③ Solenoid valve: it is divided into single electric control solenoid valve and dual electric control solenoid valve.
Single electric solenoid valve: the valve is opened or closed when power is supplied, and closed or opened when power is cut off.
Dual electric control solenoid valve: when one coil is powered on, the valve opens, and when the other coil is powered on, the valve closes.

Characteristics of non-metallic shrink joint types
The non-metallic contraction joint, also known as non-metallic compensator and fabric compensator, is a kind of compensator. The data are mainly fiber fabrics, rubber, and other high-temperature resistant data. It can compensate the vibration of fan and air duct operation and pipeline deformation.
The improvement of maintenance equipment requires the compensation of non-metallic contraction joints. The main reason is that this kind of compensator is easy to install and has strong applicability, and the application time is longer than that of ordinary contraction joints. In terms of basic structure, it can be divided into skin, stainless steel wire mesh, insulation cotton, insulation filler layer, frame and baffle.
Skin plays an important role in non-metallic contraction joints, which can absorb shrinkage and avoid leakage of air and rain. Stainless steel wire is mainly used to prevent circulating magazines from entering the contraction joint and avoid the loss of thermal insulation data. All structures have a strong compensation effect, and none is dispensable.