The 7-2108-01 Check Valve is a built-in Check Valve for the DEL Spa Ozone Generators.
These Check Valves are not very backflow resistant but are built specifically for this ozone generator.
If you have any other spa ozonator, you might want the standard Spa Ozone Check Valve or the one specific to Sundance Spas.
The 7-2108-01 is also a replacement Check Valve for the AquaNova 2 Spa Sanitizer System, 51004-001-909 (also referred to as the Del AOP Spa).