Abstract: A device for controlled feeding of a water-soluble chemical into a water line having a pressure varying between a minimum and a maximum in the line. Water flows from the water line into an air impervious chemical mixing tank through a first one-way check valve. When the pressure in the line is less than the air pressure in the tank, an air reservoir in the mixing tank forces the mixture of water and chemical back into the water line through a control valve which is set at a restricted flow value with respect to the first check valve. A second one-way check valve located in the water line between the one-way check valve and the control valve prevents the contents of the mixing tank fed through the control valve from backing up toward the first one-way check valve.

Abstract: A device for controlled feeding of a water-soluble chemical into a water line having a pressure varying between a minimum and a maximum in the line. Water flows from the water line into an air impervious chemical mixing tank through a first one-way check valve. When the pressure in the line is less than the air pressure in the tank, an air reservoir in the mixing tank forces the mixture of water and chemical back into the water line through a control valve which is set at a restricted flow value with respect to the first check valve. A second one-way check valve located in the water line between the one-way check valve and the control valve prevents the contents of the mixing tank fed through the control valve from backing up toward the first one-way check valve.