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A centimetre of water [1] is a unit of pressure. It may be defined as the pressure exerted by a column of water of 1 cm in height at 4 °C (temperature of maximum density) at the standard acceleration of gravity, so that 1 cmH 2 O (4°C) = 999.9720 kg/m 3 × 9.80665 m/s 2 × 1 cm = 98.063754138 Pa ≈ 98.0638 Pa, but conventionally a nominal maximum water density of 1000 kg/m 3 is used, giving ...
10 kPa 1.5 psi Pressure increase per meter of a water column [26]: 10 kPa 1.5 psi Decrease in air pressure when going from Earth sea level to 1000 m elevation [citation needed]
The ambient pressure in water with a free surface is a combination of the hydrostatic pressure due to the weight of the water column and the atmospheric pressure on the free surface. This increases approximately linearly with depth. Since water is much denser than air, much greater changes in ambient pressure can be experienced under water.
So if a water column meter reads "13.6 cm H 2 O", then an equivalent measurement is "1.00 cm Hg". This example demonstrates why there is some confusion surrounding pressure head and its relationship to pressure. Scientists frequently use columns of water (or mercury) to measure pressure (manometric pressure measurement), since for a given fluid ...
It is defined as the pressure exerted by a column of water of 1 inch in height at defined conditions. At a temperature of 4 °C (39.2 °F) pure water has its highest density (1000 kg/m 3). At that temperature and assuming the standard acceleration of gravity, 1 inAq is approximately 249.082 pascals (0.0361263 psi). [2]
For low pressure differences, light oil or water are commonly used (the latter giving rise to units of measurement such as inches water gauge and millimetres H 2 O). Liquid-column pressure gauges have a highly linear calibration. They have poor dynamic response because the fluid in the column may react slowly to a pressure change.
On Earth, additional height of fresh water adds a static pressure of about 9.8 kPa per meter (0.098 bar/m) or 0.433 psi per foot of water column height. The static head of a pump is the maximum height (pressure) it can deliver. The capability of the pump at a certain RPM can be read from its Q-H curve (flow vs. height).
In scuba diving, bar is also the most widely used unit to express pressure, e.g. 200 bar being a full standard scuba tank, and depth increments of 10 metre of seawater being equivalent to 1 bar of pressure. Many engineers worldwide use the bar as a unit of pressure because, in much of their work, using pascals would involve using very large ...