What are the functions of the various “holes” on the valve body of a safety valve?

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The inlet and outlet for the incoming gas, as well as the outlet for the discharged gas – the exhaust ports – the design of the safety valve body should aim to minimize the impact of medium deposition and dirt. Safety valves used for steam and liquids shall be provided with a drain hole at the lowest point where liquid collects, below the valve seat sealing surface. For safety valves with a nominal diameter greater than 65 mm, the diameter of their discharge orifice shall be no less than 9.5 mm ； For safety valves with a nominal diameter of 65 mm or less, the diameter of their discharge orifice must be at least 6.5 mm. Clause 4.4.5 of GB/T 12243-2021 \"Safety valves with direct spring loading\" also stipulates that, in order to prevent the accumulation of liquid, drain bolt holes shall be provided at locations below the valve seat sealing surface. When installing safety valves for steam and liquids, it is necessary to ensure that no fluid accumulates on the downstream side of the safety valve, as this will affect its performance and cause erosion of the spring and internal components. Many safety valves are equipped with a drain connection hole on their body; if this drain outlet is not used in practice, or if such a hole is not provided on the safety valve, a weep hole should be installed on the pipe as close as possible to the outlet of the safety valve. For diaphragm safety valves, a vent hole should be provided on the valve cover to ensure that the interior of the diaphragm is in communication with the atmosphere. In the case of flammable or corrosive media, this vent hole is connected to a safe location through a pipe, thereby preventing the release of these media in case the diaphragm is damaged and posing a hazard.   Balanced bellows safety valves come equipped with temporary dust-proof plastic plugs in the discharge hole (vent hole) at the time of manufacture. These plugs must be removed during normal operation; otherwise, pressure may build up inside the valve cover, leading to expansion and failure of the bellows. If the vent hole is artificially blocked, the same results will occur. Installing a ventilation elbow with a dust cover can prevent impurities from entering the valve chamber, thereby ensuring the proper operation of the safety valve. Note: Some manufacturers take into account the versatility of valve covers during design; the exhaust holes on the valve covers of other types of safety valves should be plugged with screw plugs to form a sealed valve cover, otherwise it will lead to leakage of the medium. The adjustment screw of the safety valve is usually located on the top or side of the safety valve, with the exact location depending on the model of the safety valve. Usually, an arrow indicating the direction of adjustment is marked on the adjustment screw; tightening the adjustment screw increases the opening pressure of the safety valve, while loosening it reduces that pressure. To prevent the mechanism for adjusting the spring compression (such as an adjustment screw) from loosening, as well as to avoid arbitrary changes to the already adjusted setting, the safety valve must be equipped with a anti-loosening device. Note: All external adjustment mechanisms of safety valves should be provided with lead-sealing areas so that they can be sealed with lead after successful debugging. After disassembly, reinstallation, and debugging, the lead seal should be applied again. The seal should be of a type that must be broken in order to make adjustments