This type of fitting reduces head loss by about 50%. How?

Think of the lateral line as a heavily travelled highway with cars (sap) running down it quickly and smoothly. Air bubbles are the empty spaces between cars. What is the best way for more cars to enter traffic? Obviously, traffic flows better if cars enter via an entry ramp where they can merge smoothly into already flowing traffic. Having cars enter a busy highway at a right angle results in mayhem where all traffic slows down (or stops) and traffic is stop and go (turbulence). A smoothly curved onramp greatly reduces the turbulence of cars (or sap) entering the traffic (or sap) flow. To further the analogy, these frictional losses are additive. Each time sap has to merge (at a tee) or change direction (in a spout, a saddle, etc.), friction reduces the energy in the system, in a similar fashion that a lot of intersections in roads will reduce traffic speed and flow. In other words, the head losses build up and vacuum drops the further you move from the mainline in the lateral line system due to these restrictions.

It is important to note that changing intersections from a right angle to a curve will produce the greatest improvement in head loss. Thus using an arc-fitting wherever sap must change direction (spouts, saddles, etc.) would result in the highest degree of
improvement. Liquids tend to flow best in straight lines and create the most turbulence at confluences (tees) and where there is a change in direction. If we’re going to incorporate an arc into “tees,” then we might as well go full-in and also use the same design principle in all other components of the lateral tubing system (unions, saddles, etc.).