Backpressure: This occurs when the pressure in the downstream piping system exceeds the pressure in the supply line, causing water to flow backward. This can happen due to pumps or thermal expansion.
Backsiphonage: This occurs when there is a negative pressure (vacuum) in the supply line, often due to a sudden drop in pressure (like a water main break), causing water to be siphoned back into the potable water system.
If check valve #2 is fouled (i.e., obstructed or malfunctioning), it would not effectively prevent backflow. During testing under backpressure, the test kit would show a pressure differential indicating that the check valve is not holding properly. Additionally, water would discharge from the relief valve, as it is designed to release excess pressure and prevent contamination, indicating that the assembly is not functioning correctly.
The pressure at the base of a water column can be calculated using the formula:
Pressure (psi) = Height (ft)×0.433
For a 100-foot high standpipe:
100ft×0.433psi/ft=43.3psi
This formula derives from the fact that 1 foot of water exerts approximately 0.433 psi of pressure due to gravity.
In a reduced pressure backflow assembly, if check valve #2 leaks and backpressure is present, it can cause the pressure differential to drop. This situation activates the relief valve, which is designed to discharge water to prevent contamination from entering the potable supply. The relief valve functions as a safety mechanism to maintain system integrity.
A check valve is designed to allow flow in one direction while preventing backflow. To ensure reliability and effectiveness, it must have a resilient seat (which provides a tight seal) and be spring-loaded to remain closed when not in use. This design helps to maintain system integrity and prevent contamination of potable water supplies.
