by Jenny Knodell, IQS Editor
Valves are simple machines that are used to regulate the flow of liquid by obstructing the pipe or passageway. They’re found anywhere liquids flow, including indoor plumbing systems—more specifically, your faucet. When you turn the sink handle, out comes water. Turn it back, and it stops flowing. This is the basic job of a valve—often taken for granted, since they are so simple and common, but what would we do without them? Probably pay hefty water bills each month. They’ve been in use for thousands of years, and are one of the most useful mechanical inventions of all time. Valves are divided into two families—the stop valves, which provide an on, off and partially on setting, and check valves, which only restrict the flow of liquid in one direction.
The valves you use most often are of the stop valve family. Ball valves, butterfly valves, globe valves and gate valves are all included in this category. They differ in construction and function, and are used for certain specific water flow applications. A closer look at the different types might help you distinguish between them and clarify where they are used.
As you might expect, the name says it all—ball valves are indeed made of a spinning ball. This ball has a hole through it, which lets water flow through. When the hole is facing the valve walls, water can’t get through. When it is faced towards the liquid, it can. A 90 degree rotation of the ball is all it takes to start or stop the flow of liquids in sanitary, hydraulic and oil systems.
These valves are also indicative of their name. The valve body is round in shape and composed of two separate halves which are separated by a disc that opens and closes. It’s a bit more complex than the others, as it’s composed of a body, bonnet, plug, stem, cage and seat ring. This type of valve only offers on and off positions, unlike its alternatives, but it is also able to control the amount of liquid. They are mostly used in applications where frequent operation requires a strong, long lasting valve.
Gate valves have wedge shaped liquid obstructions that stop or allow flow through opening and closing. They are considered the most basic constructions because they have two settings—on and off, meaning the gate is completely open or totally closed. They should never be used for throttling, which is regulating the rate of flow, because of the limited settings. They, as well as globe valves, have a bonnet, which provides the water tight seal between the gate and valve.
This valve is the only non-self explanatory type of stop valve. The name conjures images of a double-wing shaped insect, right? Well, for whatever reason, the butterfly valve in no way resembles a butterfly. In fact, a butterfly valve is actually composed of a flat, round piece which is supported in the middle that opens or closes when the shaft is rotated. When opened, the edge does provide some resistance to the flow of water. While closed, it perfectly fits the shape of the pipe and provides full obstruction. Because it is able to pivot and stay in more than two positions, the amount of liquid flow can easily be changed as necessary.
Images courtesy of Butterfly Valves and Controls,Inc.