A Beginner’s Complete Guide to Valves
When fluids move through a system, they will flow naturally when unimpeded. The fluid will run through any piping or attached components at a rate based on the amount of internal pressure and the natural inclination to achieve balance. However, allowing materials to flow at that rate isn’t always ideal for certain operations, and that’s where valves come in.
What is a Valve?
A valve is a mechanical device that controls the rate at which fluids pass from one section of a system to the next. The function is similar to that of a switch or a controlled door. When the valve is open, liquids and gasses can move between the two sections at the rate dictated by the amount of pressure built up when the valve was closed. And, once the door is closed, the flow is stopped.
Valves can also be partially opened. This controls the speed at which the fluid moves from one section to the next, by limiting the amount that can move through at any given point in time.
Parts of a Valve
To perform the required function, valves are made of multiple parts. Often, the parts of a valve are made predominately of metal or plastic, though internals seals might be made of rubber. The exact materials involved are often determined by the nature of the liquid or gas that is being controlled. Certain fluids can damage metal or plastic, so the parts of a valve that directs those materials must be chosen to limit the amount of damage through contact.
The main part of a valve is the body. This is the section that connects one part of the system to another, and that allows the fluid to pass through the valve. It also comprises the outer casing of the valves construction.
The openings within the body that allow fluid to pass through are the ports, and each port is associated with a valve member or disc. The disc can obstruct the flow of liquids or gasses through the valve body. When the port is closed by a disc, the flow of material stops. When the port is open, the flow is restored.
Valve discs rest in parts of a valve called a seat. This is an interior surface of the valve that ensures the disc remains in its proper position based on whether the valve is open or closed. Seats are classified as either hard or soft depending on the material of which it is made. Discs that operate on a hinge or trunnion only contact the seat when in the closed position. In contrast, discs that work through rotation are always in contact with the seat.
The parts of a valve that physical open or close the disc itself are called stems. Motion directed through the stem through linear force or rotational torque causes the disc to shift. In some circumstances, the stem is integrated with the disc, but that is not always the case.
Valves are controlled manually, remotely, or automatically. Manual valves often have a handle or wheel that can be used to open and close the discs based on physical position. For example, when you turn on the flow of water through a faucet, you are interacting with a manual valve.
Remotely controlled valves use the same basic mechanics as manual valves but are operated by an actuator. Actuators are devices that provide the function of a manual value without the need for physical interaction with the device.
Automatic valves are associated with self-regulating systems. For example, a relief valve automatically opens when the internal pressure in the system reaches a specific point. Once that amount of pressure occurs, the valve automatically opens to vent the excess pressure. Then, once the pressure has sufficiently decreased, the valve automatically closes.
Different Types of Valves
The parts of a valve are not universal for every valve variant. Different types of valves feature differing construction and may include different valve parts. Some common valve types include:
- Ball Valve
- Butterfly Valve
- Cock/Plug Valve
- Gate/Sluice Valve
- Globe Valve
- Needle Valve
- Poppet Valve
- Spool Valve
Different valves work best under different circumstances. Spool valves are fairly common in hydraulic systems, while needle valves provide precision for the proper operation of carburetors. Globe valves are often used in water faucets while cock valves control the flow of water in toilets.
Often, valves are used to control the flow of potentially hazardous materials. The valve prevents these liquids or gasses from escaping the system and potentially posing a safety risk. However, a single valve would have to be 100 percent reliable to meet that need.
Over time, valves can fail and, in some cases, a valve failure is desired to preserve the integrity of other parts of the system. Safety valves are designed to regulate potential hazardous situations that arise when the pressure in a system becomes too great.
For example, a steam engine often features a safety valve. When the internal pressure gets too high, the valve opens to safely vent some of the excess pressure. This helps prevent damage to the engine should the high pressure not be released, and also helps lower the chance of injury by directing the steam to a location that should not pose physical harm to those nearby.
Most safety valves are designed to open automatically when certain conditions are present, though most come with a manual operation as well. That way, if a potentially hazardous situation is imminent, a person can choose to open the safety valve in advance of the extreme pressure required for it to open automatically.
Shut Off Valves
Shut off valves are also used to prevent dangerous conditions in cases where the flow of fluid becomes uncontrolled. For example, most gas stations feature emergency shut off valves. If part of the system fails, gasoline may escape the system, such as a damaged hose spraying fuel unimpeded. The emergency shut off valve stops the flow of gasoline to every pump, quelling the potentially dangerous situation.
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