irrigation, the water is flowed through pipes of open furrow or canal with
slope. As in Lift Irrigation, the water is flowed through pipe with the help of
pump. The pressure working in the pipe is more compared to gravity irrigation.
Hence the use of Air valve & Non return valve becomes very important in
lift Irrigation or while installing any pipeline.
Non Return Valve (NRV)
Non-return Valve, as the name suggests is used in pipeline to avoid the reverse flow of water in pipeline after shutting down of pump. Here this is very essential part of the lift irrigation or pipeline system.
What happens if NRV not used?
If the pump is on & the water is flowing through 90mm pipe (84mm approx ID) pipe with the static head of 30 meters for 2 km length. While in working condition, the pipeline is full of water. You can imagine the weight of water in pipeline with the following example.
In above example, if we calculate the amount of water at any time in pipeline, it is,
Amount of water= Pipeline area (m2) x Pipeline length (mtr)
= (3.14/4) x 0.084x 0.084 x 2000
= 11.08 m3
= 11.08x 1000 Liters= 11080 liters
Since the density of water is 1000 Kg/m3, the weight of water in pipeline will be 11080 Kg. After shutting down of pump, the total 11080 kg of water will start reversing due to 30 meter slope. This 30 meter head (3 kg/cm2 pressure) of 11080 kg of water creates a huge pressure on pipe in its reverse movement, may resulting in damage of pipeline. Also continuous reverse water hammer can result in continuous damage of pipeline, reducing its life to great extent.
Hence NRV are needed in every pipeline at right places.
Location of NRV
The NRV must be installed at the start of the pipeline. The place where it is installed should be plane or vertically upward towards the pipeline (It should not be at all vertically downward).
While in Drip, mini sprinkler & micro-sprinkler Irrigation, it must be installed after the Header unit to avoid the damage of filter due to reverse flow.
Other Locations for installing NRV in Long Pipelines
In long pipelines, wherever a after a sloppy condition, a rising condition occurs, NRV needs to be installed at the start of rising condition as shown in figure.
Use of Air Valve (AV)
The use of Air valves is also of immense importance. No one should install any lift Irrigation pipeline without NRV & Air valve.
As the name suggests, air valves are for the passing away of air while passing of water through empty pipe line or entry of air after shutting down of pump.
What happens if Air Valve not used?
After starting of pump & passing of water through empty pipeline, the air present in the pipeline flows forward, creating pressure on the pipe. That air is needed to be removed from the pipeline from the appropriate place else the air pressure can damage the pipe.
Also after shut down of the pump, there is some reverse flow of water (although NRV is used) & air needs to enter in the pipeline from the right place, else the vacuum can damage the pipeline.
Air Valves are must in the pipeline to avoid any chances of damage of pipeline due to water hammer.
Location of Air Valve
When there is a sudden slope starts in pipeline after the rise, the AV should be installed at the top position as shown in figure.
Type of Air Valve
1)Air vent Valve: It is used in pipe line to eliminate the air from pipeline after starting of the pump.
2)Vacuum Break Valve: It is used to add air in pipeline shuting down of pump.
3)Continuous acting air valve: Here both of the above purposes are solved as per need in single ball valve.
Size of Air Valve
The minimum size of air valve should be 25% of the pipeline size, which can be increased depending upon the static head condition.