check valves (Backflow Prevention)

　
a) Swing-type check offer the least pressure drop and offer simple automatic closure; when fluid flow stops, gravity and flow reversal closes valve. Many bronze valves offer a Y-pattern body with an angle seat for improved performance. Resilient seating preferred for tighter shutoff.

　
b) Lift checks come in in-line or globe-style body patterns. Both cause greater pressure drop than the swing type, with the horizontal pattern similar in restriction to globe valves. Some styles are spring-actuated for immediate closure when flow stops. The in-line spring-actuated lift check also is referred to as the “silent check”because the spring closes the valve before gravity and fluid reversal can slam the valve closed. Resilient seating recommended.

　
c) Double-door checks have twin discs on a spring-loaded center shaft. These valves have better flow than lift checks and most often use a wafer body for low cost and easy installation. Resilient seating recommended.

　　
Circuit Balancing Valves

　
a) A Balancing Valve is used to regulate and measure the rate of flow of water. The valve can positively isolate the flow and be set at an intermediate position to maintain the design flow rate. Pressure tapping points on either side of the seat provide the means for flow measurement. Most Balancing Valves are globe style and incorpora