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When selecting the appropriate method for protection of the pipe system several factors have to be considered, e.g. number of pumps in operation, on-off regulation/continuous duty, normal stop/power failure, buckling risk/fatigue problems, risk for clogging etc. Common for all methods of protection is that they must be based on full understanding of how they will affect the system and be dimensioned for each specific case.
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An air chamber is a reservoir containing liquid and compressed air connected to the pipeline. When the pressure drops after a pump stop the air chamber discharges liquid into the pipe system. The flow in the pipe is stopped slowly and low pressures are avoided. An air chamber that is too closely connected to pumps and check valve can give rise to valve slamming.
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The flow is slowly restricted with a valve before the pump is shut off. The flow in the pipe is slowly retarded and low pressures are avoided.
This method is not suitable for protection of the pipe system in case of a power failure since the valve closing procedure must have been completed before the pump is shut off.
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Air inlet/release valves are mounted along the pipelines at locations where sub-pressure occurs, letting air in when the pressure in the pipe falls below a pre-set value. The air that is let in the system must be released again through an air-release valve in order not to create pockets of air at the locations of the pipe system with the highest elevations.
If the air is released too quickly, the liquid column forcing the air out can gain high speed. When all the air is discharged and the liquid column is abruptly stopped, high pressure can arise.
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Relief valves are mounted where high pressure occurs. They open and discharge liquid when the pressure is high.
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Engineering
