Kidney loops: They aren't just for hydraulics any more
When was the last time you changed the oil in your refrigerator's compressor? That was a question posed to me by Ken Stofen of Racine, Wis. The answer, of course, is never, and after changing the break-in oil, that's how many times he's changed the oil in his 1992 Mercury Sable - even after racking up more than 67,000 miles!
What's his secret? He uses synthetic oil and doesn't let it get dirty. To keep the oil clean, Stofen installed an off-line filtration circuit, known in hydraulics as a kidney loop because it cleans the oil much like kidneys clean the blood in our bodies. He said synthetic oil is also essential because it is formulated for long life at high temperatures and with no foaming.
Stofen explained that standard engines typically use a 10-µm oil filter. This helps prevent large particles from circulating through the engine, but it allows a huge amount of small contaminants to remain in the oil. So to remove smaller contaminants, he retrofitted his Sable (and later a 2000 Mercury Villager) with a Dual Remote Filtration System (DRFS).
The DRFS consists of a 1-µm filter that cleans oil from the oil pan and returns it whenever the engine is running. Because oil flow through the 1-µm filter is so slow, it cannot be used as the main oil filter. Therefore, the DRFS supplements the main oil filter. A tee in-line with the oil pressure sending unit routes oil to the 1-µm filter whenever the engine is running.
The only downside is that he still has to change the filters. He does so about twice a year. The volume of the two filters is about two quarts, so even though he doesn't change the oil, the filter changes resupply the engine with some new oil twice a year.
Oh, I forgot to mention that Stofen is a youthful 82 years old. He said he's been comfortably retired for 12 years, so he's not out to get rich. Instead, he wants to spread the word about the DRFS to help America reduce its dependence on foreign oil.
But that's not all, he's expanded this technology into pneumatics. In fact, he has two industrial air compressors in his garage and has a complete system installed and running at a local industrial plant. He's never had to change the oil in the retrofited compressor. What's more, its motor runs with an energy-conserving power factor of 95% whether fully loaded or completely unloaded, the air in the receiver is clean, and the condensate is crystal clear.
We haven't heard the last from Ken Stofen. Look for in-depth coverage in a future issue. But if you can't wait, e-mail him at firstname.lastname@example.org.
Alan L. Hitchcox