In deep well water supply systems, those seemingly insignificant valves play a crucial role in maintaining household water stability. Particularly the device known as the Air Volume Control Valve (AVC) or air release valve—what exactly does it do? This article examines the working principles, types, maintenance requirements, and troubleshooting methods for AVCs in deep well systems.
The "Air Butler" of Well Water Systems
Pressure tanks serve vital functions in deep well systems, falling into two main categories: pre-charged pressure tanks (diaphragm or bladder type) and air-over-water pressure tanks (atmospheric type). The AVC—along with its companion components, the snifter valve and bleeder valve— only applies to air-over-water pressure tank systems . If your system uses pre-charged tanks, these components are unnecessary and should be removed.
Air-over-water tanks maintain system pressure through compressed air inside the tank. Unlike water, air is compressible—functioning like a giant spring that continues pushing water even when the pump stops, ensuring continuous supply. However, over time, water absorbs the tank's air, reducing pressure and increasing pump cycles, potentially leading to water hammer. This necessitates an air replenishment system, where the AVC plays a pivotal role.
Why AVCs Are Indispensable
Typically, snifter/bleeder valve systems inject more air than needed into the tank. The AVC—installed atop the pressure tank—vents excess air to the atmosphere. Hearing a hissing sound from its exhaust port is normal, but water leakage indicates required maintenance or replacement.
Types of Deep Well AVCs
The market offers several AVC designs ( Note: Pressure gauges require separate purchase ), with two primary categories:
- AVCs with adjustable air release valves
- AVCs without adjustable air release valves
All types allow air escape until reaching the optimal water level.
How Deep Well AVCs Work
When excess air lowers the water level, a float opens the main control valve to vent air. As water rises, the float ascends, closing the valve to retain the ideal air-water ratio.
Deep Well Installation: Bleeder Systems with AVCs
These systems require bleeder components to "charge" the tank with air. The bleeder valve installs in the well's drop pipe below the frost line (typically 10-20 feet underground). When the pump stops, water drains back to the well until reaching the bleeder's port. A bronze check valve (with mounted snifter valve) prevents tank water from backflowing into the well. The snifter valve breaks vacuum to admit air, enabling drainage. Each pump start forces trapped air into the tank, while the valves close under pressure to prevent water escape during pumping cycles.
Key Components of Bleeder Air Charging Systems
- Bleeder valve: Installed below the frost line to drain water and admit air when the pump stops.
- Check valve: Ground-mounted near the tank to prevent backflow.
- Snifter valve: Positioned above the check valve to admit air by breaking vacuum.
- AVC: Tank-top mounted to vent excess air and maintain optimal air-water balance.
Advantages of Adjustable Air Release Valves
Models like AVC-DW-AR allow pressure adjustments for precise air volume control, particularly useful when greater drawdown capacity (water volume between pump cycles) is needed.
These valves create backpressure to retain air even when the float keeps the main valve open. Factory-set to ~25 PSI (±10%), they can be adjusted between 0-40 PSI (though exceeding 40 PSI isn't recommended). Fine-tuning involves:
- Reducing pressure (counterclockwise) if air blows from faucets
- Increasing pressure (clockwise) if pumps cycle too frequently
Caution: Never unscrew the adjustment completely—small internal parts may be lost.
System Failure Consequences
Malfunctioning bleeder valves, check valves, snifter valves, or AVCs disrupt proper air balance. Failed components cause "waterlogged" tanks with rapid pump cycling. The absence of hissing sounds typically indicates check valve failure, preventing pipe drainage and air replenishment. Persistent waterlogging damages pumps through excessive cycling.
Temporary waterlogging fix: Manually adding air to the tank provides interim relief until proper repairs.
Critical Pump Cycling Considerations
Daily start cycles significantly impact submersible pump longevity. Excessive cycling harms controls (pressure switches, starters, relays, capacitors) and causes motor spline/ bearing damage from overheating. Systems should minimize daily starts, with motors running ≥1 minute to dissipate startup heat. Larger motors require ≥15 minutes between starts.
Conversely, failed air release causes excessive tank air (evidenced by faucet air spurts), usually from rust-clogged valves or corroded float rods. Water leakage from the AVC indicates replacement necessity.
Given air-charging systems' complexity, most modern installations use maintenance-free pre-charged diaphragm/bladder tanks. When converting systems, all air-charging components must be removed to prevent unintended air introduction.