Soil-Water Characteristic Curves


Research at the cutting edge

Pioneering new theories and cutting-edge research require an advanced understanding of soil. Yes, you could assemble a series of complex devices on your own to help understand soil behavior. But even with a dedicated graduate student at your disposal, the process will still prove difficult. What you need is an automated instrument that provides sophisticated information.

Simple instrument—advanced scientific breakthroughs

If you want to understand complex soil issues like clay behavior, specific surface area, shrink-swell capacity, or cation exchange capacity, the VAPOR SORPTION ANALYZER (VSA) is your simplest, most accurate option. It automates the entire process of soil-water characteristic curve construction in the dry region (-10 to -475 MPa) by accurately measuring simultaneously, at regular intervals, the water potential and the moisture content of a sample. No other instrument gives this much detail about soil in the dry range.

Delve deeper into your dry soil analysis

The VSA enables you to make detailed measurements no other instrument can. This means you can study the soil at a particle level, examining its chemical makeup and how the layers of soil imbibe water as it gets wetter or lose water as it gets drier. For the first time ever, it’s possible to see hysteresis in dry soils because the VSA analyzes both wetting and drying curves. This is critical information because the area between those curves is indicative of water intrusion into clay layers at the molecular level.  

The VSA generates both Dynamic Dew Point Isotherm (DDI) and Dynamic Vapor Sorption (DVS) moisture release curves. How? It continuously wets the sample and stops periodically to measure how heavy it is (DDI), or it keeps the sample at a constant humidity, recording how long it takes the sample to come to equilibrium (DVS). In just 24 to 48 hours, the VSA generates curves with up to 200 data points (water potential vs. water content) for both adsorption and desorption.

With so much information at your fingertips, insights are now officially faster and more convenient.

Set up a test, and walk away

With the VSA, it takes about five minutes to set up a test. Simply tell the instrument the water potential range and times you’d like to use, put the sample into the instrument, and move on to other tasks. The data from your test are automatically recorded and sent to your computer. Powerful automation adds up to powerful time savings.

Explore new frontiers in science

What’s the next great scientific advancement that’s going to be made with this instrument? Only you can say. The VSA’s incredibly detailed characteristic curves let you research complex soil behaviors no one’s yet explored. Sophisticated information and powerful efficiency make it easier than ever to draw accurate conclusions about your soil’s behavior, its expansibility, its makeup, and its performance as an engineering material.

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  • Fast, expansive soil characterization
  • Automatic static and dynamic soil water characteristic curves
  • Measure soil-specific surface area
  • Generates curves with up to 200 data points for both adsorption and desorption
  • Works in the dry soil range (-10 to -475 MPa)
  • Set up a test in five minutes
  • Steady sorption dynamics with static water potential feature


View GSA details

Water potential range

-10 to -475 MPa


±1 MPa, or ± 1%

Isotherm methods

Dynamic Dew Point Isotherm (DDI) & static DVS (Dynamic Vapor Sorption)

External gas

Not needed. If external gas is used, no more than 7 PSI.

Water reservoir

20 mL

Temperature control range

15 to 60 °C (sample chamber temperature; sample temperature is measured separately and may vary)

Temperature operating range

15 to 40 °C

Computer interface


Universal power

110 V to 220 V AC 50/60 Hz


W 25.4 cm (10 in.) x L 38.1 cm (15 in.) x H 30.5 cm (12 in.)


12.7 kg (28 lbs.)

Sample weight range

500-5000 mg

Sample cup volume

10 cc

Weight accuracy

± 0.1 mg

California requires the following notice:

⚠️ WARNING: This product may contain chemicals including ethylene glycol, lead, nickel, styrene and cadmium, which are known to the State of California to cause cancer, birth defects or other reproductive harm. For more information, go to www.P65Warnings.ca.gov



Have a question or problem? Our support team can help.

We manufacture, test, calibrate, and repair every instrument in-house. Our scientists and technicians use the instruments every day in our product testing lab. No matter what your question is, we have someone who can help you answer it.

Phone US: +1 509-332-5600
Phone Europe: +49 89 12 66 52 0


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