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DRYSTIK Model ADS-2 (Discontinued)

Active Moisture Exchanger to reduce the humidity of the air entering the RAD7


The RAD7 radon monitor works most effectively when the incoming air sample has a low relative humidity. The DURRIDGE DRYSTIK Model ADS-2 transfers moisture from the incoming air to the air being pumped out of the RAD7. As the air enters a drying unit (not included) on its way to the RAD7, it will have already lost most of its moisture, greatly extending the life of the desiccant in the drying unit. In certain cases the need for desiccant is eliminated altogether.

The DRYSTIK Model ADS-2 has at its heart a Nafion humidity exchanger with diaphragm pump, fixed and variable flow limiters, and a built-in Duty Cycle Controller. These are all contained in a compact enclosure. The DRYSTIK’s pump compresses the sample air inside the membrane tubing, initiating the transfer of water molecules to the outer purge flow, drying the incoming air as it moves through the device.

The DRYSTIK Model ADS-2 is available in three variants, based on the length of Nafion tubing. The premium 144-ADS-2 model is capable of bringing the relative humidity of air flowing at 0.15 L/min down below 10% in less than four hours, and maintaining the RH below 6% indefinitely without any desiccant. This allows a RAD7 to operate under optimum conditions with the highest sensitivity and lowest operating cost. At a higher flow rate of 1.2 L/min, the DRYSTIK can bring the RH down below 12%, which is sufficient for enhanced-sensitivity thoron measurement.

For soil gas measurement, the DRYSTIK provides high flow capability for thoron measurement. For radon, the ability to lower the flow with the built-in Duty Cycle Controller means that continuous soil gas readings may be made indefinitely, without any risk of fresh air diluting the soil gas sample by diffusing down to the extraction point.

Principle of Operation

The DRYSTIK Model ADS-2 operates on a principle involving two tubes, one inside the other. The inner tube is made of NAFION, a Teflon based material that permits the movement of water molecules, while blocking air and radon. The air sample flows along the inner tube on its way to a drying unit, while the space around the inner tube is purged with dry air coming from the outlet of the RAD7.

Summary of Benefits

The DRYSTIK enables users to enjoy the full capabilities provided by the superior RAD7 technology, with its rapid response and recovery, vanishingly small background, thoron specific sniffing, and radon-in-water accessories, with the need to replace and/or regenerate the desiccant only after a long period. The cost of replacing used desiccant becomes insignificant.

With a pump upstream and a needle valve downstream of the NAFION tube, compressing the air inside the tube, the DRYSTIK Model ADS-2 works regeneratively, and can even eliminate the need for desiccant altogether.

DRYSTIK ADS-2 Performance


Initial Humidity

Humidity after 30 min.*

Model ADS-2-12



Model ADS-2-48



Model ADS-2-144



*Humidity level achieved after 30 minutes at 22° C with 100% internal pump duty cycle and no desiccant.

DRYSTIK ADS-2 Physical and Technical Specifications


11.5" x 7.75" x 3.25" (29 cm x 20 cm x 8 cm)


2.98 pounds (1.35 kg)

LCD Display Output

2 line x 16 character alpha-numeric display

Case Material

ABS Plastic


12V DC in (1.25A)

High Quality Pumps and Mounting

In 2013 the DRYSTIK Model ADS-2 was updated with a high quality pump, mounted on a shock- and sound-absorbing bridge plate. The new pumps increase the expected life span of newly assembled DRYSTIK devices to 5,000 hours of constant use (or 25,000 hours assuming a typical 20% pump duty cycle). The improved pump is offered in both brushed and brushless varieties. Existing DRYSTIKs may be shipped back to DURRIDGE to be upgraded to the pump of your choice. See the Purchasing link below for pricing details.

Water Switch Accessory

The DRYSTIK ADS-2 is very effective at removing moisture from the air, but it is not effective if liquid water is allowed to enter the device. The optional Water Switch accessory addresses this. The Water Switch is a reed switch with a magnet embedded in a float around it. The device is packaged in a small, airtight container with hose connections, and is placed upstream of the DRYSTIK Model ADS-2. When the Water Switch fills up, it cuts the power to the DRYSTIK, preventing its pump from sucking in liquid water.


DRYSTIK User's Manual (PDF)


DRYSTIK Model ADS-2 Standard Configuration Diagram

DRYSTIK Model ADS-2: Alternative Drying Tube Placement Diagram

Water Switch Accessory

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DRYSTIK Performance Graph (Click for more)

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