Pressure Gauge Product Guide: How to Choose One?

1. What are Pressure Gauges?

Pressure gauges are devices that allows an operator to determine, usually, the in-line pressure at a specific point within a pneumatic system (i.e. gauge pressure). The majority of pressure gauges in industry are ‘bourdon tube’ type pressure gauges. Another type of pressure gauge is ‘diaphragm pressure gauges’, but these are more commonly used in hydraulics where the media is more viscous. Increasingly, digital pressure gauges are becoming more common due to their ability to integrate well with other digital and electronic systems for remote monitoring, data logging, and/or automation.

Absolute vs Gauge Pressure

In the design of pneumatic systems, it is important to be clear on the distinction between absolute and gauge pressure. The gauge pressure refers to the in-line pressure at a specific point in the system above atmospheric pressure. Gauge pressure is denoted by a ‘g’ suffix.

On the other hand, absolute pressure is the pressure above vacuum pressure (i.e. 0). It is of particular importance when the compression of gases is considered.

Relationship: Absolute Pressure – Gauge Pressure = Atmospheric Pressure.

1.2 Construction of Bourdon Tube

A Bourdon tube mechanism is housed within the gauge body, where one end of tube is fixed, and the other end is left free to undergo elastic deformation as the inline pressure increases. That is – the circular tube uncoils as the pressure increases. Now, the gauge is calibrated such that a pointer displays the correct pressure reading with respect to inline pressure.

 

Most pressure gauges are calibrated in the factory using an accurate dead-weight tester. Industrial companies and other laboratories may also recalibrate in house using a dead-weight tester.

2. What are the connection types for pressure gauges?

Bottom Entry Connection	Back Entry Connection

Pressure gauges can be largely split into bottom entry or back entry pressure gauges. Bottom entry gauges, as suggested by its name, has a thread that is located at the bottom of the gauge; the most common gauges are bottom entry gauges).  On the other hand, back entry pressure gauges have the connection pipe at the back of the gauge. One way to choose between back entry and bottom entry is to consider how the operator will read the gauge relative to the pneumatic line. Is the dial pressure gauge supposed to face at 90-degree angle to the pneumatic line?

Back entry pressure gauges can also have a flange. These are designed primarily for panel mounting.

3. What is the functional use of Glycerine-filled pressure gauges?

There is notable debate on the function of glycerine, sometimes called glycerine, inside the dial cavity of a pressure gauge. British Pneumatics has consulted a number of pressure gauge manufacturers, and we have received disparate responses. Our own consensus is that there are multiple functions. For one, the glycerine helps reduce vibrations that may reach the pointer, which increases the longevity of the pointer as well as allowing the operator to more easily read the pointer. Secondly, the glycerine will reduce exposure of dial components (pointer, dial screws, etc.) to oxidation. Thirdly, the glycerine protects against temperature fluctuations. This is particularly important for pressure gauges that are used in the outdoors – the temperature between day and night time can be vast.

In general, we find that glycerine-filled pressure gauges have last about 20% longer than non-glycerine-filed pressure gauges (controlled for life cycle usage).

150 PSI Stainless Steel Pressure Gauge