What is a Diaphragm Seal Pressure Gauge? Structure, Operating Principle, and Practical Applications

The diaphragm seal pressure gauge is a reliable pressure measurement solution for corrosive, viscous, or contaminated process media. By isolating the measuring mechanism from the process fluid using a diaphragm seal, the instrument ensures measurement accuracy, improved durability, and long-term operational stability in demanding industrial environments.

Reliable Pressure Measurement Solution for Corrosive and Viscous Media

The diaphragm seal pressure gauge is designed for industrial applications where the process medium must be isolated from the pressure sensing element. This design ensures measurement accuracy, operational safety, and long service life in demanding environments.

The product series includes:

• P710 – Screwed process connection
• P720 – “I” type process connection
• P730 – Flat flange process connection

These models are suitable for various piping systems and industrial operating conditions.

1. What is a Diaphragm Seal Pressure Gauge?

A diaphragm seal pressure gauge uses a metal diaphragm and fill fluid to transmit process pressure to the measuring instrument without allowing direct contact between the process medium and the gauge mechanism.

This solution is recommended when the process medium is:

• Corrosive
• Highly viscous
• Containing suspended solids
• Crystallizing or solidifying
• Hygienic-sensitive
• Likely to clog pressure ports

It is widely used in modern industrial pressure measurement systems.

2. Working Principle

When process pressure acts on the diaphragm, the force is transmitted through silicone oil fill fluid to the pressure gauge sensing element. This transmission ensures accurate and stable pressure measurement.

This mechanism:

• Isolates the gauge from the process medium
• Protects internal measuring components
• Improves durability
• Ensures stable operation

3. Main Technical Specifications

Pressure range (MPa, kPa, bar)

• -0.1 ~ 0 đến -0.1 ~ 2.5 MPa
• 0 ~ 0.1 đến 0 ~ 35 MPa

Filling liquid

Silicone oil

Working temperature

• Ambient: -20 ~ 65°C (With Glycerin filling), -40 ~ 65 °C (With Silicone filling)
• Process fluid: max. 100°C

Temperature effect

Approx. ±0.5% of full scale per 10°C deviation from reference temperature (20°C).

Diaphragm Material

The diaphragm is available in various corrosion-resistant materials.

The selection of diaphragm material and process fluid compatibility depends on the user’s system requirements and operating conditions.

4. Materials of Construction

Diaphragm materials

• 316L Stainless Steel
• Monel
• Hastelloy-C
• Titanium
• Tantalum
• Nickel
• Alloy20

Upper flange (gauge side)

• 304SS
• 316SS
• Titanium

Under flange (process side)

• 304SS / 304L SS
• 316SS / 316L SS
• Monel
• Hastelloy-C
• Titanium
• Nickel

5. Product Models

Model P710 — Screwed connection

Suitable for small pipelines and low-to-medium pressure applications. Easy installation and maintenance.

Model P720 — “I” type connection

Robust structure for standard industrial systems.

Model P730 — Flat flange connection

Flat flange design according to ANSI or JIS standards, suitable for large pipelines and harsh environments.

6. Optional Features

Available options include:

• PTFE coating or PTFE lining
• Glycerin-filled gauge
• Silicone-filled gauge
• Flushing ring
• Purging plug
• Heating/cooling jacket
• Capillary tube

These options allow flexible configuration based on application requirements.

7. Applications

Diaphragm seal pressure gauges are widely used in:

• Chemical plants
• Food & beverage industry
• Pharmaceutical industry
• Steam systems
• Water treatment plants
• Power plants
• Cement plants
• Oil & gas industry

They are especially effective in challenging process conditions.

8. Key Advantages

• Complete process isolation
• Protection of pressure gauge mechanism
• Anti-clogging design
• High durability
• Stable measurement performance
• Wide material selection
• Suitable for harsh industrial environments
• Easy maintenance

9. Ordering Information

Ordering information typically includes:

• Model (P711 / P712 / P721 / P722 / P731 / P732)
• Process connection type
• Diaphragm material
• Flange material
• Pressure unit
• Pressure range
• Optional accessories

Selecting the correct configuration ensures long-term reliability and performance.