Flow Coefficient (Cv) for the 17YBCVxxxNL, 17CVxxxNL & 17CVSS-xxx Series Check Valves.

The chart below provides the Flow Coefficient (Cv) for the 17YBCVxxxNL No Lead Brass, 17CVxxxNL No-Lead Bronze, 17CVSS-xxx 304 Stainless Steel Check Valves.

Flow Coefficient (Cv) is the number of U.S. gallons that can pass through a valve when it is in the fully opened position at a pressure drop of 1 PSI. Testing is typically done by running water (specific gravity of 1.0 centistoke viscosity) at 60°F (°C) unless stated otherwise.

The Cv is used to properly size valves, so they have minimal effect on the hydraulic efficiency of your system. Flow Coefficient or Cv is one of the most important things to know for selecting the right size of valve. For example, a 1-1/4” valve with a Cv of 20.1 has an effective port area in the fully open position such that it is capable of passing 20.1 GPM of water with a pressure drop of 1 PSI.

CRACKING PRESSURE: Is the pressure at which a component starts to open. This term is used in reference to our check valves. When the ½ PSI cracking pressure is reached the check valve will start to open.

VELOCITY: It is also important to take Flow Velocity into consideration when selecting a valve, larger pipe is more expensive, however keeping the water velocity low is important to limit pressure losses due to friction, water hammer, and pipe movement due to water momentum changes inside the pipe. It is recommended to size piping to maintain a water velocity of 5 ft/second (1.524 LPM). Five feet per second is a threshold that is widely accepted by engineers and designers because beyond this velocity, the friction losses, danger of water hammer, and pipe movement due to water momentum changes are deemed to be too high.

HEAD LOSS: Head loss is a measure of the reduction in the total head (sum of elevation head, velocity head and pressure head) of the fluid as it moves through a fluid system. The chart below provides the head loss data for these series of valves. You will notice that when the flow velocity is maintained the head loss across the valves is typically 1.5 PSI or less (except for the 4” valves at approx. 2.3 PSI)