Pressure Gauges for Air Compressors: Range, Mounting and Testing

For an air compressor, choose a pressure gauge with a range about 50% above the maximum receiver pressure, such as a 0 to 16 bar gauge on a 10 bar system, a 63 mm or 100 mm dial, and a connection that matches the receiver or regulator port. A liquid filled gauge gives a steadier reading on a vibrating compressor, while a dry gauge is fine on a clean regulated line. This guide explains where gauges belong on a compressed air system, how to size and install them, how to use them to find leaks and pressure drops, and what to look for in accuracy and safety.

Where gauges are used on a compressed air system

A well-instrumented compressed air system has gauges at several points, and each tells you something different.

• Receiver (air tank): shows the stored pressure, and tells you whether the compressor is cutting in and out at the right pressures.
• Compressor discharge: shows the pressure leaving the pump, which helps diagnose valve and wear problems.
• After the dryer and filters: a drop in pressure across a filter or dryer tells you it needs service.
• At the regulator: shows the set pressure delivered to tools and processes.
• At the end of the line: shows the pressure the equipment actually receives, which can be much lower than at the compressor.

Comparing readings between these points is one of the simplest ways to find hidden problems.

Choosing the range

Most workshop and industrial compressors run between 7 and 10 bar. With a steady load, divide the maximum working pressure by 0.75, then round up to the next standard range. For a compressor that cuts out at 10 bar, 10 divided by 0.75 is 13.3, so the next range is 0 to 16 bar. A 0 to 16 bar gauge places 10 bar at 63% of the scale, which leaves room for the receiver to briefly overshoot. For a smaller 8 bar system, a 0 to 10 bar gauge puts the cut-out at 80%, which is higher than ideal, so 0 to 16 bar is the more comfortable choice. Our pressure gauge range selection guide includes a chart.

Gauges that read in bar, kPa or psi are all available. Dual scale gauges such as the L63 and L100, which show kPa and psi on the same dial, reduce confusion on sites that mix units. Remember that one bar equals 100 kPa or about 14.5 psi.

Dry or liquid filled for compressors?

A compressor, especially a reciprocating one, shakes the pipework and creates a pulsing pressure. A liquid filled gauge damps the pointer and protects the movement, so it is a good choice on the receiver and the discharge line. A dry gauge is cheaper and works well on a regulated line where pressure is steady, for example the outlet of a regulator at a workstation. Our liquid filled vs dry guide explains the trade-offs.

The L63 (63 mm) and L100 (100 mm) liquid filled gauges suit this duty. Both have a 304 stainless steel case and a dual kPa and psi scale, with ranges from -100/0 kPa up to 0/4,000 kPa on the datasheet. Both have an accuracy of ±2.5% of full scale, which is suitable for general indication.

Connections and mounting

Compressor ports are usually BSP, either parallel (BSPP) or tapered (BSPT), though imported machines may use NPT. The L63 uses a 1/4″ BSPT connection and the L100 uses a 3/8″ BSPT connection. Check the port on your receiver before you order, and read our guide to pressure gauge connection types and thread sizes if you are unsure.

The gauge can be mounted lower (bottom entry) or on the back. Lower mount is standard for pipe fittings, and back mount suits panels. Fit the gauge where it is easy to read and not directly on the most violently vibrating part of the compressor. A short length of tubing or a flexible hose can help isolate it.

Accuracy: how much do you need?

For routine monitoring, class 2.5 (±2.5% of full scale) is common. If you are using the gauge to set a regulator for a process, such as a paint line or a pressure test, choose a better class or a digital gauge. On a 0 to 16 bar gauge, 2.5% is ±0.4 bar, which is too coarse for setting a precise value. A digital gauge such as the PDK PDR100 offers 0.5% of full scale, and the PDR250 offers 0.25%. See our digital pressure gauge buying guide.

Using gauges to find problems

Pressure drop across filters and dryers

Read the pressure upstream and downstream of a filter. A growing difference means the element is clogging and needs replacing. The work done to push air through a blocked filter wastes energy, so tracking this saves money.

Pressure at the point of use

Many tools need a minimum pressure to work properly. If the gauge at the compressor reads 8 bar but the tool sees 6 bar, the supply line may be too small, too long or leaking. Compare the readings at both ends under load.

Leak-down test

Fill the system to its working pressure, stop the compressor, close the supply valve and note the pressure. Record how fast it falls over a set time with all equipment turned off. A steady decline points to leaks. Leaks are a well-known source of waste in compressed air systems, and guidance from bodies such as the United States Department of Energy suggests that leaks in poorly maintained systems can waste a large share of a compressor’s output, with figures of 20 to 30 percent often quoted. A digital gauge makes this test easier because it displays small changes and can hold the minimum and maximum values.

Compressor cut-in and cut-out

Watch the receiver gauge through a full cycle. If the cut-in and cut-out pressures are different from the pressure switch setting, the switch may need adjusting, or the compressor may be struggling to build pressure.

Safety around compressed air

• Never exceed the pressure rating of the receiver, hose, fittings or gauge.
• Make sure the safety relief valve is working and set at the right pressure. A gauge is an indicator and does not replace a relief valve.
• Drain condensate from the receiver regularly. Water corrodes the vessel and can damage the gauge.
• Release pressure before removing or fitting a gauge.
• Pressure vessels in Australia are subject to standards and state regulations, including AS 1210 and AS/NZS 3788, so check the requirements for your equipment with your regulator or inspector.
• Never point compressed air at skin. Air at pressure can force particles and air into the body.

Compressed air quality and the gauge

Compressed air often carries moisture and a fine oil mist. Both can affect a gauge over time. Moisture can cause condensation in a dry case, which a liquid filled case avoids. Oil carry-over is rarely a problem for brass or stainless steel wetted parts. If the air is used for breathing air, food contact or oxygen, specific rules apply and the gauge must be rated for the duty. Do not assume a standard gauge is suitable.

Gauge care and calibration

• Check the pointer returns to zero when the system is vented.
• Replace a gauge with a cracked window or a bent pointer.
• Do not use the gauge as a handle or step.
• Calibrate at an interval that suits the importance of the reading. See pressure gauge calibration.
• Keep a spare gauge for critical compressors.

Setting pressure to save energy

Running a compressed air system at a higher pressure than the equipment needs costs energy, and it increases leakage because leaks flow more at higher pressure. Use your gauges to find the lowest pressure that still runs the most demanding tool properly, then set the compressor and regulators accordingly. Check the reading at the point of use under full load, not only at the receiver. If a single tool needs a much higher pressure than everything else, consider supplying it separately rather than raising the whole system.

Selecting a gauge for a portable compressor

Portable and trailer-mounted compressors see more knocks and vibration than fixed plant. A liquid filled gauge with a stainless steel case holds up better, and a back-mounted gauge can sit flush in a panel for protection. Make sure the gauge range suits the machine’s maximum pressure, and replace any gauge with a cracked window straight away.

Frequently asked questions

What pressure gauge do I need for a 10 bar compressor?

A 0 to 16 bar gauge is the usual choice, as it keeps the working pressure at about 63% of the scale.

Can I use a tyre gauge on a compressor?

A tyre gauge is a handheld tool and is not suited to permanent installation. Fit a proper panel or pipe gauge on the receiver and regulator.

Why does my compressor gauge read differently from my regulator gauge?

There is normally a pressure drop through the filter, dryer, hose and regulator. A large difference suggests a restriction or leak.

Should I use a digital gauge on a compressor?

Yes, for testing and leak-down checks. A digital gauge shows small changes clearly. A traditional gauge still makes a good permanent indicator.

What does 2.5% accuracy mean on a compressor gauge?

It means the gauge may be wrong by up to 2.5% of the full scale. On a 0 to 16 bar gauge, that is up to 0.4 bar.

Choose a compressor gauge

See the pressure gauges category or contact us with your compressor pressure and port size, and we will suggest a suitable gauge.