Pressure Extractors are used in determining the water-holding characteristics of soil samples. Wetted soil samples are placed in the extractor, and a known pressure is applied, which forces the removal of any water held to the soil at a lower pressure. By analysing the sample at several different pressures, the characteristic pressure versus water content relationship can be determined for the soil.
A variety of extractors are available for analysing different sizes and quantities of samples, and for analysing samples in different pressure ranges. All Pressure Extractors require a source of regulated pressure for operation.
The Model 1020 100 Bar Pressure Membrane Extractor is used to analyse the waterholding characteristics of soil samples at extremely high pressures. The Model 1020 uses a cellulose membrane supported on a screen drain plate. The cylinder is 5 cm high, with an inside diameter of 25 cm. The Model 1020 consists of:
- top and bottom plates
- cylinder, all connecting bolts and seals
- screen drain plate, and
- a side exhaust valve.
A high pressure hose for connecting the extractor to a pressure source must be ordered separately. Cellulose membranes, soil sample retaining rings, and an electrical leadthrough are available separately.
The Pressure Membrane Extractor uses a cellulose membrane supported on a screen drain plate. The cylinder is 2” (5 cm) high, with an inside diameter of 10” (25 cm). The Model 1020 consists of heavy duty; heat treated steel top and bottom plates, a cylinder and 16 hardened steel connecting bolts and seals, a pressure relief valve and a side exhaust valve, which makes it a safe instrument to operate.
A high-pressure hose and special high pressure manifold with regulator for connecting the extractor to a pressure source must be ordered separately. Cellulose membranes, soil sample retaining rings and an electrical lead-through are additional accessories that make the extractor complete for operation.
1020 100 BAR PRESSURE MEMBRANE EXTRACTOR
|DIMENSIONS:||Height: 35.56 cm
Width: 43.18 cm
Length: 45.72 cm
Weight: 66.22 kg
The 100 Bar Pressure Membrane Extractor is able to force moisture from soil samples because of the microscopic pores in the wetted Cellulose Membrane which forms the bottom of the Extractor chamber.
When air pressure inside the Pressure Membrane Extractor is raised above atmospheric pressure, the higher pressure inside the Extractor chamber forces excess water through the microscopic pores of the Cellulose Membrane and out of the Extractor. The high pressure air will not flow through the pores of the Cellulose Membrane since they are filled with water. The surface tension of the water in the pores at the air-water interface supports the pressure, much the same as a flexible rubber diaphragm. When the air pressure inside the Extractor is increased, the radius of curvature of this interface decreases. Water films will not break and allow air to pass through, even at maximum extractor pressure because of the minute pore diameter (24 angstroms). There is an exact relationship between the amount of air pressure in the Extractor and the radius of curvature of the air-water interface of the water in the pores of the Cellulose Membrane.
When soil samples are placed on the Cellulose Membrane in the Extractor and saturated with water and the air pressure in the Extractor is raised above atmospheric pressure, water will flow from around each of the soil particles and out through the pores of the Cellulose Membrane. At any given air pressure inside the Extractor, water will flow until the curvature of the water films at the junction of each of the soil particles is the same as in the pores of the Cellulose Membrane and corresponds to the curvature associated with that pressure.
For example, if the air pressure inside the Extractor is maintained at 1 Bar (14.5 psi) and flow from the Extractor has ceased, the sample is described as being a “a soil suction of 1 Bar”. The volumetric water remaining in the sample at that pressure would, in field conditions, represent a 1 Bar soil suction to surrounding plants. If the air pressure in the Extractor is maintained at 15 Bars (217.5 psi), the soil suction at equilibrium would be 15 Bars, the approximate wilting point of plants.
|Pressure Extractors References|
|Azooz, R.H. and Arshad, M.A. 1995, ‘Tillage Effects on Thermal Conductivity of Two Soils in Northern British Columbia’, Soil Science Society of America Journal, vol. 59, pp. 1413-1423.
|Azooz, R.H., Arshad, M.A. and Franzluebbers, A.J. 1996, ‘Pore Size Distribution and Hydraulic Conductivity Affected by Tillage in Northwestern Canada’, Soil Science Society of America Journal, vol. 60, no. 4, pp. 1197-1201.
|Cresswell, H.P., Green, T.W. and McKenzie, N.J. 2008, ‘The Adequacy of Pressure Plate Apparatus for Determining Soil Water Retention’, Soil Science Society of America Journal, vol. 72, no. 1, pp. 41-49.
|Duniway, M.C., Herricka, J.E. and Monger, H.C. 2007, ‘The High Water-Holding Capacity of Petrocalcic Horizons’, Soil Science Society of America Journal, vol. 71, pp. 812-819.
|Fuentes, J.P., Flury, M. and Bezdicek, D.F. 2004, ‘Hydraulic Properties in a Silt Loam Soil under Natural Prairie, Conventional Till, and No-Till’, Soil Science Society of America Journal, vol. 68, pp. 1679–1688.
|Giakoumakis, S.G. and Tsakiris, G.P. 1999, ‘Quick Estimation of Hydraulic Conductivity in Unsaturated Sandy Loam Soil’, Irrigation and Drainage Systems, vol. 13, pp. 349-359.
|Katsura, S., Kosugi, K., Yamamoto, N. and Mizuyama, T. 2005, ‘Saturated and Unsaturated Hydraulic Conductivities and Water Retention Characteristics of Weathered Granitic Bedrock’, Vadose Zone Journal, vol. 5, pp. 35-47.
|Luedeling, E., Nagieb, M., Wichern, F., Brandt, M., Deurer, M. and Buerkert, A. 2005, ‘Drainage, Salt Leaching and Physico-chemical Properties of Irrigated Man-made Terrace Soils in a Mountain Oasis of Northern Oman’, Geoderma, vol. 125, pp. 273-285.
|Mecke, M., Westman, C.J. and Ilvesniemi, H. 2002, ‘Water Retention Capacity in Coarse Podzol Profiles Predicted from Measured Soil Properties’, Soil Science Society of America Journal, vol. 66, no. 1, pp. 1-11.
|Roels, S., Sermijn, J. and Carmeliet, J. 2002, Modelling Unsaturated Moisture Transport in Autoclaved Aerated Concrete: a Microstructural Approach, Building Physics 2002: 6th Nordic Symposium, Trondheim, Norway. 17-19 June pp. 167-174.
|Young, M.H., Albright, W., Pohlmann, K.F., Pohll, G., Zachritz, W.H., Zitzer, S., Shafer, D.S., Nester, I. and Oyelowo, L. 2006, ‘Incorporating Parametric Uncertainty in the Design of Alternative Landfill Covers in Arid Regions’, Vadose Zone Journal, vol. 5, pp. 742-750.