The semi-fixed foam fire extinguishing unit, also known as the trolley-type foam fire extinguishing unit, is a new type of portable foam fire extinguishing unit. It operates quickly and easily with high reliability and is used to extinguish Class A, B, and C non-aqueous liquid fires.

Composed mainly of foam liquid storage tanks, foam guns, pipeline proportioning mixers, hoses, and handles with bottom wheels. Simply connect the fire hoses provided with the unit to fire hydrants and other water supply equipment for use. Place in a strategic location for efficient fire extinguishing. As a supplement to fixed fire extinguishing systems, it can protect multiple devices within the protected area.

The semi-fixed foam fire extinguishing system connects the pipe union interfaces at both ends of its pipeline-type proportioning mixer to the fire hose and to a pressure water source. When water at a pressure of not less than 0.6 MPa flows at a high velocity through the nozzle of the proportioning mixer, due to the lateral movement and diffusion of jet particles, a vacuum (negative pressure) is formed inside the mixer. As a result, foam liquid from the foam liquid storage tank is forced into the mixer through the suction tube by atmospheric pressure, mixing with the pressure water at a predetermined ratio to form a foam mixture. When the pressurized mixture reaches the foam gun, the gun's performance draws in a certain amount of air, causing the foam mixture to foam and spray over the burning liquid surface, thereby achieving the foam fire extinguishing effect.