Pressure Sensors for Hydraulic Systems: Range, Protection and Wiring

Quick answer: choose a hydraulic pressure sensor with a range at least 1.5 times the normal working pressure, an overpressure rating well above your relief valve setting and any pressure spikes, a stainless steel body, a robust thread such as G1/4 BSPP with a bonded seal, and an output your controller can read (4 to 20 mA for long cables, 0 to 10 V for short runs). Hydraulic systems are harsh on sensors: pressure is high, it pulsates, it spikes and the oil gets hot. A sensor sized and protected for that duty can run for years, while a general-purpose one on a violent line may fail early. This guide explains how to pick, fit and protect a pressure sensor for hydraulics, with worked examples and a checklist.

Why put a pressure sensor on a hydraulic system?

A gauge lets a technician see pressure. A sensor lets the machine see it. Common reasons to fit one include:

• Control: a controller varies pump output or valve settings based on pressure.
• Protection: shut the machine down if pressure is too high or too low, for example from a leaking hose.
• Monitoring: log pressure trends to spot wear, such as a pump that can no longer reach full pressure.
• Load sensing: measure cylinder pressure to estimate the load being lifted.
• Remote diagnostics: check a machine from a laptop or a phone without a technician visit.

If you only need a person to read pressure, a gauge is simpler and cheaper. See hydraulic pressure gauges: select, install and protect.

What makes hydraulics hard on sensors?

• High pressure: hundreds of bar is common.
• Pulsation: every pump stroke sends a pulse through the oil.
• Spikes: valve closure and load changes create short peaks that can be much higher than the working pressure.
• Vibration: from pumps, engines and moving machinery.
• Temperature: hot oil heats the sensor body.
• Electrical noise: from solenoids, motors and welding.

Choosing the range

The same rule applies as for gauges. Divide the normal working pressure by about 0.66 for a pulsating load (0.75 for a steady one) and round up to the next standard range. For example, a hydraulic circuit working at 210 bar suits a 0 to 400 bar sensor. A circuit at 350 bar suits a 0 to 600 bar sensor. See the range selection guide.

But also check two further ratings on the datasheet:

• Overpressure (proof) pressure: the pressure the sensor can see without changing its calibration. Compare it with the relief valve setting and with realistic spikes.
• Burst pressure: the pressure at which the sensor may rupture. It should be a clear multiple of the full scale.

Hydraulic spikes can be several times the working pressure for a split second, so a sensor with a generous overpressure rating is worth the extra cost. Check the exact rating for the A-10 version you choose on the datasheet before ordering.

Output signal

The WIKA Model A-10 is offered with 4 to 20 mA and 0 to 10 V outputs. For wiring and checking a loop, see 4 to 20 mA pressure transmitters: wiring, scaling and calibration.

Materials and connection

• Wetted parts: stainless steel suits mineral oil, many synthetic fluids and water glycol. The A-10 has a 316L stainless steel case and wetted parts. Check compatibility for unusual fluids.
• Thread: hydraulic ports commonly use G1/4 BSPP, NPT or unified threads. A parallel BSPP thread needs a bonded washer or O-ring to seal. See connection types and thread sizes.
• Electrical connector: choose one rated for vibration and washdown, and sealed against oil and water.

Protecting the sensor

Snubbers

A snubber in the port slows the rate of pressure change reaching the sensor. It reduces pulsation noise and protects against the fastest spikes. Choose the orifice size for the oil viscosity, because one that is too small can clog.

Mounting position

Fit the sensor where pulsation is lowest, away from the pump outlet if possible, and on a rigid mount to limit vibration. Avoid hanging a heavy sensor and connector on a thin pipe.

Isolation and test points

A needle valve or test point lets you remove the sensor without draining the circuit, and lets you check it against a reference. A digital reference gauge such as the PDK PDR250 reaches 700 bar with 0.25% accuracy. See digital hydraulic pressure gauges.

Cabling and EMC

Keep the signal cable away from solenoid and motor cables. Use shielded cable, with the shield connected according to the maker and your site standard.

Worked example 1: a press with a 210 bar relief valve

• Normal working pressure: 180 bar, pulsating. Divide by 0.66: 273 bar, so choose 0 to 400 bar.
• Relief valve: 210 bar. The sensor must comfortably exceed that, and its overpressure rating must cover spikes above 210 bar.
• Output: 4 to 20 mA, because the control cabinet is 15 metres away beside welding equipment.
• Scaling: 4 mA = 0 bar, 20 mA = 400 bar. The relief valve setting appears at 4 + (210 ÷ 400) × 16 = 12.4 mA.
• Protection: a snubber in the port, a test point beside the sensor, and a digital reference gauge for calibration checks.

Worked example 2: a mobile machine

A mobile hydraulic crane monitors main system pressure. The sensor must tolerate vibration, rain and mud, with a cable run of a few metres. A 0 to 10 V output and a sealed connector fit the controller input. Mount the sensor on a bracket, protect the cable, and keep a pressure test kit for checking it. The PDR Digital Pressure Test Kit includes adaptors and a 2 metre hose for this.

Calibration and checks

• Check the zero with the circuit depressurised, as the first and simplest test.
• Compare the sensor signal with a reference gauge at several pressures, going up and down. See pressure gauge calibration.
• Re-check after any major pressure spike or fault.
• Replace a sensor that drifts or shows erratic readings.

Safety

• Never exceed the rating of the sensor, hose or fitting.
• Depressurise the circuit, including any accumulators, before removing a sensor.
• Never check for hydraulic leaks with your hand. Pressurised oil can penetrate skin and needs urgent medical attention.
• Follow lockout and tagout procedures for the machine.

Selection checklist

1. Normal working pressure and relief valve setting.
2. Range with headroom (about 1.5 times the working pressure).
3. Overpressure and burst ratings.
4. Output signal and supply voltage.
5. Thread, seal and electrical connector.
6. Fluid and temperature compatibility.
7. Snubber, isolation and test point.
8. Calibration plan.

Common sensor failures in hydraulics and how to avoid them

Fitting tips

• Clean the port and check the sealing face before fitting.
• Use the seal type that matches the thread. A parallel BSPP thread seals on a washer or O-ring, not on the thread.
• Tighten with a spanner on the hex, never on the housing or connector.
• Support the cable so its weight does not pull on the connector.

Quick sizing table for pulsating hydraulic pressure

These are starting points. Always check the overpressure rating, because the right range does not guarantee the sensor can survive spikes.

Cable and connector care

On mobile and outdoor hydraulic equipment, the connector and cable are often the first things to fail. Use a connector with the right seal rating, fit a drip loop so water runs away from the entry, avoid sharp bends near the sensor and clip the cable along its run so that it cannot flex repeatedly. A short, neat installation usually outlasts a long, loose one.

Frequently asked questions

Can I use a pressure sensor instead of a gauge on a hydraulic system?

You can, but a sensor has no display. Most systems keep a gauge for technicians and add a sensor for the controller.

What range do I need for a 250 bar system?

Often 0 to 400 bar. Divide the working pressure by 0.66 for a pulsating load, which gives about 380 bar, then round up.

Why does my sensor reading jump?

Pulsation or electrical noise. Try a snubber, improve shielding and check the supply.

How often should I recalibrate?

Annually is a common starting point. Check more often for critical systems or after spikes.

Which sensor do you supply?

The WIKA Model A-10, which lists hydraulics and pneumatics among its applications. Tell us your pressure, output and thread through the contact page.

Next steps

Read the sensor, transducer and transmitter guide and high temperature pressure sensors, and browse the pressure sensor category.