Pneumatic Piezometers

Applications

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.
Pneumatic Piezometers

Advantages

Slope Indicator's pneumatic piezometers employ a simple and reliable transducer that is free from zero drift. Long term performance is enhanced by corrosion-resistant plastic construction, polyethylene tubing, and in-line filters in all connectors. 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 the pneumatic indicator shows the reading on its pressure gauge.

schematic diagram of pneumatic piezometers in use

For more information

Please download the datasheet and manual for Pneumatic Piezometers. You may also be interested in the datasheet and manual for the Pneumatic Indicator. These documents can be viewed and printed with Adobe Acrobat Reader.

Pneumatic Piezometers Specifications

PNEUMATIC PIEZOMETER
Sensor TypeTwin-tube pneumatic transducer
RangePressure rated for 27.5 bar or 400 psi. The working range depends on the gauge supplied with a pneumatic indicator. The digital gauge provides a range of 690 kPa / 100 psi. Analog gauges provide ranges to 1000 kPa / 150 psi
Repeatability±0.25% FS
Diaphragm Displacement0.01 ml typical
FilterSintered stainless steel, 50-micron pores
MaterialsABS and PVC plastic body, synthetic rubber diaphragm
Diameter25.4 mm (1")
PIEZOMETER ONLY
Pneumatic Piezometer51417800Part number includes piezometer and one quick connect plug. Tubing is attached to the piezometer at the factory and must be ordered at the same time as the piezometer
PIEZOMETER WITH TUBING
Piezometer & 50’ of tubing51417801
Piezometer & 100’ of tubing51417802
Piezometer & 150’ of tubing51417803
Piezometer & 200’ of tubing.51417804
TUBING & CONNECTORS
Twin Tubing51416900Two polyethylene tubes bundled in polyethylene jacket
Tubing Size4.76 mm with 1 mm wall (3/16"with 0.04" wall)
Jacket12 mm x 7 mm with 1.1 mm wall (0.46" x 0.28" with 0.045" wall)
Burst Pressure3.4 MPa (500 psi)
Minimum Bending Radius75 mm (3")
Tubing Buoyancy0.021 kg per m (0.014 lb per foot)
Weight0.06 kg per meter (0.04 lb per foot)
Splice Kit51401723Includes 3 brass unions, self-vulcanizing mastic pad, and sealing tape
Quick Connect Plug51407302Brass quick-connect fitting for input tube. The plug includes an in-line filter and a 90° elbow for insertion into the panel. One quick connect plug included with sensor
INSTALLATION ACCESSORIES
Small Canvas Bag06240000Creates a sand filter around the piezometer. Also assists with sinking the piezometer in waterfilled boreholes.
A small bag is 64 x 457 mm (2.5 x 18").
The large bag is 114 x 457 mm (4.5 x 18")
Large Canvas Bag06240001
Push-In Well Point51400099Steel well point for piezometer, 30 x 610 mm (1.25 x 24"), 2 kg (4.4 lb). This part number includes labor to insert the piezometer into a good point but does not include piezometer, tubing, or quick-connect plug
TERMINALS
Terminal Pipe, 6 Positions51409900Heavy gauge, zinc-plated, iridium treated steel pipe, 70 mm x 2 m (2.75"x 80"). The inside panel accommodates quick-connect plugs from 6 piezometers. Includes panel, panel nuts, locking cap, keyed-alike padlock, and 90° PVC sweep for tubing entry
Terminal Pipe, 20 Positions51417100Heavy gauge, zinc plated steel pipe, 127 mm x 178 mm x 1.8 m (5"x 7"x 6’). The inside panel accommodates quick-connect plugs from 20 piezometers. Includes panel and panel nuts, locking cap, keyed-alike padlock, and 90° PVC sweep for tubing entry
Terminal Box, 10 Positions51401510Fiberglass box with lockable lid, 292 x 235 x 140 mm (11.5 X 9.25 x 5.5"). The inside panel accommodates quick-connect fittings from 10 piezometers. Box can be mounted to a wall or post. Includes panel and panel nuts
PNEUMATIC INDICATOR
With 0.25% Analog Gauge51425601
With 0.1% Digital Gauge51425602