Air Valve 1

Air trapped in a stockwater pipeline can reduce or even completely stop the flow of water in the line. This is particularly a critical problem in pipelines that operate under very low heads or in long pipelines.
AIR/GAS PROBLEMS
Air or gas gets into a pipeline in several ways. These include:
- When a pipeline is drained, air enters the line through hydrantsor any opening.
- There are various forms of gasses in well waters. These gases can come out of solution during pipeline operation. Some wells have more serious gas problems than others.
- If the water level in a well or other source falls below the pump intake, air is drawn into the pipeline by the pump.
- In gravity systems, air can be drawn into the pipeline when water surface falls below the ipeline entrance. In some live streams, there can also be air bubbles entrapped in the water.

In addition to the flow restriction they cause, air pockets can react in a way that aggravates water hammer problems. As velocity increases, the air pocket tends to be pushed down the pipe in some sort of elongated bubble. There may be several separate bubbles formed. If velocities are high enough, and elevation difference to the next low point is not too great, the bubble may be pushed through to the next high point or outlet.

Large air pockets can aggravate water hammer problems if they are released from the pipeline too quickly. As large volumes of air are released from the pipe, the water will rush to fill the void caused by the released air. The velocity of the water can be very high and the sudden closing of the air valve can result in water hammer and high surge pressures. The minimum air release orifice size specified in FOTG Standard 516 should be used as the design orifice size.