Why does opening the liquefied gas valve make a hissing sound?

Normal, this is because the structure of the pressure reducing valve is an air chamber, and the air chamber is sealed with rubber sheets. When it was first opened, high pressure entered and the rubber sheet was washed. Then the valve connected with the rubber sheet can be depressurized according to different degrees of high pressure. Silk noise is caused by the air above the rubber being pressed into the atmosphere and coming out of a small hole called the breathing hole of the pressure reducing valve.