The first time you see a tank farm, it is a colossal sight. Tanks at least 50 feet high with pipes connecting them completely dwarf and surround you. The entire area is filled with pipelines, occasionally mounted by valves. These valves, standing several feet tall, are critical for proper control of the system. But the pipelines, which span large expanses, must become automated to ensure proper process control and guarantee safe operations.Historically, valves were developed as individual units that required, in most cases, manual operation. It was not unusual for plant personnel to open or close large valves manually for safe shutdowns. Over time, computers gained popularity within the processing industry, and design engineers adopted this technology to develop plant management systems that could automate valve shutdown. Eventually, solenoid valves became the common way to control such automated valve systems.
Tank farms are an excellent example of how solenoid valve applications have helped systems progress from manual to automatic operation, facilitating finer and safer control in processing plants. Throughout the evolution of valve technology, there are many examples of how the need to run process systems more efficiently, reliably and safely has precipitated a new technology. An understanding of the demands of today’s chemical processors makes it possible to glimpse the future of valve technology.
Solenoid Valve Evolution
During the 1970s, the chemical industry primarily utilized linear control valves that employed a rising stem. Once automated, these valves required pipe-mounted solenoid valves. Solenoid valves designed initially for linear control valves were, at this point, playing double-duty because they were being used for quarter-turn ball valves as well.
The quarter-turn ball valve, with its suitability for automated packages, began to gain popularity in the 1980s. In time, actuator manufacturers began to develop their own flat plates. They embedded these flat plates into the actuator by using an interface that had a direct-coupled solenoid valve. This flat interface found its way in time to close coupling against a flat-style valve. Eventually, spool valves replaced the flat-style valve for this application.
However, because standardization was not widespread at the time, each actuator manufacturer tended to have a unique interface configuration. Consequently, solenoid valve manufacturers needed to design five to six different styles of valves to fit onto these various actuators. It was not until the 1990s that the valve industry instituted its own standardization for an interface with the solenoid valve.
Fortunately, the chemical industry in Germany took matters into its own hands and developed a standard referred to as NAMUR. This standard and the use of pad-mounted constructions quickly gained popularity in the European market. However, the U.S. was slow to accept the European standard because of costs and differences in wiring methods. In the mid-1990s, all other special pad configurations became obsolete as actuator manufacturers worldwide switched to NAMUR.
Higher Flows with CEN
It has been a decade since NAMUR took a firm hold in the U.S. market. However, as market conditions change, so do standards, and NAMUR has not been immune to this trend. There is a new European CEN standard called CEN/TC69/WG1/ SG10/0/N023, which is an extension of the VDI/ VDE3845 requirements. This CEN standard now covers even higher flows than NAMUR previously covered. To date, there are few manufacturers that actually have developed valves to conform to this new CEN standard. Future solenoid valve design is sure to accommodate this product gap.
RoHS and Green Design
The new RoHS standard also will change the design of solenoid valves. RoHS restricts the use of six hazardous substances within electrical and electronic equipment shipped to Europe as of July 1. It includes any product with minimal levels of lead, mercury, cadmium, hexavalent chromium Cr, polybrominated biphenyls, and polybrominated diphenyl ethers. Solenoid valves typically have small amounts of some of these restricted substances. For example, hexavalent chromium Cr has been the standard plating used in the electrical industry for corrosion protection. In the near future, solenoid valves and many other products will require alternate plating compounds.
Some companies, rather than shipping crude oil to industrially developed countries, choose to build processing plants closer to the source of oil. These geographic changes have an effect on solenoid valve design. For example, companies are looking for valves with higher temperature requirements for their processing plants in the Middle East, where the desert environment demands valves that operate at high ambient temperatures. The future will see valves that can be used in hot, arid climates as the demand for specialized designs continues to increase.
Safety, Safety, Safety
Many solenoid valves are used to control safety shutdown, one of the most important attributes of any process valve system today. By its very nature, the chemical processing industry has stricter safety standards than other industries. Valves that sit in pipelines remain open 24/7 and must continue to work reliably while allowing continuous flow.
However, in a safety shutdown, plant operating systems receive a signal indicating a problem and the need to shut down everything within seconds. In such an event, these systems require the valves to function instantly - even when the energized valves have not cycled for a year. Guidelines for safe operation suggest that all components should be routinely cycled, but in some cases this is not possible. Consequently, chemical manufacturers must select products used in safety shutdown systems carefully. Today, firms utilize computerized safety systems to ensure proper valve operations and safe shutdown. The future will bring more actions to enhance valve systems and designs to improve plant safety. The changes are discussed briefly in the following paragraphs.Redundancy Factor
Traditionally, four-way solenoid valves are designed to have a single or dual operator for momentary or maintained position control. However, new product specifications are requesting redundancy. With a redundant-type valve, both coils working in tandem do not affect the valve’s performance. If one coil fails, the other coil operates the solenoid valve on its own. This type of valve provides plant personnel with the extra assurance that the valve will function when it must. The International Organization for Standardization (ISO) has written a safety shutdown standard called S84, which suggests redundancy. In the future, numerous solenoid valve designs will institute redundancy to ensure safe systems.
A new IEC standard, 61508/61511, requires manufacturers to supply information on valve reliability. Manufacturers must obtain a SIL (safety integrity level) rating to indicate how long valves will last and how long they will work satisfactorily before replacement or repair. In the future, plant operators will incorporate reliability data into their plans as a way to develop maintenance schedules.
Historically, newly written standards have help