Excessive pressure is something that you will work with when you use measuring devices, service, install, verify, or eliminate mechanical cooling systems. Remember, unless otherwise specified, all PSI readings used in the service of work will be pressure sensor. Gauge balances for measuring pressure to look at things from a human point of view. Thus, the pressure sensor zero standard standard atmospheric pressure. In contrast to the absolute pressure scales, where zero means was absolutely no pressure (not even atmospheric pressure), gauge pressure scales read zero when no pressure is above or below atmospheric pressure. We can say that:
Absolute Press. = Sensor Press. + Optics of atmosphere and ocean. Press.
Pressure sensor that is less than or equal to), atmospheric pressure can be expressed in inches of mercury, vacuum. That is short. Hg. Vac. The word "vacuum" is actually a misnomer here. The word implies a negative pressure, which in the case of a human point of view. However, more pressure than no pressure at all. Seems to be negative for us, because it is less than the pressure created by the atmosphere.
When we compare the absolute scale pressure to measure the manometer scale at the mercury barometer tube, we see that the testimony changed places; 30.
Hg. Abs. 0. Hg. Vac. Both are normal atmospheric pressure at sea level. Similarly, 0 Century Hg. Abs. 30 Century Hg. Vac. Speaking in pressure sensor point of view, it is a perfect vacuum, because the pressure may be lower.
Pressure 4,000 feet above sea level, is 26. Hg. Abs. - or 4. Hg. Vac. In each example, the unit of measurement is the same inches of mercury. The starting point is different. Vacuum gauge readings, which are most common when removing the air, moisture and other gases inside the refrigeration system is in a process called evacuation.
Pressure sensor that is greater than or equal to), atmospheric pressure can be expressed in pounds per square inch gauge and abbreviated as pounds per square inch.
This mercury barometer tube compares PSIG scale with PSIA scale at normal atmospheric pressure at sea level. You can see from the title PSIG and PSIA, that each scale transactions with the same unit of pressure in pounds per square inch. They simply have different starting positions. PSIA always 14.7 psi above the same pressure is measured in pounds per square inch.
We see it manifested here on the barometer. Systems using R-22 as a refrigerant pressure in the evaporator 63,0 PSIG) will be read to the absolute pressure of the scale 77.7 PSIA (63.0 PSIG + 14.7 psi = 77.7 psi). In PSIA reading will be needed if R-22 pressure-enthalpy diagram used to repair system defects.
Pressure sensor normally read on the sensor, as shown here. This connection of the sensor, since it has a value above and below the atmospheric pressure in conjunction with one of the rut. This sensor, you can see how PSIG indications decrease to zero, and the pressure drops in relation to atmospheric pressure.
As pressure continues to fall below atmospheric pressure, increased to 30. Hg. Vac., as the ideal vacuum approached. It is also possible to use two separate sensors to perform this task: one for pressure above, and the other for pressure below atmospheric pressure...