The diverter cartridge represents a shower valve system, while the shunt prevents water from escaping from the bathtub spout and sending it to the shower head. Some shower faucets use faucets that can also divert water.
The diverter cartridge regulates the flow of water between the bathtub tap and the showerhead. When the valve is open, water flows directly into the tub through the faucet. When the valve is closed, the pressure forces the water up to the showerhead.