Double check backflow preventer with improved toggle linkage check valve

A backflow preventer valve comprising:

• a housing having an inlet and an outlet;
• a first valve assembly disposed within said housing and including
• a first sealing plug adapted for movement between a first, closed position for preventing flow of liquid between said inlet and said outlet, and a second, open position for substantially permitting flow of liquid between said inlet and said outlet, and
• a first spring assembly removably disposed within said first valve assembly, said first spring assembly contacting said first sealing plug and biasing said first sealing plug towards said first, closed position, said first spring assembly comprising a first rod member and first means for biasing said first rod member toward said first sealing plug, and
• a second valve assembly disposed between said first valve assembly and said outlet, said second valve assembly including
• a second sealing plug adapted for movement between a first, closed position for preventing flow of liquid between said inlet and said outlet, and a second, open position for substantially permitting flow of liquid between said inlet and said outlet, and
• a second spring assembly removably disposed within said second valve assembly, said second spring assembly contacting said second sealing plug and biasing said second sealing plug towards said first, closed position, said second spring assembly comprising a second rod member and second means for biasing said second rod member toward said second sealing plug,
• in said second, open position of said first sealing plug, said first rod member lies at a first acute angle to a plane of said first sealing plug, and
• in said second, open position of said second sealing plug, said second rod member lies at a second acute angle to a plane of said second sealing plug.