A digital hydraulic tester measures the main parameters needed to assess the performance of a hydraulic circuit: flow, pressure and fluid temperature.

The Webtec DHM displays all three values simultaneously. It also shows peak pressure, hydraulic power, volumetric efficiency and flow direction. Readings are presented numerically, while fast-updating bar charts can be used to make rapid changes or fluctuations easier to identify.

Measuring flow, pressure and temperature together helps establish whether a machine is failing to deliver sufficient flow, unable to maintain the required pressure or generating excessive heat.

The readings should be taken under representative operating conditions and compared with the machine or component manufacturer’s specification. Testing at several load points can help narrow down where performance is being lost before components are removed or replaced. Hydraulic power and volumetric-efficiency readings provide additional information when assessing pump and system performance.

Yes. A portable hydraulic tester can be connected into the machine’s hydraulic circuit so the pump can be assessed under real operating conditions.

The built-in loading valve allows pressure to be increased progressively while flow, pressure, temperature, power and volumetric efficiency are monitored. This enables the pump’s actual output to be compared with the manufacturer’s performance data without first removing the pump from the machine.

Hydraulic power is determined from the measured flow and pressure. Volumetric efficiency compares the pump’s actual delivered flow with its theoretical or expected output.

The DHM calculates and displays hydraulic power and volumetric efficiency during the test, removing the need to calculate them separately. Monitoring these values as system pressure increases can help show how effectively a pump maintains its output under load. Results should always be assessed against the pump or machine manufacturer’s data.

Short pressure spikes can be difficult to see on a conventional pressure gauge because they may occur and disappear too quickly.

The DHM measures peak pressure 1,000 times per second, allowing brief pressure events to be captured and displayed. Its fast-response bar chart also updates more quickly than the main digital readings, helping technicians identify transient fluctuations that may be linked to intermittent machine problems.

Yes. The DHM is designed to measure hydraulic flow in both directions.

Built-in flow straighteners reduce turbulence through the turbine block, supporting accurate measurement regardless of flow direction. The TrueFlow® indication clearly shows which direction the oil is travelling, while the integrated loading valve can apply progressive pressure loading in either direction. 

A digital hydraulic tester can be used to assess hydraulic pumps, motors, control valves and hydrostatic transmissions. Depending on where it is connected, it can help test an individual component or investigate the performance of a wider hydraulic circuit.

The DHM can also be used to confirm or preset the available flow and pressure before fitting a hydraulic attachment to a machine. This helps establish whether the machine’s hydraulic output is suitable for the attachment’s operating requirements.

A loading valve creates a controlled restriction in the circuit, allowing system pressure to be increased progressively. This makes it possible to observe how flow, pressure, temperature and hydraulic power change as the system is placed under load.

The DHM loading valve operates in either flow direction. It also incorporates Webtec’s Interpass® safety protection system. Replaceable safety burst discs operate if the tester is over-pressurised, allowing oil to bypass to the return line. This protection does not replace the need to remain within the tester and machine’s rated operating limits.

The tester must cover the machine’s maximum expected flow and pressure, but it should not be unnecessarily oversized for the normal test conditions.

The DHM range includes:

• Models covering 10–400 L/min, or 2.5–105 US gpm, at pressures up to 420 bar or 6,000 psi. 
• Models covering 20–800 L/min, or 5–210 US gpm, at pressures up to 480 bar or 7,000 psi. 
   

Where possible, normal test readings should fall between 15% and 100% of the selected flow range, as this is the range over which the stated flow accuracy of ±1% of the indicated reading applies. The 800 L/min models have limited pressure control below 86 L/min or 23 US gpm, which should also be considered when selecting a tester.

For readings between 15% and 100% of the calibrated flow range, the DHM flow accuracy is ±1% of the indicated reading. Below 15% of full-scale flow, the specified accuracy is fixed at 0.15% of full scale.

Pressure accuracy is ±0.5% of full scale and temperature accuracy is ±1 °C or ±2 °F. Hydraulic power accuracy is better than ±1.5% of full scale, volumetric-efficiency accuracy is ±1% and repeatability is better than ±0.2%

Yes. The QuickCert®+ app communicates with the DHM using Bluetooth® wireless technology and displays live hydraulic readings on a compatible phone.

This allows a technician to see flow, pressure, peak pressure, power and temperature while working from another position around the machine. It can be particularly useful when the tester, machine controls and test point cannot all be viewed from the same location. The app is available for iPhone® and Android™ devices.
 

The DHM can save up to 99 test points or sets of data to its internal memory.

The recorded information can then be retrieved through the QuickCert®+ app. Test details can be reviewed, presented in a report and used to create a hydraulic test certificate that can be emailed to a customer or retained as part of the machine’s service record.

The DHM flow block should be connected using flexible hoses approximately 1–2 metres or 3–6 feet long.

The inlet and outlet connections should have a similar bore size to the tester’s flow block. Undersized fittings or hoses can create unwanted restriction or venturi effects that may influence system operation and test results. Where repetitive pulsation causes lateral hose or pipe movement at the ports, the hoses should be firmly clamped.
 

The DHM datasheet specifies fluid cleanliness better than DIN ISO 4406 code 21/19/16 or NAS 10.

This level of cleanliness is typically achieved using filtration in the region of 20–25 microns. Maintaining suitable filtration helps prevent contamination from passing through the measurement block and supports reliable operation of the tester.
 

The DHM is designed for use with mineral hydraulic oils complying with ISO 11158. Webtec should be consulted before using other fluid types.

The rated fluid-temperature range is 0–120 °C or 32–250 °F, while the ambient operating range is −10–50 °C or 14–122 °F. The tester is IP65 rated for protection against dust and water jets and uses a standard 9-volt battery, which can provide up to six months of normal testing. A battery indicator shows the remaining charge. 

Webtec recommends servicing the DHM every 12 months. The maximum stated period between services is 36 months.

The appropriate interval may be affected by the tester’s operating cycle, the condition of the hydraulic fluid and the environment in which it is used. A service reminder is displayed when the unit is switched on to help users keep the tester within its recommended service schedule. Each DHM is supplied with a traceable calibration certificate.