Shearex VM-50SR excavator mulcher

The model where the pump decides, not the tonne class

There is a point in the Shearex VM excavator mulcher range where a buyer stops shopping by excavator size and starts shopping by hydraulic circuit, and the VM-50SR is it. Its published continuous flow demand of 159 to 238 L/min is more than many 20 tonne excavators can dedicate to an attachment for an hour at a time, whatever their pump totals suggest. Two machines of identical tonnage, identical age and identical brand can sit at opposite ends of this head’s production range, and nothing on the dataplate will tell you which is which.

Below it, the VM-40SL asks 114 to 167 L/min of a 12 to 15 tonne carrier and forgives a lot. Above it, the VM-60SR shares this exact flow window but demands 130 hp instead of 80 and takes 40 cm material. The VM-50SR is the head for a contractor whose 20 tonne excavator already lives on easements, pipeline corridors and firebreak construction, and who wants real vegetation capacity without buying a dedicated mulching machine.

Working the hydraulic power sum properly

This is the calculation every page in the family refers back to, so it is worth doing once and doing it carefully. Theoretical hydraulic power in kilowatts is flow in litres per minute multiplied by pressure in bar, divided by 600.

Take the top of this head’s window. At 238 L/min and an assumed 300 bar, which is an illustrative working pressure rather than a published figure, the sum gives 238 × 300 ÷ 600, or about 119 kW. That is roughly 160 hp of hydraulic power alone, at or beyond the total engine output of a good many 20 tonne excavators, before anything is left for tracking, slewing, the cooling fan and pump inefficiency. At the bottom of the window, 159 L/min at the same assumed pressure gives about 79.5 kW, or close to 107 hp.

Set that against the published minimum carrier power of 80 hp (59 kW) and the picture is clear: a machine that merely meets the minimum lives at the bottom of the flow window permanently, and the head will run, cut and disappoint. The buyer’s job is to establish where in that 119 kW to 79.5 kW span their specific carrier can actually sit, then price the work accordingly. Three further numbers complete the picture, because the sum above is theoretical: the pressure the carrier will genuinely hold at that flow, the return back-pressure it imposes, and whether a case drain runs to tank. Substitute the measured figures in the hydraulic power calculator before ordering, and read hydraulic matching for the way to ask a dealer for them.

The VM range’s maximum operating pressure is published as up to approximately 410 bar, which means the carrier’s auxiliary relief setting is part of the specification rather than a detail for commissioning day.

123 cm and 25 cm on an easement

The 123 cm cutting width clears a corridor edge or a firebreak strip in wide overlapping sweeps from one stance, which on transmission work is worth more than raw swath because the machine spends less time repositioning between towers. The published optimal target material diameter of 25 cm now covers most regrowth eucalypt, wattle and pine understorey encountered on maintained easements. Heavier stems remain occasional events to be worked from the top down, and the rate quoted should reflect the 25 cm figure; maximum diameter versus production diameter shows how fast wood volume climbs once diameter rises.

At 975 kg the head is close to a tonne before bracket, hoses and any grapple, tilt or heel option, and on a 20 tonne machine at full reach across a drain that mass has to be read off the chart rather than assumed away.

Heat, the other half of the flow question

Flow that the carrier can supply for ten minutes is not flow it can supply all afternoon. An excavator digging sheds heat during every slew and dump; a mulcher never stops asking. Ask what the oil temperature reaches after an hour of continuous work on a 38 degree day, and whether the dealer has seen that carrier derate. Hydraulic cooling and heat covers the failure modes in full, and the VM-65SV page carries the range’s detailed treatment of cooler specification.

Easement, pipeline and firebreak contracts

The head suits powerline and transmission easements, mining and pipeline corridors and firebreak construction inside bushfire fuel reduction programs. All three share a characteristic that matters commercially: the ground has been disturbed before. Old spoil, buried debris and rock in cuttings punish tooling in a way standing bush does not, which pushes most corridor operators to carbide and leaves blades to clean green material where finish is being sold. Blades versus carbide teeth sets out the trade.

Where the VM-50SR gives way

On flat, traversable ground a front-mount head such as the HM-88LV runs nearly twice the width and cuts while travelling, so it produces more area per hour whenever the terrain permits; excavator mulcher versus skid steer mulcher covers the choice. This head wins on batters, around towers and structures, and wherever material has to be reached rather than driven over. Step down to the VM-40SL if the fleet is lighter and stems stay under 20 cm. Step up to the VM-60SR when 40 cm material is routine and a 20 to 25 tonne carrier with 130 hp or more is available, remembering that both heads draw the same flow.

Support at a distance

Easement and pipeline work is usually remote, which changes what a parts conversation should cover. The price of a belt matters far less than how many days it takes to reach a crew camped two hours past the nearest town, so ask Machinery Specialist for Australian stock positions and realistic freight times on the critical items, and carry the cheap ones on the truck. The circuits required by the standard hydraulic door and by any option are documented on the VM-25SK page, and the full consumable list is in wear parts to price before buying.

What to measure at the dealer, and in what order

Because the whole argument of this head is that measured hydraulics beat quoted tonnage, it is worth setting out what that measurement actually looks like. The test should happen on the carrier being bought, with the oil hot, and it should take an hour rather than ten minutes.

1. Warm the machine to normal operating temperature
2. Measure flow under loadat the auxiliary coupler, not the pump
3. Record pressure at that same flow
4. Record return back-pressure
5. Hold it for an hourwatch oil temperature and any derate

Flow measured with the circuit unloaded tells you almost nothing, because a pump will happily deliver its nameplate figure into an open line and then fall away under pressure. Flow and pressure have to be read together, at the coupling the head will use, with the machine at temperature. Return back-pressure is the figure most often skipped and the one that most often explains a disappointing head, because a restrictive return raises case pressure and takes power straight out of the rotor.

Ask for the results in writing, and ask what the dealer has seen on the same model in the field. A dealer who cannot produce figures for a machine they are selling into mulching work is telling you something useful about how often they do it.

Stalling, relief and what it costs

A mulching rotor carries energy in its mass, and production comes from spending that energy into the timber and recovering it before the next bite. When the carrier cannot supply enough power to recover rotor speed, the operator either feeds more slowly, which is the correct response, or pushes on, which takes the circuit to relief.

Oil dumped over relief does no work at all. It becomes heat, which raises oil temperature, which reduces viscosity and increases internal leakage, which reduces the flow reaching the motor, which makes the next recovery slower still. On a carrier without headroom this becomes a cycle across an afternoon rather than a single event, and it presents to the operator as a head that “got tired” rather than as a hydraulic limit. This is why the measured figures matter more here than anywhere else in the range, and why a carrier at the top of the window is worth paying for on continuous work.

Firebreak construction is not vegetation maintenance

Firebreak work gets grouped with fuel reduction and it should not be, because the deliverable is different. Maintenance mulching reduces fuel load across an area; firebreak construction produces a defined strip to an agreed standard, usually specified by width, residual fuel height and continuity, and inspected against it.

That changes how this head is used. Continuity matters more than average production, because a strip with untreated gaps fails its purpose entirely, so the operator works to a line rather than to an area. Width is specified rather than chosen, which means the 123 cm swath becomes a planning unit: a four metre break is a defined number of overlapping passes, and the rate should be built on passes per kilometre rather than hectares per hour. And residual material has to be managed, since a heavy mulch layer on a break can itself carry fire. Housekeeping around the machine matters in the same way, and fire risk in clearing operations covers what belongs in the daily routine during the season.

Exclusion zones and the material the rotor throws

A rotor of this size working 25 cm stems throws material with real energy, and on easements the nearest asset is often a tower footing, a conductor, a marker post or a pipeline riser rather than a person. Exclusion zones should be set for thrown material and for the machine’s slew envelope, and crews should be working to applicable WHS procedures and the manufacturer’s instructions rather than to custom. Where the corridor carries live conductors, the approach distances and permits belong to the asset owner and should be settled before mobilisation rather than at the gate.

Confirm before ordering

• Continuous flow the carrier can dedicate to the attachment under load, measured, not the pump total
• Pressure genuinely held at that flow, and where the resulting kW figure falls between the ends of the window
• Return pressure limit, case drain to tank, and auxiliary relief against the approximate 410 bar maximum
• Oil temperature after an hour of continuous mulching in summer, and any cooler upgrade that implies
• Head mass with the options quoted, read off the chart at working radius
• Tooling choice for corridor ground that has already been disturbed
• Australian stock and freight time to a remote crew for belt, bearings, teeth and holders
• Delivered price including bracket, hoses, commissioning and operator training

Frequently asked questions