In a typical installation, the piezometer is sealed in a borehole, embedded in fill, or suspended in a standpipe.
Twin pneumatic tubes run from the piezometer to the surface of the ground. Readings are obtained with a C109 Pneumatic Readout.
The piezometer contains a flexible diaphragm. Water pressure acts on one side of the diaphragm and gas pressure acts on the other.
When a reading is required, a pneumatic readout is connected to the tubing connector.
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Compressed nitrogen gas from the readout flows down the input tube to increase gas pressure on the diaphragm.
When gas pressure exceeds water pressure, the diaphragm is forced away from the vent tube, allowing excess gas to escape via the vent tube.
When the return flow of gas is detected at the surface, the gas supply is shut off.
Gas pressure in the piezometer decreases until water pressure forces the diaphragm to its original position, preventing further escape of gas through the vent tube.
At this point, gas pressure equals water pressure, and the pneumatic readout shows the reading on its display.
