Thermostatic mixing valve with thermostat failure compensation

Abstract

A thermally controlled mixing valve assembly includes a valve body having a hot fluid inlet, a cold fluid inlet, a fluid mixing chamber, and a fluid outlet in communication with the mixing chamber. A thermally responsive control member, or thermostat, is disposed within the mixing chamber. A cylindrical liner is situated within the valve body with slots for cold fluid flow and an opening at the bottom of the liner for hot fluid flow. Concentrically located piston and valve disc are connected through an actuator to the thermostat so that the piston and disc move according to the thermostat response to the fluid temperature in the mixing chamber. The piston controls flow through the cold fluid slots while the disc controls flow through the hot fluid opening in the liner. Also connected to the actuator is a back-seat which is situated opposite the valve disc across the hot fluid opening. A spring biases the back-seat, as well as the actuator assembly, upward against the downward motion of the thermostat. In the event of a failure of the thermostat, the bias spring pushes the back-seat upward until the back-seat closes the hot fluid opening in the liner, thereby terminating hot fluid flow into the mixing chamber. Bleed orifices may be provided in the back-seat to permit restricted hot fluid flow. The liner and piston dimensions can be calibrated to permit restricted cold fluid flow even when the liner covers the cold fluid slots in the liner.