Abstract

A fluid mixing valve has a canister which defines a chamber divided into an upper additive subchamber and a lower carrier subchamber by a plunger and diaphragm. A pressurized carrier liquid enters the carrier subchamber through an inlet and exits the carrier subchamber through a restriction, which produces a pressure differential across the plunger piston to pressurize a supply of additive liquid held within the additive subchamber above the piston. The pressurized additive liquid is injected past an adjustable metering valve into the flow stream of carrier liquid downstream of the restriction. As the additive liquid is depleted, the volume of the additive subchamber diminishes and the extension of the plunger out of the canister increases, to provide an indication of the amount of additive left in the additive subchamber. When the supply of additive liquid is exhausted, the plunger can be manually returned so as to enlarge the additive subchamber to prepare it to receive a new supply of additive liquid. The plunger can also be manually reciprocated when the additive subchamber is empty so as to clean out mineral deposits in the carrier subchamber.