KCB Gear Pump for Heavy Oil: How Viscosity and Temperature Drive Selection

Why Gear Pumps Are Used for Heavy Oil

Heavy fuel oil, a residual fuel burned in power plants, marine engines and industrial boilers, must be transferred while viscous but still liquid. Engineers commonly choose the KCB line of external gear pumps: meshing gears trap oil in the tooth spaces and squeeze it out as the teeth mesh, giving steady flow at the pressure the pipework demands.

The pumped oil itself is the seal between gears and casing, so gear pumps need clean, lubricating oil — abrasive solids or free water quickly erode the close-clearance parts.

Viscosity and Temperature Drive the Selection

Viscosity is the governing variable for a gear pump on heavy-oil duty. Thicker oil seals internal clearances and raises volumetric efficiency, but shaft power rises steeply with viscosity, and cold-start oil can be orders of magnitude thicker than at running temperature.

The medium-viscosity sweet spot

Most KCB-type duties sit in the medium-viscosity band, where oil fills the gear spaces without excessive torque. Very heavy, tarry oils behave less like liquids, so the practical answer is temperature: heat the oil into the pump's comfortable range.

Cold start sets the motor

Never size the motor from the running condition alone: breakaway torque at the lowest expected temperature can far exceed running torque, so heating before start-up is usually cheaper than oversizing the drive.

Heating and Insulating the Suction Line

Oil viscosity falls sharply as temperature rises, and this must be exploited on the suction side. Heating the tank outlet and suction line lets the oil fill the gear teeth as the cavities open; if it is too thick, the pump starves, suction vacuum climbs and delivery falls.

Steam or electric trace heating, hot-oil jacketed piping and tank suction heaters are typical, with insulation holding the temperature to the pump. Keep the suction run short, size the strainer for cold oil, and avoid vortexing in the day tank.

The Relief Valve Protects the Pump and the Line

A gear pump is positive displacement: if the discharge is closed while the pump runs, pressure climbs until a casing, seal or pipe fails. KCB-type pumps therefore carry an integral relief valve that returns oil to the suction side at its set pressure, set below the maximum allowable pressure of the pump and downstream system.

When Heavy Oil Is Too Thick for a Gear Pump

Every gear pump has a practical limit. When the oil is too viscous, tarry or bituminous, or carries solids, an industrial screw pump is usually the better technology — smooth axial flow, low pulsation and higher pressures — while non-contacting lobe pumps suit very viscous product needing gentle handling. For such duties Qingdao Green Power publishes G/3GB industrial screw-pump configurations covering 0.1–241.7 m³/h at 0.6–2.4 MPa.

Gear pumps suit medium-viscosity oils kept hot and clean; screw or lobe pumps take over where the oil stops behaving like a pumpable liquid. See the heavy oil pump selection guidance before specifying.

Key Checks for a Heavy-Oil Gear Pump Duty

• Working viscosity: specify viscosity at pumping temperature and the worst-case cold-start value.
• Heating and insulation: confirm suction heating keeps the oil fluid up to the pump inlet.
• Flow, pressure and relief: define normal and maximum flow, discharge pressure and relief setting.
• Cleanliness: fit a strainer sized for cold oil; keep water and abrasives out.
• Model confirmation: KCB-type pumps are a technical-reference topic here — confirm current model availability and specifications with Qingdao Green Power before procurement.

Frequently Asked Questions