Drilling mud is heavier than it has any right to be, loaded with barite and cuttings and kept in suspension by agitators that turn above every compartment of the mud tanks. If a compartment stops mixing, the barite settles, and the section of hole being drilled finds out before anyone on the surface does. The MC3PVHF05 vertical hollow shaft gearbox drives those agitators: three helical stages in an upright case, a hollow bore through which the agitator shaft passes, footed pads bolted to the tank top steel.
These notes cover the drive the way the mud system sees it: abrasion from the tank, weather from the deck, and a duty cycle the rig decides without asking.
Mud Heavier Than Concrete
A weighted mud can reach densities that make a bucket of it a two-hand lift, and the paddle that keeps it moving works in a fluid more like slurry than liquid. The torque is high, steady and unglamorous, and it continues for as long as the well does.
The gearbox above the paddle does not touch the mud, but it lives with its consequences: continuous torque, a shaft that must not wander, and a tank top that vibrates gently every hour the rig runs.
The Code on a Rig Nameplate
Seven characters, each fixing one part of how the drive meets the tank.
| MC | Industrial gear unit family built for continuous plant duty |
| 3 | Three helical reductions inside one upright case |
| P | Parallel-shaft layout, input and output on parallel axes |
| V | Vertical build, output axis pointing down into the vessel |
| H | Hollow output bore, the process shaft passes through it |
| F | Footed reaction pads, bolted to the vessel bridge or plate |
| 05 | Fifth frame of the vertical hollow band |
In one breath: three-stage industrial unit, parallel-shaft, vertical, hollow output bore, footed pads, fifth frame of the vertical hollow band.
Why Agitators Sit on Every Compartment
A mud system is a row of compartments - suction, mixing, trip tank, reserve - and each holds a different fluid at a different moment of the well. Settlement in any one of them is a drilling problem, so each carries its own agitator, and the drives multiply accordingly.
Fleets therefore buy this drive by the dozen, and the specification that matters most is the one that makes twelve units swappable in the store: same bore family, same pad pattern, same oil grade.
Hanging a Three-Stage Case Over the Tank
The case stands on the tank top steel, and the tank top is the most flexible structure on the rig that still carries machinery. The pads must land on members, not on plate; the bolt pattern must resist the reaction couple; and the shaft must pass through the bore without the tank's flex becoming the shaft's runout.
Rigs that have bolted a drive to unsupported plate know the symptom: a drive that runs sweetly on the test bench and hums its own note once the tank is full. The fix is steel, not oil.
Barite, Sand and the Bore Surface
Everything in the mud is abrasive, and some of it is airborne. The bore and key see grit that settles on the shaft during shaft changes and on the case during sandstorms; the seal arrangement and the bore finish decide whether that grit does harm or just sits there.
A bore finish that sheds grit, a purgeable arrangement at the bore, and a habit of capping the bore whenever the shaft is out are worth more on a rig than any of the figures on the gearbox datasheet.
Duty Cycles the Rig Decides
Mud agitators run continuously while the well is live, then stand while the rig moves, then run again - sometimes harder, in a heavier fluid for the next section. The drive's real duty cycle is the drilling programme, not a standard classification.
The programme belongs on the enquiry: mud weights by section, expected downtime between wells, and the ambient the rig will actually work in, from North Sea deck to desert pad.
Three Stages and Continuous Torque
Agitator speed is low and the ratio from a motor is deep; three stages make that ratio without a wheel pair the tank top could not carry, and they share the continuous torque across more tooth contacts than two stages would.
The fifth frame is the tier for the larger compartments and the heavier muds: paddle torques that punish smaller frames, shafts long enough to want real stiffness, cases still liftable by the rig's own gear.
Oil in a Case That Stands in the Weather
The case stands in the open, from Arctic deck to tropical pad, and its oil sees the full range. Cold starts on a northern winter yard are a real load case: oil stiff, torque unchanged, and a paddle that must turn when the crew needs it to.
Oil grade chosen for the coldest start the rig will actually make, synthetic where the range demands it, and a note of that range on the order are the whole discipline. The gearbox does not know the season; the oil does.
Seals, Splash and Washdown on Deck
Decks are washed, seas come over the rail in bad weather, and the case stands in both. Its breather is the point where water most wants to enter, and its output-side bore is the second.
A breather piped to a protected point, sealing at the bore arranged for a shaft that also carries weather, and a finish that takes salt water without complaint are lines the fleet standard should already contain. Where it does not, this drive's order is the place to write them.
The Bore, the Key and the Couplingless Fit
The hollow bore deletes the coupling, and with it the alignment work and the spare-part politics of every coupled drive on the rig. What it adds is a fit discipline: bore and key dimensioned to the agitator shaft, surface finish agreed, and the fit checked with the real shaft at every change.
Fleets that standardise the bore across the agitator population buy the real prize: any gearbox fits any shaft, and a rig stores one spare instead of one per compartment.
What a Mud Plant Should Send
The enquiry that gets a fleet-quotable answer carries the shaft diameter, finish and material; paddle torque at the heaviest mud weight of the programme; the tank top drawing with pad members marked; the ambient range by location; motor frame and speed; and the wash-down and salt exposure the deck actually sees.
One added line - "spares must fit any shaft in the fleet" - does more for the quotation's shape than any efficiency figure.
Frame Five in the Mud System
The fifth frame is the heavy end of this family's usual rig duty: large compartments, weighted muds, and the agitators that keep the most expensive fluid on the location moving.
Smaller trip and reserve tanks sit frames below; specialty fluids move up the band. The frame follows the paddle and the mud weight, and the drilling programme writes both.
Barite that must never settle, on a deck that washes down - three stages drive the mud agitator:
- Mud tank agitator on an onshore drilling rig
- Shaker tank mixer in a solids control system
- Bulk mud plant blending agitator
- Trip tank mixer on a drilling spread
- Reserve pit agitation at a drilling location
- Cement slurry tank mixer at a mud plant
Selection Example: Mud tank agitator on an onshore drilling rig
Take an 11 kW motor at 1460 rpm turning the mud tank paddle at 30 rpm. The ratio follows directly: 1460 / 30 = 48.7, so a ratio near i=48.5 is drawn from the three-stage vertical band, and the frame is sized on the heaviest weighted mud of the drilling programme rather than on the average section. In this case frame five stands on the tank top steel with pads landed on real members, grips the agitator shaft through a standardised bore so one spare fits the whole fleet, and carries an oil grade argued from the coldest start the rig will make. Work through the same three steps - speed, output speed, torque - and the model number falls out; we verify it against the duty class before quoting.
![gear reducer ratio calculation steps]()
From duty point to model number - the same four steps every time.
Applications in Industry
Ship loader slew drive
A port terminal selected heavy-duty gear units for the travel drives of its ship loader. Salt-laden air is handled by the heavy-duty coating option, and spare seal kits are held on site for the annual service.
Sugarcane carrier drive
A sugar mill drives its cane carriers with industrial gear units sized for fully loaded starts. The generous torque margin covers cane jams, and the right-angle build keeps the motor clear of the carrier slat path.
![gear reducer industries served - WGT]()
Industry map: the sectors where the M3 series is most common.
Buyer Questions and Answers
Do you supply spare parts such as seals and bearings?
Seal kits, bearings, output shafts and covers are available from stock or on short lead time. We keep the drawings for every unit we ship, so a replacement part ten years from now is still traceable to your original order.
How is each unit tested before shipment?
Every unit is run in on the bench before packing. Noise, temperature rise and backlash are recorded and the test sheet travels with the shipment, so you can file it with your incoming-inspection records.
M3 Series Model Overview
| Model | Centre distance | Output | Typical duty |
|---|
| M3PSF50 | size 50 | solid shaft, foot | conveyors, feeders |
| M3PSF60 | size 60 | solid shaft, foot | crushers, mixers |
| M3PSF70 | size 70 | solid shaft, foot | ball mills, shredders |
| M3PSF80 | size 80 | solid shaft, foot | kilns, heavy conveyors |
| M3PSF90 | size 90 | solid shaft, foot | mill and kiln drives |
| M3RSF50 | size 50 | solid shaft, foot, right-angle | inclined conveyors, elevators |
| M3RSF60 | size 60 | solid shaft, foot, right-angle | screw classifiers, feeders |
| M3RHF70 | size 70 | hollow shaft, foot, right-angle | agitators, drum drives |
| M3PHT80 | size 80 | hollow shaft, torque arm, parallel | shaft-mounted conveyors |
| M3RHT90 | size 90 | hollow shaft, torque arm, right-angle | heavy shaft-mounted drives |
The series is sized for continuous heavy duty rather than by motor power alone: the required torque with the service factor decides the frame, and the stage count (2 to 5) decides the ratio band.
Send the Nameplate - Get the Equivalent Frame
Matching an existing installation? Run your duty point through the WGT Motor & Gearbox Online Selection System first: it saves a round of emails and gets you to a firm price faster.
Photograph the nameplate or note the model and ratio. We identify the equivalent frame, confirm the torque margin and return a quotation with the outline drawing - usually within one working day. Looking for a speed reducer for bucket elevator? Tell us the duty point and we will confirm the model in writing.
