Computer-generated image of check valve made of carbon-reinforced PEEK and installed in valve sandwich valve poppet is shown at left. Equivalent valve made of stainless steel is shown at right.
Victrex USA, Greenville, S.C., has begun production of valve poppets made of carbon reinforced PEEK (polyether-etherkeytone). for Bosch Rexroth. Jon Frey, of Bosch Rexroth, said the material will be used for poppets in standard sandwich check valves. Initial product introductions will involve direct-and pilot-operated check valve modules.
One of the most critical criteria for material selection was compressive strength. Victrex product manager Andrew Ragan revealed, " Carbon fiber reinforced Victrex PEEK fulfills all mechanical requirements for these valves. It has very high creep resistance, which is a prerequisite for long service life. And with its outstanding chemical resistance, Victrex PEEK can withstand any hydraulic fluid, such as petroleumbased and fire-resistant fluids, water, and bio-friendly oils.
Because the valve poppets are injection molded, they exhibit high dimensional stability without the need for costly post-machining operations. "Another advantage of injection molding," continues Ragan, "Is freedom of design. Flow simulation software showed that Victrex PEEK valve poppets exhibited 20% lower pressure drop at maximum flow rate. Simultaneously, orientation of the carbon fibers can be optimized for higher mechanical strength."
When compared to stainless steel valve poppets, which must meet very tight tolerances, Victrex PEEK poppets fit the valve seat more readily. This relaxes tolerances for the valve set, thus saving machining costs. Ragan adds, " Victrex PEEK has lower density (than stainless steel), so valve response is improved."
Bosch Rexroth has successfully tested the Victrex PEEK valves at 350 bar for more than 10 million cycles at 3 Hz. Ragan also says Victrex-PEEK valves require no additional rubber seal to ensure leakfree operation at lower pressures.