Once the type of hydraulic test bench has been determined, the next step is to define its technical specifications. This means translating the test procedure into the pressure, flow, hydraulic power, measurement capability, automation functions, and thermal capacity that the machine actually needs.
A common mistake is to start with the largest possible numbers. A higher pressure rating, larger flow capacity, or more powerful motor may appear to make a test bench more capable, but unnecessary oversizing can increase cost, energy consumption, heat generation, component size, and system complexity.
The better approach is to define the actual operating envelope of the test and build the test bench around it.
How to Determine the Required Test Pressure
The required pressure should be based on the highest pressure that must be generated during the test procedure, not simply on the normal working pressure of the component.
For example, a hydraulic cylinder may operate at one pressure in the machine but require a higher proof-pressure test during production or repair verification. A hydraulic valve may also need to be tested above its normal setting in order to verify relief, cracking, or pressure-control performance.
The complete high-pressure circuit must be rated for the intended test condition. This includes pumps, valves, manifolds, hoses, fittings, sensors, adapters, and test fixtures, not only the main hydraulic power unit.
It is also important to consider whether all tests are performed within the same pressure range. A bench may need high pressure for proof testing but much lower pressure for functional cycling or leakage testing. In this situation, using one very large pressure range for every test may reduce controllability and measurement usefulness.
A better design may use separate pressure stages, multiple pressure sensors, or different pump circuits so that both low-pressure and high-pressure tests can be performed effectively.
How to Determine the Required Flow
Flow requirements depend on what must happen during the test.
For hydraulic cylinder testing, flow mainly determines movement speed. A larger cylinder or faster extension speed requires more oil, while a static pressure-holding test may require very little flow after the target pressure has been reached.
The basic relationship is:
Flow = Effective Area × Velocity
This means that the required cylinder flow should be calculated from the largest effective area and the required test speed rather than selected from a general catalog value.
Pump, valve, and motor testing create different flow requirements. A pump test bench may need to handle the pump’s full output, while a valve test bench may need enough flow to evaluate pressure drop or flow-control performance at rated conditions. A hydraulic motor test bench needs sufficient flow to reach the required speed while the motor is operating under load.
The main point is that maximum system flow and measurement flow are not always the same requirement. A test bench may need a high-flow main circuit while also requiring a much smaller measuring range for leakage or low-flow testing.
How Pressure and Flow Determine Hydraulic Power
Once the required pressure and flow are known, the approximate hydraulic power can be estimated.
For pressure in bar and flow in L/min:
Hydraulic Power (kW) = Pressure (bar) × Flow (L/min) ÷ 600
If a test condition requires 250 bar at 60 L/min, the theoretical hydraulic output is:
250 × 60 ÷ 600 = 25 kW
The actual electric motor normally needs more input power because the pump, motor, coupling, and hydraulic circuit all have efficiency losses.
However, the most important design question is whether maximum pressure and maximum flow must occur at the same time.
Consider a test bench that needs 400 bar for a low-flow proof-pressure test but 300 L/min only during lower-pressure cylinder cycling. Designing the system to produce 400 bar and 300 L/min simultaneously would create a hydraulic power requirement of 200 kW, even though the real test procedure may never require that operating point.
This is why test benches are often designed around several operating zones rather than one maximum pressure-flow combination. Separate high-pressure and high-flow pumps, multi-stage pump systems, or variable-displacement pumps can reduce installed power while still covering the required test envelope.
The power unit should therefore be based on the real pressure-flow combinations used during testing, not simply on two independent maximum values.
How to Specify Measurement Accuracy and Range
A hydraulic test bench should not be assigned one general accuracy value for the entire machine. Pressure, flow, temperature, leakage, force, torque, speed, and position can all have different measurement requirements.
The required accuracy should be determined by the acceptance criteria of the test. If a component passes or fails based on a very small difference in pressure or leakage, the measurement system must be capable of distinguishing that difference reliably. For general functional testing, the required accuracy may be less demanding.
Measurement range is equally important. A 600 bar pressure sensor may be suitable for a high-pressure test, but it may not be the best instrument for accurately evaluating a much lower operating range, depending on the sensor specification and required uncertainty.
The same issue becomes even more obvious in leakage testing. A main flow meter may be sized for hundreds of liters per minute, while the leakage being evaluated may be only a few liters per minute or less. Using separate flow ranges or a dedicated leakage measurement circuit can provide much more useful data.
A practical specification should therefore define what must be measured, the expected range, and the required measurement performance for each important parameter.
How to Define the Required Automation Functions
Automation should be specified by function, not simply by saying that the test bench must have PLC control.
A request such as “we need a PLC-controlled test bench” does not explain which parts of the testing process should actually be automated. The machine may still require manual component loading, fixture adjustment, hose connection, or visual inspection.
A more useful specification describes the required sequence. For example, the system may need to automatically increase pressure to a target value, maintain that pressure for 60 seconds, cycle the component a defined number of times, monitor leakage, record test data, generate an alarm if limits are exceeded, and produce a pass/fail result.
This gives the test bench manufacturer a much clearer understanding of the required control architecture.
The automation functions may include pressure ramping, timed pressure holding, automatic cycling, valve switching, test-step sequencing, leakage monitoring, data recording, alarm management, pass/fail logic, and report export. These functions do not all have to be included in every machine; they should be selected according to the actual testing workflow.
The key question is:
Which test steps need to be automated to improve repeatability, productivity, safety, or traceability?
How Duty Cycle Affects Power Unit and Cooling Design
Pressure and flow define the instantaneous hydraulic requirement, but duty cycle determines how long the test bench must operate under those conditions.
A machine used for occasional repair verification may operate only for short periods. A production test bench may run repeatedly throughout the working day, and an R&D or endurance system may operate for much longer test cycles.
This difference has a major influence on reservoir size, oil temperature, cooling capacity, filtration, motor duty, and pump selection. Hydraulic inefficiency, throttling, relief-valve operation, and pressure loss convert part of the input energy into heat, so a high-power system operating continuously may require a much more substantial cooling arrangement than the same system used intermittently.
Duty cycle should therefore be considered together with pressure, flow, and power rather than added as an afterthought.
Putting the Specification Together
The most effective way to define a hydraulic test bench is to move from the test procedure toward the machine specification.
| Step | Main Question |
|---|---|
| Test Procedure | What must the component actually do during the test? |
| Pressure | What is the highest required test pressure? |
| Flow | What flow is needed at each operating stage? |
| Power | Which pressure and flow conditions occur simultaneously? |
| Measurement | What parameters, ranges, and accuracy are required? |
| Automation | Which steps should be controlled or recorded automatically? |
| Duty Cycle | How long and how frequently will the bench operate? |
This sequence helps prevent oversizing while also reducing the risk of missing a critical capability.
Instead of requesting a test bench only by saying “400 bar, 300 L/min, PLC controlled,” a more complete specification might describe the required test stages, the operating pressure-flow combinations, the measurement requirements, the automated sequence, and the expected daily workload.
That information provides a much stronger basis for hydraulic circuit design, motor sizing, sensor selection, control architecture, and quotation.
Conclusion
Selecting pressure, flow, power, accuracy, and automation for a hydraulic test bench requires these specifications to be considered as one connected system.
Pressure defines the hydraulic test condition, while flow determines actuator speed or the operating point of pumps, valves, and motors. Together they determine the hydraulic power required at each test stage. Measurement range and accuracy determine whether the resulting data is useful, while automation defines how consistently and efficiently the procedure can be repeated.
Duty cycle then determines whether the power unit, reservoir, cooling system, and filtration are suitable for the actual operating workload.
The best hydraulic test bench is therefore not the machine with the highest specifications. It is the one whose pressure, flow, power, measurement capability, automation functions, and duty cycle are matched to the real test procedure.
For a custom test bench project, defining the test sequence first is usually the most effective way to arrive at the correct technical specification.
