Pressure Chambers (Extractors)

Low-Pressure Chamber

The low-pressure chamber is an inexpensive pressure vessel used in soil-moisture and water-retention analyses. The chamber is safe for use to a maximum pressure of 1 bar (100 kPa). The low-pressure chamber is constructed of aluminum.

The large-volume chamber can accommodate several porous ceramic plates at once, allowing many soil samples to be analyzed concurrently. A quick-connect fitting allows easy connection to a compressor/manifold unit or other source of pressurized air.

Safety-relief features prevent over-pressurization, assuring safe operation of the system. A safety-relief valve releases pressure automatically if the pressure exceeds 1.3 bar (130 kPa), and can also be used to manually reduce the pressure inside the chamber. A blowout plug prevents over-pressurization of the chamber.

 

 

Specifications:

Dimensions: outside maximum: 16 in (41 cm) diameter x 20 in (50 cm) high 

inside chamber: 12 in (30 cm) diameter x 12 in (308 cm) deep

Weight: 9 kg (20 lbs)  

 

Pressure range: 0 to 1 bar (0 to 100 kPa) 

Safety features: pressure-relief valve set to release at 1.3 bar (130 kPa)  

rubber blowout plug

 

Construction: aluminum pressure vessel and lid  

six clamping bolts

 

Low-pressure chamber components

Pressure chamber vessel

The pressure chamber is a low-pressure vessel which contains the regulated air pressure.

Lid

The lid closes and seals the pressure vessel. Six clamping bolts on the pressure chamber vessel hold the lid securely when the chamber is pressurized.

Lid alignment markers

The lid and pressure chamber are designed to fit together tightly and form an air-tight seal without the use of an O-ring or gasket. In order to form this seal, the lid must be aligned properly prior to closing and sealing the chamber. Triangular alignment marks, found on the top surface of the lid flange and on the side of the pressure chamber, are used to properly orient the lid.

Pressure hose connection

A quick-connect fitting is used to connect the pressurized air-supply hose to the pressure chamber. The quick-connect fitting allows the hose to be quickly and easily attached and removed.

Safety relief valve

The safety relief valve ensures that the extractor chamber is not over-pressurized. The valve is set to open and release pressure when the air pressure exceeds approximately 20 psi (1.3 bars or 130 kPa). The valve automatically resets when the excess pressure is released. The valve can also be operated manually to release pressure in the chamber by pulling the release ring, which opens the valve immediately.

Rubber blowout plug

The blowout plug is a secondary safety device which releases pressure if the pressure inside the chamber becomes unsafe. The rubber plug is blown out of the lid and the pressure is released immediately. The plug must then be reinstalled in the lid before the chamber can be pressurized again.

Outflow tube connections

The outflow tube connections allow attachment of outflow tubes to the porous plates inside the chamber. The outflow tubes carry water displaced from soil samples due to the air pressure inside the chamber.

 

High-Pressure Chamber

The high-pressure chamber is used in soil-moisture and water-retention analyses. The chamber is safe for use to a maximum pressure of 15 bar (1500 kPa).

The chamber and lid are constructed of heavy-wall steel. Eight high-strength bolts clamp the lid and seal the chamber securely. Each high-pressure chamber is hydrostatically tested to 500 psi (34 bar or 3400 kPa) to ensure its safety.

The chamber can accommodate several porous ceramic plates at once, allowing many soil samples to be analyzed concurrently. A quick-connect fitting allows easy connection to the compressor/ manifold unit or other source of pressurized air.

A safety-relief valve prevents over-pressurization, assuring safe operation of the system. The safety-relief valve automatically releases pressure if the pressure inside the chamber exceeds 17 bar (1700 kPa). The valve can also be used to manually reduce the pressure inside the chamber.

 

Specifications:

Dimensions: outside maximum: 18 in (46 cm) diameter x 13 in (33 cm) high inside chamber: 12 in (30 cm) diameter x 8 in (20 cm) deep  

Weight: 39 kg (85 lbs)  

 

Pressure range: 0 to 15 bar (0 to 1500 kPa) 

Safety features: pressure-relief valve set to release at 17 bar (1700 kPa)  

 

Construction: steel pressure vessel and lid  

eight high-strength clamping bolts

hydrostatically tested and certified to 500 psi (34 bar, 3400 kPa)

 

High-pressure chamber components

 

Pressure chamber vessel

The pressure chamber is a high-pressure vessel which contains the regulated air pressure. The heavy-wall steel chamber is built to withstand very high pressures, and each unit has been hydrostatically tested and certified to withstand 500 psi (34 bar or 3400 kPa) pressure.

 

Lid

The lid closes and seals the pressure vessel. Eight Grade-9 high-strength clamping bolts hold the lid securely when the chamber is pressurized.

 

Pressure hose connection

A quick-connect fitting is used to connect the pressurized air-supply hose to the pressure chamber. The quick-connect fitting allows the hose to be quickly and easily attached and removed.

 

Safety relief valve

The safety relief valve ensures that the extractor chamber is not over-pressurized. The valve is set to open and release pressure when the air pressure exceeds approximately 250 psi (17 bars or 1700 kPa). The valve automatically resets when the excess pressure is released. The valve can also be operated manually to release pressure in the chamber by pulling the release ring, which opens the valve immediately.

 

Outflow tube connections

The outflow tube connections allow attachment of outflow tubes to the porous plates inside the chamber. The outflow tubes carry water displaced from soil samples due to the air pressure inside the chamber.

 

 

Further Information
More information about developing water retention curves, analyzing a soil sample’s moisture or water-holding characteristics, and using a compressor/manifold and extraction chambers can be found in the following references:

ASTM.  2000.  D2325-68(2000) Standard Test Method for Capillary-Moisture Relationships for Coarse- and Medium-Textured Soils by Porous-Plate Apparatus. AMERICAN SOCIETY FOR TESTING AND MATERIALS, West Conshohocken, PA.

ASTM.  2000.  D3152-72(2000) Standard Test Method for Capillary-Moisture Relationships for Fine-Textured Soils by Pressure-Membrane Apparatus. AMERICAN SOCIETY FOR TESTING AND MATERIALS, West Conshohocken, PA.

ASTM.  1998.  D421-85(1998) Standard Practice for Dry Preparation of Soil Samples for Particle-Size Analysis and Determination of Soil Constants. AMERICAN SOCIETY FOR TESTING AND MATERIALS, West Conshohocken, PA.

ASTM.  1998.  D2217-85(1998) Standard Practice for Wet Preparation of Soil Samples for Particle-Size Analysis and Determination of Soil Constants. AMERICAN SOCIETY FOR TESTING AND MATERIALS, West Conshohocken, PA.

Klute, A. 1986. Water retention: laboratory methods. in Klute, A. (ed), Methods of Soil Analysis: Part 1 – Physical and Mineralogical Methods, American Society of Agronomy/Soil Science Society of America: Madison, Wisconsin, USA.

Richards, L.A. 1941. A pressure-membrane extraction apparatus for soil solution. Soil Science, 51(5):377-386.

Richards, L.A. and L.R. Weaver. 1944. Moisture retention by some irrigated soils as related to soil-moisture tension. Journal of Agricultural Research, 69(6):215-235.

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