In the design and construction of farmland or garden irrigation, the exhaust and intake of pipelines are often overlooked or installed incorrectly, leading to pipeline safety accidents. The discussion of this issue in this article is as follows

one, the pipeline gas come from?
Before the irrigation system was built, it was filled with gas. After completion, most of the gas is discharged through a water filler or water inlet valve, while some gas, due to accumulation at the high points of the pipeline, cannot be discharged.

2. Some air will dissolve in water. In summer, as water temperature rises, the dissolved air in the water inside the pipes will settle, and the settled air on the inner walls will gradually accumulate at the high points.

3. Due to the negative pressure in the pipeline, the gas is sucked away by the safety valve or the intake and exhaust valve.

Two, the working principle of the intake and exhaust valve
The intake and exhaust valves are based on the principle that water exerts buoyancy on stainless steel float balls. When the water level in the intake and exhaust valves rises, the float ball will automatically float up under the buoyancy of water while entering the intake and exhaust valves until it touches the sealing surface of the exhaust port. When the float ball reaches a certain pressure, it will automatically close. When the water level inside the valve drops, the ball will descend along with the water level, and then a large amount of air will be injected into the pipe through the exhaust port. When the pipeline is in operation, the float ball stops at the bottom of the ball bowl and discharges a large amount of air. When all the air in the pipe is discharged, water rushes into the valve, passes through the ball bowl and reacts with the float ball, causing it to float up and close. When the pipeline is operating normally, if there is a small amount of gas, it will concentrate to a considerable extent in the valve, the water level in the valve will drop, the float ball will descend, and the gas will be discharged through the small hole.

When the water pump stops, negative pressure may occur at any time and the float ball may fall down at any moment. Therefore, a large amount of suction is needed to ensure the safety of the pipeline. In the exhaust state, the buoy pulls down one end of the lever due to gravity. At this point, the lever is in a tilted state, and there is a gap at the contact part between the lever and the exhaust hole. Air is discharged through this gap. As the air is expelled, the water level rises and the buoy floats up under the buoyancy of the water. The sealing end face on the lever gradually presses against the exhaust hole until the entire exhaust hole is completely blocked and the exhaust valve is completely closed.

Three, intake and exhaust valve design
The intake and exhaust valves have the function of continuously and rapidly (or in large quantities) discharging any section of gas in the water pipeline when there are multiple water columns, alternating gas columns or multiple discontinuous airbags in the water pipeline. That is, when there is pressure, when the intake and exhaust valves are filled with gas, the large and small exhaust ports open to release gas, and when they are filled with water, they close without leaking. When negative pressure occurs, gas can be injected into the water pipeline. Under normal circumstances, an intake and exhaust valve should be installed every 0.5 to 1 kilometer

The diameter of the intake and exhaust valves should be 1/8 to 1/5 of the diameter of the water transmission pipeline, or calculated according to the following formula. However, the effective exhaust diameter of the intake and exhaust valves shall not be less than 70% of their nominal diameter. The actual diameter selected is larger than the calculated diameter.