The purpose of this guide is to assist the asphalt emulsion end user in pumping emulsion. The brochure covers the pros and cons of positive displacement and centrifugal pumps, the need for specific pump features, proper pump installation, and suggested pump sizing. Proper cleaning, maintenance and off-season storage procedures are given. Finally, a troubleshooting guide is included.


The most common type pumps used for emulsions are positive displacement and centrifugal pumps. The following is general information on these two types of pumps.

Positive Displacement Pumps

Mechanical Operations of the Pump

The rotating member(s) inside the pump creates a vacuum at the suction port. Liquid is drawn into the port and carried between the rotating member and the pump housing since there is close tolerance between the two. As the liquid reaches the outlet port it is forced outward as the pumping chamber is squeezed down by some means. For each revolution of the pump, a fixed amount of liquid is displaced. The liquid must flow somewhere since there is little slippage and thus the name positive displacement.

Pump Features

The following are special suggested pump features:

  1. Relief Valve

    In case of downstream blockage, this valve opens dumping liquid back to the suction side of the pump or back to tank, depending on the type relief valve used. Most valves are adjustable so relief pressure can be regulated.

  2. Jacketing

    These pumps require some type of heat and can be ordered with various jacket arrangements for the circulation of hot oil, water or low pressure steam.

  3. Extra Clearance

    Due to the nature of asphalt emulsion, most pump manufacturers suggest special clearances between certain pump members. This varies for different pump manufacturers. Be sure to emphasize the material to be pumped is asphalt emulsion, not asphalt cement or asphalt cutback.

  4. Special Materials

    Since asphalt emulsion pumps can be exposed to shock loads during startup or while running, it is suggested that a steel alloy fitted pump be considered rather than a standard fitted one. However, many pumps are in operation whose working members are made of ductile iron or high grade carbon steel.

  5. Packing Seal

    Normally specified for any type of asphalt usage because of its lower cost and because mechanical seals damage easily due to asphalt glued faces.

Centrifugal Pump

Mechanical Operations of the Pump

Material is fed into the center of the pump by gravity and a high speed impeller slings the material to the outside of the pump casing and through the outlet.

Pump Features

Normally, no special pump features are required with a centrifugal pump.

Pros and Cons Between the Two Types of Pumps

Positive Displacement

  1. Will create a suction lift.
  2. Is reversible.
  3. Will pump to a higher discharge head.
  4. Meters


  1. Is less expensive since the initial pump cost is less and a direct non-reducing drive can be used.
  2. Requires heat only with high viscosity materials, or cold weather.
  3. Less efficient with higher viscosity emulsions.
  4. Takes more power.
  5. Not all are self-priming.
  6. Max. speed should be 1750 RPM or less.