Drain valve

An evaporating cooler comprising:

• a reservoir for holding water at atmospheric pressure, said water being used to keep a filter medium saturated with water;
• a water supply line for replenishing the reservoir with fresh water;
• and
• a dump valve for draining the reservoir of water, the valve including:
• a housing mounted within the reservoir and having a first inlet for supplying water under pressure to the housing, an outlet for draining water from the reservoir and a second inlet for allowing water from the reservoir to flow into said housing and out through said outlet;
• a plunger slidably received in said housing and adapted to move between an open position in which said outlet is open and water can drain out, and a closed position in which said plunger closes said outlet and said water is prevented from draining out, and wherein when water is supplied to the housing under pressure it causes said plunger to move from its open to its closed position;
• biasing means provided within the housing for biasing the plunger to its open position, wherein the pressure of the water supplied to the housing must overcome the force of said biasing means in order to move the plunger from its open to its closed position and wherein when the pressure of the water supplied to the housing is reduced sufficiently, said biasing means automatically moves the plunger to its open position thereby allowing the water to drain from the reservoir;
• and
• pressure relief means, fitted in said plunger, including a passage through which a controlled quantity of said water under pressure escapes continuously into the reservoir to relieve the pressure of water acting on the plunger within the housing whereby, in use, when the supply of water to the housing is cut off the pressure of water within the housing is reduced sufficiently by said pressure relief means to allow the biasing means to automatically move the plunger to its open position.