Single and double air valves are essential components in watermain systems, serving distinct but complementary roles in maintaining system integrity and functionality.
Single Air Valves: These valves automatically release air from the pipeline under high-pressure conditions. They are strategically located at high points along the watermain where air pockets tend to accumulate. By venting trapped air, single air valves prevent pressure buildup, reduce the risk of water hammer, and ensure efficient flow within the system.
Double Air Valves: While double air valves share the air release function of single valves, they possess an additional capability crucial for low-pressure scenarios. These valves can both release and admit air into the pipeline. This bi-directional functionality is vital during maintenance activities.
WSD Practice and Maintenance: In the Water Supplies Department (WSD) practice, watermains are typically divided into sections by sectional valves to facilitate maintenance. Each isolated section, bounded by two sectional valves, requires at least one double air valve. During maintenance tasks like watermain cleansing, water is drawn from washout valves. However, the high operating pressures of watermains (e.g., 1.5MPa) can create transient vacuum conditions when water is suddenly withdrawn. This vacuum poses a significant risk of damage to the pipeline. Double air valves counteract this by allowing air to enter the pipeline, balancing the pressure and protecting the system from collapsing.
In summary, the strategic placement of single and double air valves is essential for the safe and efficient operation of watermain systems. Single air valves address air release under high pressure, while double air valves provide bi-directional air flow for maintenance and pressure stabilization. By understanding their roles and implementing them correctly, engineers can ensure the long-term integrity and reliability of water supply infrastructure.