• Air gap fittings are plumbing code required to mount in the drain line(waste line) of water treatment equipment and their primary purpose is to prevent non-potable water from flowing backwards possibly mixing and contaminating potable (drinking) water. One could think of the function of an air gap fitting as a no-fail check valve but without an internal seat or any moving parts. Properly designed and installed, air gaps, like check valves, allow water to flow only in the desired direction.
• The key characteristics for an air gap is protection from back flow and back siphonage. Back flow occurs when there is a clog or blockage downstream in the drain line which with more water entering causes the nonpotable water to back up fully engulfing the air gap unit or at least reach in the back siphonage critical level (C/L) of the air gap unit. Back siphonage happens when there is suction on the potable water line and air gap inlet that sucks non-potable water port back into the potable (drinking) water line. The ideal air gap would provide protection from back flow and back siphonage.
• A true air gap is a physical separation in the drain line that one could pass their hand through. All existing air gap fittings aren’t true air gaps because one cannot pass their hand through the air gap opening but if properly designed and installed, during back siphonage they can function esentially like a true air gap. Don’t be fooled by any misleading advertising that claims an air gap fitting is a “true air gap” or a “true 1 inch air gap”, or "true 2" air gap", etc.

Key Consideration: Water Softener air gaps generally are installed near the laundry facilities in the garage, basement or in the laundry room for convenient access to the house drainage piping and secondly, there almost never exists a dedicated (unused) standpipe just waiting to be used by the instaler for surmounting their drain line air gap. Thus the critical feature of the air gap is its ability to share a standpipe with the washing machine drain hose.

Comments:
Air Gap International offers several models of air gaps that are easy to install, can share the standpipe, as well as provide back flow and back siphonage protection. The Gap-a-flo, Mr. Drain and Gap-it™, model #s (21, MD-10A and 61-S) respectively provide all the necessary features an installer is looking for. All units are dual listed by NSF and UPC. Dual listing conveys generally this important message: countrywide as well as international acceptanc. In those circumstances (very seldom), where a standpipe doesn’t have to be shared (and in addition to the above models), Air Gap International offers the model #8500 Gap-Cap™. The Gap-Cap™ unit is a value priced, dual inlet air gap unit that can accommodate 1 1/2” or 2” metal or schedule 40 plastic pipe. The Gap-Cap™ comes standard with a dual barb elbow for easy connectivity.

Sink Hole Flexibility -- the Model T52 fits 1 1/4” sink hole diameters (the smallest common size found).

Decorative Cap Flexibility -- homeowners can keep their existing cap (assuming it fits) or purchase from a wide variety of lowest profile dishwasher air gap caps from us or possibly at their local Ace hardware, Home Depot, Lowe’s, OSH.

Ease of Installation -- The Model T52 high flow unit comes complete with rubber cuffs and stainless screw drive clamps allowing an easy transition from the hard plastic dishwasher hose to the T52 inlet port. The T52 RO unit comes with a 1/4” John Quest quick connect fitting allowing for a quick, easy connection. The long threaded body (over 2” of usable threads) enables the installer to mount the T52 unit on top of thick countertops.

Backflow & Back Siphonage Protection -- the Model T52 provides both
desirable features as well as dual listing by UPC and NSF.