Tests Validate Product Name
For several years now, EPCO Products, Inc., Fort Wayne, has offered its Zero-Leak Gold line of plugs and fittings for fluid power systems. Zero-Leak Gold plugs interchange physically with the SAE J514 plugs currently used in SAE J1926 ports. Installing EPCO plugs requires no retooling or reengineering. What makes them unique is a taper under the head of the plug that forms a metal-to-metal seal with the taper already machined into the SAE port. By bringing the two tapers into intimate contact, Zero-Leak Gold plugs achieve exceptionally high unit loading at the interface. An O-ring located below the taper contact point of the plug acts as a backup seal. (In contrast, the seal in a standard SAE J514 plug is achieved by forcing an O-ring into the port taper.)
As you might guess from the product name, EPCO claims that these plugs will not leak under any circumstances. They back up their claim with a lifetime replacement guarantee. For some manufacturers, that proved enough incentive to give Zero-Leak Gold a try. But many specifying engineers wanted to see hard evidence that Zero-Leak Gold plugs and fittings can stand up to the EPCO claim. To deliver that evidence, the company commissioned a series of tests to be conducted by the Fluid Power Institute at the Milwaukee School of Engineering.
For these tests, FPI installed samples of the EPCO plugs into six specifically designed manifolds. Three of these manifolds were made from ductile iron with a rated working pressure of 5,000 psi; the others were made from aluminum with a rated working pressure of 3,000 psi. This setup allowed three samples of each size plug to be tested.
One test sought to establish the minimum installation torque needed for a reliable seal. Not the casual "zero leak" that is commonly defined as so many drips or drops within a specified time period, but literally no drips or drops at all. To do this, the plugs were put through the NFPA 106-cycle endurance test. The initial test was conducted with 0.5 ft-lb of torque applied to each plug. This modest torque was unexpectedly successful at static rated pressures (but predictably failed early as torque values then were gradually increased for the endurance test).
For the formal endurance test, cyclic pressure applied was 3,688 psi for aluminum and 6,156 psi for ductile iron, with a pulse duration of 92 ms for ductile iron and 98 ms for aluminum. At 60% of SAE published torque values, all Zero-Leak Gold plugs completed the cycle test without leaks. Furthermore, before the test, a scribe line was made across the top of each plug and onto the manifold to indicate its installed position. At the end of the test, all plugs were still in their original position - they had not backed out at all. And, except for brief maintenance shut-downs, the plugs ran continuously for all 1,000,000 cycles.
The final tests were the proof- and burst-pressure tests. Again, they were conducted to the NFPA/T2.6.1 R1-1991 standard. To pass the proof-pressure tests, three samples must withstand twice the working pressure for a minimum of 60 seconds. The burst-pressure test requires three samples to withstand a minimum of four times the working pressure. The proof-pressure test was conducted at 10,000 psi for ductile iron and 6,000 psi for aluminum. Time at pressure was 120 seconds. All samples passed the test without failure. The burst test ran at pressures ranging from 21,769 to 26,453 psi. Again, all Zero-Leak Gold plugs passed without a detected leak. (A thread failed in one of the aluminum manifold ports at 23,339 psi - more than seven times the rated working pressure for aluminum - and a leak resulted there.)
The results of the test run at the Fluid Power Institute provide proof that zero-leak performance is not just theoretical. EPCO's plugs withstood the rigors of the 1,000,000-cycle test without leaking - or loosening - and they also proved to seal effectively at assembly torques well below the SAE recommendations.
Reprinted with permission from Hydraulics & Pneumatics, October 2000.
Phone EPCO at 800/879-EPCO; or visit www.zero-leak.com
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