Drivers of next-generation vehicles in India can be thankful that the country's natural-gas fueling stations are employing solenoid valves that can operate for as many as 20 million cycles.
The solenoid valves, employed in dispensers that meter alternative fuels, are said to be critical because drivers in India often must wait in mile-long lines to reach the stations. Engineers say that with such long lines, and with stations serving between 300 and 400 customers per hour, stations can't afford to shut down pumps because a valve has failed.
"If the solenoid valve fails, there's no way you can use the dispensing system," says Zubin Canteenwalla, a design engineer for Ontario-based Fueling Technologies, Inc. (www.fuelingtech.com), maker of the dispensing equipment used in the Indian application. "With the huge lines they have at the stations, they can't afford to have a lot of downtime."
Fueling Technologies, which specializes in the design of equipment that dispenses compressed natural gas (CNG), liquefied petroleum gas (LPG), and hydrogen, is currently using a Skinner 7000 Series Valve from Parker Hannifin (www.parker.com) to engage the dispenser's ball valve actuator. During operation, gas is piped into the dispenser and then flows to the actuated ball valve before it is distributed to customers. The actuated ball valve, however, can't distribute the fuel until it receives a pneumatic control signal from the solenoid valve. When fuel is needed, an electrical signal is sent to the solenoid, which then opens the air line that actuates the ball valve.
Fueling Technologies says that it employs the Parker solenoid valve because the valve has been said to operate for as many as 20 million cycles without failure, and because service station applications are notoriously harsh environments.
"Cycle life is important, but it also has to endure the dirty conditions we encounter in the field," Canteenwalla says. "There's a lot of oil, moisture, and dirt."
Parker Hannifin engineers say that their 7000 Series valve has reached 20 million cycles, compared to typical cycle lives of five million for similar products, because of the way the 7000 is designed and built. In contrast to conventional solenoid valves, which typically use so-called "eyelet" sleeves, the 7000 employs a thick-walled, three-piece welded sleeve. The welded sleeve is said to be better, not only because it's stronger against external forces, but also because perpendicularity of the sleeve walls is said to be better controlled by the manufacturing process. Perpendicularity, in turn, reduces potential lateral motion and frictional problems between the valve's plunger and its sleeve walls.
"It minimizes the amount of side-to-side wear that you get," notes Michael D'Amato, technical sales and service manager for Parker Hannifin's Fluid Control Division (New Britain, CT). "You still get some wear, but it's not as great as it would be if the sleeve walls were not as perpendicular."
Parker engineers say that the valve's sealing techniques are equally important, especially in fueling stations that are exposed to temperature extremes ranging from -40 to 150F. The company uses Viton fluoroelastomer seals for high temperatures, nitrile rubber for low temperatures, and ethylene propylene for any applications that involve hot steam.
"You need to get the right formulation of elastomers to handle those temperatures," D'Amato says.
For dispensing of fuels such as compressed natural gas, liquefied petroleum gas, and hydrogen (which is pressurized at 5,000 psi), engineers also say that the design of the solenoid valve and coil are critical. To meet safety requirements, Fueling Systems employs a Series 7000 Hazardous Location Coil, which can protect against possible ignition if the coil sparks. The company makes coils that are contained in enclosures, and some that are encapsulated in molding compounds to prevent ignition.
Fueling Technologies says that such features make the solenoid valves an attractive choice for fuel cell applications, which have been gaining momentum as a result of the White House's recent push toward hydrogen-based fuels.
"Because of our success with compressed natural gas, we're also going to be using the solenoid valves for fuel cell demonstration projects in North America and Japan," Canteenwalla says.
In the meantime, however, the company says that it will continue to emphasize the use of low-maintenance components in future dispensing systems, especially those used in remote locations. "Reliability is always a concern," Canteenwalla says. "For these kinds of systems, frequent maintenance would certainly be an issue."