By Gobind Khiani – Consulting Fellow-Piping/Pipelines. Posted by Sarah Bradley.
Comparing the Options
Valve Operators are indispensable accessories for reducing plant operating costs, and improving safety. This is especially true in current critical service and complex plant operations, where safety is of utmost importance.
Valve Operators are also extremely valuable on large valves requiring considerable torque, energy, and power, to open and close. Cylinders and motor operators are ideal for hazardous and difficult to reach and remote locations, and for valves that must be operated either infrequently or frequently. Controls can be provided integrally or at remote positions and can be programmed to respond to practically any signal or operating cycle requirement.
Alternatively, Gear Operators are standardized, easily mounted operators for rising stem, and non-rising stem gate valves. Further, gear operators are used in all types of valves in lieu of a handle operator. The gear operators are completely self-contained units that are totally enclosed and permanently lubricated. They can be factory installed on new valves, or they can be used for field conversion to gear operation, and this usually can be done without removing valves from the line. Changeover is often simple and fast with the complete conversion kits available to install with each operator.
Extension stems are frequently required for valves that are to be operated from a distance or below ground services. Ordinarily, a floor stand is used to support the stem and hand wheel, but in many installations, only the extension stem is used. Extension stems that are long must be rigidly and properly guided with supporting brackets. Extension stems can be furnished for outside screw and yoke gate valves, non-rising stems gate valves, globe valves and angle valves. Floor stands are suitable for operating either non-rising or rising stem valves. They are available either with or without indicators and can be installed with bell bottom bases for use on non-rising stem gate valves projecting over floor lines.
Sprocket Rims are for convenience in operating valves above a normal reach from floor levels. They are designed to provide a positive grip on the chain under the most severe operating conditions. Guides hold the chain in close contact with a large portion of the circumference of the wheel preventing slipping or jumping of the chain. Hammer blow sprocket rims are used to facilitate opening and closing large size or high pressure valves, especially in power plants with steam applications.
Butterfly Valves and Stem Extensions
Butterfly valves offer great performance capabilities including bubble-tight on/off service, dead-end service and ease of installation, along with a variety of trim options to handle a wide array of service conditions. The lighter weight of butterfly valves (compared to traditional gate valves), quarter-turn operation, and the smaller overall product envelope make butterfly valves perfect for buried service, or on original equipment where stem extensions may be required.
Valve manufacturers provide butterfly valve extensions from just a few inches in length to over 16 feet, and can customize extensions to meet conditions. Clearly, smaller extensions are not very challenging, but as the extension gets longer and heavier, design criteria of the valve must be considered. For instance, the weight of the extension sitting on top of the stem can affect valve performance. A longer extension may require a different gear operator. Extensions can prove to be custom to each application. A good example of a well-engineered extension stem for a particular service and butterfly valve is a 48” extension on a 16” stainless steel high-performance butterfly valve. This allows for the use of the standard gear operator and mounting hardware. The added weight of the extension should be considered during design and negated by the use of bearings and a shoulder in the outer tube to carry the total weight of the extension, thus leaving the valve to perform as originally designed. In addition, a factory designed and assembled extension insures a perfectly vertical stem, reducing operating torque. Field designed extensions may not incorporate all of the valve design features and may not yield the service life expected from the valve.
Conclusion
If you find yourself in need of a butterfly valve with stem extension, do consider the listed items to help design an extension with the valve and application in mind. Valve operator maintenance is an essential part of the valve process and must not be overlooked. Routine maintenance can assist in satisfactory valve performance.
Quick Tips
Do not get caught with your pipe hangers down: Hanging piping is not enough, pipe hangers must function not only before, but after, a system is put into service. It is good piping practice to check hangers, as well as valves. If a line seems to be settling or sagging in spots, a few turns on the hanger adjustment will restore the pipe to proper position.
Do not overlook leaks: A leak in a valve, small or big, often can be remedied simply and in a hurry, if caught in time. Stem leaks normally can be fixed by slightly tightening the packing nut or gland. Bonnet and flange leaks can be caused by bolts loosening under service strain. If tightening the joint does not stop the leak, then inserting a new gasket probably will.
Do not spare the oil can: Wear on stem packing is due mainly to the rising and turning motion of the valve stem, combined with deteriorating effects of service conditions. A few drops of oil on the stem, regularly, can help to reduce friction and wear, including lubricating exposed stem threads for multiple operating valves.
Pull up evenly on packing glands, and repack when necessary: Stuffing box leaks usually can be stopped by merely “pulling” up the packing nut. On bolted glands, care must be taken to tighten bolts evenly as severely cocking the gland will bind the stem. If the stuffing box must be repacked, it usually can be done while the valve is in service.
Periodic inspection, the best preventive maintenance: Most valves are designed to permit periodic inspection without seriously interrupting service. Without removing the valve body from the line, the complete bonnet and disc assembly can be removed for cleaning and inspection. Seating surfaces in the body can be checked at the same time.
About the Author
Gobind N Khiani, a UCalgary alumnus of Masters in Mechanical Engineering is a seasoned change-maker. He has a proven track record in technical and value engineering and holds a Fellowship in Engineering and an MBA. He is the Chairman of the End User Group at API and Vice Chairman of the Standards Council of Canada. He has done peer review on Emissions Management regulatory documents for ECCA and participated in research and development initiatives. Further, his experience is in the energy sector in the improvement of standards, technical compliance, strategy,governance, digital innovation, engineering management, technology, sustainable development, and operations. He is also skilled in Asset Integrity and Maintenance Management. As a volunteer, he is involved in technical standards (energy,tech, public safety) and has been a mentor/judge at First Robotics Canada. He is also the past chair of the CBEC of APEGA.