Why Bitumen Needs a Gear Pump

Pump Notes · engineering notes from Vimpo Pump

Hot bitumen is thick, sticky and expensive to keep warm. The pump that moves it must work with this viscosity, not against it.

A centrifugal pump loses performance with viscosity

A centrifugal pump adds speed to the fluid. When the viscosity increases, friction in the impeller increases and head and flow fall quickly. Our VKY centrifugal pumps operate at max. 20 cSt without correction and max. 200 cSt with correction. Typical paving grade bitumen 50/70 is 300 cSt at 150 °C, and PMB is 2,000 cSt at 160 °C. These values are outside the centrifugal range.

A gear pump moves a fixed volume

A gear pump is a positive displacement pump. Each revolution moves a fixed volume of fluid from the suction side to the discharge side. Flow follows speed. When the viscosity increases, internal slip decreases. Thick fluid therefore does not stop a gear pump; it changes the motor power and the maximum speed.

• VD and VDK internal eccentric gear pumps: 10 – 55,000 cSt, max. 230 °C.
• VH external helical gear pumps: 10 – 55,000 cSt, max. 230 °C, low speed of max. 461 rpm.
• VKY centrifugal pumps: bitumen emulsion and cut-back loading at low speed, and thermal oil circulation at max. 140 °C.

Three rules for hot bitumen

1. Use a thermal oil jacket (code T) and insulate the pump and the lines.
2. Do not start the pump before the jacket is at working temperature.
3. Heat the suction line and keep the pump full between cycles.

Above 50,000 cSt a suction lift is not possible. Use flooded suction and a suction line one size larger, as short as possible.

Tell us the fluid, the temperature, the flow and the pressure. Vimpo engineering selects the pump size, the drive and the heating for your line.

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