The pHi-Tech device has two working modes for a Dual system.
The first mode is Oil & Oil - for vaccinating with two oil-based vaccines and is used for both the Dual and the Twin Injection Heads.
The second mode is Oil & Water for vaccinating an oil-based vaccine together with a water-based vaccine. It is used only when injecting with the Dual Injection Head (not the Twin Injection Head).
The difference is the injection sequence.
In the Oil & Oil mode- the secondary unit waits before the injection starts in order to finish the injection together, and begin to pump together.
In the Oil & Water mode- the secondary vaccine gets pumped only when the Primary has finished injecting.
The water-based vaccine MUST be in the Secondary unit at all times.