Recently enacted worker safety regulations in Europe and the U.K. are among the factors behind a surge in use of an innovative remote mechanical valve actuator (RMVA) from Smith Flow Control Ltd.
The company, based in Witham, England, with a U.S. office in Erlanger, Ky., is a longtime supplier of FlexiDrive, which uses a patented continuous-loop cable system to open and close valves located as much as 60 m (196.8 ft) from an operator's station.
The regulations stipulate that RMVAs can no longer be chain-driven. Simon Read, U.K.-based project sales manager for Smith Flow Control (SFC), says this is because many chain drives suffer from corrosion, which creates safety hazards for operators if they break as torque is applied. As a result of the regulations, petroleum companies - notably BP and Shell - are replacing chain-driven RMVAs, opting instead for cable-driven systems.
In the United States, safety is also a factor in FlexiDrive's sales, though from a different source: insurance companies. "A guy who needs to climb down a pit to reach a valve, build a scaffold, or reach over a railing for access could hurt himself," said Andy Hugenberg, site technician for SFC Inc. in Erlanger.
As a result, when insurance companies conduct risk analyses of facilities, they look for safer alternatives. FlexiDrive and related equipment from the company permit operators to open or close valves from level platforms or the ground.
Other factors driving sales of SFC's RMVA include growing demand for remote-actuated valves in the petroleum and chemical industries and in nuclear power plants, many of which are being built or updated around the world. According to data from the World Nuclear Association, an industry group based in London, more than 60 reactors are under construction in 13 countries, and plans are in place to extend the life and electricity-generating capacity of more plants, including those in the United States.
In addition, there is word of mouth. Hugenberg remarks that a lot of people move around in the petrochemicals industry and often take information with them about products. "Our systems are not usually specified on the front end of plant design," he said, but are often installed after a risk analysis or similar review.
SFC supplies two FlexiDrive models: the LV, or large valve version, and SV, for small valves. LV drives are primarily suited for high-flow installations such as oil and gas rigs, refineries, and chemical and water plants. SV drives are designed for lower-capacity applications -- one target of which, Read notes, is nuclear plants. LV drives generate up to 225 Newton-meters (166 ft-lb) of force in a 4:1 geared turning ratio, while SV drives generate 20 N-m (14.75 ft-lb) of force.
What separates FlexiDrive from competitive systems, Read explains, is the continuous-loop cable that extends operating length. The patented design comprises an inner cable and a helically wrapped outer cable, both of which are made of high-tensile steel. The cables are encased within a polypropylene liner.
The patented aspect of the construction covers the hard-crimp design that connects the assembly into a continuous cable and the use of spring-loaded heads in the gearbox at the operator's station that depress when they come in contact with the crimp. As a result, the cable can travel 180 deg around the gearbox without obstruction. Most competitive systems, in contrast, only achieve cable turns until the crimp or other connecting point comes in contact with the gearbox.
This feature allows remote actuation from up to 60 meters in direct applications, and as much as 540 deg of bend, a measure of how many angles the cable accommodates from the operator's station to the valve. (The more degrees of bend means the less operational distance there is between stations.)
"The straighter the route, the more torque an operator gets," Read said. Nevertheless, with its ability to accommodate multiple bends, FlexiDrive can be installed to operate through walls, over (or under) walkways, up or down spaces, and across angles. The system is also submersible to 20 m (65.6 ft), a benefit that's mainly for valves in flood-prone pits, drains, sewers, and other water-intense installations.
The system is relatively simple, at least in the number of components. These include the operator's station actuator, which provides torque to a remote valve, usually by use of a handwheel, the cable assembly, and the valve station actuator, which is a coupling that attaches to the remote valve stem and transmits motion to it. The stations have stainless steel casings and internal parts and bronze bearings. The system operates in a range of -30 to 175°C (-22 to 347°F).
FlexiDrive is a manual system. Read says SFC has had discussions with customers about installing an automated actuator with it, but nothing has developed.
The U.S. Navy developed the system to operate valves below deck. SFC acquired exclusive worldwide rights to the design for sale to the oil and gas industry but found that the system needed to be more robust. Initial systems emerged from these upgrades a dozen or so years ago.
A FlexiDrive valve actuator at an industrial plant. The inset photo shows the operator's station handwheel with gearbox and valve "open" and "closed" indicators in red. Credit: Smith Flow Control