Abstract: An injector for injecting into a flow of a first liquid passing through a flow passage formed in the body of the injector a second liquid, which is pressurized for injection by the pressure of the first liquid. Pressurization of the second liquid is accomplished by means of a liquid-tight canister separated into first and second pressure chambers by a flexible diaphragm. The pressure of the first liquid flowing through the injector is tapped off to pressurize the first pressure chamber, and through the diaphragm, the second chamber containing the second liquid. The second chamber is connected to the flow passage at a point downstream of the point where the pressure of the first liquid is tapped off to pressurize the canister, and the passage is venturi-shaped adjacent the point at which the second liquid is injected into the flow passage to provide an additional force drawing the second liquid into the flow passage.

Abstract: A trigger actuated fertilizer spray gun has a herbicide injector mounted on its muzzle with the valve for the injector having an actuator which is also accessible from the handle of the gun, so that an operator, while spraying fertilizer, can make spot applications of a herbicide as weeds are encountered in the area being fertilized. The herbicide is carried in a canister which can either be mounted on the handle of the spray gun or on a belt worn by the operator and the canister is divided into first and second, variable volume chambers by a flexible diaphragm. The first chamber is connected to the flow passage of the fertilizer to pressurize it to approximately the line pressure of the fertilizer flow, and the second chamber, containing the herbicide, is connected to the injector at a venturi-shaped portion of a passage through it.