Dehydrator Plugs

I suppose if dehydrator plugs were part of a secret club and they had a motto they recited out loud in unison it would be something like, “Don’t wet yourself!”

In order to understand what these plugs do, you have to know what they are and what they are used for. Like many products, name defines function. Dehydrator plugs are transparent plastic tubes that, well, de-hydrate. They have two ends; while one is sealed the other end is fixed with a threaded and perforated plug. By removing moisture, these plugs protect engines from the ill-effects of water-induced rust and corrosion while a plane is sitting in storage.

Hangars and other storage areas are like any other place—subject to humidity. Of course, like other atmospheric conditions, humidity affects not only the appearance of parts, but the performance of a vehicle as well. It seems strange that a plane’s engine can be harmed while inactive, but ‘tis the reality of owning an aircraft. Installing dehydrator plugs by screwing them into an engine’s spark plug holes will combat humidity.

A disassembled Military Standard MS27215-1 18mm dehydrator plug. Notice the blue silica gel beads; this indicates that they have not been exposed to moisture.

A disassembled Military Standard MS27215-2* 18mm dehydrator plug. Notice the blue silica gel beads; this indicates that they have not been exposed to moisture.

The magic involved in the prevention of rust and corrosion comes from the plugs’ composition. Dehydrator plugs contain silica gel—a desiccant (drying agent)—as well as an indicator such as cobalt chloride. The beauty or rather practicality of this gel and its corresponding indicator is that they change color as moisture is absorbed. Blue is the default color while pink shows the presence of moisture. The fact that dehydrator plugs contain substances that act as a sort of litmus paper is super convenient as that color change will catch the eye and alert you to when these plugs need changing…or fixing.

A common question that often arises when purchasing dehydrator plugs is whether or not they last. In a word or three: yeah, they last. But what’s more important to know is that they are reusable as well as refillable (at least some part numbers; outdated versions might not be refillable). Once the silica gel is soiled, more can be purchased in various sizes (e.g. 1/4 or 5 lb). Or if you prefer to reuse pre-existing crystals, try this: simply take out and spread out the moisture-compromised crystals and dry them in an oven (sources indicate that the recommended heating process should last 16 hours at a temperature of 250 degrees F). Bam, good as new! In this way, it’s plain to see that dehydrator plugs are a sound investment into proper maintenance.

Another common issue raised is whether or not four or eight dehydrator plugs should be used—i.e. four on the top, four on the bottom of an engine. Of course, there is no right or wrong answer to this. It really is a matter of preference. Some say it’s better to be safe and put eight in, especially if you are leaving them in and not planning on checking them. Others argue that four is plenty and won’t lower performance. Still others follow the old adage, “less is more.” Why? Because they find putting four additional at the bottom leaves the plugs susceptible to being filled with oil. While SkyGeek appreciates your business, we promise not to tell you yours. The choice is up to you. One of our goals on this site is providing service that will translate into your satisfaction and that doesn’t mean forcing you into a bad decision.

In terms of selecting an appropriate dehydrator plug, I’ve found that since many aircraft are for military purposes, dehydrator plugs that conform to military standards are a good choice. In this case, you would be looking for dehydrator plugs with a MS27215 or MS3396 designation. Of course, if you are interested in purchasing one or more, you can check here. But that might just be the inner SkyGeek inside me speaking. If there are any more dehydrator plugs that are just as effective, please feel free to mention them in the comments below.

And as always, if there is any aspect of dehydrator plugs that is unclear or you have some more suggestions on the topic, don’t hesitate to let us know.

*UPDATE (6/27/2013): The caption for the image has been changed. The item featured is in fact a MS27215-2 NOT a MS27215-1. Upon inspection we have found that the MS27215-1 is an outdated model that cannot be disassembled; the MS27215-2 can, however. Thanks to David Halmos for steering SkyGeek in the right direction.

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Otto the Owner

About Otto the Owner
Otto the Owner

I'm Otto. Friends call me Otto. As an avid owner of aircraft I know the costs and benefits of flying. I've had enough experience with planes to grow rust on my mustache. While I'm not the best at words, my buddy Skylar helps me write these posts so I can transfer any knowledge onto other aviators out there.