Hydraulic Motor Duty Cycle: Continuous, Intermittent And Peak Ratings

Read a hydraulic motor's intermittent rating with its time footnote. The permitted duration and spacing of overloads determine whether the machine's duty fits. Peak amplitude needs another check. A shift average can look modest while a brief part of the cycle exceeds the motor's allowed pressure, speed or exposure time.

Describe the repeated production sequence, including loaded starts, reversals, jams and stops. Keep fractional-second events in that record. A motor can rotate for the whole shift yet spend little time above its continuous-pressure boundary. Calling that “10% motor duty” would lose most of its running history.

BLINCE's hydraulic motor range includes different motor families. For a selection inquiry, ask for the applicable continuous, intermittent and peak limits for the exact proposed build, together with their time definitions. A family headline or an unexplained maximum-pressure number leaves the duty assessment unfinished.

Read the rating and its footnote together

Keep the rating value and its conditions in the same row of the comparison sheet. The word “intermittent” by itself leaves the allowable duration unresolved.

As a published example, Danfoss's General Orbital Motors technical information, page 13, permits the stated intermittent speed or pressure-drop duty for at most 10% of each minute and excludes simultaneous intermittent speed and intermittent pressure drop. It also gives a 1% per-minute peak-load allowance above the intermittent pressure-drop/torque boundary, within the motor's specified peak limit. These rules apply to the motors covered by that document.

The Parker TS Series technical information, PDF page 3, printed page 53, similarly attaches a per-minute 10% allowance to intermittent operation. A performance table read without that footnote would give an incomplete account of the rating. Neither manufacturer's timing rule establishes the allowance for a BLINCE model.

On a 60-second time base, the two allowances translate to six seconds and 0.6 seconds. Keep that time base in the comparison sheet. Another supplier may use the same duty label with different conditions.

Continuous operation still has operating conditions

Plot the working point on the selected motor's function diagram. The maximum torque entry and maximum speed entry may describe different places on that map. Check the fluid conditions, shaft load and drainage requirements attached to the point as well.

In Parker's F10 technical specifications, the operating-pressure entries are 300 bar continuous and 350 bar intermittent. The speed rows are also separated by duty and displacement. Read them as specifications for that Parker product. A BLINCE selection needs its own limits, and either selection needs the conditions beyond the summary table.

Identify the source beside each quoted rating: model and suffix, displacement, document revision, units and footnote. If a distributor table omits the footnote, obtain the manufacturer's applicable document before comparing it with another offer. An attractive pressure number may be from a different duty column.

Build a time record that describes the machine

Give each state a start time and duration, then record shaft speed, working-port pressures and what the machine is doing. Label estimated torque or flow separately from measurements. Retain the conditions for a measured value so the supplier can see what the evidence supports.

For a proposed machine, begin with the intended sequence and the calculated resisting loads. For an existing machine, use a representative recorded cycle. Include operation at the expected production rate and the relevant oil temperature. A cold idle demonstration may help with another question, but it cannot replace a warm loaded-duty record.

Separate movement from pressure exposure. A stationary shaft may remain pressurized. A rotating shaft may be lightly loaded. A stopped, depressurized interval differs from a stopped interval holding a load under pressure. State what the valve and load do during the supposed “rest” period so the reviewer can determine which limits remain active.

Also record events outside normal production. A loaded restart after an interruption can demand a different pressure from an empty start. A reversing drive can produce an event that a forward-running test never includes. If a jam is a credible machine state, describe the intended response and how long pressure could persist before the system removes the command or unloads.

The duty sheet should distinguish three time scales:

• The event: one high-load stroke, switch, restart or pressure pulse.

• The repeated cycle: the sequence that establishes how often the event returns.

• The operating period: production runs, shift length and the expected pattern over the machine's service use.

Use the manufacturer's specified interval for the short-term limit. Keep the longer history for heat and any manufacturer life assessment. A one-minute trace should say whether it represents a rare event or a sequence repeated throughout production.

Work through a 60-second cycle

For this hypothetical cycle, choose 160 cm³/rev displacement and 120 rpm rotation throughout the minute. All loads, limits and efficiencies in the exercise are assumed inputs, with no BLINCE rating or model approval implied.

Apply these assumed limits to the exercise:

Replace the entire assumed limit set with the selected model's data and combined operating envelope for an actual selection.

The 200 bar state falls in the assumed intermittent band. Four seconds divided by 60 gives a 6.67% share, using four of the six available seconds. The two other pressure states and the stated 120 rpm remain in the exercise's continuous envelope.

The constructed cycle clears that pressure/time screen. Starting torque, temperature, shaft load, actual speed-pressure compatibility, outlet pressure and case pressure remain open checks for the selected build. Retain those rows when recording the result.

Rotation occupies the whole minute; above-continuous pressure occupies four seconds. Describe both in the inquiry. Writing only “6.67% motor duty” would conceal the other 56 seconds of running.

Over eight hours, 480 repeats accumulate 480 × 4 = 1,920 high-load seconds, or 32 minutes. Record that total with the cycle history.

A faster production cycle changes the exposure

Shorten the production cycle to 20 seconds while retaining its four-second heavy-load event. The local exposure triples:

The faster schedule exceeds the exercise's six-second allowance. Cooling capacity cannot change that published type of time restriction. Review a motor with an appropriate continuous envelope, a lower load requirement, or a different approved machine sequence. Preserve the production behavior the machine actually needs when comparing those options.

Clustering the load makes another difference. Twelve high-load seconds followed by 168 seconds of waiting average 6.67% over three minutes. Yet a minute containing that whole event has twice the allowed six-second exposure. Keep the duration and spacing with every percentage supplied for selection.

If events straddle the boundary of a logger's reporting minute, keep the underlying time trace. A spreadsheet must not hide a concentrated burst by placing parts of it in adjacent summary rows. Ask the motor supplier to state how the specified interval is to be assessed when the document leaves that interpretation unclear.

Keep pressure peaks separate from the heavy-load interval

The load table describes four seconds at a steady 200 bar. Any switching excursion at the start or end needs its own amplitude and timing record.

Take a separate hypothetical peak-timing case, with the earlier 150/220/240 bar limit set. Three quarter-second excursions reach 230 bar during a minute. Adding their durations gives 0.75 seconds, a 1.25% share. All three enter the peak band between 220 and 240 bar. This timing exercise is separate from the original three-state cycle used in the later thermal calculation.

The assumed 1% rule allows 0.6 seconds, so the three events exceed it by 0.15 seconds despite remaining below 240 bar. A 245 bar excursion would instead fail the amplitude check regardless of a short duration. Keep both results in the review; a time average settles neither maximum amplitude nor allowed exposure.

Two 0.2-second events would use 0.4 of the assumed 0.6 seconds available. That clears the stated time test alone. Count events during stops and reversals as well as starts, and check the remaining envelope and measurement conditions before accepting the duty.

Do not choose a relief setting by subtracting an arbitrary margin from a catalog peak number. The pressure at the motor during a transient depends on the actual circuit and the response of the protection path. Have the machine's qualified circuit reviewer establish the applicable settings and verification procedure. This article supplies no field-adjustment value.

Identify the sensor location with every excursion. A pump-outlet trace, an upstream valve trace and a motor-port trace describe different places in the circuit. State the measurement basis for duration too. A slow display or unsuitable recording setup can miss a narrow pulse or distort its shape, leaving the actual peak unresolved.

Check the operating point behind each rating

Motor torque depends on pressure difference across the working ports. If the inlet is at 208 bar gauge and the outlet at 8 bar gauge, the differential is 200 bar. Those numbers are another hypothetical operating point. The selected motor must accept both working-port conditions as well as the differential used in the torque calculation.

An outlet or case-pressure limit can be lower than a working-port pressure limit, with its own continuous and short-term conditions. Trace the external case drain separately from the main return. Where there is no external drain, use the selected construction's documented seal-pressure relationship. A motor that clears the differential-pressure time screen can still be unsuitable for its return or drain arrangement.

For the running estimates below, use these motoring equations:

• Inlet flow: Q = D × n / (1,000 × ηv).

• Shaft torque: T = Δp × D × ηhm / (20 × π).

Use the following quantities in the equations. Danfoss's discussion on pages 14–15 distinguishes the two efficiency terms.

For the example, the calculation inputs are D = 160 cm³/rev, n = 120 rpm, ηv = 0.92 and ηhm = 0.90. They give 20.87 L/min inlet flow. The torque results sit beside the power results in the next table. Actual curves and starting-torque data are still needed for selection.

Speed moves the operating point across the function diagram. Plot each recorded state as a pressure-speed or torque-speed pair, then apply the document's restrictions to that pair. Permission for high pressure at one speed leaves the high-pressure, high-speed corner unresolved.

On a variable-displacement motor, record displacement alongside the pressure trace, identifying command and actual values where available. For a fixed-displacement replacement, provide the full model suffix and its configuration drawing. That identifies the shaft, bearing, seal, port and brake options involved in the review.

Keep a separate heat balance

Make the energy balance for the original three-state cycle. Retain the example's assumed efficiencies, 0.92 and 0.90. The result adds a heat estimate to the selection record, alongside the time and amplitude checks.

With the units in the symbol table, hydraulic input is Δp × Q / 600 kW. Shaft output is T × 2 × π × n / 60,000 kW. The loss column subtracts shaft output from hydraulic input and covers the motor alone. Add the rest of the machine's losses separately.

To obtain energy, multiply each unrounded loss value by its seconds in the cycle, then sum the three products. The result is 37.45 kJ in 60 seconds. Dividing by 60 gives an average loss of 0.624 kW. Weighting input and output the same way gives averages of 3.629 and 3.005 kW, whose difference agrees with the loss result.

The light-load row contributes energy throughout its 14 seconds. A real machine's rest state must be identified just as carefully: rotation, pressure-held standstill and isolated standstill have different flow and loss conditions. Use the applicable curves or measurements for that state.

Carry the motor contribution into the system heat balance, then add the other losses and the cooling conditions over the operating period. A cooler cannot be selected from this example alone. The fixed efficiencies were assumed to make the arithmetic reproducible; actual pressure, speed and oil condition change them. Starting and stalled operation need their own applicable data.

Average pressure answers a limited question

Average the pressure states with their recorded durations: (42 × 120 + 4 × 200 + 14 × 30) / 60 gives 104.33 bar. This is below the exercise's 150 bar continuous boundary. It leaves the 200 bar event in the record, subject to the intermittent allowance.

Constant inlet flow is what makes that pressure average useful for the example's average hydraulic input. Where flow changes, work from the individual pressure-flow pairs: calculate each state's power first, then weight it by duration.

Send the load history and construction data for a manufacturer life assessment covering the relevant bearing, contact and fatigue loads. Use a mean-pressure life calculation only where the manufacturer provides an applicable method. The energy calculation above supplies no such life relationship.

Measure the cycle at useful locations and time resolution

Tell the technician whether the unresolved question concerns the four-second load or a quarter-second excursion. Instrument response and logging must suit that event. Agree the setup with the technician or motor supplier; a universal sample-rate rule would leave the circuit and event shape unspecified.

Take an illustrative logger that records one instantaneous sample each second. A quarter-second event could fit between two samples and disappear from the record. Extra decimal places would change neither sample's timing. Review bandwidth, sampling, sensor location and installation together when investigating such a pulse.

For a fast differential-pressure calculation, align the two working-port traces in time. Pairing the maximum inlet reading with an outlet reading from another state can produce a fictitious operating point. Retain both original traces and the valve command behind the summary.

Label the case-drain pressure and temperature locations separately. A reservoir temperature reading supplies context; a case or outlet value describes another location. State whether the number came from an instrument, an estimate or a catalog. Keep enough timing information to place it in the cycle.

Have a qualified technician use the intended test points under the machine's approved procedure. Secure the load and select instruments rated for the circuit. Keep hydraulic lines closed while energized. Changes to protection settings require their own qualified, authorized procedure.

Record the state producing an exception: brake release, a jam, warm loaded operation or switching. That identifies the relevant flow path for investigation. A symptom alone leaves the cause and any replacement decision unresolved.

Compare quotations using the same duty sheet

Give competing candidates the same load-cycle table and the same required motion. An offer with a higher intermittent pressure can still be unsuitable if the machine spends too long above the continuous rating. Another offer may have a lower headline maximum but a continuous envelope that covers the production duty. Compare the applicable curves and conditions before interpreting the difference.

In a hypothetical comparison, one offer lists 180 bar continuous and 240 bar peak. A sustained 200 bar duty falls outside that continuous entry. An alternative covering 200 bar continuously is worth assessing at the actual speed, fluid and drain conditions. These assumed entries illustrate a screening decision and identify no products.

Keep the rating review separate from interface compatibility. A motor with a better duty envelope can still have the wrong shaft, flange, ports or rotation arrangement. The BLINCE orbital motor category is a useful starting point for family discovery; the selected model drawing and limits are needed for the actual comparison.

Include a known service history with the old motor's model tag. Record any changes in cycle rate, load, oil temperature, valve arrangement or pump delivery since installation. Assess the proposed replacement from its own limits and configuration; service history helps describe the machine without establishing a rating for another motor.

What to send with a motor duty-cycle inquiry

Send one complete cycle with the most demanding repeated state identified. Include:

• State duration and rpm.

• Shaft torque and the calculation or measurement behind it.

• Both working-port pressures where measured.

• Cycles per minute or hour, plus the expected operating period.

Label measured, calculated and assumed entries so the supplier can separate established requirements from estimates.

Attach the existing motor tag or complete proposed code and the circuit with its working, return, drain and brake/control connections marked. Replacement inquiries need an interface drawing too. Give the oil type, recorded condition and temperature locations used in the duty sheet.

Keep loaded starts, reversals, stops, jams and detected excursions in an exception record. Include time axes and the measurement setup with any traces. Leave an unmeasured peak marked unknown; the highest number noticed on a dial supplies a different kind of evidence.

Request a written duty review against the submitted states, supported by the applicable curves and document revision. It should identify the accepted continuous points, the intermittent time definition, peak exposure and outlet/case limits. Any missing state or undefined allowance remains an open item before ordering.

Send the packet through BLINCE's contact page for a configuration review. If the production cycle falls outside a stated rating, identify the proposed change to the motor or machine duty and have that change reviewed before ordering. Keep any unresolved measurement or operating state on the inquiry record so it remains visible when the final configuration is released.

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✉️ Email: sales16@blince.com

Website: https://blince.com

Disclaimer

This article is a general engineering guide. Final component selection should be based on machine drawings, measured hydraulic data, working conditions, safety requirements, and confirmation from a qualified hydraulic engineer or supplier.

Blince Hydraulic Team

Blince Hydraulic is an industry-leading company dedicated to precision-engineered fluid power manufacturing and custom hydraulic solutions. Backed by decades of deep field expertise in industrial machinery and thousands of successful global deployments, our engineering team focuses entirely on high-performance hydraulic component manufacturing, including specialized orbital motors, high-pressure travel drives motor, and robust directional control valves. Our production infrastructure utilizes state-of-the-art multi-axis CNC machining systems and is fully ISO 9001 certified to guarantee repeatable volumetric accuracy across every single manufacturing run.

We deliver fast, highly dependable, and cost-efficient hydraulic solutions to heavy industry distributors, machinery OEMs, and maintenance crews across more than 150 countries. Whether your active project calls for a small-volume batch of customized shaft profiles or a large-scale production run of severe-duty cast iron gear pump, we configure our flexible production schedules to meet your target lead times with total pricing predictability. Partnering with Blince means securing maximum system efficiency, elite material quality, and uncompromised fluid power professionalism.

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