In our review of oil filters in the August 2009 issue, we picked Champions line as the best overall choice in a field where both Tempest and Kelly Aerospace offer competitive products. Tempest wrote us this month to contest our findings, contending that our research glossed over some key technical advantages of Tempest filters. What follows is a summary of Tempests response.
Bypass Valve
First, the filter bypass valve. Tempest says we overlooked what it argues is the “biggest safety enhancement made in spin-on oil filters in years.” Specifically, says Tempest, is its safety containment cap surrounding the bypass valve. Bypass valves have been known to disintegrate at the spot welds, spewing bits of the valve into the engine or blocking the filter outlet hole, starving the engine of oil. Tempest says its containment cup will eliminate this problem. “Additionally,” says the company, “the absence of a gasket under the valve eliminates the potential for leakage.”
Tempest says our observation on the relative travel of bypass valve discs and springs is irrelevant. “When Tempest introduced its filters, its bypass valve was the only one of the three brands mentioned that opened within Continentals specified range,” Tempest told us. “The maximum oil volume generated by an engine isn’t sufficient to push the valve disc solidly down against the spring, the point at which, theoretically at least, flow might be restricted by the disc. The Tempest valve can provide full bypass for engines larger than the Lycoming IO-720, an eight-cylinder engine with a really big oil pump.”
Magnetic Catcher
We liked the addition of a magnetic element in the filter to collect ferrous metal particles and although Champion claimed that collected metal could put the filter into bypass, Tempest dismisses this. Tempest says, “The magnet attracts fine particles but not at such a high rate as to overload it (in a normally running engine) between filter changes. However, in an engine making metal, its a different story.
“The high particle concentration makes the magnet get fuzzy. Astute mechanics can identify a fuzzy magnet instantly. The system has saved many engines that were experiencing progressive valve stem or cam failures from extensive, unnecessary damage. Caught early, they were less expensive to repair. And, preventing just one in-flight failure that may have put lives at risk was worth the price of the magnet and the costs of its certification to Tempest.”
Internal Gaskets
We commented on the difference in internal gaskets between the filter element and spring used to hold the element against the base. Tempests reply: “Tempest filters use purpose-designed top and bottom pleat pack caps. While adapting parts might make economic sense, it doesnt, in our opinion, make good aviation safety sense. Replacing one part with two, doubles the probability of failure in a number of ways. Either part could be left out, for example.
“There’s twice as much product control required and, thus, twice the potential for a manufacturing quality escape to cause field service problems. While it is quite common to see the adapted pleat pack approach in automotive and industrial filter manufacturing, its rare in aviation.”
Inner Springs
We also noted that Champion uses a hefty coil spring to keep the filter element mated to the two-piece internal gasket and aligned with inlet and outlet ports. Both Kelly and Tempest use a flat, stamped steel spring. Tempest argues that the flat steel spring is better. “Use of the more expensive, sophisticated (compared to a spring) stamped steel element guide in an airplane filter makes sense.
“The element guide must keep the top of the filter element in line (laterally) with the outlet. A part that provides both lateral control and sufficient spring pressure to keep the element pack against the gasket is a superior design. When the filter element is heavy with oil and the airplane experiences Gs, as in a tight, sustained turn, the top of the filter element can tend to move laterally (reference the cans centerline), allowing leakage at the gasket.”
Tempest says the steel element guide prevents this movement and a boss in the center of the guide helps keep the element from tipping out of line. Tempest says a coil spring doesnt provide as much centering control.
Last, a note on nomenclature regarding the -2 suffix for the redesigned 48108. Tempest says FAA rules required the part number change. “The majority of the shortness was achieved from a design change to the can (thus the FAA part number change). It was not necessary to add pleats,” Tempest says. You can find out more about Tempest filters at www.tempestplus.com.
