This web-page is designed to give newcomers a fast track introduction to valves such that they will be better equipped to follow the Valve Essentials course and obtain the maximum benefit from the course day.
What is a valve and what does it do?
If you are uncertain what an industrial on/off valve is or does, then consider this simple comparison between the shower in your home and a pipeline in a factory. To take a shower, you turn a tap which allows the flow of water to the shower head. To stop the water, you turn the tap the other way. It’s the same principle with an on/off valve in a factory or on a pipeline: to start the flow of a fluid the operator turns the handwheel. When he needs to stop the flow, he turns the handwheel in the opposite direction.
Types of valves
Over the years, engineers have come up with a huge number of different designs for valves. During the course, we will focus on the principal types, namely the gate, globe, check, ball, butterfly, plug, needle, diaphragm and pinch valves. The photo shows all nine valve types, arranged clockwise, starting with the gate valve (large silver valve with a red handwheel on the far left)
Valves are manufactured using a range of components and it is helpful to familiarise yourself with the main parts. For example, the diagram below shows a cut-away photo of a gate valve with the main components clearly labelled.
The body refers to the outer casing of the valve. This is connected to the pipework on either side of the valve. In the picture, the outside of the body is painted blue, with the inner surface of the body painted white. This valve is a cut-away demonstration model, so the surfaces painted red show the cuts through the body. The medium being controlled by the valve flows through the white section.
On a gate valve, practical reasons mean that the body cannot be made from a single piece of metal. Instead, an opening is left at the top in order to insert the internal components. That’s why gate valves will have a so-called bonnet (like a lid), which after the internal parts have been fitted will be connected to the body. In this case, by using bolts.
To ensure a tight fit, and so to prevent any of the medium being controlled from leaking to the atmosphere between the body-bonnet joint, a gasket will be fitted. Gaskets have to be flexible so that they will completely fill the space between the body and the bonnet, yet resilient enough to withstand years of use in a hot environment.
To operate the valve, a technician will turn the handwheel at the top of the valve (not shown on this photo). This raises or lowers the stem which in turn is connected to the disk. When the disk is moved fully down, the valve will be closed. When the disk is moved upwards, the valve will open. The image shows the valve in the open position.
In order for the valve to close properly, the disk needs to fit tightly against the valve surface on closing. To improve the fit most valves are therefore fitted with so-called seats. Seats can be made of metal or an elastomeric material, depending on the design.
Finally, it is also important to prevent any leaks from occurring along the stem to the atmosphere. That’s why this particular valve is fitted with a packing system, comprising several layers of so-called packing rope. The packing rope is pressurized so that it completely fills the gap between the stem and the bonnet.