Carrier matching

Hydraulic power calculator

Hydraulic power is flow times pressure divided by 600 — but a single flow figure is not a specification. This gives the order of magnitude, then sets out what a buyer actually needs before committing to a carrier-and-attachment match.

Carrier hydraulic supply

Continuous flow

L/min

Continuous, not peak. Ask the dealer for the sustained figure.

Pressure at that flow

bar

= 30.0 MPa

Assumed system efficiency

Losses through hoses, couplers, valve blocks and return lines. 75-85% is a common working range.

Attachment power requirement

From the attachment manufacturer, for continuous duty.

Theoretical hydraulic power

110.0kW

220 L/min × 300 bar ÷ 600

Estimated usable power

88.0kW

After 20% assumed system losses.

Headroom against requirement

-12%

Usable power falls short of the stated attachment requirement at these figures.

A flow figure is not a specification

This calculation gives an order of magnitude, nothing more. Before committing to a carrier-and-attachment match, obtain all nine of the following:

1Continuous attachment flow
2Pressure at that flow
3Return pressure
4Case drain requirement
5Cooling capacity at sustained full load
6Hydraulic hose size
7Coupler restriction
8Pump control arrangement
9Permitted continuous duty

A mulcher in particular is a continuous-duty attachment. It does not draw peak flow occasionally — it draws close to maximum flow continuously for hours, which is a fundamentally different demand from a bucket or a hammer.

What this answers

The decision behind the calculation

Attachments are specified in required hydraulic power; carriers are specified in flow and pressure. Converting between the two is the check that determines whether a proposed combination will work at all, and it is routinely skipped in favour of comparing operating weight.

The consequence of skipping it is distinctive: an underpowered attachment does not simply work a little more slowly. A mulcher on a marginal circuit cuts slowly, overheats, and consumes teeth and bearings at a rate that erases the margin — which then presents as an attachment problem and is a carrier problem.

This calculator converts continuous flow and pressure into hydraulic power, applies a system efficiency, and compares the usable figure against the attachment's requirement so the headroom is explicit before purchase rather than after the first hot day.

The inputs

Where an honest number for each field comes from

A calculator is only as good as what goes into it, and most of these fields have a value that is easy to assume and a value that is true.

Field	Where the number comes from	The trap
Continuous flow	The carrier's auxiliary circuit continuous flow rating, from the manufacturer's specification for that exact configuration.	Peak or momentary flow figures overstate what the circuit can sustain. Attachments that work continuously need the continuous rating.
Pressure at that flow	The circuit's working pressure at the stated continuous flow, not its maximum relief setting.	Using relief pressure with continuous flow combines two figures the machine never delivers together, and produces a comfortable answer that is wrong.
Assumed system efficiency	An allowance for losses in hoses, couplers, rotators and the attachment's own motor. Be conservative rather than optimistic.	Long hose runs, undersized couplers and additional circuit components all reduce delivered power, and the effect is larger than most buyers expect.
Attachment power requirement	The manufacturer's stated requirement for the attachment in the duty you will run it at.	A requirement quoted for intermittent use will understate what sustained work — mulching in particular — actually demands.

The output

How to read the result

Theoretical hydraulic power

Flow multiplied by pressure, before losses. It is the ceiling, and no real installation delivers it.

Estimated usable power

The theoretical figure after your efficiency allowance. This is the number to compare against the attachment requirement.

Headroom against requirement

How much margin the combination has. Little or negative headroom means the attachment will be worked at or beyond the circuit's capability, with the wear and heat consequences that follow.

Worked example

Why headroom matters more than a pass mark

1An attachment whose requirement is met exactly by the calculated usable power has no margin for hose losses beyond the assumption, hot-day derating, or a filter approaching service.
2Sustained duties — mulching, grinding, continuous saw work — spend most of their time at full load rather than peaking briefly.
3Cooling capacity is a separate question from power, and a circuit that can supply the flow may still overheat supplying it all day in Australian summer conditions.

A combination that passes on paper with no headroom will underperform in the field and wear faster doing it.

Specify headroom deliberately, and confirm cooling separately. Both questions are cheap before purchase and expensive afterwards.

Avoid

Errors that make the answer wrong, not just imprecise

Using peak flow or relief pressure

Continuous duty needs continuous ratings. Combining peak flow with relief pressure describes an operating point the machine never sustains and makes a marginal combination look comfortable.

Assuming an optimistic efficiency

Hoses, couplers, rotators and the attachment's motor all take a share. A generous efficiency assumption is the easiest way to make an unsuitable combination pass.

Treating power as the only check

Cooling capacity, return-line sizing and case-drain requirements are separate and can each limit an otherwise adequate installation. Confirm them with the attachment manufacturer.

Forgetting the lift chart

Hydraulic adequacy says the attachment will run. It says nothing about whether the carrier can hold what the attachment cuts at working reach, which is a separate and equally decisive calculation.

Questions

Common questions about this calculation

How much headroom should I specify?

Enough to absorb the things the calculation cannot see: hose losses beyond your assumption, hot-day derating, filters approaching service, and duty that is heavier than the requirement was quoted at. A combination that only just passes on paper is one that will disappoint in the field, so treat 'exactly adequate' as a fail for sustained duties like mulching.

Does the carrier need a dedicated cooling package?

For sustained high-flow attachments in Australian conditions, usually yes, and it is a separate question from whether the circuit can supply the flow. Ask the attachment manufacturer what cooling they specify for continuous duty at your ambient temperatures, and confirm the carrier's configuration meets it rather than assuming the standard build does.

What if the attachment's stated requirement is a range?

Specify against the top of the range, and check what duty the range refers to. Manufacturers commonly quote a lower figure for intermittent use and a higher one for continuous work, and sustained duties spend most of their time at the top. Sizing to the bottom of a range is sizing to the easiest job you will ever do.

Is hydraulic adequacy the same as compatibility?

No. Coupler type, hose sizing, return-line and case-drain requirements, control provisions in the cab, and the lift chart at working reach are all separate checks. Power tells you the attachment can run; the others tell you it can be fitted, controlled and used safely on the work you have.

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