The non-return / solenoid option can be fitted to prevent back siphoning of fluid into the chiller when it is turned off for refilling or maintenance.
This option is recommended when the chiller and application are at different levels (more than 6.5 feet height difference), or where a long length of flexible tubing is used between the chiller and the application. It is also advisable to add this when the pipe-runs will be going up into ceiling ducts.