• Pneumatic Piezometer

Pneumatic Piezometer

  • DGSI - Slope Indicator 51417800

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Pneumatic piezometers are used to measure pore water pressure in saturated soils.

Applications include

  • Monitoring pore pressures to determine safe rates of fill or excavation.
  • Monitoring pore water pressures to determine slope stability.
  • Monitoring the effects of dewatering systems used for excavations.
  • Monitoring the effects of ground improvement systems such as vertical drains and sand drains.
  • Monitoring pore water pressures to check the performance of earth fill dams and embankments.
  • Monitoring pore water pressures to check containment systems at land fills and tailings dams.


Slope Indicator’s pneumatic piezometers employ a simple and reliable transducer that is inherently free from drift.

Long term performance is enhanced by corrosion-resistant plastic construction, polyethylene tubing, and in-line filters in all connectors.

Twin-tube design is compatible with both “flow” and “no-flow” reading techniques.

Operating Principle

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 a terminal at the surface. Readings are obtained with a pneumatic indicator.

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 indicator is connected to the terminal or directly to the tubing. Compressed nitrogen gas from the indicator 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 a reading can be obtained from the pressure gauge on the indicator.


CAT. NO. Description
SI51417800 Pneumatic Piezometer
SI51416900 Twin Tubing
SI51407302 Quick Connector
SI51417801 Piezometer with 15m • 50' tubing
SI51417802 Piezometer with 30m • 100' tubing
SI51417803 Piezometer with 45m • 150' tubing
SI51417804 Piezometer with 60m • 200' tubing
  • Sensor Type: Twin-tube pneumatic transducer.
  • Range: Pressure rated for 27.5 bar or 400 psi. Working range depends on gauge supplied with pneumatic indicator. Digital gauge provides range to 690 kPa / 100 psi. Analog gauges provide ranges to 1000 kPa / 150 psi.
  • Repeatability: ±0.25% FS.
  • Diaphragm Displacement: 0.01 ml typical.
  • Filter: Sintered stainless steel, 50 micron pores.
  • Materials: ABS and PVC plastic body, synthetic rubber diaphragm.
  • Diameter: 25.4 mm (1").