The QYL is a two-phase flow steam trap equipped with automatic liquid level control. It utilizes a phase-change signal tube to detect vapor/liquid phase transitions. When the liquid level rises to the phase-change tube port, the signal shifts from vapor-phase to liquid-phase, which in turn controls the throttle throat to maintain optimal condensate discharge and water level. The unit includes an inlet gate valve, bypass valve, steam valve, heater, and connecting tube, and achieves a back pressure ratio of up to 95%.