What is a valve actuator?
An actuator is a device that assists or semi-automatically opens a valve. An actuator that is hand-operated assists a user in opening and closing a valve is meant to make it easier to turn a handle or lever in order to open a valve. A semi-automatic actuator opens a valve when a button is pressed by a user. Actuators can be very convenient for operating valves and some can even be operated remotely. It’s important to understand how each actuator operates before you use one. Each design has pros and cons that must be accounted for when implementing into a system. This article will cover 5 common styles of actuators used in the pipe, valve, and fitting (PVF) industry.
The first style of actuator we’ll discuss is the most simple and is referred to as a manual actuator, or hand actuator. A manual actuator usually has a hand wheel on top. Under the handle is a box containing a set of gears, and sometimes bearings. These gears make it easier to rotate the handle and open the valve.
Another type of actuator used in the marine PVF industry is the solenoid actuator. This style uses an electromagnet to open a disc and, usually, a spring to hold the disc open or closed, depending on the design (discussed later in this article). The way this works is that the valve is naturally resting in an open or closed position. Then, a user presses the operating button, sending an electrical current through the actuator. This powers a magnet, which moves the disc away from its resting position and either opens or closes the valve. When the electrical current is removed, the spring moves the disc back into its resting position.
A solenoid actuator is fine to use when operating smaller valves which control flows at low pressure. However, solenoid valves need a lot of energy to power a magnet, so the more pressure in a valve operated with a solenoid actuator, the more energy is required to open or close it. As a result, solenoid actuators are not recommended for high-pressure valves.
Using a solenoid actuator is a fast, simple way to operate a valve, but it does not allow for throttling. As an exception, some solenoid actuators may include a hand-operated lever or handle as well as the operating button. This allows for manual throttling of the valve, but the intended purpose of a solenoid actuator for normal operation is not throttling. Manual override of a solenoid valve is usually done only in emergencies, such as when power goes out and there is no electricity to power the solenoid actuator.
Another style is the electric actuator. These actuators operate by the use of a button which signals a motor to either open or close a valve. Unlike a solenoid valves, these are normally slower in operation. The disc can be positioned at closed, opened, or anywhere in-between, and some electric actuators even have indicators to help a user determine how much a valve is being throttled. The clear downside to an electric actuator is that if there is no power, the valve is stuck in its current position. These valves can be followed with a check valve or other safety precaution in case the power goes out.
Pneumatic valve actuators are held in an opened or closed position by a spring. This style of actuator uses an air-tight sealed chamber with a diaphragm separating the top and bottom of the actuator. A pump pushes air into the chamber forcing the diaphragm down, which either opens or closes the valve (depending on the design). These types of valves are not intended for situations in which air pressure is likely to change dramatically such as high elevation or deep underwater. Using a pneumatic actuated valve in the wrong atmospheric conditions will likely result in failure or malfunction.
This hydraulic actuator can be used on various valves, such as gate valves or butterfly valves, and has a hand wheel for manual override.
Hydraulic valve actuators are very similar to pneumatic valve actuators. The primary difference is that hydraulic actuators use hydraulic fluid instead of air. Like a pneumatic actuator, a hydraulic actuator is also held in place by a spring. The downside to a hydraulic valve actuator is that it can require regular maintenance and refilling of fluids, which can leak after a period of time. These are also pressure-sensitive, so check your operating conditions before choosing a hydraulic valve actuator.
Hydraulic valve actuators, as well as the other styles of actuators, may be designed to fail open or fail closed. This is a safety feature for a situation in which the power to the valve actuator fails. For example, if there is a sudden shift of atmospheric pressure, a pneumatic valve actuator may be designed to fail closed, meaning that when it doesn’t function the way it’s intended to, a spring will force it closed. If it is fail open, a spring will force it to stay open instead. Unless your actuator is only assisted, plan for the worst case scenario. Think about atmospheric pressure, consistency of power to the actuator, and how accessible the valve is (actuators can take up a lot of space).
Most of all, when you’re ready to install an actuator on your valve, contact the Marine Valve Experts™ at Tork Systems, Inc. We’re here to make your job easier and find you the parts you’re looking for fast!
- Ask The Experts: What is a valve actuator? - October 27, 2015
- Ask The Experts: What is a butterfly valve? - October 20, 2015
- Ask The Experts: Bolt Patterns - October 6, 2015
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