The
piezometer is a device to measure pressure and the compressibility of
liquids. This is a form devised by Regnault and was used to show that
water is nearly incompressible.
Working 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.
Limitations:
1). This can’t be used
for gases.
2). Its diameter of tube should be more than 12mm.
2). Its diameter of tube should be more than 12mm.
3). It can use only for
low pressures.
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