Pressure-driven metered mixing dispensing pumps and methods

A method of operating a pressure-driven metered mixing dispensing pump having first, second and third chambers at least partially defined by a piston, the method comprising:

• supplying first fluid into the first chamber to eject second fluid, different from the first fluid, from the second chamber into the third chamber when the piston is moved in a first direction;
• ejecting at least some of the first fluid from the first chamber into the third chamber to form a mixture of the first and second fluids when the piston is moved in a second direction;
• and
• ejecting the mixture from the third chamber, and further comprising siphoning an additional amount of the second fluid into the second chamber as the at least some of the first fluid is ejected from the first chamber into the third chamber.

A method of operating a pressure-driven metered mixing dispensing pump having first, second and third chambers at least partially defined by a housing and a piston, the method comprising:

• supplying first fluid into the first chamber to eject second fluid, different from the first fluid, from the second chamber into the third chamber;
• ejecting at least some of the first fluid from the first chamber into the third chamber to form a mixture of the first and second fluids;
• ejecting the mixture from the third chamber;
• and
• further comprising siphoning an additional amount of the second fluid into the second chamber as the at least some of the first fluid is ejected from the first chamber into the third chamber.