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.
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.
The following are special suggested pump features:
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.
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.
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.
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.
Normally specified for any type of asphalt usage because of its lower cost and because mechanical seals damage easily due to asphalt glued faces.
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.
Normally, no special pump features are required with a centrifugal pump.