The “bar” is a common metric pressure unit used in specifications for consumer equipment and industrial systems. Although it is not part of the official International System of Units (SI), the bar is widely used because it aligns closely with the atmospheric pressure experienced daily. A 20 bar rating is a high-pressure specification, indicating a product is built to handle significant force.
Defining the Unit of Pressure
The pressure unit “bar” is defined precisely as 100,000 Pascals (Pa). The Pascal is the SI unit of pressure, equivalent to one Newton of force per square meter. Defining the bar as 100,000 Pa makes it a convenient, round number for technical and scientific measurements.
One bar is nearly identical to the average atmospheric pressure at sea level, which is technically 1.01325 bar, or one standard atmosphere (atm). This near-equivalence makes the unit intuitive for measuring pressures relative to the air around us. The bar is favored because it avoids the large numbers associated with the Pascal unit when dealing with typical working pressures, and it is frequently seen in Europe, oceanography, and hydraulics.
Practical Equivalents of 20 Bar
Translating 20 bar into more familiar units helps illustrate this pressure rating. The most common conversion for American audiences is to Pounds per Square Inch (PSI). Since one bar is equivalent to approximately 14.5 PSI, a rating of 20 bar translates to a pressure of about 290 PSI.
To visualize this pressure, consider its equivalent in a column of water. Pressure underwater increases by roughly one bar for every 10 meters of depth. Therefore, 20 bar is roughly equivalent to the water pressure experienced at a depth of 200 meters (about 660 feet). This represents twenty times the pressure of the atmosphere at sea level and is typically based on gauge pressure, which measures pressure above the ambient atmosphere.
Common Uses of the 20 Bar Rating
The 20 bar pressure rating is prominently used in two consumer product categories: water-resistant timepieces and high-performance machinery. For watches, a 20 bar rating is often written as 20 ATM (atmospheres) or 200 meters (200m). This rating signifies the watch has been tested in a laboratory to resist static pressure equivalent to that found at 200 meters underwater.
A watch with a 20 bar rating is suitable for high-impact water activities, including swimming, snorkeling, and recreational scuba diving. This rating does not guarantee the watch will function perfectly at a dynamic depth of 200 meters. Professional dive watches often carry an additional ISO 6425 certification, which is a stricter standard that includes testing for dynamic pressure and thermal shock.
In the realm of high-pressure machinery, the 20 bar rating frequently appears on home espresso machines. The optimal pressure for extracting a balanced shot of espresso is widely considered to be around 9 bars. When a machine is advertised as having a 20 bar rating, this value refers to the maximum pressure capacity of its pump, not the pressure actually used for brewing.
The higher pump capacity provides a buffer, helping the machine maintain a stable 9 bar pressure even if the coffee grind or tamping is inconsistent. This high-capacity pump ensures consistent performance and can offer advantages like pressure profiling, where the pressure is varied throughout the extraction process.