A Type AF Airgap is a specialized, non-mechanical backflow prevention arrangement designed for water fittings, uniquely characterized by an air gap with a circular overflow. This essential plumbing safeguard prevents the contamination of potable water supplies by ensuring a physical break between the clean water inlet and any potential source of contamination.
Understanding Type AF Airgaps
At its core, a Type AF Airgap functions as a protective barrier in water systems. It's an arrangement where the water fitting discharges freely into a receptacle (like a cistern or tank) with a specific, measurable air gap. The "AF" designation specifically highlights its design incorporating a circular overflow feature within that receptacle, which plays a crucial role in maintaining the integrity of the air gap even under varying conditions.
Key Characteristics
Type AF Airgaps are defined by several critical features:
- Non-Mechanical: Unlike valves or other moving parts, an air gap relies purely on a physical separation of air to prevent backflow, making it highly reliable as there are no parts to wear out or fail.
- Air Gap Measurement: The protective gap is precisely measured downwards from the lowest point of the discharge orifice (where the water exits the supply pipe) to the critical level of the receiving receptacle. The "critical level" refers to the highest point the water can reach in the receptacle before it begins to overflow, which is often the invert level of the overflow pipe.
- Circular Overflow: The distinguishing feature of Type AF is the integration of a circular overflow within the receptacle. This design helps manage water levels and ensures the air gap remains effective even during overfilling, preventing water from reaching the supply pipe's discharge point.
How a Type AF Airgap Works
The principle behind any air gap, including Type AF, is simple yet highly effective: if there's a physical gap of air between the water supply and the potentially contaminated water in a tank or appliance, it's impossible for water to flow backward (back-siphonage or back-pressure) into the clean supply.
Consider a common scenario: a cold water storage tank. The main water supply pipe fills the tank. With a Type AF Airgap:
- The end of the incoming supply pipe (the discharge orifice) is positioned a specific, regulated distance above the highest possible water level (the critical level) in the tank.
- The tank itself is designed with a circular overflow outlet. This ensures that if the tank overfills, the excess water exits through this overflow rather than rising high enough to bridge the air gap to the supply pipe.
- Even if there's a sudden drop in pressure in the main water supply (causing a vacuum that could draw water back), or if the water in the tank is under higher pressure, the physical air break prevents any contaminated water from entering the potable supply system.
Importance of Backflow Prevention
Backflow prevention is paramount for public health and safety. Without adequate measures, contaminated water from various sources—such as heating systems, chemical mixing tanks, or even garden hoses — could be drawn back into the municipal drinking water supply. This can lead to serious health risks, including the spread of diseases. Type AF Airgaps provide a robust, passive defense against such contamination. For more information on the critical role of backflow prevention, refer to resources from organizations like the Environmental Protection Agency (EPA).
Applications of Type AF Airgaps
Type AF Airgaps are commonly employed in situations requiring high-level backflow protection where a physical air break is feasible and effective. They are often found in:
- Cold Water Storage Cisterns: Ensuring that potable water stored for domestic use remains uncompromised.
- Expansion Cisterns for Heating Systems: Where water in a heating system might contain treatment chemicals, preventing its return to the potable supply.
- Tanks Supplying Appliances: Any appliance or system that stores water and presents a risk of contamination, benefiting from the reliable separation.
- Commercial and Industrial Settings: In process water tanks or other receptacles where the incoming water supply needs absolute protection from the contents.
Ensuring Compliance and Safety
The design and installation of Type AF Airgaps are governed by stringent plumbing regulations and standards to guarantee their effectiveness. Adherence to these codes, often overseen by bodies like the Water Regulations Advisory Scheme (WRAS) in the UK or local plumbing authorities elsewhere, is crucial. This ensures that the air gap dimension is correct, the circular overflow is appropriately sized and positioned, and the overall arrangement provides the intended level of protection.
