Pounds per square inch

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Pound per square inch
Psidial.jpg
A pressure gauge reading in psi (red scale) and kPa (black scale)
General information
Unit system Imperial units, US customary units
Unit of Pressure, Stress
Symbolpsiorlbf/in2
Conversions
1 psi in ...... is equal to ...
    SI units    6.894757 kPa

The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2; [1] abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied to an area of one square inch. In SI units, 1 psi is approximately equal to 6895 N/m2.

Contents

Pounds per square inch absolute (psia) is used to make it clear that the pressure is relative to a vacuum rather than the ambient atmospheric pressure. Since atmospheric pressure at sea level is around 14.7 psi (101 kilopascals ), this will be added to any pressure reading made in air at sea level. The converse is pounds per square inch gauge (psig), indicating that the pressure is relative to atmospheric pressure. For example, a bicycle tire pumped up to 65 psig in a local atmospheric pressure at sea level (14.7 psia) 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 units would be pounds per square inch differential (psid).

Multiples

The kilopound per square inch (ksi) is a scaled unit derived from psi, equivalent to a thousand psi (1000 lbf/in2).

ksi are not widely used for gas pressures. They are mostly used in materials science, where the tensile strength of a material is measured as a large number of psi. [4]

The conversion in SI units is 1 ksi = 6.895 MPa, or 1 MPa = 0.145 ksi.

The megapound per square inch (Mpsi) is another multiple equal to a million psi. It is used in mechanics for the elastic modulus of materials, especially for metals. [5]

The conversion in SI units is 1 Mpsi = 6.895 GPa, or 1 GPa = 0.145 Mpsi.

Magnitude

Conversions

The conversions to and from SI are computed from exact definitions but result in an inexact number that must be rounded at some point. [6] [7]

As the pascal is very small unit, relative to industrial pressures, the kilopascal is commonly used. 1000 kPa ≈ 145 lbf/in2.

Approximate conversions (rounded to some arbitrary number of digits, except when denoted by "≡") are shown in the following table.

Pressure units
Pascal Bar Technical atmosphere Standard atmosphere Torr Pounds per square inch
(Pa)(bar)(at)(atm)(Torr)(lbf/in2)
1 Pa≡ 1 N/m210−51.0197×10−59.8692×10−67.5006×10−30.000 145 037 737 730
1 bar105≡ 100 kPa

 106  dyn/cm2

1.01970.98692750.0614.503 773 773 022
1 at98066.50.980665≡ 1 kgf/cm20.967 841 105 354 1735.559 240 114.223 343 307 120 3
1 atm1013251.013251.0332176014.695 948 775 514 2
1 Torr133.322 368 4210.001 333 2240.001 359 511/760 ≈ 0.001 315 7891 Torr

≈ 1  mmHg

0.019 336 775
1 lbf/in26894.757 293 1680.068 947 5730.070 306 9580.068 045 96451.714 932 572≡ 1 lbf/in2

See also

Related Research Articles

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Pressure Force distributed continuously over an area

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The torr is a unit of pressure based on an absolute scale, defined as exactly 1/760 of a standard atmosphere. Thus one torr is exactly 101325/760 pascals (≈ 133.32 Pa).

Atmospheric pressure, also known as barometric pressure, is the pressure within the atmosphere of Earth. The standard atmosphere is a unit of pressure defined as 101,325 Pa, which is equivalent to 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth, that is, the Earth's atmospheric pressure at sea level is approximately 1 atm.

Pascal (unit) SI unit of pressure

The pascal is the SI derived unit of pressure used to quantify internal pressure, stress, Young's modulus and ultimate tensile strength. The unit, named after Blaise Pascal, is defined as one newton per square metre. The unit of measurement called standard atmosphere (atm) is defined as 101325 Pa.

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The pound of force or pound-force is a unit of force used in some systems of measurement including English Engineering units and the Foot–pound–second system. Pound-force should not be confused with foot-pound, a unit of energy, or pound-foot, a unit of torque, that may be written as "lbf⋅ft"; nor should these be confused with pound-mass, often simply called pound, which is a unit of mass.

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Bar (unit) non-SI unit of pressure

The bar is a metric unit of pressure, but not part of the International System of Units (SI). It is defined as exactly equal to 100,000 Pa (100 kPa), which is the atmospheric pressure on earth at an altitude of about 111 meters and a temperature of 15 °C or slightly less than the current average pressure at sea level.

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Cold inflation pressure

Cold inflation pressure is the inflation pressure of tires before the car is driven and the tires warmed up. Recommended cold inflation pressure is displayed on the owner's manual and on the placard attached to the vehicle door edge, pillar, glovebox door or fuel filler flap. 40% of passenger cars have at least one tires under-inflated by 6 psi or more. Drivers are encouraged to make sure their tires are adequately inflated, as suboptimal tire pressure can greatly reduce fuel economy, increase emissions, increased wear on the edges of the tire surface, and can lead to premature failure of the tire. Excessive pressure, on the other hand, may lead to impact-breaks, decrease braking performance, and cause uneven wear.

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Inches of water, inches of water gauge (iwg or in.w.g.), inches water column (inch wc or just wc), inAq, Aq, or inH2O is a non-SI unit for pressure. The units are conventionally used for measurement of certain pressure differentials such as small pressure differences across an orifice, or in a pipeline or shaft.

Sectional density Value calculated by taking the total mass divided by area cross sectional area. Used in projectile and speed boat design.

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Metre sea water Unit of pressure equal to one tenth of a bar

The metresea water (msw) is a unit of pressure used in underwater diving. It is defined as one tenth of a bar.

References

  1. IEEE Standard Letter Symbols for Units of Measurement (SI Units, Customary Inch-Pound Units, and Certain Other Units), IEEE Std 260.1™-2004 (Revision of IEEE Std 260.1-1993)
  2. "Glossary of Industrial Air Cleaning Technology". United Air Specialists, Inc. Archived from the original on August 1, 2011.
  3. "Gage v. Sealed v. Absolute pressure" (PDF). Dynisco.
  4. "Tensile Strength of Steel and Other Metals". All Metals & Forge Group. Retrieved 2016-07-26. A metal’s yield strength and ultimate tensile strength values are expressed in tons per square inch, pounds per square inch or thousand pounds (KSI) per square inch. For example, a tensile strength of a steel that can withstand 40,000 pounds of force per square inch may be expressed as 40,000 PSI or 40 KSI (with K being the [multiplier] for thousands of pounds). The tensile strength of steel may also be shown in MPa, or megapascal.
  5. An example of the use of Mpsi in mechanics for the elastic moduli of several materials
  6. BS 350: Part 1: 1974 – Conversion factors and tables. British Standards Institution. 1974. p. 49. ISBN   0 580 08471 X.
  7. NIST Special Publication 811 – Guide for the Use of the International System of Units (SI) (PDF). National Institute of Standards and Technology. 2008. p. 66.