Desiccant Packs (HWH)

After paying almost $50 for a 4 ounce bag of indicating desiccant at FoT, we did some research to find some lower cost options. This desiccant is used on the outlet of the HWH pump to dry the air before its used.

The dried air can either go to the slide bladders / accessory tank and more importantly to the main air (brake) tanks. In our era coach, there is a driver switch to enable filling the main air tanks from the HWH pump, when doing this, you really want dry air.

In our research we purchased across the following 5 lb can of 2-4mm indicating silica gel : Bulk Sorbents You can find similar products on Amazon, for example Blue Premium Indicating Silica Gel

We also purchased Mylar® and Foil Ziplock bags bags so we could divvy up the silica gel to individual packets.

We bought the 5 pound can of blue indicating silica gel 2-4 mm for $25.75 and 100 of the open top mylar foil zip top 5.5” x 5.25” (055MFD0525OZE) bags for $50 (which unfortunately are not currently available on-line in quantities less than 1000.)

Weighed out portions of the desiccant, manually forced the air out of the mylar bags before zipping shut, and used our home Foodsaver to heat-seal the zip-tab end (sealing only, not vacuum-packing; it seemed to work OK). Now we have 20 pre-packaged, moisture-sealed portions of desiccant and 80 bags leftover for future use. Factoring in shipping, cost per portion was around $2.50 instead of near $50.

Recharge Silica Desiccant

Blue to Pink Desiccant Fresh (Unsaturated) (Left) vs Saturated (Right). You can recharge your used desiccant using a few simple steps.

Take saturated silica out of its container or bag and put it in a microwave safe dish that spreads the silica out fairly thin (like a normal plate). In selecting your dish, keep in mind that you’ll need to collect the silica from it afterwards, so something from which you can pour might make your life easier.

Put the dish in the microwave and set it for a medium power defrost cycle (which offers an intermittent duty cycle, such as a few seconds on, a few seconds off, and so on). Watch it the whole time it is in, and stop it when it appears fairly blue. The time will depend on many factors (how saturated the silica is, how much silica you’re recharging, what kind of dish you’re using, how powerful your microwave is, what the duty cycle of the defrost setting is, your ambient humidity level, and probably others), but most likely 2 to 3 minutes will do the trick.


We made these packages over 4 years ago, and they have worked perfectly. The mylar bags keep the moisture out, each one I have opened is still a bright blue.