What is air valve and why air valves are used
Air valves are used in pipelines, these valves are capable to introduce or remove the air from the pipeline. In a pipeline, air must be removed or reduced otherwise it would create many problems. Pipelines would contain air and it must be removed. The air could enter the pipeline because of the water, water has two percent of air, and the air would come out of water because of the rise in temperature or a drop in pressure. Air can also enter in a pipeline because of the equipment like pumps, and fittings. The operation of a system and efficiency would be affected if the air is present in the pipeline. If the air is not removed from the pipeline then it will cause many problems such as it could damage the pumps, valves, and pipe. It can be the reason for faulty instrumentation readings. So air valves are an exceptional factor in pipelines.
Why air must be removed from a pipeline and what are the problems caused by the air in a pipeline
- The efficiency of the pump would be reduced
- There would be difficulties in measuring and filtering operations
- Air pockets can cause hydraulic jumps in the pipe and blowback effects with vibration and structural damages to the system
- Air pockets would increase the head loss and it can be the cause to reduce the flow rate and thus interrupts the water supply
- The surge pressure would increase, during the hydraulic transients with the presence of air pockets
- The presence of air pockets in ferrous pipes would enhance corrosion
- Water leakage could cause because of the breakage
- The head loss of the system would increase because of the air pocket and because of this higher pump’s power is needed
Why do we need air valves and why is it used in pipeline
- It can prevent cavitation damage
- Inaccuracy in the measurement of fluid flow can be removed
- High-pressure surges can be removed
- It can prevent the energy loss, hammer in the system and total air locking
- The accelerated wear of moving parts can be prevented
- Pumping efficiency would be improved
- The drainage efficiency of the system can be improved
What are the functions of air valves
The function of the air valve is to automatically exhaust small amounts of air that collect at system high points once the system is filled and up-to pressure. These valves would vent the pipeline during the initial filling and draining. It would remove the accumulated air at high points during pressurized operation of the system. Air valves are capable to decrease the sub-atmospheric pressures during transients.
How to install air valve
The air valves must be located at high points so that it can do proper venting. The mounting of the air valve must be in a vertical position. The installation of the air valve must be done properly otherwise it would badly affect the efficiency of the pipeline. The location must be considered while installing the air valve, it must need protection from freezing, contamination, and flooding. The connection of the air valve the inlet piping and isolation valve must be the same size as the valve inlet. Short inlet piping and vent lines. Dirt or tubing chips must be removed from the fitting and tubing before installation. The air valves must be positioned in location wide enough and easily accessible to allow maintenance, operations, and inspection.
How air valves are constructed
The body of the air valve would be constructed by using cast ductile iron or stainless steel. The top plate of the valve is made up of ductile iron or stainless steel. The float assembly is made up of glass-reinforced nylon, or polypropylene. Stainless steel is used for making orifice.
What are the types of air valves and how do they work
Air release valve
These valves would remove small air pockets that are accumulated in the pipeline. Mostly the orifice size of the air release valve could be between 1/16 and 3/8 it would be depended upon the valve design and working pressure. So when the air bubbles enter the valve then the liquid will be displaced within the valve because of the air bubbles and it will lower its level in relation to the float. If the level of the liquid is lowered in a place where the float is no longer buoyant, then the float will drop. Due to this process, the valve seat would open and releases the air that is in the upper part of the valve. So when the air is released the liquid level in the valve rises lifts the float and closes the valve seat.
Air vacuum valve
These valves are float operated and its orifice is big which is in the same size as the valve inlet. This valve can remove a large amount of air. The major function of this valve is to remove a large amount of air from the system when it is being filled and also it must allow a large amount of air into the pipeline when the pipeline is emptied. So when the system is filled the fluid lifts the float until it closes the orifice. So the orifice will remain closed until the system is emptied. During the operation of the system, the air could enter the valve and displace it. The valve will be closed because of internal pressure. The valve won’t open again until the system pressure reduces and reaches atmospheric pressure.
Combination air valve
This valve can act as an air release and air vacuum valve. It can do both these valves function and hence the name combination valves. The combination air valve combines air and vacuum, large orifice, and an automatic small orifice in a single body. These valves can be used with liquids that carry solid particles such as sewage and effluent. These valves can remove large amounts of air when it is being filled and also allow air into the system when it is drained. These valves can also remove air that is collected at the high point of the system. When the system is filled completely. So basically this valve has all the features of the above two valves and is also known as double orifice valves.
What is a kinetic air valve
These valves have three orifices, the features of the kinetic air valve are similar to the combination air valve. These valves have throttling mechanism to throttle air outflow through a third orifice when a preset pressure differential is reached. Kinetic air valves have a better closure phenomenon than the other type of air valves.
How to size air valves
Valve size must be determined for filling and draining. Air vacuum valve sizing must be done with a larger diameter. The sizing for pipeline filling is done by venting the air at the same rate as the pipe being filled. In the case of pipeline draining the air, the valve must be sized to receive air at the same volume as the pipeline being drained. Pipe burst analysis and pipe collapse pressure must be checked.
How to do the maintenance of the air valve
Inspection and flushing of the air valves must be done annually and must watch for external leakage. The performance and life span of the valve is depended on the working conditions.
What are the applications of the air valve
- Water distribution and transmission
- Municipal wastewater collection
- It is useful for certain pumps like centrifugal, booster and fire pumps
- Used in storage tank valves
- Pressure filters
- Venturi meters
To get more info about the control valve check the following link
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