Digital Hydraulic Pressure Gauges: How to Choose and Use One

A digital hydraulic pressure gauge gives technicians a precise, easy-to-read value when they set, test and troubleshoot hydraulic systems. Compared with a traditional dial, it offers finer resolution, selectable units, and minimum and maximum memory that can catch a pressure spike a needle would miss. This guide explains how to choose a digital gauge for hydraulics, which range and connection you need, how to run common tests such as relief valve and pump checks, and what to look for in a hydraulic pressure test kit.

Why measure hydraulic pressure?

In a hydraulic system, pressure is the direct measure of the load on a pump, valve or actuator. Most faults show up as a pressure problem long before a component fails outright. Regular pressure checks help you to:

• Confirm that a relief valve opens at its set pressure.
• Check pump output and spot internal wear.
• Verify accumulator pre-charge.
• Diagnose slow or weak actuators.
• Commission new circuits against the design specification.
• Detect pressure spikes that could damage seals and hoses.

A reliable reading depends on a gauge with the right range, a suitable connection and enough accuracy for the decision you are making.

Why use a digital gauge instead of an analogue gauge?

Hydraulic pressure can change rapidly. A mechanical needle can lag, flutter or hide the peak. A digital gauge has several advantages here:

• Clear numeric reading. There is no parallax error or estimating between graduations.
• Min/max recording. The gauge holds the highest and lowest pressure seen during a test, so a short spike is not missed.
• Selectable units. Switch between bar, MPa, psi and kPa to match service manuals.
• Better accuracy. The PDK PDR250 is specified at 0.25% of full scale, and the PDR500 at up to 0.1%.
• Optional data logging. The PDR500 and PDR1000 can record pressure over time for later review.

For a wider comparison of the two technologies, read our digital pressure gauge buying guide.

Choosing the pressure range for hydraulic work

Hydraulic systems often work at several hundred bar, so range selection matters for both safety and accuracy. The steps are:

1. Find the relief valve setting. This is the maximum pressure the system should reach in normal operation.
2. Choose a gauge range comfortably above it. A steady reading in the upper-middle of the range gives the best balance of resolution and headroom. Common guidance, such as that in EN 837-2, suggests holding steady pressure to about 75% of full scale.
3. Check the overpressure rating. A short spike above the relief setting should not damage the gauge.
4. Consider the lowest pressure you need to read. A wide range reduces resolution at the low end.

The PDK PDR250 is offered in ranges including 0 to 10, 0 to 20, 0 to 35, 0 to 100, 0 to 200, 0 to 250, 0 to 400 and 0 to 700 bar, which covers most low, medium and high pressure hydraulic circuits. The PDK PDR100 covers compound ranges from -1 to 2 bar and positive ranges from 0 to 10 bar up to 0 to 100 bar, which suits lighter-duty and pneumatic checks.

Connections and fittings

Hydraulic ports use a range of thread standards, and many test points use minimess or quick-release fittings. Before you buy:

• Identify the port thread, such as BSPP, NPT or UNO.
• Check the seal type. BSPP threads usually seal against a washer or bonded seal, while tapered threads seal on the thread itself.
• Use a hose rated well above the maximum test pressure.

The PDK PDR100, PDR250 and PDR500 use a G1/4″ BSPP male bottom-entry connection. The PDR Digital Pressure Test Kit adds adaptors so you can reach more ports: 1/4″ BSPP, 1/8″ NPT, 1/4″ NPT, 7/16″ UNO and 9/16″ UNO male connectors, plus a 2 metre hose. The kit is available with a PDR100 or PDR250 gauge.

Common hydraulic tests with a digital gauge

Relief valve setting test

1. Fit the gauge at a test point on the pressure line, close to the valve.
2. Start the system and bring it to operating temperature.
3. Slowly raise pressure until the relief valve opens. Note the peak on the min/max memory.
4. Compare the value against the machine specification and adjust only as the manufacturer allows.

Pump output check

Read pressure at a known flow and compare the result with the pump specification. A pump that cannot reach its rated pressure may have internal leakage or wear. Always follow the manufacturer’s procedure for the specific pump.

Accumulator pre-charge check

Pre-charge is usually checked with the system depressurised and a dedicated charging and gauging kit. Use the method in the accumulator manual, because incorrect procedures can be hazardous.

Intermittent fault tracing

A gauge with logging can be left connected during a work cycle. Reviewing the record afterwards can reveal a pressure drop or spike that happens only under certain conditions.

Safety when testing hydraulic pressure

• Never exceed the rating of the gauge, hose or fittings.
• Depressurise and isolate the circuit before connecting or disconnecting a gauge.
• Do not use your hand to check for leaks. Pressurised hydraulic fluid can penetrate skin, which is a medical emergency.
• Use personal protective equipment, including eye protection and gloves.
• Follow lockout and tagout procedures and your site’s safe work method statement.
• Use only components rated for the fluid and temperature in the circuit.

Digital hydraulic gauge comparison

Keeping your gauge accurate

Hydraulic work is demanding. Shock loads, contamination and temperature swings can all shift a gauge over time. Protect your investment by:

• Using the gauge only within its stated range.
• Bleeding pressure slowly before disconnecting.
• Storing the gauge in a case with the port capped.
• Having it calibrated on a regular schedule, and after any shock event. Our article on pressure gauge calibration explains how this works.

Worked example: setting a relief valve on a 210 bar circuit

Suppose a machine handbook states a relief valve setting of 210 bar. You need a gauge that reads comfortably above that value, so a 0 to 400 bar range gives a steady reading near the middle of the scale and leaves room for a spike. A 0 to 250 bar range would put the setting near 84% of full scale, which is higher than the usual guidance for steady pressure.

With a PDR250 at 0.25% FS on a 0 to 400 bar range, the permitted error is 0.25% of 400 bar, which is 1 bar. That is more than enough resolution to confirm a 210 bar setting to within a bar. If the handbook allows a tolerance of plus or minus 5 bar, you can be confident in the result. If the tolerance is tighter, step up to a more accurate gauge.

Always follow the manufacturer’s procedure for the specific valve and machine. The numbers above are an illustration, not a setting for your equipment.

Digital hydraulic gauges vs pressure transducers

Technicians sometimes ask whether to use a handheld digital gauge or a pressure transducer connected to a data logger. A digital gauge is quick to fit and reads on the spot. A transducer with a logger suits long-term monitoring and automatic alarms. Many workshops keep both. Our guide to the WIKA pressure gauge and sensor options explains how electronic sensors differ from gauges.

Battery, display and handling tips

• Check the battery before heading to site, and carry a spare.
• Use the backlight in dark engine bays and pump rooms, but remember it uses extra power.
• Keep the protective cover on where supplied, such as the silicone cover that comes with the PDR500.
• Store the gauge with its port capped so dirt and moisture do not enter.
• Do not leave a gauge in a hot vehicle, because extreme temperatures can affect the display and the battery.

Selecting between the PDR models for hydraulic work

The PDR100 is a sensible choice for light-duty checks, low pressure hydraulics and pneumatics, where 0.5% accuracy is enough. The PDR250 is the workhorse for most hydraulic fault finding thanks to its range of up to 700 bar. The PDR500 is a better fit when you need IP66 protection or optional datalogging. The PDR1000 belongs in a laboratory or calibration workshop, where 0.025% accuracy and built-in logging are essential. If you are unsure, start with the pressure you need to measure and the accuracy that your procedure demands, then work out the smallest model that meets both.

Frequently asked questions

What accuracy do I need for hydraulic testing?

For general fault finding, 0.25% to 0.5% of full scale is common. For calibration work or acceptance testing, a higher grade such as the PDR500 or PDR1000 is more appropriate.

Can a digital gauge handle pressure spikes?

A gauge can record the maximum value seen, but it must always stay inside its overpressure rating. Check the datasheet before testing circuits with severe shocks.

How do I convert bar to psi?

Multiply bar by about 14.5 to get psi. A digital gauge with selectable units does the conversion for you.

Do I need a liquid filled gauge for hydraulics?

A liquid filled analogue gauge is a good permanent fitting because the fill damps pulses. For testing, a digital gauge with min/max memory is often better. See liquid filled vs dry pressure gauges.

Is a test kit worth buying?

If you service different machines with different ports, yes. A kit with a hose and several adaptors avoids delays and improvised fittings.

Ready to choose?

Browse the full digital pressure gauge range, or contact us with your maximum pressure, port type and the accuracy you need, and we will recommend a suitable gauge or test kit.