Short Answer:

A diaphragm pressure gauge works by using a thin, flexible metal membrane called a diaphragm that deflects when pressure is applied. This movement is small but measurable and is converted into a readable value using a mechanical linkage connected to a pointer on a dial.

As pressure increases, the diaphragm bends due to the force of the fluid acting on it. The amount of deflection depends on the pressure level, and this movement is used to indicate the pressure. Diaphragm gauges are commonly used for low-pressure and corrosive fluid applications.

Detailed Explanation:

Working of a Diaphragm Pressure Gauge

A diaphragm pressure gauge is a mechanical instrument used to measure pressure by converting fluid pressure into the deflection of a flexible diaphragm. It is especially suited for low-pressure ranges, where traditional pressure gauges like the Bourdon tube may not work as effectively. Diaphragm pressure gauges are commonly used in chemical plants, food processing units, and gas pipelines, particularly when corrosive or viscous fluids are involved.

Construction of a Diaphragm Pressure Gauge

1. Diaphragm Element
   The key sensing part is a thin circular metal diaphragm, usually made from stainless steel, Hastelloy, or Teflon-coated materials, depending on the application.
2. Pressure Chamber
   The diaphragm is placed between two flanges that create a sealed chamber. Pressure is applied to one side of the diaphragm while the other side remains at atmospheric or reference pressure.
3. Mechanical Linkage
   The center of the diaphragm is connected to a mechanical pointer system through levers and springs that amplify its movement.
4. Dial and Pointer
   The amplified motion turns a pointer over a calibrated dial that shows the pressure value.

Working Principle

1. Pressure Application
   When fluid (gas or liquid) enters the pressure chamber, it pushes against the diaphragm.
2. Diaphragm Deflection
   The diaphragm bends or bulges depending on the amount of pressure. The amount of movement is directly proportional to the pressure applied.
3. Motion Transfer
   The center of the diaphragm is linked to a transmission mechanism (levers, springs, or gears) that converts the small diaphragm movement into rotary motion.
4. Reading the Pressure
   This rotary motion moves the pointer on the dial, indicating the pressure value in units like bar, psi, or kPa.

Types of Diaphragm Gauges

• Single diaphragm: measures pressure against atmospheric pressure
• Dual diaphragm: used in differential pressure measurement
• Sealed diaphragm with fill fluid: used for corrosive or sanitary applications

Applications

• Low-pressure gas and liquid systems
• Corrosive media where metallic parts need isolation
• Pharmaceutical and food industries
• HVAC systems for air pressure measurement
• Laboratory setups for sensitive pressure monitoring

Advantages

• Suitable for low-pressure measurement
• Can handle corrosive and sticky fluids
• Simple and reliable mechanical operation
• Can be easily cleaned in hygienic environments
• High repeatability and accuracy in small pressure ranges

Limitations

• Not suitable for very high pressures
• Requires frequent calibration if used in harsh conditions
• Mechanical parts may wear out over time
• Limited diaphragm material choices for extreme applications

Conclusion

A diaphragm pressure gauge works by using the deflection of a flexible diaphragm to measure pressure. When pressure is applied, the diaphragm bends, and this movement is mechanically amplified and displayed on a dial. It is especially useful for low-pressure, corrosive, or hygienic applications, providing reliable and accurate readings without complex electronics. Its simplicity and effectiveness make it a widely used pressure sensing device in many industries.