safety valves can be divided into three types: fully enclosed, semi-enclosed and open.
1. Fully enclosed safety valve
When the fully enclosed safety valve is exhausted, all the gas is exhausted through the exhaust pipe, and the medium cannot leak out from time to time. It is mainly used for the poisonous medium. Flammable gas container.
2. Semi-closed safety valve
Part of the gas discharged by the semi-closed safety valve passes through the exhaust pipe, and part of it leaks from the gap between the valve cover and the valve stem. It is mostly used in containers where the medium is a gas that does not pollute the environment.
3. Open safety valve
The valve cover of the open safety valve is open to make the spring chamber communicate with the atmosphere, which helps to reduce the temperature of the spring. It is mainly suitable for containers with steam as the medium and high-temperature gas that does not pollute the atmosphere.
Divided by the ratio of the maximum height of the valve flap to the flow channel
According to the ratio of the maximum opening height of the valve disc to the diameter of the safety valve flow path, safety valves are mainly divided into two types: micro-opening safety valves and full-opening safety valves.
1. Micro-lift safety valve
The opening height of the micro-opening safety valve is less than 1/4 of the diameter of the flow channel, usually 1/40 to 1/20 of the diameter of the flow channel.
The action process of the micro-lift safety valve is proportional action, which is mainly used in liquid occasions, and sometimes also used in gas occasions with small emissions.
2. Full lift safety valve
The opening height of the full-open safety valve is greater than or equal to 1/4 of the diameter of the flow channel. The discharge area of the full lift safety valve is the small cross-sectional area of the seat throat z*.
The action process is a two-stage action type, which must be fully opened with the help of a lifting mechanism. The full-lift safety valve is mainly used for occasions with gas media.
Divided by principle of action
According to the principle of action, it can be divided into direct-acting safety valves and indirect-acting safety valves.
1. Direct acting safety valve
The direct-acting safety valve is opened under the direct action of the working medium, that is, relying on the working medium pressure to overcome the mechanical load imposed on the valve clack by the loading mechanism, so that the valve opens.
This kind of safety valve has the advantages of simple structure, rapid action and good reliability. However, due to the structural loading, the load size is limited and cannot be used in high pressure and large diameter occasions.
2. Indirect acting safety valve
Such safety valves can be divided into pilot safety valves and safety valves with power assist devices.
The pilot-operated safety valve is driven or controlled by the medium discharged from the pilot valve. The pilot valve itself is a direct-acting safety valve, and sometimes other forms of valve are used.
The pilot-operated safety valve is suitable for high pressure and large diameter occasions. The main valve of the pilot-operated safety valve can also be designed to rely on the working medium to seal, or it can impose a much larger mechanical load on the disc than the direct-acting safety valve, so it has a good sealing performance.
At the same time, its actions are rarely affected by back pressure. The disadvantage of this kind of safety valve is that its reliability is related to the main valve and pilot valve, the action is not as fast and reliable as the direct-acting safety valve, and the structure is more complicated.
The safety valve with power assist device uses a power assist device to force the safety valve to open when the opening pressure is lower than the normal opening pressure.
This kind of safety valve is suitable for occasions where the opening pressure is very close to the working pressure, or where the safety valve needs to be opened regularly for inspection or blowing off sticky or frozen media. At the same time, it also provides a means of forcibly opening the safety valve in an emergency.
Selection of safety valve
Determination of various parameters of safety valve
1. Determine the nominal pressure of the safety valve.
The nominal pressure is selected according to the valve material, working temperature and z*max working pressure.
2. Determine the working pressure level of the safety valve.
According to the design pressure and design temperature of the pressure vessel, the working pressure level is selected. The working pressure of the safety valve and the working pressure level of the spring have different meanings.
The working pressure of the safety valve refers to the static pressure in front of the valve during the normal operation of the safety valve, which is the same as the working pressure of the protected system or equipment.
The working pressure level of a spring refers to the allowable working pressure range of a spring. Within this pressure range, the opening pressure (ie, the set pressure) of the safety valve can be adjusted by changing the preload compression of the spring.
The safety valve of the same nominal pressure can be divided into a variety of different working pressure levels according to the spring design requirements.
When selecting a safety valve, the working pressure level of the valve should be determined according to the required opening pressure value.
3. Determine the discharge pressure Pd of the safety valve
The discharge pressure of the safety valve is generally 1.1 times the set pressure (opening pressure), and the discharge pressure of the steam boiler safety valve is 1.03 times the set pressure.
4. Determine the diameter of the safety valve
According to the necessary discharge volume, the discharge capacity of the safety valve is greater than or equal to the necessary discharge volume.
The amount of emissions required by the protected system refers to the amount that must be eliminated to prevent overpressure when abnormal overpressure occurs in the system. It is determined by the working conditions and capacity of the system or equipment, as well as factors that may cause overpressure.
5. Determination of material
When selecting the material of the safety valve, various factors such as the working temperature, working pressure, performance of the medium and the manufacturability and economy of the material should be considered.
Determination of the special structure of the safety valve
For safety valves for steam with an opening pressure greater than 3MPa or safety valves for gases whose medium temperature exceeds 320℃, safety valves with radiators (fins) should be used.
For safety valves that bear additional back pressure, and the back pressure variation exceeds 10% of the set pressure, bellows safety valves should be selected.
In addition, for safety valves that use corrosive media, in order to prevent the spring and guiding mechanism from being corroded by the media, bellows safety valves should also be selected.
For flammable, extremely toxic or highly hazardous media, a closed safety valve must be used. If a lifting mechanism is required, a closed safety valve with a wrench should be used.
For non-hazardous media such as air, hot water above 60°C or steam, a safety valve with a wrench should be used.
The liquefaction tank (tank) truck should adopt a built-in safety valve.
For working conditions with large discharge volume, full lift type should be used; for working conditions with stable working pressure and small discharge volume, micro lift type should be selected; for high pressure and large discharge volume working conditions, indirect starting type should be selected, such as Impulse safety valve; two or more safety valves should be provided for vessels with a length of more than 6m.
For fixed containers with low working pressure, deadweight (pressure cooker) or lever-weight safety valves can be used. Mobile equipment should use spring-loaded safety valves.
For thick media and easy to block, a series combination relief device of safety valve and bursting disc should be selected.