Drain valve

An automatic drain valve for use in combination with a fluid system having pressurized gas system and a liquid collection reservoir, said automatic drain valve, comprising:

• a housing having:
• a) a float chamber,
• b) a piston chamber positioned lower than the float chamber extending between a head end and a seat end,
• c) a plenum fluidly communicating with the seat end of the piston chamber through a valve seat,
• d) a liquid inlet passage adapted for fluid communication with the liquid collection reservoir and extending to a liquid inlet port adjacent the valve seat,
• e) a liquid outlet passage extending from a liquid outlet port at the plenum to a liquid outlet opening in the housing,
• f) a float chamber passage fluidly communicating the float chamber with the liquid inlet passage, and
• g) a pressurized gas inlet passage adapted for fluid communication with the pressurized gas system and extending to a gas inlet port at the float chamber;
• a tube extending upward into the float chamber and having a tube passage extending downward from an upper port at an upper end of the tube and fluidly communicating with the piston chamber;
• an annular float having a central opening sized for receiving the tube, the float being buoyant in liquid so the float moves up and down along the tube as the float rises and falls in the float chamber, respectively, in response to liquid flowing into and out of the float chamber;
• a seal body operatively connected to the float and positioned above the upper end of the tube so the seal body rests on the upper end of the tube when liquid is absent from the float chamber to block the upper port of the tube passage to prevent pressurized gas in the float chamber from entering the tube passage and rises away from the upper end of the tube passage when a predetermined amount of liquid is present in the float chamber to unblock the upper port of the tube passage to permit pressurized gas in the float chamber to pass through the tube passage to the piston chamber;
• and
• a piston slidably mounted in the piston chamber and biased toward the seat end of the piston chamber, the piston including:
• a) a head positioned between the gas inlet port and the head end of the piston chamber so the piston moves away from the valve seat when pressurized gas enters the piston chamber through the gas inlet port, and
• b) a valve element operatively connected to the head, the valve element moving within the valve seat as the piston head moves away from the valve seat to expose the liquid inlet port and allow liquid to flow from the liquid inlet passage through the plenum and into the liquid outlet passage.