By Tim Daly
According to Meriam Webster’s online dictionary (m-w.com), the word “valve” is defined as:
“ any of numerous mechanical devices by which the flow of liquid, gas, or loose material in bulk may be started, stopped, or regulated by a movable part that opens, shuts, or partially obstructs one or more ports or passageways; also: the movable part of such a device.”
Of all components in mechanical systems, valves are the most numerous, both in terms of how many are installed, and also in how many different types there are. We’ll discuss some basic what, why, and how here.
If you are installing a large system or component in a new facility, or one being upgraded, blueprints and engineering plans have instructions included telling the installers exactly which valves to use. These plans will be very specific as to which valves to install, right down to the part number of the valve from the manufacturer’s catalog.
Occasionally though, a mechanic will be tasked with gathering materials to make repairs on a system or add a new component to a system. He’ll be charged with buying and installing suitable valves for the installation.
Although the World Wide Web has made choosing the correct valves easier than ever, a mechanic still has to have a basic understanding of what he’s looking for. For instance, what pressure and temperature will the new valve be subjected to, or does it need to stand up to corrosive fluids like salt water or some type of acid? How fast does the system operator need to be able to open or shut the valve in an emergency, or does he need to be able to positively identify the valve’s position without actually putting his hands on the valve? Does he need a valve that can be operated at all, or is a check valve a better option?
Many valves will be stamped with the letters WOG, followed by a number. This means Water, Oil, or Gas and the number is the maximum pressure in psi (pounds per square inch) that the valve is rated for. If the valve is good for steam, it will also have a SWP stamp followed by a number. This stands for Steam Working Pressure, or the maximum pressure in psi that the valve is rated for in steam applications. The SWP pressure is almost always well below the WOG pressure. If the valve doesn’t have an SWP stamp, you should assume that it is not designed for the high temperatures of steam systems, and is not to be used as such.
If the system being worked on carries potentially corrosive fluids, then you need to define what the different fluids are, and do some research to find suitable valves. You may need to buy CPVC or stainless steel, or a valve made of a metal alloy. If it’s a flanged valve, you may also have to buy fasteners made of a specific anti-corrosive material as well.
If the valve you’re installing needs to be easily identified as open or shut from a distance, for an example, a valve installed in the overhead of a room or compartment, then you should be thinking about ball valves and butterfly valves with straight handles (the position of these valves is identified by the handle position. If the handle is in line with the pipe it’s installed on, it is open. If the handle is perpendicular to the pipe, it is shut), or rising stem gate valves with an OS&Y (Open Stem and Yoke) configuration. Rising stem valve’s positions are easily identifiable by the threads coming through the hand wheels of the valves. If the threads are out and visible the valve is open, if the threads are not visible the valve is shut. These are the only type of gate valves to be installed on boiler steam systems.
If you are a veteran mechanic in the trades, charged with mentoring an apprentice or young worker, then you need to ensure that he or she understands how ball valve and rising stem gate valve positions are identified very early on in their training. I have worked in a power plant with supposed journeymen who couldn’t tell, and it’s a potentially dangerous situation.
Now we can discuss a few of the more common types of manually operated valves. We’ll save check valves, pressure reducing valves, less common valves, and remotely operated valves for another day.
Gate valves are exactly what they sound like they are. They have a gate that rises in the center of the valve to emit flow, and it lowers across the center to stop flow. When a gate valve is open, the fluid runs straight through the middle of the valve.
With many gate valves, it’s easy to know what position they are in because of a rising stem. On the OS&Y valves we discussed before, the threaded stem will rise out of the valve when the gate is open, and retract into the valve when the gate is closed. Other rising stem valves are a little trickier, because if you don’t actually see the valve operate, you may not be sure if the hand wheel is far enough away from the valve body to actually indicate that it’s open.
Gate valves are designed to be open or shut and should not be used for throttling—that is regulating pressure.
Many globe valves have a similar outside appearance to gate valves, in that both are similar in shape—though globe valves have a more spherical shape, hence the term globe valve—and both have a hand wheel on top to operate it.
Globe valves have a disc that is raised and lowered by the stem onto, and off of, a seat and seat ring. Generally, flow comes into the valve below the seat, and when the valve is open flow exits out the other side above the seat.
Globe valves are designed so that they can be used in flow or pressure regulating situations.
Globe valves are generally much more expensive than comparable gate valves, so if you’re not going to use it for regulating, you’re better off spending less and getting a gate valve.
Ball valves have a round ball that sits in the middle of the valve. It has a hole through the center of the valve. It operates using a lever that turns 90°. When the hole in the center is lined up with the pipe, flow is emitted through the valve; when the lever is turned 90°, the solid part of the ball is now obstructing flow.
The beautiful thing about a ball valve is the ease at which you can determine the position it is in. When the handle is lined up parallel with the pipe that it is installed on, then the valve is open. When the handle is lined up perpendicular to the pipe, it is shut.
If you need a valve that you can get from open to shut, or shut to open very quickly, ball valves are often the best answer. It is this same ease of operation that can also make them dangerous in the wrong situation.
You must be careful where you install ball valves, because they can be opened or shut by accident quite easily. If you walked by one in a precarious position, you might hit the handle with your foot, or your loose fitting clothes might catch on it and turn the handle. Either of these situations could lead to very dangerous results.
Butterfly valves would seem to be a cross between a ball valve and a gate valve. They have a gate that restricts the flow when shut like a gate valve, but instead of rising, the gate turns 90° to stop flow. Like ball valves, they are easy to open and shut, but they don’t always have a lever like a ball valve. Sometimes they have a round hand wheel like a gate valve.
Most PVC and CPVC valves are of the gate valve or ball valve variety.
As was stated before, there are many more types of fittings and components that can fall under the umbrella labeled valves. It is best that we take a look at valves like check valves, remotely operated valves, and pressure reducing valves, in separate articles rather than try to cover them all in one article.
The important points to remember for installing manually operated valves are:
Make sure the valve you install is rated to withstand the pressure and temperature of your system.
Make sure the valve you install can stand up to the elements that it will be exposed to, whether they are internal elements like corrosive fluids, or external elements like weather conditions.
Make sure the valve you install has all of the characteristics that you need in your particular situation.
Make sure the valve you install operates correctly before you install it, and grease the stem as necessary to ensure that it does.