Corrosion proof substitute?

T Chap · 2012-10-26 17:33

I use this plunger as a limit switch. In a first use on a boat, the plunger has stuck pressed in, supposedly it is corroded and no longer is free to move. The switch is in a tight condition and cannot be replaced with a something larger in any direction. I cannot find a corrosion proof drop in. The plunger travels around 3/8" and some travel is required for the system to decelerate to a stop upon contacting the switch. I have to send a replacement out first part of the week. One idea is to fill the button part with marine grease, and hope to gain a few years at least if not more of free movement. The switch rarely gets used, only in a power off condition, so it stays fully extended most of it's life with little exercise. Another idea is to replace it with the same and attempt to seal the switch with a plastic bag or rubber cover. I am looking for any suggestions to solve this problem, suggestions are appreciated. One photo shows the actual plunger stuck pressed in, it is attached to the plastic mount.. normally the plunger sticks out of the plastic by 3/8" and the plastic takes any punishment if the system doesn't stop the travel in time. There are not options to change the circuit or wiring options at this point. The contacts are normally closed, a Prop reads an input pulled low by the switch. When the switch is pressed, the contacts open, the input is held to 3v3 with a 10k, the Prop sees 3v3. There are two of the systems. One is frozen, and I am told the other is becoming difficult to press in, so it is the same corrosive effect on both.

Prophead100 · 2012-10-26 18:30

Unless the switch face gets submerged or water gets in from the back then the rubber cover should cover the occasional spray or drips. Heat from the sun can cause the grease to run. You may want to put a little conductive grease on the contacts as well to avoid corrosion.

T Chap · 2012-10-26 18:46

Thanks. The switch does not get direct water contact.

idbruce · 2012-10-26 18:58

What type of material contacts the pushbutton? If it is metal, is there any chance of a spring loaded n.c. proximity switch?

EDIT: Never mind, that would require power

Phil Pilgrim (PhiPi) · 2012-10-26 19:07

You didn't mention whether it was a fresh- or salt-water environment. That makes a huge difference. In a salt-water environment, being within a whiff of the sea is enough to promote salt deposits and corrosion. Typically, switches designed to operate in such environments are equipped with rubber boots over their levers or plungers to prevent salt and moisture incursion. Would it be possible to enlarge the hole in the plastic mount to accommodate such a boot? Also, for electrical integrity, conformal coating all exposed joints will help prevent electrical corrosion.

-Phil

T Chap · 2012-10-26 19:13

Phil, it is a boat in salt water.

Phil Pilgrim (PhiPi) · 2012-10-26 19:22

Whoa! Nice! But, yeah, electrical systems and salt-water do not mix. Their maintenance is a constant headache. I live in a seaport town and have helped friends with their boat electrical issues. I've seen green copper corrosion creep several feet into insulated wire, where the wire was never in contact with the water. And the manufacturers of so-called marine electrical components -- Perko being the worst -- really don't have a clue. For my money, some of the best-quality sealed switches are made by Otto Engineering.

-Phil

Lawson · 2012-10-26 20:53

That plunger looks brass. How about adding a zinc nut or washer to the threaded mounting of the switch? (a loop of zinc wire used as a washer maybe?) It should corrode first, keeping the brass intact until it's used up. (brass propellers often do this)

Have you tried searching for "washdown" or "food-grade" switches? Those two keywords should find a lot of industrial switches meant for similarly difficult situations. Also, searching http://www.thomasnet.com/ and calling several switch manufacturers (especially the small ones) can find solutions fast.

Lawson

LoopyByteloose · 2012-10-27 08:18

Phil recommended a salt water military spec switch. The salt in the marine environment just loves to seek out electricity and dissimilar metals. It would seem that if the US Navy is customer, you would have a better product - read the referenced military spec to see if that is so.

If you do add zinc to prevent corrosion, add a lot so that maintenance is less frequent. A little bit will just be enough to let your guard down. But I am not sure you have to. Is that really brass? Is it heavily chrome plated? or is it stainless steel?

Corrosion proof substitute?

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