Anatomy of a Pressure Gauge – Components & How It Works

The importance of a pressure gauge is often overlooked. A well-designed and properly sized pressure gauge should provide accurate service for years. The performance of spray nozzles, pumps and other fluid components are evaluated by pressure gauges in the fluid system. A quality pressure gauge will pay for itself by increasing the accuracy and control of your process.

Since the Bourdon tube style is the most commonly used design, this article focuses on Eugene Bourdon’s invention over 175 years ago.

How a Bourdon Tube Pressure Gauge Works

The basic operating principle of a Bourdon tube gauge is a hollow, C-shaped tube which is opened to pressure at one end and welded shut at the other. When the tube is pressurized it tries to straighten-out, moving attached linkage and a pointer to indicate the precise pressure. The design of the Bourdon tube, having a curvature and thus the inside radius being less than the outside radius makes it possible to correlate the movement of the tube to a specific pressure.

Inside a Pressure Gauge – Component by Component

Case

The outer case is typically plastic, painted or plated steel, brass or — most commonly — stainless steel. Some cases are designed to be opened for servicing. Cases for liquid-filled gauges must seal properly. Solid-front cases direct process fluid backward in case of failure. Cases can be panel or wall mount.

Socket (Inlet)

The first part the process fluid contacts (unless using a diaphragm seal). Better gauges have a threaded hole for a removable restrictor orifice that dampens surges and protects the Bourdon tube from particles.

Bourdon Tube & Welding

Quality materials and welding at both the socket and closed end are critical for long life and accuracy.

Movement & Linkage

A pivot point connects the linkage to a geared movement. Machined components and finer gears deliver higher accuracy and longer endurance than stamped parts. Stainless steel outlasts copper alloy.

Pointer

Pointers vary in complexity. Some allow fine adjustments for altitude or wear from pulsation/vibration. High/low pressure pointers can record extremes.

Dial (Face)

Calibrated to the Bourdon tube. Custom dials with company name, logo or colors are available (artwork charge + longer lead time).

Accuracy (ASME B40.1)

Commonly expressed as “3-2-3% Grade B” or “2-1-2% Grade A”. The middle third of the scale is most accurate. Choose a range so normal operating pressure falls in the middle for best accuracy. 1% full-scale options available.

Window

Glass, tempered glass or plastic. Soft plastic windows flex for thermal compensation in filled gauges (often with an air bubble for expansion).

Ready to Select or Quote the Right Gauge?

With this understanding of how a Bourdon tube gauge works, the components, and accuracy grades, you can now choose the most appropriate pressure gauge for your application.

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Related: Gauge Accessories | Liquid Filled Gauges