Two-way injection
For systems with a differential pressure across the primary circuit supplied by a main pump. Hot water is injected through a two-way valve into the secondary system by opening the valve. The two-way valve can also be operated as a pressure-independent valve. It is considered to be the most modern way of doing hydraulics in heating systems.
Three-way mixing
For systems where the heat source allows a variable flow to pass through it and where no differential pressure is available for the hydraulic circuit. The primary side of the circuit can have a pump together with a hydraulic decoupling or be without a primary pump. The necessary differential pressure across the valve is generated by the secondary pump.
Three-way injection
For when a fast response time is required. It is found in systems with long distances between heat generation and load (outmoded). As this circuit gives an elevated return temperature, it is not recommended for use in any other case. This setup needs differential pressure at the primary side of the hydraulic circuit.