Differential Pressure Gauges

Differential pressure gauges are instruments used to measure the difference in pressure of a gas or liquid between two points. Pressure gages are used to measure fuel, oil, water, air and vacuums. They indicate the internal pressure within vessels or systems and are used particularly for environments where the pressure changes frequently, therefore requiring constant monitoring.

A differential pressure gauge’s components are housed in a metal enclosure; materials include stainless steel, cast iron, bronze, brass and aluminum. The windows are usually double-strength glass. Specific pressure gauges have additional materials such as plastic or rubber. Differential liquid pressure gauges are themselves filled with certain liquids including oil, glycerin and silicone. Pressure gauges are often used in tandem with protective accessories like shutoff valves.

Other accessories include pipe coils, chemical seals and secondary valves to minimize condensation and to allow calibration against an external pressure source such as atmospheric pressure. Differential pressure gauges have two inlet ports that monitor the pressure in two separate vessels. These pressure gauges are used in applications where it is important to take two measurements and compare them, determining which vessel or system has the highest flow velocity, for example. Differential pressure gauges are utilized by manufacturing and industrial plants and companies.

Differential pressure gauges perform subtraction in order to indicate the difference between the two readings. This eliminates the need for an operator or computer system to watch two gauges and perform the math. It is fast and efficient to have the information immediately and constantly displayed in one location. There are three main types of differential pressure gauges: Bourdon, diaphragm and piston. The Bourdon gauge has two C-shaped or coiled tubes connected to the chambers or pipes where the pressures must be read.

Stainless Steel Differential Pressure Gauge
Differential Pressure Gauge – Ashcroft® Inc.

When pressure increases, the tubes uncoil. The motion of the two tubes is registered and a mechanical linkage compares the readings. Diaphragm gauges use two hermetically sealed membranes that flex in accordance with the pressure. The ports of the membranes are open to each other to compare pressures.

Piston type differential pressure gauges are also called deadweight testers because they counterbalance the pressure of a fluid with a solid weight or spring. As is the case with all three kinds, the difference is measured by a sensor and indicated on the gauge. The results may be displayed as analog, such as a needle on a dial, or they may be digital with numbers on a LED panel.