The compressor/manifold unit is an innovative design that combines a 1500 kPa (15 bar) compressor with a manifold to run two separate pressure chambers simultaneously. The system has regulators for controlling independent high- and low-pressure outputs, electronic pressure transducers and digital readouts for each pressure output, and pressure-release mechanisms for safe operation.  The unit is exceptionally quiet and is packaged in a small, conveniently sized metal enclosure, allowing desktop placement and operation.  Units are available for operation with 110V-60Hz or 220V-50Hz AC power. 

Low-Pressure Chamber

The low-pressure chamber is an inexpensive pressure vessel for use in soil-moisture and water-retention analyses. The chamber is safe for use to a maximum pressure of 100 kPa (1 bar). The chamber accommodates 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. Safe operation is assured via an automatic safety-relief valve which prevents over-pressurization of the system.

Compressor / Manifold Unit

Power switch: The power switch controls the supply of electricity to the compressor/manifold unit. Turning the switch on supplies power to the compressor, which immediately begins pressurizing and filling the storage tank, to the pressure transducers and digital displays, and to the compressor-motor cooling fan. 

Emergency stop: The emergency stop is a safety relief valve which immediately releases the air pressure in the compressor/manifold unit. Air pressure is released from both the high-pressure and low-pressure sides, and from the extractor chambers connected to the pressure outlets. 

Air filter: The air filter cleans and dries the air prior to being drawn into the compressor. Particulate matter is filtered out and a water trap removes water vapor. 

Storage tank drain: The storage tank drain is used to release air pressure and water from the pressure tank.

High-Pressure Side 

High-pressure regulator: The high-pressure regulator is used to regulate the pressure on the high-pressure output line. The high-pressure regulator provides regulated air pressure in the range of 5 to 15 bars (500 to 1500 kPa). 

Pressure display: The pressure of the regulated air is monitored with an electronic pressure transducer. The LED display provides a continuous readout of the pressure in the high-pressure air outlet. 

Extractor chamber exhaust valve: The extractor chamber exhaust valve is used to release the air pressure in the high-pressure side and inside the chamber prior to opening the chamber. The valve is closed when the chamber is pressurized, and opened to relieve pressure and exhaust the air. 

Air outlet: The air outlet provides access to the regulated supply of air pressure from the high-pressure side. A quick-connect fitting allows connection of a high-pressure hose, which is connected to a high-pressure extractor chamber.

Low-Pressure Side

Low-pressure regulator: The low-pressure regulator is used to regulate the pressure on the low-pressure output line. The low-pressure regulator provides regulated air pressure in the range of 0 to 6 bars (0 to 600 kPa). 

Pressure display: The pressure of the regulated air is monitored with an electronic pressure transducer. The LED display provides a continuous readout of the pressure in the low-pressure air outlet. 

Extractor chamber exhaust valve: The extractor chamber exhaust valve is used to release the air pressure in the low-pressure side and inside the chamber prior to opening the chamber. The valve is closed when the chamber is pressurized, and opened to relieve pressure and exhaust the air. 

Air outlet: The air outlet provides access to the regulated supply of air pressure from the low-pressure side. A quick-connect fitting allows connection of a low-pressure hose, which is connected to a low-pressure extractor chamber.

Low-Pressure Extractor Chamber

Pressure chamber vessel: The pressure chamber is a low-pressure vessel which contains the regulated air pressure. An alignment marker on the side of the vessel indicates the correct orientation of the lid to ensure that the vessel is sealed properly. Six clamping bolts retain and secure the chamber lid. 

Lid: The lid closes and seals the pressure vessel. The 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 ensure the proper orientation of the lid. 

Pressure hose connection: The pressure hose connection is a quick-connect fitting 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. 

Safety relief valve: The safety relief valve is a safety device which ensures that the pressure chamber is not over-pressurized. The valve is set to open and release pressure when the pressure exceeds 20 psi (approximately 1.3 bars or 130 kPa). The valve is automatically reset and closes when the excess pressure is released. The valve can also be operated manually to release pressure in the chamber by pulling the release ring up, 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. If the pressure inside the chamber is too high, the plug is blown out of the lid and the pressure is released. 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 for the porous plates inside the chamber.

Operation

1.  Ensure that the unit is ready for safe operation. Ensure that all regulators are closed, exhaust valves are open, and the emergency stop button is pushed in. The regulators are turned counter-clockwise completely, unit no pressure (0 bars) passes through the regulator. The exhaust valves are turned clockwise to the "Exhaust" setting. The emergency stop button is pushed in, ensuring that all pressure is released from the system.

2.  Plug in and turn on the compressor/manifold unit. Plug the power cable at the back of the unit into an electrical outlet which supplies 120 V. Turning the unit on with the power switch causes the cooling fan to begin operating and the pressure transducers and digital displays to begin functioning. The compressor controller will check the storage tank pressure and will start the compressor if the tank needs to be pressurized.

3.  Connect the compressor/manifold unit to the low-pressure extractor chamber. A low-pressure hose is connected to the low-pressure air outlet fitting on the compressor/manifold, and to the pressure hose connection on the extractor chamber.

4.  Install the porous plates inside the extractor chamber. An outflow tube is connected for each porous plate. A short length of plastic tube is connected to each plate and to a tube fitting on the inside of the chamber. A short length of tubing can also be connected to the tube fitting on the outside of the chamber to facilitate in draining or collecting the outflow water.

5.  Close and seal the extractor chamber. Ensure that the lid is properly oriented by matching the alignment markers on the top of the lid and the side of the chamber. Lock the lid securely in place by aligning and tightening the six clamping bolts. Unused outflow-tube connections can be sealed by connected a short length of outflow tubing to the fitting, and closing the tubing with a tubing clamp.

6.  Reset the emergency stop. Pulling the emergency stop button out, away from the compressor/manifold front panel, resets the valve and allows the system to be pressurized. If the emergency stop is not properly and safely reset, the high- and low-pressure sides will not be pressurized.

7.  Set the extractor exhaust valve. The extractor exhaust valve on the low-pressure side is turned counter-clockwise to the "Pressurize" position. This will enable the low-pressure side to be pressurized using the low-pressure regulator.

8.  Pressurize the chamber. The pressure in the low-pressure side is controlled using the low-pressure regulator. Pressure is increased by turning the regulator handle clockwise, and decreased by turning the handle counter-clockwise. The digital display provides a continuous readout of the pressure. The large chamber volume, volume of air in the air hose, and the compressibility of air can cause a lag time between the time when the regulator is set to the time when the air pressure in the system equilibrates. When setting a pressure, it is best to adjust the regulator slowly, monitoring the pressure shown on the display.

9.  Release pressure and open the chamber. When the tests being run in the chamber are finished, the pressure is released and the chamber is opened. Pressure is released by turning the exhaust valve clockwise to the "Exhaust" setting. Pressure can also be released by turning the regulator counter-clockwise, reducing the pressure in the system, and by pulling the ring on the safety relief valve on the low-pressure chamber lid. After all pressure has been released, the clamping bolts retaining the lid can be loosened and the chamber opened safely.

Further Information

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.