A Yale Duplex Hoist is a hand-operated chain hoist that uses two load-chain falls and a duplex (double) pawl-and-ratchet load brake to lift and hold heavy loads with a small pulling force on a hand chain. The classic Yale & Towne No. 2 Duplex Hand Chain Block, common in 1900s machine shops and railway yards, is the named example. It exists to give a single worker controlled, self-sustaining lift of loads up to 5 tons without slipping when the hand chain is released. Mechanical advantages of 30:1 to 60:1 are normal.
Yale Duplex Hoist Interactive Calculator
Vary load, gear ratio, chain falls, and efficiency to see required hand-chain pull and load sharing in the duplex hoist.
Equation Used
The load is converted to pounds-force, then divided by the gear ratio, number of supporting chain falls, and overall efficiency. The default 1 ton load, 2 falls, 20:1 gear ratio, and 50% efficiency reproduce the article statement that about 100 lbf on the hand chain lifts a 1-ton Yale Duplex block.
- Load is treated as a static vertical lift.
- 1 US short ton equals 2000 lbf.
- Load is shared equally by the supporting chain falls.
- Brake and gear friction are represented by one efficiency factor.
The Yale Duplex Hoist in Action
Pull the hand chain on a Yale Duplex Hoist and you are turning a small hand-chain wheel that drives a pinion through a reduction gear set, which then turns a load sheave that the load chain wraps around. Because the load chain is reeved as two falls — that is where the word duplex comes from — the load is split between two chain legs, doubling the mechanical advantage you already get from the gear reduction. Pull about 100 lbs on the hand chain on a 1-ton block and you can lift the full ton, because the combined ratio sits around 40:1 to 50:1 once you account for friction in the load brake.
The self-sustaining behaviour is the part that matters on the shop floor. Between the pinion and the load sheave sits a Weston-style load brake — two friction discs sandwiching a ratchet wheel, with a duplex pawl arrangement holding that ratchet against reverse rotation. When you stop pulling, the load tries to back-drive the gear train, the friction discs clamp tighter against the ratchet, and the two pawls (the reason it is called duplex) prevent the ratchet from spinning backwards. The load hangs. Release the hand chain in the lowering direction and you are slipping the friction discs in a controlled way against the held ratchet, which is why a Yale Duplex lowers smoothly instead of in jerks.
Get the tolerances wrong and the hoist becomes dangerous fast. The friction disc faces must stay clean and dry — a drop of oil between them and the ratchet drops holding capacity by half, and the load creeps. The pawl springs must hold the pawls fully seated; a weak spring lets a pawl skip a tooth under shock load and the ratchet jumps. Load chain pitch on a 1-ton Yale Duplex is typically 9.5 mm — wear past 10.0 mm and the chain no longer seats properly in the load sheave pockets, and you get chain jump under load. Those three failure modes — oiled brake faces, weak pawl springs, stretched load chain — cause the majority of incidents on this style of hoist.
Key Components
- Hand Chain Wheel: The wheel the operator pulls. Typically 150-200 mm pitch diameter on a 1-ton unit, with shaped pockets that capture each link of the hand chain. Hand pull of roughly 65-85 lbs lifts the rated load on most Duplex sizes.
- Reduction Gear Train: A spur gear set, usually single-stage 5:1 to 8:1 between the hand-chain pinion and the load sheave shaft. Multiplies the operator's pull and slows the lift speed to a controllable rate, typically 0.3 to 0.5 m/min at full hand-chain speed.
- Load Sheave (Pocket Wheel): The grooved wheel the load chain wraps around. Pockets are machined to a specific chain pitch — 9.5 mm pitch for a typical 1-ton block — and any deviation greater than ±0.2 mm causes the chain to ride high in the pocket and skip under load.
- Duplex Pawl and Ratchet: Two spring-loaded pawls engaging a single ratchet wheel. Two pawls instead of one give redundancy — if one pawl misses a tooth on a sudden load drop, the second pawl catches within half a tooth pitch, limiting load drop to under 5 mm in most designs.
- Weston Friction Brake: Two friction discs, often bronze or asbestos-substitute composite faced, that clamp the ratchet wheel between them. The brake is screw-actuated by the pinion shaft so that any back-driving torque from the load increases clamping force — the brake holds itself tighter the harder the load pulls.
- Load Chain: Calibrated alloy steel chain, typically Grade 80 or Grade 100 on modern units, with a stated pitch and link diameter. A 1-ton block uses 6 mm Grade 80 chain at 9.5 mm pitch. Replace the chain when any link reaches 110% of its original pitch length.
- Top and Bottom Hooks: Forged alloy steel hooks fitted with safety latches. The bottom hook block houses the lower load-chain sheave that creates the second fall. Hook throat opening must be measured at every inspection — a 15% increase over the original opening means the hook has yielded and the hoist must be removed from service.
Where the Yale Duplex Hoist Is Used
Yale Duplex Hoists found their home wherever a fixed crane was overkill but a person needed to lift hundreds or thousands of pounds repeatedly and hold the load in place hands-free. The duplex pawl made them the default choice for industries where a slipping load was unacceptable — mill maintenance, railway shops, foundry pattern handling, theatre rigging. You still see original Yale & Towne units from the 1920s in service today, alongside modern Yale, CM, and Harrington equivalents that use the same Weston-brake duplex-pawl architecture.
- Steel Mill Maintenance: Pulling roll-stand bearing housings on a Morgan rod mill — a 2-ton Yale Duplex hung from a monorail trolley lifts the housing clear so a millwright can change bearings.
- Railway Locomotive Shops: Lifting brake rigging and traction motor support bearings during periodic inspection on EMD SD40-2 locomotives at heritage railroad shops like Steamtown NHS in Scranton.
- Foundry Pattern Handling: Hoisting wooden match-plate patterns weighing 800-1500 lbs into position over a Disamatic moulding line — the self-sustaining brake holds the pattern while a rigger aligns the dowel pins.
- Theatrical Rigging: Spot-rigging chain motors and counterweighted scenery on Broadway-house fly systems where a hand-chain hoist serves as the failsafe holding device above an automated CM Lodestar.
- Shipyard Outfitting: Positioning auxiliary pumps and small diesel gensets into engine room spaces on tugboats at shipyards like Diversified Marine in Portland — the hoist holds the unit while crew bolts it down.
- HVAC and Building Services: Lowering a 1500-lb chiller compressor through a roof hatch during a mechanical retrofit — riggers hang the Duplex from a temporary I-beam and pay out chain a foot at a time.
The Formula Behind the Yale Duplex Hoist
The pull a worker must exert on the hand chain to lift a given load is the headline number on any chain hoist spec sheet. At the low end of typical operating range — a 250 lb test load on a 1-ton hoist — the operator barely feels the chain. At nominal rated load, hand pull sits in the 65-85 lbf range, which is what the Yale catalogue specifies as a sustainable two-handed pull for an average worker. Push past rated load and hand pull climbs sharply because friction in the brake and gears is non-linear; at 150% rated load a 1-ton Duplex demands close to 130 lbf, which most operators cannot sustain — and that is the design intent, because exceeding rated load should feel wrong.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Fhand | Force applied to hand chain by operator | N | lbf |
| W | Load suspended from bottom hook | N | lbf |
| Dload | Pitch diameter of load sheave | m | in |
| nfalls | Number of load chain falls (2 for a Duplex) | — | — |
| igear | Reduction ratio of gear train | — | — |
| Dhand | Pitch diameter of hand chain wheel | m | in |
| η | Overall mechanical efficiency (gear + brake friction losses) | — | — |
Worked Example: Yale Duplex Hoist in a paper mill maintenance crew lifting a press roll bearing housing
A paper mill maintenance team in Kalamazoo Michigan is changing the journal bearings on a Voith press roll. The bearing housing weighs 1800 lbs and they are hanging a 1-ton Yale Duplex Hand Chain Block from the overhead crane runway as a precision lowering tool. They want to know what hand-chain pull the millwright will feel at rated load, and how that changes if they are pulling the slack 400 lbs starter housing versus the full 1800 lbs production housing.
Given
- Wnom = 1800 lbf
- Dload = 4.0 in
- Dhand = 7.0 in
- nfalls = 2 —
- igear = 6.5 —
- η = 0.75 —
Solution
Step 1 — compute the overall mechanical advantage of the Duplex at nominal efficiency:
Step 2 — solve hand-chain pull at the nominal 1800 lb production load:
That is right at the upper edge of what an average worker can sustain two-handed. The millwright will feel real strain on each pull but can complete the lift without help. The Yale catalogue lists ~85 lbf for this size unit, and the gap is exactly why you should never assume catalogue numbers — the η you actually have on a 40-year-old hoist is rarely the η it left the factory with.
Step 3 — at the low end of the operating range, the 400 lb starter housing:
Almost nothing. The millwright pulls the chain one-handed and the housing rises quickly. This is the regime where operators tend to get sloppy — fast lifts, no spotter, hand chain running through fingers. Most chain-pinch injuries on Duplex hoists happen here, not at rated load.
Step 4 — at the high end of practical operation, an off-spec 2700 lb lift (50% over rated, which you should not do but operators do):
No worker sustains 158 lbf two-handed on a hand chain. The operator stalls, the load hangs on the brake, and they typically try to step on the chain or get a second person on the pull. This is the regime where the Weston brake is being asked to hold a load it was tested for but not rated for, and brake-disc glazing accelerates with every overload event.
Result
The millwright will pull about 105 lbf on the hand chain to lift the 1800 lb bearing housing — heavy work but doable. At the 400 lb low end the pull drops to 23 lbf and the lift feels almost effortless, while a 50% overload pushes hand pull to 158 lbf which no operator can hold steady, so the practical sweet spot is the 60-90% rated-load band where pull sits between 60 and 95 lbf. If the measured hand pull comes in 30% higher than the 105 lbf prediction, check three things in order: (1) gummed grease in the gear train pushing η below 0.6, common on units that have sat unused for years; (2) a partially seized load-chain pocket on the bottom block sheave, which adds drag at every link transition; (3) a hand chain running off-pocket on the upper wheel because the chain stripper is bent — this is the failure that makes the hand chain feel notchy on every pull.
When to Use a Yale Duplex Hoist and When Not To
A Yale Duplex Hoist competes with two other lifting tools in the same load class. The differential chain hoist (the Weston block, often called a chain fall) and the lever-operated ratchet hoist (the come-along) both move similar loads but differ on the dimensions a rigger actually cares about — speed, headroom, holding behaviour, and cost.
| Property | Yale Duplex Hand Chain Hoist | Differential (Weston) Chain Block | Lever Ratchet Hoist (Come-Along) |
|---|---|---|---|
| Typical load capacity | 0.25 to 5 tons | 0.5 to 3 tons | 0.75 to 9 tons |
| Lift speed at rated load | 0.3-0.5 m/min | 0.1-0.2 m/min | 0.05-0.1 m/min |
| Hand pull at rated load | 65-105 lbf two-handed | 75-95 lbf two-handed | 60-85 lbf single-arm lever |
| Self-sustaining when released | Yes — duplex pawl + Weston brake | Yes — high friction inherent in differential | Yes — pawl ratchet only |
| Headroom required | Moderate (350-450 mm) | Large (450-600 mm) | Compact (250-350 mm) |
| Mechanical advantage | 30:1 to 50:1 | 20:1 to 35:1 | 40:1 to 80:1 |
| Suited application | Repeated overhead lifts at fixed station | Slow precision lifts, low-cost installations | Pulling, tensioning, short-lift rigging jobs |
| Relative purchase cost (1-ton) | $$$ (highest) | $ (lowest) | $$ (middle) |
| Inspection interval (industrial use) | Quarterly + annual load test | Annual + visual before each shift | Quarterly + annual load test |
Frequently Asked Questions About Yale Duplex Hoist
The pawls only stop reverse rotation of the ratchet wheel — they do not, on their own, hold the load. The Weston friction discs do that. If oil, grease, or solvent residue gets between the friction faces and the ratchet wheel, the discs slip even though the pawls are seated, and the load drifts down at a steady rate.
Pull the hoist out of service, dismantle the brake cover, and degrease both friction faces and the ratchet wheel with brake cleaner. Never lubricate the brake assembly. The gear train gets grease, the brake stays bone dry — that distinction kills more loads than any other single mistake on this style of hoist.
80 cycles per shift is the threshold where hand-chain hoists stop making economic sense. A Yale Duplex is rated for occasional duty — class H1 or H2 in CMAA terms — and the Weston brake heat-soaks if you cycle it more than about 30 lifts per hour. The friction discs glaze, holding capacity drops, and you start re-facing brake parts every six months.
For 80 cycles per shift go to an electric chain hoist with a mechanical load brake plus motor brake — a CM Lodestar or Harrington NER class. Keep the Duplex as the backup or for the off-station lifts that do not justify running power.
This is almost always the hand-chain stripper or the hand-wheel pockets. The stripper is a curved guide that peels each link off the hand wheel as it leaves the pocket — if it bends inward by even 1-2 mm from a side impact, every link drags as it exits and you feel a pulse on every pull.
Less commonly, the hand-wheel pockets themselves have worn unevenly, usually because someone has been pulling on the chain at a sharp angle to the wheel for years. Run a finger around each pocket — if one feels noticeably deeper than the others, the wheel is done and the only fix is replacement.
Retire the load chain when any link reaches 110% of its original pitch — typically 10.45 mm on a chain that started at 9.5 mm. Yale and every other reputable maker specify pitch per link rather than overall length because chain stretches non-uniformly. The links that ran through the load sheave under shock load stretch first; the links that lived in the chain bag never see load and stay at original pitch.
Measure 11 consecutive links pin-to-pin and divide by 10 — that gives you average pitch. Then check three or four individual links with calipers to catch local stretch. One stretched link will jump out of the load-sheave pocket and that is when chains break.
In theory no, in practice sometimes yes. The duplex pawls are timed so that when one pawl is mid-tooth the other is fully seated — that is the whole point of having two. If one pawl spring fails completely the surviving pawl still catches, and you lose at most half a tooth of drop, around 2-4 mm.
The dangerous failure is when both pawl springs are weak but not failed. Under shock loading both pawls bounce off the ratchet face for a fraction of a second and the load drops several teeth before something catches. Replace pawl springs in pairs at every annual inspection — they are cheap, and matched spring rates are what makes the duplex action work as advertised.
No. The Weston brake relies on gravity to keep the friction discs aligned and the pawls resting against the ratchet teeth in a known orientation. Run the hoist on its side and the pawls hang off the ratchet by gravity rather than into it, and the brake-disc clearance changes. Yale and every other manufacturer rate these hoists for vertical lift only.
For horizontal pulling use a lever ratchet hoist — a come-along — which has positive pawl engagement that does not depend on orientation. That is one of the few jobs where the come-along genuinely outperforms a chain block.
Probably not failing, but it is no longer at factory efficiency. New hoists test at η ≈ 0.85, and a 20-year-old hoist with original gear grease and partially glazed brake discs typically runs at η ≈ 0.65-0.70. That alone explains a 30-50% increase in hand pull.
Pull the gear cover, clean out the old grease (often dried to the consistency of wax), repack with a moly-EP grease, and re-test. If hand pull drops back toward catalogue, you have just bought another decade. If it does not, the load sheave bushings are likely the culprit — they wear axially and add drag that no amount of grease fixes.
References & Further Reading
- Wikipedia contributors. Hoist (device). Wikipedia
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