Hydraulic Pressure Gauges: How to Select, Install and Protect Them

A hydraulic pressure gauge should have a range of at least 1.5 times the normal working pressure, a case that survives vibration and pulsation, wetted parts that suit the hydraulic fluid, and a way of being isolated or replaced without shutting the system down. Most permanently fitted hydraulic gauges are 63 mm or 100 mm Bourdon tube gauges, often liquid filled and often protected by a snubber or gauge isolator. This guide covers how to select, install and protect a hydraulic pressure gauge, and when to use a digital gauge instead.

What a hydraulic gauge has to cope with

Hydraulic systems are among the harshest places for a pressure gauge. Pressure is high, often hundreds of bar, and it is rarely steady. Each stroke of a piston pump creates a pulse. Valves opening and closing create sudden spikes that can be many times the working pressure for a split second. Machines also shake, and the oil can run hot. A gauge that is not built or protected for this duty will read erratically, drift quickly and eventually fail.

The main threats are:

• Pulsation: a rapid cycle of pressure rise and fall that makes the pointer flutter and wears the movement.
• Pressure spikes: brief peaks caused by valve closure or load changes that can overstress the tube.
• Vibration: from pumps, motors and mobile machinery.
• Temperature: hot oil conducts heat into the gauge.
• Contamination and shock: dirt in the oil, knocks and harsh outdoor conditions.

Choosing the range

Work from the relief valve setting, not the usual running pressure, because the gauge must be able to survive the relief setting every time the system reaches it. A practical method is:

1. Find the relief valve setting for the circuit you are measuring.
2. Divide by about 0.66 for a pulsating load, which is typical in hydraulics, or by 0.75 for a steady load.
3. Round up to the next standard range, such as 0 to 250, 0 to 400, 0 to 600 or 0 to 1,000 bar.

For example, a circuit with a 210 bar relief valve suits a 0 to 400 bar gauge. Our pressure gauge range selection guide sets out the method with a chart.

Not every gauge suits every pressure. Our L63 and L100 liquid filled gauges cover ranges only up to 4,000 kPa (40 bar), so they suit low pressure hydraulics and pneumatics rather than high pressure circuits. For higher pressures, the stainless steel AD-D-2 (up to 100,000 kPa, which is 1,000 bar), the AL-F-2 and AL-H-2 (both up to 160,000 kPa, which is 1,600 bar) and the Solfrunt 1981 (up to 80,000 kPa, which is 800 bar) are the models to consider. Check each datasheet for the exact ranges available.

Liquid filled or dry for hydraulics?

In most hydraulic applications a liquid filled gauge is the better permanent fitting. The fill damps the pointer, lubricates the movement and cuts wear from vibration. Our stainless steel gauges are supplied dry, with liquid filling available on request, and the Solfrunt can be filled when the high point indicator is not used. Our full comparison is in liquid filled vs dry pressure gauges.

Protecting the gauge

Snubbers and restrictors

A snubber, also called a pulsation dampener or restrictor, is a small orifice or porous element fitted in the gauge port. It slows the rate at which pressure changes reach the tube, which steadies the pointer and cuts wear. Some of our gauges accept restrictors as an option. Pick the size to suit the viscosity of the oil, because an orifice that is too small can clog and one that is too large will not damp the pulsation.

Isolation valves and test points

A needle valve or gauge isolator between the system and the gauge lets you remove it without losing oil or shutting down the machine. Close it when the gauge is not needed, and open it slowly to avoid shock. Minimess-style test points allow a portable gauge to be attached to a circuit without a permanent fitting. See our guide to digital hydraulic pressure gauges for test procedures.

Blowout protection

At high pressure, a failed gauge releases stored energy. A solid front and a blowout back direct the release away from the operator. The Solfrunt 1981 has full rear blowout protection and a solid front, which makes it suited to hazardous duty.

High point indicators

A high point indicator, sometimes called a lazy hand, stays at the highest pressure reached until it is reset. This is a good way to detect spikes in a circuit that happen too quickly for the eye to see. The Solfrunt 1981 can be fitted with one.

Cooling

Mount the gauge away from hot pipework where possible, or use a pigtail or a length of tube to cool the oil before it reaches the gauge. Our datasheets give a working temperature of up to 60 degrees Celsius and recommend a pigtail above that.

Installing a hydraulic pressure gauge

1. Depressurise and isolate the circuit, and follow your lockout and tagout procedure.
2. Confirm the port thread. Hydraulic ports are commonly BSPP or NPT, and some use unified threads. Our guide to pressure gauge connection types and thread sizes explains how to tell them apart.
3. Fit the correct seal. Parallel threads use a bonded washer or O-ring, and tapered threads use a thread sealant suitable for hydraulic oil.
4. Tighten with a spanner on the socket flats, never on the case.
5. Position the dial where the operator can see it clearly, and where it is protected from knocks.
6. Open the isolation valve slowly and bleed any air from the line. Trapped air makes the pointer jump and can cause a spike when it compresses.
7. Check for leaks at normal operating pressure.

Fluid and material compatibility

Most mineral hydraulic oils are compatible with brass, copper alloy and stainless steel wetted parts. Some synthetic fluids, water glycol mixtures and fire-resistant fluids can attack certain metals and seals. Where the fluid is unusual, use stainless steel wetted parts and confirm compatibility with the fluid maker. The AD-D-2, AL-F-2, AL-H-2 and Solfrunt gauges use 316 stainless steel in the tube and connection.

When to use a digital gauge

An analogue gauge is ideal as a permanent visual indicator. A digital gauge is better for testing and fault finding, because it records the highest and lowest pressure during a test and shows the reading to a fine resolution. The PDK PDR250 reaches 700 bar with 0.25% accuracy, and the PDR Digital Pressure Test Kit includes adaptors and a 2 metre hose. Our digital pressure gauge buying guide compares the options.

Safety

• Never exceed the rating of the gauge, hose or fitting.
• Do not check for leaks with your hand. High pressure oil can penetrate the skin and needs urgent medical attention.
• Wear eye protection and use a barrier where a failure could cause injury.
• Depressurise the system, including any stored energy in accumulators, before removing a gauge.
• Replace any gauge that has been subject to severe overpressure, because the damage may not be visible.

Maintenance and calibration

Check hydraulic gauges every time you service the machine. Look for a pointer that rests away from zero, a cracked window, oil on the dial or a slow response. Calibrate gauges that are used for settings and acceptance tests at a regular interval, and keep the record. Our article on pressure gauge calibration explains how.

Choosing between 63 mm and 100 mm dials

A 63 mm dial is compact and suits crowded manifolds, test points and mobile equipment. A 100 mm dial is easier to read from a distance, which matters on a plant floor where the operator may be a few metres away. If the gauge sits behind a guard or in a panel, consider the viewing angle as well. Where vibration is severe, a larger case also carries more fill liquid, which gives better damping. Whichever size you choose, mark the maximum working pressure on the dial so any operator can see at a glance if the system is running out of range.

Keeping a record of hydraulic pressures

A simple log of normal pressures at each test point, taken when the machine is healthy, is a powerful diagnostic tool. When a fault appears, you can compare the current readings against the baseline and quickly see which circuit has changed. Record the date, the oil temperature, the load condition and the gauge used, so the readings are comparable over time.

Frequently asked questions

What size gauge is best for hydraulics?

100 mm is the common industrial size for permanent mounting because it is easy to read. 63 mm suits compact panels and test points.

Why does my hydraulic gauge bounce?

The cause is usually pump pulsation. Fit a snubber, use a liquid filled gauge, or both.

What does a snubber do?

It restricts the flow into the gauge, which slows the pressure changes the tube sees. This steadies the pointer and extends the life of the gauge.

Can I use a water pressure gauge on a hydraulic line?

Only if the range, material and thread suit the duty. Most low cost water gauges are not built for the pressures or pulsation in hydraulics.

How often should a hydraulic gauge be replaced?

There is no fixed interval. Replace it when it fails a check, shows damage, or after a major overpressure event.

Find a gauge for your system

Browse our pressure gauges and digital pressure gauges, or contact us with your working pressure, relief valve setting, thread and fluid, and we will suggest a suitable model.