The purpose of GATE VALVESof this type, as compared with more conventional single- Gate Valves, is that they seal against a predominant pressure on either side and exclude debris which might otherwise collect in the cavity. Also, they permit the cavity to be pressure-tested without the need for plugs in each end of the body flowway. However, because of friction between the outer sides of both gates and the body seating surfaces, due to pressure in the cavity, as well as compression springs or the like which may be disposed between their inner sides, the force required to operate gate valves of this type is normally double that required to operate a single- gated valve.

In an effort to overcome this problem, double gate valves have been proposed in which the outer sides of the gates are tapered to permit them to be wedged tightly between similarly tapered sides in the valve body cavity as the gates are moved to closed position. More particularly, the actuator for the gates permits them to be operated independently of one another so that one may be moved into and out of opened and closed positions before the other. Although this permits the second gate to be so moved to open position by overcoming only the friction between its outer side and its seating surface, in order to move the first gate from its closed position, it is necessary to exert a large force to cause its outer side to "break away" from the seating surface in the valve body.

The primary object of this invention is to provide a valve of this type having parallel side gates which is of such construction as to require considerably less force to open the gates and, more particularly, in which the actuator need only provide the force which would be required to open a gate valve having a single gate.Cast Gate, Globe, Check Valves

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