Cylindrical Gear Reducer Selection: ZDY/DBY Stages, Cooling

A cylindrical gear reducer built to Chinese national standards is, in our range, a ZDY / DBY series unit: hardened-tooth cylindrical and bevel-cylindrical gear reducers in five type variants, 13 ZDY and 17 ZLY frame sizes, with nominal input powers in the ZDY table from about 5 kW to about 6,666 kW at input speeds of 750, 1,000 or 1,500 r/min. Two things make this family a different selection job from the rest of our range. Its main parameters — centre distance and nominal ratio — are optimised at the design stage and its principal parts are interchangeable, which is what shortens delivery. And the catalogue rates it by nominal input power rather than output torque, so the selection runs on power and a thermal check rather than on a torque table. This guide takes the variant, the designation, the frame size and the cooling condition in that order. Which family of reducer you need in the first place is a different question, answered in our gear reducer selection guide.

Key definitions

• Cylindrical gear stage: a mesh between two cylindrical gears on parallel axes. Stack one, two or three of them and you have the YFZDY, YFZLY and YFZSY types.
• Bevel-cylindrical: a bevel stage followed by cylindrical stages, so the input shaft sits at 90 degrees to the output. The YFDBY and YFDCY types.
• Hardened tooth surface: gears in premium alloy steel, carburised, quenched and precision ground, giving high accuracy, large load capacity, high efficiency, long service life, smooth running and low noise.
• Centre height: the height from the mounting plane to the final-stage shaft axis, in millimetres. It is the size field in this family's designation, where the H/B series carries a frame number instead.
• Nominal ratio: the catalogue ratio, taken from the ratio list rather than calculated. It is rarely exactly the ratio you worked out.
• Nominal input power: the power the catalogue rates a size and ratio at, for a stated input speed. It is how this family is rated; the catalogue prints no output torque figure for it.
• Interchangeable main parts: principal components common across the range rather than made per order, which is the design decision behind the shorter delivery time the catalogue claims.
• Thermal capacity: the power the unit can shed as heat continuously, published here as PG1 and PG2 for two cooling conditions. A second limit alongside mechanical strength.

Where the ZDY/DBY series sits

Above the geared-motor range there are three answers in our catalogue, and they are not interchangeable.

Series	Transmission	Sizes	Rated by	Ratio	Output torque in the catalogue
H/B	modular helical (YFH) or bevel-helical (YFB), 1–4 stages	22 (1–22)	motor power 2.52–5,366 kW	1.25–450, assembled from per-type tables	up to 470,000 N·m
ZDY / DBY	cylindrical or bevel-cylindrical, 1–3 stages, national standards	ZDY 80–560 (13), ZLY 112–710 (17)	nominal input power approx. 5–6,666 kW (ZDY table)	1.25–100 cylindrical; 8–50 bevel-cylindrical	none printed; rated by nominal input power
P	planetary, 2–3 stages	9–36	0.4–1,293 kW	output speed 0.19–60 r/min	up to 2,600,000 N·m

Read two boundaries off that table before anything else.

Against the H/B series, the decision is contractual as much as mechanical. Both families use carburised, quenched and precision-ground hardened gears, and both cover the heavy-industrial band. The H/B series is a modular unit structure in which stages, output shaft, mounting and cooling are four separate options against one frame number, and it is specified in our H/B series selection guide. The ZDY/DBY series is the national-standard answer: optimised centre distance, optimised nominal ratio, interchangeable main parts. If the specification names a national standard, or if the plant wants a unit whose main parts it can obtain as replacements, that is the deciding argument and the torque comparison never happens.

Against the P series, the decision is output speed. Below 60 r/min a stacked cylindrical train runs out of ratio before it runs out of housing, and the planetary family is the right machine — see our planetary speed reducer guide. Three cylindrical stages reach a nominal ratio of 100 and three bevel-cylindrical stages reach 50; a drive needing more than that in one unit is not a ZDY/DBY drive. All nine series are compared side by side in our industrial gear reducer round-up.

The five type variants

Variant	Structure	Stages	Nominal ratio
YFZDY	parallel-shaft cylindrical	1	1.25–6.3
YFZLY	parallel-shaft cylindrical	2	6.3–20
YFZSY	parallel-shaft cylindrical	3	22.4–100
YFDBY	right-angle bevel-cylindrical	2	8–14
YFDCY	right-angle bevel-cylindrical	3	16–50

The layout drawing picks the structure and the required ratio picks the stage count, and the bands barely overlap: 6.3 is the only number shared between the single and two-stage cylindrical types, and the two bevel-cylindrical bands are separated by two points. In practice the ratio alone names the variant for most drives. Every variant has a K hollow-shaft version — ZDY-K, ZLY-K, ZSY-K, DBYK, DCYK — and KD denotes a hollow shaft with shrink disc. Forward and reverse rotation and four mounting arrangements are available across the family.

Reading the designation field by field

The printed pattern is YFD B Y K 160 14 III S:

Field	In the example	What it fixes
Type	YFD	right-angle bevel-cylindrical; YFZ for the parallel-shaft cylindrical types
Number of stages	B	the stage code; read with the first and third fields it spells the variant, here YFDBY
Hardened tooth	Y	hardened tooth surface
Output shaft	K	hollow shaft; KD hollow shaft with shrink disc; absent for a keyed solid shaft
Final-stage centre height	160	the size field of this family, in millimetres
Nominal ratio	14	the catalogue ratio, not the calculated one
Assembly design	III	installation pattern I to IV, from the pattern table
Input rotation	S	clockwise; N counter-clockwise

The fifth field is the one to notice. This family is sized by a final-stage centre height; the H/B series is sized by a frame number. Two units of equivalent duty from the two families therefore carry size fields that cannot be compared by eye, and an enquiry that quotes one number without naming its family is ambiguous. State the series, not just the size.

Frame sizes, input speed and nominal input power

Structure	Frame sizes as printed	Count
ZDY, single-stage cylindrical	80, 100, 125, 160, 200, 250, 280, 315, 355, 400, 450, 500, 560	13
ZLY, two-stage cylindrical	112, 125, 140, 160, 180, 200, 224, 250, 280, 315, 355, 400, 450, 500, 560, 630, 710	17

The ratio tables are built around nominal input speeds of 750, 1,000 and 1,500 r/min, and the rating moves with all three of size, ratio and input speed at once:

Table	Nominal input power
ZDY, Table 1	approx. 5 kW (size 80, high ratio, 750 r/min) to approx. 6,666 kW (size 560, ratio 3.15, 1,500 r/min)
ZLY, Table 3	approx. 6.8 kW (size 112, ratio 20, 750 r/min) to approx. 6,229 kW (size 710, ratio 6.3, 1,000 r/min)

Those two rows carry a warning worth reading twice. The top of the ZDY range sits at a low ratio of 3.15 and the highest input speed, and the bottom of it sits at a high ratio and the lowest input speed. Power capacity in this family is not a property of the frame size on its own. Quoting a size without the ratio and the input speed does not identify a rating. The nominal ratios the tables actually offer are 1.25, 1.4, 1.6, 1.8, 2, 2.24, 2.5, 2.8, 3.15, 3.55, 4, 4.5, 5, 5.6 and 6.3 for ZDY and 6.3, 7.1, 8, 9, 10, 11.2, 12.5, 14, 16, 18 and 20 for ZLY, and the designation carries one of those, not your calculated figure.

The thermal check, and why it decides the order

Oil-bath splash lubrication is the standard arrangement on this family. For special duty a fan, a cooling coil or an oil-pump circulation system can be fitted, and the catalogue publishes the reducer's thermal power separately for each cooling condition. For the ZDY sizes the two published conditions are:

Cooling condition	Catalogue designation	Thermal capacity, sizes 80–560
No cooling measures	PG1	13–1,020 kW
Cooling coil or circulating lubrication	PG2	43–1,780 kW

Both ranges depend on the size and on the ambient air velocity, for which the tables give three conditions: at least 0.5, 1.4 and 3.7 m/s. That is the single most consequential pair of figures in this series. Fitting a coil or a circulation system moves the ceiling from 1,020 kW to 1,780 kW at the top of the range — close to a doubling of the rating from cooling hardware alone, with no mechanical number changed. The practical consequence is an order of operations: if the absorbed power is above the PG1 figure for your size, add cooling before you consider a larger frame.

The ambient air velocity matters as much as the hardware and is the input most often left out of an enquiry. A unit in a closed, still gearhouse and the same unit outdoors in moving air are two different ratings. Where the unit will stand, and whether anything is blowing past it, belongs on the enquiry alongside the power.

Selecting a ZDY/DBY unit, step by step

1. State the duty: absorbed power at the driven machine, input speed, required output speed or ratio, load character, starts per hour, and the direction of rotation.
2. Pick the structure from the layout — parallel-shaft cylindrical (YFZ) or right-angle bevel-cylindrical (YFD).
3. Take the stage count from the required ratio: 1.25–6.3, 6.3–20 or 22.4–100 for cylindrical; 8–14 or 16–50 for bevel-cylindrical.
4. Apply the service factors for the driven machine, the prime mover and the starting condition, as set out in our selection guide, to arrive at the power the unit must be rated for.
5. Find a size and nominal ratio whose nominal input power at your input speed covers that figure — size, ratio and input speed are read together, never separately.
6. Confirm the nominal ratio on offer and the output speed it actually gives you, which will differ from your calculated ratio.
7. Run the thermal check against the cooling condition and the ambient air velocity you will really have. If PG1 is short, specify a fan, a coil or oil-pump circulation.
8. Fix the rest of the scope: solid or hollow output shaft (K, or KD with shrink disc), the assembly design I to IV, and input rotation S or N.

Our recommendation

Specify ZDY/DBY when the standard matters, and H/B when the configuration matters. Those are the two reasons to choose between families that use the same hardened gears for the same kind of drive. A national-standard unit with an optimised centre distance and interchangeable main parts is the right answer for a plant that specifies to a standard, holds its own spares, or expects to replace a unit years from now; the modular H/B range is the right answer when you want stages, shaft, mounting and cooling chosen independently against one frame number. Below 60 r/min output, neither is the answer and the planetary series is.

Then treat two things as selection inputs rather than afterthoughts. The input speed, because 750, 1,000 and 1,500 r/min give materially different ratings from the same size. And the cooling condition together with the ambient air velocity, because they move the thermal ceiling by roughly a factor of two and are the cheapest capacity on the page.

What our published data does not give, and we will not invent. The catalogue prints no output torque figure for this family — it is rated by nominal input power, and any torque number for a ZDY/DBY unit has to come from us against your duty rather than from a table. It also prints no oil grades, viscosities, fill volumes or change intervals for these sizes, no efficiency percentages, no unit weights and no bearing-life figures, and we publish no prices, lead times or delivery terms. For the general maintenance regime across our reducers, read our gear reducer maintenance guide; for a belt conveyor specifically, our conveyor gearbox selection guide sizes the drive from belt speed and drum diameter before it reaches a series name.

Send the absorbed power, input and output speeds, load character, starts per hour, the layout, the mounting arrangement and where the unit will stand — including the air movement around it — through the enquiry form. Our Reducer Sales department and engineers return a structure, a frame size, a nominal ratio, a complete type designation, the nominal input power against it, the thermal rating for your cooling condition and a dimension drawing; the ZDY series catalogue and every other series catalogue are on the gear reducers pages. Yanfeng Group Co., Ltd. has designed and built gear reducers and plastic weaving machinery in Pingyang, Wenzhou since 1987. Office hours are Monday to Saturday 08:00–17:30 and Sunday 09:00–17:30, China Standard Time (UTC+8).