Abstract: The present invention provides a diaphragm having a generally truncated conical body for use in diaphragm actuating piston assemblies, such diaphragm comprising at least one layer of an elastomeric material selected from a group consisting of natural rubber, synthetic rubber, fabric reinforced rubber and mixtures thereof. There is further a first central opening, having a first predetermined diameter, disposed at a first edge of such diaphragm for mounting on a diaphragm actuating piston, such first central opening being formed by a bead like portion having a second predetermined diameter. There is further included a second central opening, having a third predetermined diameter, disposed at a second edge of such diaphragm for mounting on a body portion of such diaphragm actuating piston assembly, such second central opening being formed by a bead like portion having a fourth predetermined diameter.