Thermal Expansion and your Asphalt Gear Pump

Author: Tom Schroeder | July 12, 2016 | Category: Pumps

Laying asphalt is a hot job. Well over 300 degrees hot. The gear pumps that work to lay asphalt get hot, and must stay hot in order to ensure the material stays in a pump-able form. As pumps heat up, thermal expansion and reliability become a hot topics. Here's a couple things to consider to make sure the next asphalt gear pump you select provides a long life of reliable operation. 

What's Thermal Expansion?

Thermal expansion is an increase in volume of components as heat is transferred.  Since different components of the pump such as the rotor and casing are different size masses they will have different expansion characteristics. It is important that the pump is designed to compensate for these changes in volume. If not, stationary and rotating parts could make contact and cause damage or failure.

At ambient temperatures, asphalt can be very viscous making it difficult to pump. In most cases, lines and pumps will be traced with heat to keep it in a pump-able form. Asphalt inside the pump must be kept at temperature so viscosity does not increase, and the pump is operates efficiently at optimal temperature.

Let’s talk about what should be taken into consideration when selecting a pump for asphalt.  

Extra Clearance

Clearances on the internals of the pump are a balance between operating efficiently and providing enough space so specific surfaces are not contacting. Pump design is further complicated when heat is added and components are changing size. Thermal expansion characteristics are going to depend on the amount of mass the component has, as well as the material it is made of.

If the pump material has galling or seizing characteristics, or there are build-up tendencies of the liquid being pumped, extra clearances should also be considered. Pump manufacturers provide specific clearance requirements for operating temperatures and viscosities for a given pump model.


Jacketed pumps are designed to have steam or hot oil circulated through them. Before the pump has begun to operate, any liquid in the lines or pump will need to be heated so the viscosity is low enough. Starting prematurely, may result in a motor going out on high amperage or causing damage to the pump.

The steam or hot oil can be circulated through the casing head, bracket and relief valve – which are used and depend on the size and model of the pump. Another option if you do not have oil or steam available is to use electrical thermocouples to transfer the heat to these components.

Need help with your asphalt pump? Is thermal expansion giving you a “hot head?” Ask us about it! Our team has the knowledge and insight to help select or fix your pump.

Download the Metering with Gear Pumps Ebook

Tom Schroeder

Tom Schroeder

Tom Schroeder is an Application Engineer II at Crane Engineering. He has more than 7 years of experience in the general industry sector. He specializes in the proper selection of fluid processing equipment like pumps, filters, mechanical seals, and mixers.

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