Recent advances in the design of solenoid valves that control the flow of steam and hot water combine several features proven to offer significant benefits in traditional valves, such as threaded bonnets, a floating diaphragm made of polytetrafluoroethylene (PTFE) and a zero-minimum operating differential design. These new designs also add innovative new approaches — such as optimized geometry, DC construction and a lower power coil. A recent white paper from ASCO Valve Inc., based in Florham Park, N.J., part of Emerson Industrial Automation, demonstrates how its 8220 steam valve series, based on these design advances and already operating in the field for several years, can deliver benefits such as 60-percent higher flow rates and four times longer operating life.
Computational fluid dynamics was used to design valves with flow rates that test out at 20 to 60 percent higher than conventional models, enabling higher flow rates or downsizing valves in existing equipment. An additional flow feature in the new valves is zero-minimum operation. Whereas traditional valves require a minimum of 5 psi to open, these models can open even at 0 psi. This attribute is a critical capability in applications with low steam supply pressures.
Explains Anne-Sophie Kedad-Chambareau, product marketing manager at ASCO Valve: “Zero-min is related to the valve construction. The valve has an ‘over-centered’ design; this means that the solenoid directly pulls the diaphragm when energized. [Neither] fluid/steam nor air is necessary to pull the diaphragm; as a consequence, the valve starts opening at 0 psi.”
A feature that contributes to longer valve life, meanwhile, is the floating PTFE diaphragm. “A floating diaphragm means that there is no compression or pinching of the external part of the diaphragm, and it is free to float between the diaphragm support and the retainer,” says Kedad-Chambareau. “On the other hand, a clamped diaphragm design is pinched between the support and the retainer.” Floating PTFE diaphragms strongly resist corrosion and mineral buildup for better sealing, minimized leakage and fewer closing problems.
Together with other life-extending design changes, the 8220 Series steam valves reportedly deliver up to 500,000 cycles of reliable performance, even in demanding high-pressure steam use. This compares with between 50,000 and 250,000 cycles with conventional solenoid valves.
A threaded bonnet, meanwhile, enables much easier access to the valve for maintenance purposes; heavy-duty threads ensure stability under stress. Traditionally, steam valve designs emphasize stability at the expense of accessibility. Many models are held together by multiple heavy bolts, guaranteeing that valve components won’t come apart when stressed by high temperatures and pressures, but this translates to less convenient maintenance or replacement.
Lower energy consumption is another feature of the latest solenoid valve designs. Conventional solenoid steam valves require electrical currents of around 16 W for normal operation. Newer-generation valves improve on this with new coil designs that require only 6 to 10 W.