How Does a KCB Gear Pump Work?

The Working Principle in Three Steps

KCB-type gear pumps are external gear pumps, a member of the positive displacement (PD) family. One gear is keyed to the drive shaft; the second, identical gear is turned by the mesh, so the rotors stay in tight, synchronised contact and the pumped oil itself seals the clearances.

1. Suction phase

On the inlet side the teeth separate as they rotate out of mesh. Each tooth space opens into a larger cavity, pressure falls slightly below line pressure, and liquid flows in to fill the space between the tooth flank and the casing.

2. Transport phase

Each filled tooth space is then carried around the casing periphery as a sealed pocket. The liquid is not compressed or heavily sheared here; it simply travels with the gears, separated from the discharge side by the tooth mesh.

3. Discharge phase

When the teeth re-enter mesh at the outlet, the pocket collapses and the trapped liquid is forced out against the discharge pressure. Delivery is continuous, with only the small pulsation of each tooth pass; theoretical flow is displacement per revolution times speed, minus internal slip.

Viscosity and Slip Set the Practical Limits

A gear pump relies on the pumped liquid to seal its clearances, so the medium decides performance: a clean, lubricating oil of moderate to high viscosity keeps internal slip small and volumetric efficiency high, while shaft power rises with viscosity, especially at cold start.

Thin, low-viscosity fluids leak back from discharge to suction through the clearances, so delivered flow falls at low speed and high pressure. That is why external gear pumps suit oils and fuels rather than water-like liquids — and why the centrifugal-side guidance is to consider a gear or screw pump above roughly 150 cSt.

Fixed Displacement Means a Relief Valve

Because displacement is fixed regardless of discharge pressure, closing the discharge line while a gear pump runs makes pressure climb until a component fails. KCB-type pumps therefore carry an integral relief valve that bypasses liquid to the suction side, set below the maximum allowable pressure of the pump and piping.

Typical KCB-Type Gear Pump Duties

The KCB designation refers to a widely used external gear pump layout for clean petroleum products, covered here as a technical-reference topic with dedicated application guides. The best-suited duties are steady transfers of clean, lubricating oils at low to moderate pressure:

• Fuel-oil transfer and burner supply — day tanks and boiler houses.
• Lubricating-oil circulation and change-over — clean oil at steady duty points.
• Heated heavy-oil transfer — oil kept fluid by heating.
• Clean, non-corrosive chemical transfer — compatible lubricating liquids.

When Another Pump Technology Fits Better

Not every oil duty is a gear-pump duty: centrifugal pumps move large flows of thin liquids economically, screw pumps take over for very viscous, high-pressure or tarry services, and lobe pumps suit products that must be handled gently. Qingdao Green Power's G/3GB industrial screw-pump range covers 0.1–241.7 m³/h at 0.6–2.4 MPa for such heavy services.

Key Checks for a KCB-Type Gear Pump Duty

• Flow and speed: PD output rises with speed — match the drive and gear size to normal and maximum flow.
• Viscosity: specify the oil at pumping temperature and at cold start; the motor is often set by the cold start.
• Pressure and relief: confirm the maximum discharge pressure and set the relief valve below the system limit.
• Seal and materials: match the mechanical seal or gland and the wetted materials to the oil and its temperature.
• Cleanliness: fit a suction strainer sized for the coldest oil and keep water and abrasives out.
• Model confirmation: KCB-type gear pumps are a technical-reference topic here — confirm current model availability and specifications with Qingdao Green Power before procurement.

Frequently Asked Questions