{"id":2010,"date":"2026-07-22T07:34:48","date_gmt":"2026-07-22T07:34:48","guid":{"rendered":"https:\/\/gearrack.top\/?p=2010"},"modified":"2026-07-22T07:37:56","modified_gmt":"2026-07-22T07:37:56","slug":"spur-gears-for-pump-drives","status":"publish","type":"post","link":"https:\/\/gearrack.top\/ko\/spur-gears-for-pump-drives\/","title":{"rendered":"Spur Gears for Pump Drives"},"content":{"rendered":"
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GEAR APPLICATION GUIDE \u00b7 SPUR GEAR \u00b7 S10<\/span><\/p>\n

Spur Gears for Pump Drives:
\nCentrifugal Pumps, Gear Pumps and Hydraulic Pump Auxiliaries<\/span><\/h1>\n

Pump drive spur gears serve a deceptively simple purpose \u2014 transmitting motor torque to the pump shaft at the correct speed ratio \u2014 yet they operate under conditions that challenge many standard gear designs: centrifugal pump drives must cope with the full motor starting torque (which can be 5\u20137\u00d7 the rated running torque for a direct-on-line started motor), gear pump internals must meet the dimensional tolerances of the pump body to maintain the correct tip clearance that controls the pump’s internal leakage, and hydraulic pump auxiliary drives on mobile equipment must sustain the shock loads and vibration from the vehicle powertrain while maintaining hydraulic pressure for the implement circuit. This guide covers spur gear specification for all three pump drive contexts across water infrastructure, oil and gas, chemical process, and mobile hydraulics.<\/p>\n

42CrMo4 \u00b7 20CrMnTi \u00b7 316L \u00b7 M3\u2013M16 \u00b7 DIN 6\u20138<\/span>
\nStarting Torque KS 1.5\u20132.5 \u00b7 Tip Clearance \u00b10.05mm<\/span>
\nCentrifugal \u00b7 Gear Pump \u00b7 Hydraulic \u00b7 ATEX<\/span><\/div>\n<\/div>\n<\/div>\n
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MODULE RANGE<\/p>\n

M3 \u2013 M16<\/p>\n

Pump drive spur gear module range. Gear pump internal rotors: M3\u2013M6 (tight tolerance, tip clearance critical). Centrifugal pump parallel-shaft drive: M5\u2013M10. Large centrifugal booster pump drive (desalination, water supply): M10\u2013M16. Mobile hydraulic PTO gear drive: M4\u2013M8. Each application has different tolerance and material priority<\/p>\n<\/div>\n

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STARTING FACTOR<\/p>\n

KS 1.5 \u2013 2.5<\/p>\n

Starting torque application factor for centrifugal pump drive spur gears. Direct-on-line (DOL) motor start: KS = 2.0\u20132.5 (peak motor starting torque 5\u20137\u00d7 rated; gear sees 2\u20132.5\u00d7 rated for duration of acceleration). Star-delta or VFD start: KS = 1.5\u20131.8. The spur gear must sustain the starting torque without tooth fracture for 10,000+ starts over the pump’s design life<\/p>\n<\/div>\n

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GEAR PUMP CLEARANCE<\/p>\n

\u00b10.05 mm<\/p>\n

Tip clearance tolerance between the gear pump rotor OD and the pump body bore. Internal gear pump and external gear pump both require this clearance to be maintained within \u00b10.05 mm of the design value \u2014 too large and the pump loses volumetric efficiency (internal leakage increases), too small and the rotor contacts the body under thermal expansion at operating temperature<\/p>\n<\/div>\n

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ATEX OPTION<\/p>\n

Zone 1 \/ 2<\/p>\n

Pump drive spur gears for ATEX Zone 1 (explosive gas atmosphere present continuously or frequently) and Zone 2 (explosive atmosphere present occasionally) applications \u2014 chemical process pumps, LNG, refinery. ATEX requirements: non-sparking materials (bronze or aluminium for exposed gears), maximum surface temperature below auto-ignition temp, and enclosed gear drive without potential ignition sources<\/p>\n<\/div>\n<\/div>\n

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Pump Drive Spur Gear Engineering \u2014 Three Applications, Three Design Priorities<\/h2>\n

The spur gear appears in three functionally distinct pump drive contexts, each demanding a different engineering priority. In the centrifugal pump parallel-shaft drive (where the motor and pump have non-coaxial shafts and a spur gear pair bridges the speed ratio and axis offset), the priority is fatigue life under the cyclically variable torque of centrifugal pump operation \u2014 the pump torque varies as the square of the flow rate, which itself varies as the pump operates across different points on its head-flow characteristic curve as system demand changes. In the internal gear pump (where the spur gear IS the pump element \u2014 a cycloidal or involute internal rotor pair that traps fluid between the teeth and the pump body), the priority is dimensional accuracy of the rotor to body clearance, which directly controls the volumetric efficiency. In the mobile hydraulic PTO pump drive (where a spur gear on the power take-off shaft drives a hydraulic gear pump for excavator implements, tractor loaders, or truck-mounted cranes), the priority is shock and impact resistance from the engine torque pulses and implement load reversals.<\/p>\n

Korea Ever-Power’s spur gears for pump drives<\/a> are manufactured across all three contexts \u2014 42CrMo4 QT and 20CrMnTi carburized for centrifugal pump parallel-shaft drives and mobile hydraulic PTO pump drives, grey cast iron (GGG50) and 316L stainless for internal gear pump rotors in water, chemical, and food service, and non-sparking bronze CuSn8 for ATEX Zone 1 and Zone 2 pump drive applications. The production range covers M3 through M16 with quality class DIN 6 through DIN 8 depending on the application precision requirement \u2014 centrifugal pump drives at DIN 7\u20138 (where cost is the primary criterion and transmission error is not the design driver), gear pump rotors at DIN 6 (where the rotor OD accuracy directly affects volumetric efficiency), and speed-increasing pump drives (where the pump runs faster than the motor \u2014 common in booster pump sets) at DIN 6\u20137 for the higher pitch line velocity.<\/p>\n

\"gear-for-construction-industry\"<\/p>\n

The DOL (direct-on-line) motor start condition imposes a design challenge that is often underestimated in pump drive gear specifications. A 4-pole induction motor driving a centrifugal pump DOL draws 5\u20137\u00d7 its full-load current during starting and produces a peak torque of 2\u20133\u00d7 its rated torque at approximately 80% of synchronous speed during the acceleration transient. This starting torque peak is applied to the pump drive spur gears during every start event \u2014 which, in a water supply pump station with frequent demand cycles, may occur 20\u201350 times per day. Over a 20-year pump life, the spur gear accumulates 150,000\u2013365,000 starting torque cycles at 2\u20133\u00d7 rated torque \u2014 a significant fatigue loading that must be included in the service factor calculation alongside the normal running load fatigue. Korea Ever-Power uses a starting factor KS in the gear design service factor (SF = KA \u00d7 KS \u00d7 KH\u03b2 \u00d7 KH\u03b1 \u00d7 Kv) based on the motor starting method \u2014 KS = 2.5 for DOL, 1.8 for star-delta, and 1.5 for variable frequency drive (VFD) soft-start \u2014 to ensure the gear tooth bending fatigue safety factor S_F \u2265 1.5 at the peak starting torque condition as well as at the rated running condition.<\/p>\n

\"steel
Korea Ever-Power 42CrMo4 QT through-hardened spur gear for centrifugal pump parallel-shaft drive \u2014 M8, 38 teeth, OD 320 mm, face width 80 mm, HB 300\u2013340, DIN 7 quality class. Designed for direct-on-line motor start service (KS = 2.5), 500 kW motor rating, 1,470 RPM motor speed, 960 RPM pump speed (gear ratio 1.53:1). Bending fatigue safety factor S_F = 1.62 at starting torque (peak 2.5\u00d7 rated), S_F = 3.1 at rated running torque \u2014 the higher rated running margin confirms the gear is starting-torque-limited, not running-torque-limited, which is typical for DOL pump drives. The gear is supplied as a matched pair (pinion + wheel) with the pinion in 20CrMnTi case carburized (for higher fatigue resistance per the smaller pinion\u2019s higher stress concentration) and the wheel in 42CrMo4 QT \u2014 the differential hardness pair (HRC 58\u201362 pinion, HB 300\u2013340 wheel) promotes initial run-in contact pattern development and extends the paired gear set\u2019s life beyond an equivalent same-material pair.<\/figcaption><\/figure>\n<\/section>\n
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Pump Drive Application Specifications<\/h2>\n
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PUMP 01<\/p>\n

CENTRIFUGAL PUMP
\nPARALLEL DRIVE<\/p>\n<\/div>\n

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Spur gear specification:<\/strong> M5\u2013M14, differential hardness pair (20CrMnTi carburized pinion + 42CrMo4 QT wheel), DIN 7\u20138, starting factor KS per motor start method, centre distance held within \u00b10.05 mm for proper backlash. Centrifugal pumps \u2014 water supply and distribution, irrigation, cooling water, fire fighting, and process pumps \u2014 are the single largest pump category and produce the highest volume demand for pump drive spur gears. The parallel-shaft arrangement (motor shaft and pump shaft parallel, connected by a spur gear pair) is used when the motor speed does not match the pump speed, or when the motor and pump cannot be directly coupled due to the pump’s overhung impeller mass requiring the motor to be offset from the pump shaft centreline. Desalination plant booster pump drives in the 500 kW\u20135 MW power range use M10\u2013M16 spur gear pairs in 42CrMo4 or 20CrMnTi, with the gear set often the largest-cost single component in the pump station mechanical equipment. Korea Ever-Power desalination pump drive spur gears are specified with an enhanced corrosion inhibitor coating on all non-tooth machined surfaces (the bore, keyway, and side faces) to prevent surface rust from the humid coastal environment during transport and storage at the desalination plant site before commissioning.<\/p>\n<\/div>\n<\/div>\n

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PUMP 02<\/p>\n

EXTERNAL GEAR
\nPUMP ROTORS<\/p>\n<\/div>\n

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Spur gear specification:<\/strong> M3\u2013M6, hobbed and lapped (not profile ground \u2014 the lapping produces the smooth, matched rotor-to-rotor and rotor-to-body fit that controls volumetric efficiency), tip OD tolerance within \u00b10.02 mm of the pump body bore (to maintain the 0.05\u20130.15 mm tip clearance that is the primary volumetric efficiency parameter), face width matched pairs from the same production cut. External gear pumps (used for hydraulic oil transfer in mobile equipment, lube oil pumping in engines and compressors, chemical transfer in process plants, and fuel transfer) use a matched pair of spur gears as the pumping elements \u2014 fluid is trapped between the gear teeth and the pump body as the gears rotate outward from the mesh zone and transported around the periphery to the outlet port. The OD tolerance of the gear rotor is the most critical dimension \u2014 Korea Ever-Power gear pump rotors are ground to OD tolerance h5 (within 0.011 mm for M4 gears) and individually measured before pairing, with the matched pair’s tip clearance calculated and documented. Gear pump rotors are supplied in matched sets and are not interchangeable with rotors from different manufacturing batches, even of the same part number \u2014 the matched pairing is essential for the correct meshing noise and volumetric efficiency.<\/p>\n<\/div>\n<\/div>\n

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PUMP 03<\/p>\n

MOBILE HYDRAULIC
\nPTO PUMP DRIVE<\/p>\n<\/div>\n

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Spur gear specification:<\/strong> M4\u2013M8, 20CrMnTi carburized, DIN 7, shock factor KA = 1.5\u20132.0 (for agricultural tractor PTO: KA = 1.5; for truck-mounted hydraulic crane pump: KA = 2.0), sealed housing for dust and water ingress protection (IP54 minimum). Mobile hydraulic pump drives (the gear train between the vehicle engine or transmission PTO and the hydraulic gear pump that powers the implement circuit) are exposed to the most severe shock loading of any pump drive spur gear application. An agricultural tractor PTO pump drive experiences the rotary torque pulses of the diesel engine at combustion frequency \u2014 at 2,000 RPM with 4 cylinders, this is 67 Hz torque pulsation imposed on the PTO spur gears. An excavator hydraulic pump drive experiences the combined shock of engine torque pulses, track travel impacts, and the sudden pressure surges when the operator opens the implement control valve against the hydraulic system relief valve. Korea Ever-Power mobile hydraulic PTO pump drive spur gears are specified with root fillet radius at 0.3 \u00d7 module (larger than the standard 0.2 \u00d7 module) to reduce the stress concentration at the gear tooth root under these shock loads, improving impact fracture resistance at the expense of a slight reduction in the contact ratio and addendum tooth area.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

\"forged
Korea Ever-Power 20CrMnTi forged blank spur gear for mobile hydraulic PTO pump drive application \u2014 M6, 24 teeth, OD 156 mm, face width 60 mm, case carburized HRC 58\u201362, DIN 7 quality class, enlarged root fillet radius 1.8 mm (0.3 \u00d7 module vs standard 1.2 mm). Forged blank (not bar-machined): the forging process aligns the steel grain flow around the tooth profile, creating a fibre flow pattern that increases the tooth root impact fracture resistance by 20\u201330% vs a machined-from-bar gear of the same specification. The forging traceability (heat number, forge date, forging die number) is retained in Korea Ever-Power\u2019s production records for 5 years, enabling the failure analysis of any field-returned gear to be correlated with the specific melt and heat treatment batch. Korea Ever-Power forged pump drive spur gears are used as OEM replacements in Bosch Rexroth, Parker Hannifin, and Eaton Vickers hydraulic pump drive assemblies on agricultural tractors, excavators, and truck-mounted hydraulic equipment.<\/figcaption><\/figure>\n<\/section>\n
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ATEX Pump Drives and Special Environment Spur Gears<\/h2>\n

Chemical process plants, LNG terminals, petroleum refineries, and paint manufacturing facilities require pump drives that comply with ATEX Directive 2014\/34\/EU (or IECEx for non-EU markets) \u2014 the European regulation governing equipment intended for use in explosive atmospheres. The ATEX requirements that affect pump drive spur gears specifically are: (1) maximum surface temperature classification (T-class, ranging from T1 = 450\u00b0C maximum to T6 = 85\u00b0C maximum, determined by the auto-ignition temperature of the explosive gas or vapour present); (2) avoidance of electrostatic charge accumulation on non-conductive parts; (3) avoidance of sparking from gear tooth impact that could ignite the explosive atmosphere. Standard steel spur gears, when two teeth impact in the event of a tooth fracture or debris between the teeth, can produce metallic sparks at temperatures of 1,000\u20132,000\u00b0C \u2014 well above the ignition temperature of most flammable gases.<\/p>\n

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ATEX PUMP DRIVE SPUR GEAR \u2014 MATERIAL SELECTION BY ZONE<\/p>\n

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ZONE 1 (GAS ALWAYS PRESENT)<\/p>\n