Correct Answer - Option 3 : Reflux valve
Check valves or reflux valves: It prevent water to flow back to opposite directions. They are provided on the delivery side of the pumping set and at interconnections between a polluted water system and a potable water system. These are generally provided on the delivery side of the pump. These valves work automatically.
Pressure reducing valve: In hydraulics, a pressure reducing valve serves the same purpose as a "pressure regulator" valve in a compressed air system. It is one of a variety of pressure control valves available for hydraulic circuits. It is always used in a branch circuit and never in the full pump flow line.
Air Relief Valve: it is a type of safety valve used to control or limit the pressure in a system, pressure might otherwise build up and create a process upset, instrument or equipment failure, or fire. The pressure is relieved by allowing the pressurized fluid to flow from an auxiliary passage out of the system.
Scour valve: This valve is used to drain the water out of the pipe system.
Sluice valve: These valves are used to regulate the flow of water in the pipe system by dividing into a number of sections.
