●Non-return valve

A check valve is a device that prevents reverse flow of the fluid, keeping it flowing in one direction only.

●NRTL (National Recognized Test Laboratories)

Testing organizations capable of certification (of UL or CSA standards etc.) which have been recognized according to Occupational Safety and Health Law set forth by OSHA (the US Occupational Safety and Health Administration). At present, 18 organizations have been recognized as NRTLs. UL and CSA are examples of certified organizations.