There can be a maximum of 8 buttons per Control Panel to any configurations. Example: CP-A1-W1-V2 would be a Control Panel with 1 Air button, 1 Water button and 2 Vacuum buttons Example: CP’W1-V2 would be a Control Panel with 1 Water button and 2 Vacuum buttons.  
At least one water button must be used with each Vacuum Unit to ensure that vacuum units are not turned on without water.