Proportional additive dosing pump with bidirectional rolling diaphragm

A hydraulic proportional additive dosing pump (ADP) driven by a flow of water from an inlet to an outlet to introduce a proportional dose of a liquid additive into the flow of water, the ADP comprising:

• (a) a cylinder;
• (b) a plunger displaceable axially within said cylinder and subdividing said cylinder into an upper chamber and a lower chamber, said plunger having a cylindrical outer surface, said plunger being rigidly associated with an actuator rod;
• (c) a bidirectional roll diaphragm deployed at least partially in a gap between an internal surface of said cylinder and said cylindrical outer surface of said plunger, said bidirectional roll diaphragm sealingly interconnected with said cylinder and with said plunger so as to form a rolling seal between said upper chamber and said lower chamber;
• (d) a pump body having a water inlet, a water outlet, and defining a plurality of flow paths from said water inlet to said upper chamber and said lower chamber, and from said upper chamber and said lower chamber to said water outlet;
• (e) an additive pump having an additive inlet for drawing a quantity of the liquid additive and an outlet for releasing the liquid additive into a water flow within said pump body, said additive pump being driven by motion of said actuator rod;
• and
• (f) a switchable valve arrangement associated with said plurality of flow paths and with said actuator rod, said valve arrangement switchable between a first state in which:
• said flow path from said water inlet to said upper chamber is open;
• said flow path from said water inlet to said lower chamber is closed;
• said flow path from said upper chamber to said water outlet is closed;
• and said flow path from said lower chamber to said water outlet is open, thereby applying an inlet pressure above said plunger to power a down-stroke of said plunger, and a second state in which:
• said flow path from said water inlet to said lower chamber is open;
• said flow path from said water inlet to said upper chamber is closed;
• said flow path from said lower chamber to said water outlet is closed;
• and said flow path from said upper chamber to said water outlet is open, thereby applying an inlet pressure below said plunger to power an up-stroke of said plunger, said valve arrangement being toggled between said first and second states at end positions of said down-stroke and said up-stroke so as to generate reciprocating motion of said plunger,
• wherein said bidirectional roll diaphragm is deployed such that, for at least part of said down-stroke and for at least part of said up-stroke, a majority of an area of said bidirectional roll diaphragm is supported in contact with either said cylinder or said cylindrical outer surface of said plunger as a region of convolution rolls along said bidirectional roll diaphragm.