- Published on Monday, 28 July 2014 10:24
- Written by Chris Warnett
The use of automated valves has increased continuously as the global demand for industrial and municipal infrastructure has grown around the world. Many developing countries have seen significant investment in both the private and public sectors which often involves building or expanding automated plants.
Automation allows plants to run efficiently and continuously with fewer personnel. Automated valves are always available for immediate operation in environments that could be inaccessible, hazardous or uncomfortable for physical manual operation. In addition, these valves can easily be operated together or individually from a remote control station.
Extreme Environmental Demands
While there continues to be disagreement on the extent and causes of climate change, there is now recognition in many countries, particularly in Europe, that weather extremes are real. And, while automated valves and their controls have become increasingly sophisticated to handle taxing conditions in difficult environments for decades, these new extremes in precipitation, wind and temperature are creating new challenges. There is no question that equipment on plants must be proof against the worst possible weather that may occur at their particular location.
Valve actuators are perhaps the most vulnerable item of an automated valve assembly. If electrically powered, they will contain a mixture of electric, electronic, elastomeric and metallic components. Fluid powered devices, though not directly electrically powered, could contain similar materials for control and feedback components. The environment in which these devices are installed will determine the material selection and to some extent their design.
Modifying for the Extremes
As a general rule, most standard valve actuators are suitable for about -20F to 150F (Approximately -30C to 70C). However, in ever increasing circumstances, these devices are required to operate in greater extremes of temperature, either because equipment is being used in more remote and hostile environments or because of climate change.
In Russia, some engineering specifications are calling for capabilities down to -76F (-60C). Conversely, some Arabian countries require capacity to operate up to 176F (80C). Clearly these extremes are outside the typical standard range of even heavy duty actuators. Special modifications, materials and even design changes are needed to accommodate these extremes.
Elastomers for sealing fluid power cylinders and other enclosures must retain resilience to form an effective seal. At low temperatures, some elastomers become too stiff, and leaks occur. At high temperatures, the seal must neither melt nor harden. Special seal materials such as Viton are often chosen for extremes of temperature rather than the commonly used Nitrile rubber. Care must be taken with the selection of lubricant used to ensure compatibility with the seal material to avoid swelling or other deterioration of the seal.
For cold temperatures, there is often a misunderstanding regarding the “wind chill factor”. Wind chill is a factor describing the rate of heat transfer, and although it’s of significant impact to living creatures, it has no bearing on the temperature rating for valve actuators.
Precipitation, humidity and moisture are the enemies of field devices such as valve actuators. The electric and electronic control and position sensing components are vulnerable to moisture and corrosion. The extremes of precipitation, storms and flooding that have occurred in recent years highlight the increasing need for actuators that can withstand torrential rain and humidity to the point of temporary submersion.
Many municipal water and wastewater plants are located in low elevations. They are particularly vulnerable to flooding from the streams and rivers that provide their inflow water or accept their treated outflow. Some plants are regularly flooded, putting field devices and automated valves at risk of submersion. Many actuators are now capable of withstanding these extremes and can be submerged for several days without damage. The sealing capability of electrical enclosures has also been substantially refined, particularly on electric actuators. Many manufacturers can now claim enclosures to the NEMA 6 standard “occasional temporary submersion” (IP67), or even NEMA 6P “occasional prolonged submersion” (IP67 or even IP68).
Perhaps the most arduous environment is that found offshore. Not only does the actuator enclosure have to protect the internals from moisture ingress, but the body of the actuator itself is constantly under attack from the salt-laden moisture in the atmosphere. For that reason, there are a variety of user specifications for materials and coatings for offshore valves and actuators such as the Norwegian Petroleum Industry standard NORSOK M-501.
The valve and actuator industry has for some time been providing specialty equipment to operate in the most extremes climates found on the planet. The experience gained in developing and applying sealing and other technologies to ensure reliable operation in these environments is invaluable. Many types and makes of valve actuator (both electric and fluid powered types) now have sealed enclosures with non-intrusive set up and configuration capabilities. The ability to make adjustments to the actuator without exposing the internal electric and electronic components to dirt and moisture is a large factor in their improved resistance to extreme environments.
These designs allow actuators to be located in places that would be hostile and dangerous for human beings. The valve and actuator industry is ready to supply equipment for any extreme climate, regardless of its location in the world.