Pressure gauges are instruments used to measure the pressure of gases or liquids in a system. There are several types of pressure gauges based on different working principles. Here are some common types:

1. Bourdon Tube Pressure Gauge: This is one of the most widely used types of pressure gauges. It operates on the principle that a curved tube, typically C-shaped or helical, tends to straighten when pressure is applied. As the pressure increases, the Bourdon tube straightens, and this motion is transferred to the pointer mechanism, indicating the pressure on a scale.

2. Diaphragm Pressure Gauge: Diaphragm pressure gauges use a flexible diaphragm as the sensing element. When pressure is applied, the diaphragm deforms, and this deformation is measured using a mechanical linkage or strain gauge to determine the pressure.

3. Piston Pressure Gauge: In a piston pressure gauge, pressure is applied to a piston or cylinder, causing it to move against a spring or a hydraulic fluid. The movement of the piston is then converted into a pressure reading.

4. Manometer: A manometer is a simple pressure gauge that measures pressure by balancing the weight of a fluid column between the measured pressure and a reference pressure (usually atmospheric pressure). Common types of manometers include U-tube manometers, well-type manometers, and inclined-tube manometers.

5. Bellows Pressure Gauge: Bellows pressure gauges use a collapsible metal bellows as the sensing element. When pressure is applied, the bellows expand or contract, and this motion is translated into a pressure reading.

6. Piezoelectric Pressure Gauge: Piezoelectric pressure gauges utilize the piezoelectric effect, where certain materials generate an electric charge in response to applied mechanical stress. When pressure is applied to a piezoelectric material, it generates a voltage proportional to the applied pressure, which can be measured electronically.

7. Strain Gauge Pressure Transducer: Strain gauge pressure transducers use strain gauges bonded to a flexible diaphragm or a metal element. As pressure changes, the strain gauges deform, causing a change in electrical resistance, which is measured and converted into a pressure reading.

8. Capacitive Pressure Sensor: Capacitive pressure sensors measure pressure changes by detecting changes in capacitance between two conductive plates separated by a flexible diaphragm. As pressure changes, the distance between the plates changes, altering the capacitance, which can be measured electronically.

These are just some of the common types of pressure gauges based on different working principles. Each type has its own advantages and limitations, and the selection of the appropriate pressure gauge depends on factors such as the application requirements, accuracy, range, and environmental conditions.