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Introduction of pressure units commonly used in hydraulic industry

There are four commonly used pressure units: kgf / cm2, bar, MPa and 1mmh2o.
1. Kgf / cm2 (kgf / cm2)
Until the 1960s and 1970s, the unit of pressure was kgf / cm2, which is commonly known as "kg". It's very easy for people to remember the meaning of 1kg and 2kg.
2、bar
When the unit of force in unit kgf / cm2 is changed from KGF (kilogram force) to n (Newton), i.e. n / cm2, a new unit bar is introduced. Because 1bar = 10 N / cm2 ≈ 1.02 kgf / cm2, many hydraulic practitioners use 1bar as 1kg.
3、MPa
Our country uses the international system of units, so we use the PA:
1 Pa= 1N/m2=0.0001 N/cm2=0.00001bar
Of course, for hydraulic technology, the unit of PA is too small, so we generally use MPa as the unit, that is, 1 MPa = 1x106 PA = 10bar.
4、1mmH2O
As we all know, the gravity of the liquid column will also cause pressure, which is mainly determined by the height h of the liquid column and the density ρ of the liquid.
It is known that the density of water is 1g / cm3 and the acceleration of gravity g is about 10m / S2; therefore, at the bottom of the water column with a height of 10m, the pressure caused by the gravity of the water column is 10mx1g / cm3x10m / S2 = 10 N / cm2 ≈ 1bar = 0.1 MPa.
In other words, 1 MPa is equivalent to the pressure at the bottom of 100 m water column; 1 bar is equivalent to the pressure at the bottom of 10 m water column. The medium used in hydraulic system is usually hydraulic oil. As we know, the density of hydraulic oil is smaller than that of water. Therefore, the pressure at the bottom of oil column at the same height is lower than that of water column. I hope you can have some quantifiable references to these units in your mind.

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