Common safety valves generally include the following types:

1. They can be categorized into heavy hammer lever safety valves, spring-loaded, and control types based on their overall and loading structure forms.

2. Valves can be categorized into two types of safety valves based on the ratio of the lift height of the valve disc to the valve's flow diameter: micro-lift and full-lift.

3. Gas emissions can be categorized into three types: fully enclosed, semi-enclosed, and open.

The term "safety valve" commonly refers to the more prevalent spring-loaded type.

The selection of safety valves should be considered from the following aspects:

1. The structural form primarily depends on the equipment's process conditions and working medium characteristics. Generally, spring-loaded safety valves are preferred for boilers and pressure vessels. If the equipment medium is toxic, flammable, or explosive, a sealed safety valve should be selected.

2. For medium and low-pressure vessels with large safety relief volumes and small wall thickness corrosion reserve, full-open safety valves are recommended.

3. Pressure Range: Each safety valve has a specific working pressure range. When selecting, choose a suitable safety valve based on the equipment's maximum allowable working pressure.

4. The discharge volume must be greater than the equipment's safe relief volume to ensure that during overpressure situations, the safety valve can open promptly to discharge a portion of the medium, preventing further pressure increase. For boilers, the total discharge volume of the safety valve must exceed the maximum continuous evaporation rate. For pressure vessels, the discharge volume of the safety valve must be greater than or equal to the safe relief volume of the pressure vessel.

Safety valves are important safety accessories on special equipment, and their installation also requires certain specifications. Below are some common considerations:

1. Boilers with a rated evaporation capacity greater than 0.5t/h must be equipped with at least two safety valves; boilers with a rated evaporation capacity of 0.5t/h or less must have at least one safety valve. Safety valves must be installed at the outlet of the divided economizer and at the outlet of the steam superheater.

2. Safety valves should be vertically mounted at a high position on the boiler or the header. There should be no outlet pipes or valves for extracting steam between the safety valve and the boiler drum or header.

3. The lever safety valve must have a device to prevent the heavy hammer from moving independently and a guide frame to restrict the lever from derailing. The spring safety valve must have a lifting handle and a device to prevent the adjustment screw from being randomly twisted.

4. For boilers with a rated steam pressure of 3.82MPa or less, the safety valve throat diameter should not be less than 25mm. For boilers with a rated steam pressure greater than 3.82MPa, the safety valve throat diameter should not be less than 20mm.

5. The connecting pipe between the safety valve and the boiler should have an area not less than the inlet area of the safety valve. If several safety valves are installed together on a short pipe that is directly connected to the drum, the passage area of the short pipe should not be less than 1.25 times the total exhaust area of all the safety valves.

6. Safety valves should generally be equipped with exhaust pipes, which should lead directly to a safe location and have sufficient cross-sectional area to ensure smooth exhaust. The bottom of the safety valve exhaust pipe should have a provision for a drain pipe leading to a safe location, and no valves should be installed on either the exhaust pipe or the drain pipe.