Determining the Pressure Required to Blow Air Under 2 Meters of Water
To determine the pressure needed to blow air under 2 meters of water, one must carefully consider the pressure exerted by the water column and the atmospheric pressure at the surface. Accurately measuring and manipulating these variables is key for successful underwater applications.
Water Pressure Calculation
The pressure exerted by a column of water is calculated using the formula:
P ρ · g · h
where:
P is the pressure in pascals (Pa) ρ (rho) is the density of water, approximately 1000 kg/m3 g is the acceleration due to gravity, approximately 9.81 m/s2 h is the height of the water column in metersCalculating Pressure at 2m Depth
For a depth of 2 meters of water:
P 1000 kg/m3 · 9.81 m/s2 · 2 m 19620 Pa or 19.62 kPa
Total Pressure Required
In addition to the pressure needed to counteract the water, one must also account for atmospheric pressure, which at sea level is approximately 101.3 kPa. Thus, the total pressure required from the compressor would be:
P_{total} P_{water} P_{atmospheric} 19620 Pa 101300 Pa 120920 Pa or 120.92 kPa
Head Pressure
The pressure exerted on a one square meter surface 2 meters under water effectively has the weight of two cubic meters of water pushing down on it. A cubic meter has a volume of 1000 liters, and the original definition of one kilogram of mass was the mass of a liter of water. Thus, we have the weight of 2000 liters of water with a mass of 2000 kilograms. Multiplying the mass by Earth's acceleration of gravity (9.8 m/s2) results in a weight of 19600 Newtons of force on the square meter of area. A Newton per square meter is the definition of the SI pressure unit called a Pascal, resulting in 19600 Pascals of pressure at that depth.
One Pascal is:
19.6 kPa ≈ 0.193 atmospheres or 2.84 psi (pounds per square inch)These calculations are all gauge pressures, not absolute pressures.
Understanding Head Pressure Across Vertical Columns
Head pressure is the same whether you are lifting water up in a column or blowing air down a column, as either action displaces a vertical distance of water. The size of the column diameter makes no difference.
Head Pressure at Surface and Depth
At the surface, there is zero feet of water above or below you, so the head pressure is zero. For each foot of depth, the head pressure is 0.433 psi at 2 meters (6.56168 feet), the pressure is 2.84120744 psi.
Pressure Exertion Explained
In terms of a one square meter surface 2 meters under water, the pressure effectively has the weight of 2000 liters of water. Multiplying the mass (2000 kg) by Earth's gravity (9.8 m/s2) gives a weight of 19600 Newtons. Since a Newton per square meter is a Pascal, the pressure is 19600 Pascals or 19.6 kPa. This is equivalent to 0.193 atmospheres or 2.84 psi.
It is important to understand that these are gauge pressures, not absolute pressures.
Practical Applications
This information is crucial for a variety of applications such as:
Underwater construction and mining Installing underwater pipes and cables Submerged structural repairs and maintenanceConclusion
To blow air under 2 meters of water, a compressor needs to generate a pressure of approximately 120.92 kPa or about 1.21 atmospheres. Understanding and correctly calculating the necessary pressure is essential for effective and safe underwater operations.