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For example, a bicycle tire pumped up to 65 psig in a local atmospheric pressure at sea level (14.7 psi) will have a pressure of 79.7 psia (14.7 psi + 65 psi). [2] [3] When gauge pressure is referenced to something other than ambient atmospheric pressure, then the unit is pound per square inch differential (psid).
120–290 psi Pressure used in boilers of steam locomotives [citation needed] 1.1 MPa 162 psi Pressure of an average human bite [citation needed] 2.8–8.3 MPa 400–1,200 psi Pressure of carbon dioxide propellant in a paintball gun [64] 5 MPa 700 psi Water pressure of the output of a coin-operated car wash spray nozzle [58] 5 MPa 700 psi
An example of this is the air pressure in an automobile tire, which might be said to be "220 kPa (32 psi)", but is actually 220 kPa (32 psi) above atmospheric pressure. Since atmospheric pressure at sea level is about 100 kPa (14.7 psi), the absolute pressure in the tire is therefore about 320 kPa (46 psi).
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth.The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, [1] 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. [2]
Using atmospheric pressure as reference is usually signified by a "g" for gauge after the pressure unit, e.g. 70 psig, which means that the pressure measured is the total pressure minus atmospheric pressure. There are two types of gauge reference pressure: vented gauge (vg) and sealed gauge (sg).
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 ).
Since 1982, STP has been defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 1 bar (100 kPa, 10 5 Pa). NIST uses a temperature of 20 °C (293.15 K, 68 °F) and an absolute pressure of 1 atm (14.696 psi, 101.325 kPa). [3] This standard is also called normal temperature and pressure (abbreviated as NTP).
Ambient pressure may in other circumstances be measured in pounds per square inch (psi) or in standard atmospheres (atm). The ambient pressure at sea level is approximately one atmosphere, which is equal to 1.01325 bars (14.6959 psi), which is close enough for bar and atm to be used interchangeably in many applications.