- Published on Tuesday, 12 November 2013 09:47
- Written by David Montgomery
There is something about opening a box labeled “some assembly required” that causes one of two reactions—the joy of the challenge or dread. In actuator commissioning, the dread comes from not being an actuator expert, in which case installing and commissioning that actuator may appear at first glance to be difficult.
But even though the task may look daunting, actuator manufacturers have taken great care to simplify the setup of both simple and robust feature sets so that the commissioning process can be as smooth and error-free as possible. How to make that a reality is the subject of this article.
One of the first tasks faced in commissioning comes from the fact not all actuators are installed as soon as they are received. In many cases, they need to be stored for an extended period of time. Short-term and long-term storage procedures are found in the actuator installation-operation-maintenance manual (IOM) or are available from the manufacturer in a separate document. It is critical that these procedures be followed so the actuator is properly protected and ready to work when the installation takes place. Also, product warranties are normally voided if the procedures are not followed, so taking the time to read and follow the steps is critical.
Once the box is opened and contents removed, there are a few basic steps to walk through. Like any product in a box with “some assembly required,” the first step is to ensure you have what you ordered, including all the parts promised. Electric actuators are supplied with a product nameplate on the gear housing that provides the model, size, motor information, lubrication type and often tagging data that identifies its installation location or provides other information relative to the actuator’s place in the plant process. Check that data against the purchase order or similar document. Not all valve torque, thrust or speed requirements are the same; the actuator needs to be mounted to the correct valve, and the valve and actuator assembly needs to be mounted in the correct process location to perform properly.
SAFETY PRECAUTIONS AND PRACTICES
Safety precautions and practices identified in either the product IOM, on the actuator itself or in other documents need to be followed. Such procedures are typically listed near the front of the manuals and are associated with the installation instructions. Read through the warnings, cautions and notes and become familiar with them. Failure to follow precautions can cause a serious safety risk to personnel or permanent damage to the equipment. Follow all outlined practices to keep people and equipment safe.
OUT OF THE BOX, INTO THE PROCESS
Both mechanical and electrical considerations guide the commissioning process. The mechanical steps include mounting the actuator to the valve or mounting the valve/actuator combination into the plant or pipeline system. Follow the valve manufacturer’s guidelines provided or made available for the installation of the valve/actuator combination.
For multi-turn valve applications such as gate or globe valves, or slide gates, it is important to pay close attention to the stem and stem nut connection when mounting the actuator to the valve.
For a threaded stem nut, the stem to stem-nut engagement should be smooth with a good, close fit. The stem should be lubricated, suited to operating requirements and environmental factors. Some actuator designs allow top entry of the stem nuts. Once the actuator is bolted into place on the valve adapter with the proper length, the stem nut can be installed by hand-threading onto the valve stem until it engages with the drive sleeve. After that, rotate the actuator hand wheel until the stem nut is seated in the proper position within the drive sleeve. Thread the lock nut or similar locking hardware into the top of the stem nut and stake into place.
Some actuator designs require the stem nut to be mounted into an actuator thrust base, which is then bolted to the actuator gear housing. When the thrust base is disassembled to install a separately supplied stem nut, be careful to reassemble the bearings and other components in the correct location and order. Consulting the actuator IOM provides help with this step.
There are two ways to mount the actuator to the valve mounting adapter:
- Once the thrust base is reassembled with the machined stem nut in place, hold the base steady and thread the stem nut within the base onto the valve stem (or thread the thrust base assembly) until it comes into contact with the valve mounting adapter. Bolt the thrust base to the valve mounting adapter. Lower the actuator onto the thrust base, ensuring that the actuator thrust base stem nut lugs properly engage and align with the drive sleeve slots in the actuator gear housing. Bolt the actuator to the thrust base.
- With the thrust base containing the machined stem nut attached to the actuator housing, suspend the actuator above the valve stem and align it vertically with the stem. Lower the actuator until there is contact between the stem and the stem nut. Rotate the actuator hand wheel to engage the stem threads with the stem nut threads. Continue to lower the actuator until it contacts the valve mounting adapter. Bolt the thrust base to the valve mounting adapter.
Pay attention to the stem-to-stem-nut engagement when the valve is in the fully closed position. At a minimum, the engagement length should be 1.5 times the stem diameter.
In butterfly valve, ball valve, plug valve or damper applications, electric actuators come in two designs: a direct mount, part-turn or multi-turn actuator in a single housing or an electric actuator coupled to an external gearbox. In these designs, the stem adapter is bottom-entry, with bore and keyway dimensions that mate to the valve shaft. Typically, the stem adapter is installed on the valve shaft and the actuator or gearbox is lowered into place, engaging the external splines on the stem adapter with the mating splines on the actuator or gearbox drive sleeve. Take care to align the stem adapter to the valve shaft so that the full-open and full-close valve disk positions can be set correctly.
For electro-mechanical actuators, there are a few basic steps that should be followed to achieve favorable results.
First, the power supply needs to be brought into the control compartment and connected to the terminals on a terminal strip marked for these leads. Give careful attention to the conduit connections to the actuator conduit entries. Improper conduit sealing can result in moisture entering the control compartment or terminal housing. In some cases, moisture can be introduced into these areas from inside the conduit. A thorough inspection of the conduit piping and the conduit installation on the actuator can eliminate short-circuiting caused by moisture on the contacts, which can in turn cause actuator failure.
Second, set the open and close position limit switches or position limiting device. Depending on the manufacturer, up to 16 contacts allow for setting the end limits, for position indication, and for sequencing or interlocking with other plant equipment. The IOM serves as a guide through the setting procedures. The valve can be moved from the open to closed position by the hand wheel or by electricity. If the actuator is operated electrically, it is important to move the valve disk well off the valve seat in case the actuator runs in an opposite direction to the intended direction because of phase reversal of the power supply. If the phase rotation is incorrect, disconnect the power leads and rewire them to the power terminals. This process normally will correct phase reversal conditions. Recheck the rotation of the drive sleeve to confirm that the phasing is correct.
Third, set the actuator torque switch or torque limiting device. Consult the IOM for proper setting to ensure the actuator and valve are properly protected during electrical operation.
For electronic, non-intrusive actuators, the commissioning process is much different because of the digital technology used for setup and operation. For these actuators, the setup is achieved by answering a series of questions visible on an LCD display installed in the actuator control compartment cover.
Simple, trouble-free commissioning is achieved for some manufacturers’ products through use of the locally mounted control station, where the selector switches serve two functions: local or remote operation of the actuator, and actuator commissioning by toggling the same switches to step through the setup menus in the display.
Other manufacturers use hand-held devices to accomplish the setup, in which case care must be taken to ensure the batteries are fresh in the device and that it can be secured so it is available when needed.
As with electro-mechanical actuators, the IOM for non-intrusive actuators will serve as a guide through display options such as languages, calibrations, settings and option selections. Some considerations include:
The power supply needs to be brought into the control compartment and wired to the proper terminals on the terminal block. For most manufacturers, the terminal block is housed in a separate compartment rather than in the controls compartment. The precautions mentioned above for conduit connections on electro-mechanical actuators also apply to electronic, non-intrusive actuators. Improperly installed conduit poses a serious risk to actuator performance.
Once the actuator is powered up, follow the on-screen instructions to select the language. Up to 15 languages can be made available, depending on the manufacturer. The display screens vary by manufacturer, using either normal language or symbols. Language-based displays provide the user easy-to-understand menus and selections. But symbol-based displays also can be effective once the symbols are understood. In either case, understanding the choices in the setup routines is critical to obtaining the desired operation of the actuator.
Calibrate the position limits, following the same precautions as required for an electro-mechanical actuator relative to valve disk positioning. Most non-intrusive actuators employ encoders for accurate and repeatable positioning. Absolute encoders with redundancy have an advantage in that the design does not require batteries to maintain position information on loss of power, providing the user with maintenance-free and reliable setup.
Enter the setup mode by operating the control station knobs or similar device, as described in the IOM. Once in this mode, questions to complete the commissioning process can be answered. The software guides users through the menus based on how the questions are answered. Non-intrusive actuator IOMs are normally supplemented by or include guides that provide detailed instructions on the menu selections. Manufacturers have tailored these documents to address the wide range of features available in electronic actuators. The easy-to-follow formats are important to provide clear, step-by-step instructions that enable the user to commission the actuators with confidence.
Operate the valve from fully open (100% open) to fully closed (0% closed) or reverse to confirm the position and torque limit settings are accurate and the desired features are working properly. If the power supply is three-phase, checking for correct phasing is not needed. Non-intrusive actuators correct electronically and also notify the user if a phase is lost
The oft-heard phrase: “first, read the instructions” certainly applies to successful commissioning of an electric or electronic actuator. This is because success relies on understanding the product purchased, following safety precautions and practices, and following instructions explicitly as described in the manufacturer’s IOM. Following these steps can remove the “dread” and result in proper actuator performance.