Chapter 7: Valves Flashcards
What is a check valve
A check valve is a device that permits fluid flow in only one direction. It opens under the influence of pressure and closes automatically when flow ceases. Usual installations are in the discharge pipes of centrifugal pumps to prevent backflow when the pump is not operating.
What is a shutoff valve?
Valves to stop the flow of fluid through a pipeline are the most abundant valves in treatment plants. Water pipe networks are sectionalized by installation of shutoff valves so that areas can be isolated with minimum reduction in service and fire protection. Gate valves and plug valves are among the most common shutoffs, however, butterfly valves may be installed in larger diameter pipes. Other common shut-off valves include globe and ball valves
What are two other valves other than check and shutoff?
- Ball valve
- Globe shutoff valve
What is a pressure reducing valve?
Pressure reducing valves used on smaller piping diameter units are cast from brass; larger piping diameter units are made from ductile iron. In water distribution systems, the common application is installation in a main connecting separate pipe networks located on two different elevations. As the water flows through the valve from the higher zone to the lower zone, the water pressure is reduced to prevent excessive pressure in the pipe network at the lower elevation.
-Adjusting a water-pressure regulator valve is easy. Loosen the locknut and turn the adjusting screw counterclockwise to reduce the pressure.
Describe a pressure reducing station?
A pressure reducing station automatically reduces a higher inlet pressure to a steady lower downstream pressure. The station valve is capable of holding downstream pressure to a predetermined amount, regardless of upstream pressure fluctuations.
-During low flow demand, an oversized valve will operate in a nearly closed position causing premature wear and an undesirable noise may occur.
What is a pressure relief valve?
This valve is installed so that one port is connected to the pressure line or the inlet and the other port to the reservoir. The valve is held closed by the thrust of the spring, which can be changed by turning the adjusting screw. When pressure at the valve’s inlet is insufficient to overcome spring force, the valve is closed, preventing flow through it. When pressure at the valve’s inlet exceeds the adjusted spring force, the valve is opened. Liquid flows from the pressure line through the valve to the reservoir. This diversion of flow prevents further pressure increase in the pressure line. When pressure decreases below the valve’s setting, the spring thrust closes the valve again.
What is an air valve?
Air valves are very common in water distribution networks and force mains in sewage treatment. Air trapped in a pipeline can cause many operational problems including broken pumps, pipes and valves. Air can become trapped in pipes in a number of ways.
- Air accumalates in highpoints causing distributions which could result in headloss.
- The second, and more likely occurrence, is that the increased velocity will cause all, or part of, the pocket to suddenly dislodge and be pushed downstream. The sudden and rapid change in fluid velocity when the pocket dislodges and is then stopped by another high point, can an often will, lead to a high pressure surge (water hammer).
What is a air release valve?
An Air Release Valve (Figure 4), sometimes referred to as a “small orifice” valve, will continuously release accumulated air during system operation. As air from the pipeline enters the valve, it displaces the water, allowing the float to drop. The air is then released into the atmosphere through a small orifice.
What is a air vaccum valve?
permits air to escape during filling. This type of valve is designed to remain closed after the pipeline is full so it does not permit the release of small amounts of air during pipeline operation. The valve immediately opens when the pipeline pressure drops below atmospheric pressure.
