What to check on a Gear Pump.
32 models from Viking Pump in Gear Pump. Below: the full model list.
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.
Legend
- Discharge (outlet)
- Casing
- Driving shaft
- Gears mesh here
- Driving gear
- Driven gear
- Fluid carried around the casing wall
- Suction (inlet)
Read the full guide
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.