ABSTRACT
There are four different types of check valve: split-flapper check valves, single-flapper check valves, poppet check valves, and umbrella poppet valves. Figure 6 shows the configuration of the split-flapper check valve. It is typically used in aircraft systems. The valve has two semicircular closure elements, called flappers, which rotate about a hinge pin. The total rotation of each flapper from the seat to the stop, called the stop tube, is between 70 and 90°. Wear between the flapper and the stop tube is caused by aerodynamic forces combined with vibration. Increasing the pressure force on the flapper by minimizing the rotating angle will result in reducing the wear. The pressure drop across the valve determines how small the angle can be. Figure 7 shows the single-flapper check valve configuration, which can be designed either as a two-port or a three-port valve. These valves are difficult to fabricate because they are not symmetric, and they are chosen over the split-flapper check valves only for special environmental conditions, such as in the environmental control system of the Boeing 767/757 and 737-300 airplanes. The single-flap valve is selected for these applications
because it has fewer stagnation areas where ice can form. In line sizes around 1 in., the single-flapper check valve has lower pressure drop than the split-flapper check valve.
