Key Takeaway
A diaphragm pressure gauge uses a flexible membrane (diaphragm) that deflects under pressure. The diaphragm is sealed between two flanges and separates the pressure medium from the gauge’s movement mechanism. As pressure is applied, the diaphragm flexes and this movement is mechanically transmitted to a pointer on the dial or to an electronic sensor in digital versions. Diaphragm gauges are ideal for low-pressure, viscous, or corrosive media because the diaphragm can be coated or made from chemically resistant materials like PTFE or stainless steel. These gauges are commonly used in food, chemical, and pharmaceutical applications for safe and sanitary pressure monitoring.
Elastic Deformation of the Diaphragm Element
In diaphragm gauges, the core sensing element is a thin, circular metal sheet. When pressure is applied, it bulges slightly. This elastic deformation is transferred to a mechanical or electronic signal system.
Diaphragm elements are ideal for low-pressure or corrosive applications. Since they don’t have complex gear systems, they’re reliable and easier to clean.
Materials used include stainless steel, Hastelloy, or PTFE-coated metal. Their response is quick, and deformation is reversible — until the diaphragm wears out or is punctured.
Transfer of Force to a Pointer Mechanism
In mechanical gauges, pressure creates force on a sensing element (Bourdon tube, diaphragm, etc.). This force is small — often less than a few grams — but it’s enough to drive a mechanical linkage system.
The system includes:
Sector gear
Pinion gear
Pivot spring
These convert the linear or curved deflection into a rotary movement, which moves the pointer across the dial.
The smoother the transfer, the better the reading. Any dirt, wear, or friction in the mechanism affects performance, causing sluggish or erratic needle behavior.
Suitable Applications in Sanitary and Corrosive Environments
Sanitary and corrosive environments require specialized gauge design.
Sanitary Applications (Food, Pharma):
316L stainless steel
Flush-mounted diaphragm
3A or EHEDG certified
SIP/CIP capable
Corrosive Applications (Chemical, Wastewater):
PTFE, Monel, or Hastelloy wetted parts
Chemical seal assemblies
Isolated sensing elements
Never use standard brass gauges with aggressive media. And never compromise on hygiene in clean zones. Always verify material compatibility, sealing integrity, and maintenance routines before deployment.
Comparison with Bourdon Tube Gauges
Manometers:
Simple, highly accurate at low pressure
Require leveling and clear fluid columns
Sensitive to temperature and vibration
Bourdon Tube Gauges:
Rugged, compact, and easier to install
No fluid handling
Suitable for a wider pressure range
Use manometers in labs, calibration settings, and low-pressure gas monitoring. Use Bourdon tubes in industrial settings where reliability and ease of use are prioritized.
Each has its role — choose based on environment, pressure range, and required precision.
Key Design Features and Material Choices
The performance and durability of a pressure gauge depend heavily on its design and materials.
Key Design Features:
Overrange protection: Prevents damage during pressure spikes
Dampening systems: For vibration resistance (e.g., liquid-filled)
Sealed casings: IP-rated for dust/water ingress
Safety blowout back: Directs pressure away in case of rupture
Material Choices:
Bourdon tube: Often brass or stainless steel
Case: Plastic (cheap), aluminum, or stainless steel (durable)
Lens: Acrylic, glass, or polycarbonate
Diaphragms: Teflon, stainless steel, or elastomers
Applications determine material: food/pharma needs stainless and hygienic design, while HVAC may use cheaper plastic casings. Chemical resistance, pressure rating, and environmental protection should all influence material selection.
Conclusion
Diaphragm pressure gauges are perfect for low-pressure, hygienic, or corrosive environments where standard Bourdon tube designs may fail. They use a thin, flexible membrane to isolate the pressure medium from internal components—ideal for food, pharmaceutical, and chemical processes. These gauges are often flush-mounted to prevent clogging and contamination. Their sealed design ensures cleanability and media compatibility, supporting CIP (Clean-in-Place) or SIP (Sterilize-in-Place) protocols. Diaphragm gauges also handle viscous and crystallizing fluids better than traditional gauges. Their ability to provide accurate, stable readings at low pressures makes them indispensable in sensitive applications where precision and hygiene go hand-in-hand.