How To Read A Vacuum Pressure Gauge

15 psig or 760 mmhg equals total vacuum.

How to read a vacuum pressure gauge. A vacuum gauge is a pressure gauge used to measure pressures lower than the ambient atmospheric pressure which is set as the zero point in negative values e g. Diaphragm vacuum gauge in the case of. This definition is referring to a high or hard vacuum. Most gauges measure pressure relative to atmospheric pressure as the zero point so this form of reading is simply referred to as.

3 read from zero at atmospheric pressure down to a full scale vacuum reading of 30 inches of hg. As the vacuum pressure reduces the capsule bulges. It is referred to as pounds per square inch. This is called gauge pressure and will vary depending on the atmospheric pressure.

So for example at ambient air pressure the vacuum reading is 0 bar gauge and if a suction pressure of 0 25 bar is applied the vacuum reading will be 0 25 bar gauge. Check to make sure all vacuum hoses are connected and not leaking. This movement is transferred via a system of levers to a pointer and can then be read off as the pressure on a linear scale. Vacuum gauges are often in this category but the insight that a vacuum gauge can provide is as valuable today as it was 30 40 or 50 years ago.

This a normal reading between 17 and 22 inches of mercury. Remember that engine vacuum is just air pressure lower than atmospheric pressure. As the pressure drops or goes down the vacuum reading number rises or goes up. This vacuum gauge contains a hermetically sealed evacuated thin walled diaphragm capsule which is located within the instrument.

This means that a mechanical gauge usually calibrated in english units might have a dial reading from zero to something called 30 inches of vacuum. Vacuum gauge is measured from ambient air pressure in the negative direction. We have both absolute pressure and gauge pressure to contend with. Gauge pressure is pressure measured relative to ambient atmospheric pressure approximately 14 7 psia.

Below are some of the most common readings and diagnoses you ll find. Figure 1 illustrates that relationship of absolute and gauge pressure with 0 psia equal to a high or hard vacuum. Once you re engine is up to operating temperature you can begin reading your vacuum gauge. Absolute pressure uses a perfect vacuum as zero while gauge pressure uses atmospheric pressure as zero.