#  > Petroleum Industry Zone >  > Oil And Gas Process >  >  >  How to Convert Absolute Pressure to Gauge Pressure  Read more: How to Convert Absolut

## Mohamed

Most modern pressure gauges take into account the use of atmospheric  pressure on the systems being read. Appliances and machines such as well  pumps, air compressors and tire gauges will read by gauge pressure.  This of course does not take into account the total system or absolute  pressure. By using a basic formula, you can convert absolute pressure to  gauge pressure or visa versa.
Understand that absolute pressure or total  system pressure is generally defined as the pressure measured from an  absolute vacuum or zero pounds per square inch (PSI). Gauge pressure is  that which is generally read on a gauge and takes into consideration the  atmospheric pressure we are placed under every day. Atmospheric  pressure changes with temperature and altitude above sea level. On  average this would be 14.6 pounds per square inch (PSI) above an  absolute vacuum reading of 0 PSI. In other words, the reading of 0 on a  gauge would really have 14.6 PSI already into account.

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                                                                  Realize that the basic formula for finding gauge pressure is  Pg = Ps -- Pa. Where Pg is equal the gauge pressure reading, Ps is the  total system pressure reading or absolute pressure, and Pa is the  atmospheric pressure that on average will be 14.6 PSI.
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                                                                  Covert the absolute pressure or system pressure of 100 PSI  into a gauge pressure reading. Plug the numbers into the formula and the  equation will read Pg = 100 - 14.6.; the gauge pressure is equal to  85.4 PSI.
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                                                                  Find the absolute pressure or total system pressure on a tire  gauge reading when testing a tire that reads 36 PSI. Translating the  formula will read as follows, Ps = Pg + Pa. The answer will be 36 + 14.6  = 50.6 PSI.






See More: How to Convert Absolute Pressure to Gauge Pressure  Read more: How to Convert Absolut

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## Mohamed

*Negative Pressure*

The term negative pressure is used in physics and engineering to refer to a situation in which an enclosed area has lower pressure than the area around it. Any compromise in the divide between the area of negative pressure and the more highly pressurized area around it would cause substances to flow into the area of negative pressure. Negative pressure is useful for a number of applications, including the prevention of oil spills, quarantine of highly contagious patients, and in the household vacuum cleaner.

Pipelines commonly have areas of negative pressure. Usually this is an intentional choice. For example, undersea pipelines used for oil and other materials are kept in a state of negative pressure so that if they rupture, seawater will flood the pipe. If the pipes were positively pressurized, their contents would explode into the ocean, potentially creating a hazardous spill. Negative pressure can also be dangerous, as is the case when municipal waterlines lose pressure, potentially sucking contaminated groundwater up into the water supply. In pipes, pressure is carefully monitored with the use of gauges, and is controlled with valves.

In quarantine situations, a room with negative pressure will suck air into it when doors or windows are opened. This prevents contagions from escaping through opened doors and windows, and makes it safer for medical personnel to care for the patient. Most research labs have rooms with negative pressure for studying dangerous diseases, preceded by a series of checkpoints to ensure that only authorized individuals enter the room. Negative pressure pipelines and vent hoods are also used in laboratory situations, to vent dangerous substances away from scientists.

Many homeowners interact with negative pressure on a fairly frequent basis, when they use a vacuum cleaner. When a vacuum is switched on, an area of negative pressure is formed in the bag or canister of the vacuum, which sucks air in as it tries to even out its internal pressure. Along with the air, the vacuum picks up particulate matter, leaving the floors cleaner. The basic vacuum principle is also used in a great deal of electronics and industrial applications. 
The understanding and control of negative pressure have greatly contributed to many scientific and technological advances. The opposite principal, positive pressure, or an area of higher pressure than the surrounding regions, is also used to help control environments. Many manufacturing facilities, for example, use positively pressurized clean rooms for handling delicate substances such as computer chips.

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## Mohamed

*There are two reference points for measuring a vacuum pressure:  either you can measure how much the pressure is below local atmospheric  pressure or how much it is above absolute zero vacuum.*


Both methods are measuring the same pressure point but each  will lead to differing results over time because the measuring reference  point for one is fixed (absolute zero vacuum) and the other is variable  (atmospheric air pressure).
If for example you are looking to  ensure that there is adequate suction pressure being drawn by a vacuum  pump or you are trying to maintain a slightly lower pressure in a  laboratory than the local barometric pressure to ensure no laboratory  air escapes, you would be interested in measuring a negative gauge  pressure.  Therefore as the barometric pressure changes you will always  be able to maintain suction pressure and containment of the laboratory  air because the pressure you are controlling will track with changes in  barometric pressure.
However, if you are looking to simulate  altitude in an environmental chamber or determine whether an adequate  vacuum seal has been achieved for preserving food you would measure the  absolute pressure.  Since you need to apply a vacuum that is a fixed  value independent of the ambient baro pressure reading you can be sure  that changes in atmospheric air pressure will not influence the pressure  measurement.
The typical negative gauge pressure range for  measuring vacuum is 0 to -1 bar gauge but if the barometric pressure is  below 1 bar absolute -1 bar will never be achieved and if the barometric  pressure is above 1 bar absolute then full vacuum cannot be measured.   Negative gauge pressures can be combined with positive pressures to  create a compound pressure range such as -1 to 2 bar gauge for processes  that involve vacuum purging and pump filling.

The typical absolute pressure range for measuring vacuum pressures is 0 to 1 bar absolute.

Since  negative gauge and absolute reference vacuum ranges are measuring the  same pressure it is often assumed that they are the same measurement  carried out in different directions.  However as explained above this is  not the case, so it is important to understand which type of  reference is required before selecting a  pressure instrument for  measuring over the vacuum range.

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## mbc.engg

Thanks Mohamed. Good information.

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