Gear Pump

medium 230 / 230 models (Inspector)

A gear pump is a positive-displacement pump that moves a fixed volume of liquid per revolution between meshing gear teeth and the casing wall, giving it a steady flow largely independent of discharge pressure, unlike a centrifugal pump whose output falls as head rises.

What sets a gear pump apart

A gear pump traps liquid in the pockets formed between meshing gear teeth and the pump casing, then carries it around to the discharge side, where the meshing teeth force it out. Because each revolution displaces a fixed volume, flow stays close to constant regardless of discharge pressure, which is exactly why gear pumps are chosen for fuel and lubricating oil duties where a steady, self-priming flow matters more than the high volumes a centrifugal pump can deliver. Unlike a screw pump, which handles higher viscosity and larger flows more smoothly, a gear pump is simpler, cheaper to overhaul, and well suited to smaller transfer and circulating duties.

Gear pump operating principle — Cross-section of a gear pump showing the driving and driven gears meshing inside the casing, the suction and discharge ports, and the path fluid takes trapped between the gear teeth and the casing wall.

Main components

Drive and idler gears

One shaft is driven directly by the motor; the second, the idler, meshes with it and rotates in the opposite direction. Tooth profile and clearance to the casing set both the pump's volumetric efficiency and its tolerance for entrained solids.

Casing and wear plates

The casing bore is machined close to the gear tip diameter to minimise internal slip; wear plates at each end control axial clearance and are usually the first parts to need renewal.

Relief valve

Because a gear pump is positive displacement, it will build pressure indefinitely against a closed discharge valve unless a relief valve, either built into the pump or fitted in the line, bypasses flow back to suction.

Shaft seals

Mechanical seals or packed glands seal the drive shaft where it passes through the casing; the seal choice depends on the liquid handled, since fuel and lubricating oil demand different seal face materials.

Selection and sizing

Sizing follows the required flow rate at the pump's rated speed, the viscosity of the liquid at its lowest expected operating temperature, and the differential pressure the pump must work against. Viscosity matters more for gear pumps than for centrifugal types: a pump sized for warm fuel oil can struggle to prime and can cavitate on cold, more viscous fuel unless clearances and speed are chosen with that condition in mind.

Typical faults

Fault	Consequence
Worn wear plates or increased tip clearance	Falling volumetric efficiency, reduced delivered flow at rated speed
Relief valve stuck closed	Pressure runs away against a closed or blocked discharge, risking pipe or seal failure
Relief valve stuck open or set too low	Continuous internal bypass, pump appears to run but delivers little useful flow
Shaft seal wear	External leakage of fuel or lubricating oil around the drive shaft
Entrained solids scoring the gear teeth	Increased internal slip and eventual tooth or bearing failure

What to look for in a supplier

Rated flow and pressure curve at the actual viscosity and temperature the pump will see in service
Gear and casing materials suited to the specific fuel or oil grade, including any additive packages
Seal type matched to the liquid and to the crew's realistic maintenance interval
Relief valve setting matched to the downstream pipework's safe working pressure
Spare gear sets and wear plates held for the exact model and size fitted

Warm heavy fuel oil to its specified viscosity before starting a gear pump on that duty; running it cold against high internal friction is a common cause of premature gear and bearing wear.

Technical drawings & plates

Historical engineering archive — public domain sources, cited per plate. Principles shown remain valid; always consult the OEM manual for model-specific data.

Schutte and Koerting gear pump.
Diesel Engine Maintenance Training Manual, Bureau of Ships, U.S. Navy (1946) — public domain

Action of simple gear pump.
Engineman 2, NAVPERS 10540, U.S. Navy (1957) — public domain

Sectional view of herringbone gear pump.
Engineman 2, NAVPERS 10540, U.S. Navy (1957) — public domain

Herringbone gear pump.
Machinist's Mate 3, NAVPERS 10522, U.S. Navy (1958) — public domain

Inspector Mode Show All 230 / 230 with inspector value

8 manufacturers · 230 models

Kracht

51 ✓ 51 verified

KP 1/3 ✓ verified

Application

Marine gearbox and propeller lubrication, CPP

Common Failures & Inspection Points

Area: Bearing wear and tooth profile degradation affecting CPP reliability
Check: Visual inspection of journal bearings, bearing bushes, and gear tooth surfaces for scoring, pitting, and wear patterns. Measure clearances with dial indicators.
Area: Seal leakage compromising marine hydraulic system integrity
Check: Hydrostatic test at 1.5x operating pressure to detect O-ring and shaft seal degradation. Check for oil seepage at all wetted interfaces.
Area: Pressure regulation failure under marine duty cycle (peak transients from propeller operation)
Check: Pressure relief valve bench-test at rated displacement and validate against nameplate maximum pressure specifications for the KP/KF series.
Area: Thermal degradation of hydraulic oil at sustained operating temperatures
Check: Measure viscosity stability at 40°C and 100°C per ISO 3055 using samples from circulation tests. Verify oil type meets DIN 51524 Part 2/3.
Area: Acoustic and vibration emissions exceeding ship noise regulations (IMO MARPOL Annex VI)
Check: Run pump at rated displacement and speed, measure sound pressure level at 1m and analyze vibration spectrum using accelerometers. Compare against marine noise class limits.

Typ-universelle Inspektionspunkte fuer Pumps (verifiziert, 2026-06).

Gear Pump

What sets a gear pump apart

Main components

Drive and idler gears

Casing and wear plates

Relief valve

Shaft seals

Selection and sizing

Typical faults

What to look for in a supplier

Technical drawings & plates

8 manufacturers · 230 models

Kracht

Bornemann

Viking Pump

IMO

Marzocchi Pompe

IMO/Colfax

DESMI

Speck Pumpen