According to another aspect, the present invention provides a diaphragm valve comprising: an actuator: a valve body formed with: an inlet passage; an outlet passage which is brought into communication with the inlet passage; a valve chamber which has an open upper end and is provided with a valve seat, the valve chamber being placed between the inlet passage and the outlet passage; a suck-back chamber which has an open lower end and is placed between the inlet passage and the outlet passage;Needle & Gauge Valves a through hole through which the valve chamber and the suck-back chamber are brought into communication with each other when the diaphragm valve is opened, a surrounding portion of the through hole forming the valve seat; a first diaphragm which integrally includes a valve element and an circumferential edge portion and is placed to have an outward curve with respect to the valve chamber and to close the open end of the valve chamber, the first diaphragm being deformable so that the valve element is brought into and out of contact with the valve seat by operation of the actuator; a second diaphragm which includes an circumferential edge portion and is placed to have an outward curve with respect to the suck-back chamber and to close the open end of the suck-back chamber; and a first retaining member which retains the circumferential edge portion of the first diaphragm against the valve body to fix the first diaphragm in place;Forged Steel Valves a second retaining member which retains the circumferential edge portion of the second diaphragm against the valve body to fix the second diaphragm in place; and a connecting rod which is movably placed through the through hole and connects the first and second diaphragms so that the first and second diaphragms are synchronously deformed by operation of the actuator.

According to the diaphragm valve of the invention, the first and second diaphragms integrally are connected by the connecting rod to be synchronously deformed in association of the opening/closing operation of the valve by the actuator so that the volume of the valve chamber and the volume of the suck-back chamber are changed equally but increased and decreased inversely. Therefore, for example, the diaphragm valve stops discharge of the liquid while performing suck-back of the liquid by an adequate amount from a nozzle tip connected to the outlet passage.

In the diaphragm valve of the invention, furthermore, the first and second diaphragms are placed in the valve chamber and the suck-back chamber respectively so that each diaphragm is curved outwardly.WATER POWER CONTROL VALVE It is therefore possible to prevent crushing of a film portion of each diaphragm by the pressure of the liquid allowed to flow in the passage in the valve body. As a result, the durability of the second diaphragm can be increased. The diaphragm valve does not need frequent replacement of the diaphragm as compared with the conventional diaphragm valve.

The diaphragm valve of the present invention is structured such that the circumferential edge portions of the first and second diaphragms are tightly retained by the retaining members for assembling those diaphragms in the valve body in which the passages are formed. Consequently, the assembling can be facilitated, a manufacturing cost can be reduced, and replacement of components can easily be made.

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