First introduced by the Farval Lubrication company, the Dual Line centralized delivery system (also known as a Twin-Line Parallel) was designed to accurately displace and move oil or grease over great distances from a single pumping station to as few as 20 lubrication points and up to many hundreds of points.The system’s heavy-duty construction and use of small-bore piping and tubing made it an ideal choice for automated lubrication in medium- and large-sized industrial equipment typically found in the steel, mining, pulp and paper, power-generation and petrochemical industries.
The Dual Line lubrication system bears many similarities to the Positive Displacement Injector (PDI) or Single Line Parallel system, in that each metering valve—or point—can be set independently or easily adjusted during operation. This unique feature also enables additional injectors (lube points) to be added into the system at a later date, without the need to re-engineer the entire system.
How the System Works
As its name suggests, the Dual Line system employs two main lubrication lines that run in parallel from the pump to the last lubrication point through a series of lubrication delivery valves. Once the pump is activated, line pressure is built up on the pressure or delivery supply line to fire the lubrication point injectors while simultaneously venting the second return line back through a reversing valve to the reservoir.
Dual Line injectors differ from Single Line injectors in that they do not use a spring arrangement to fire and load the injector. Instead, they employ a dual-acting hydraulic spool valve set up to feed two separate lubrication points (one per each pressure cycle).
Once an end-of-line pressure switch signals that a preset line pressure has been reached and all injectors have fired, the system has completed one pressure cycle—or a one-half lubrication cycle. The reversing valve is then actuated to its changeover position to allow the previous venting line to become the new primary pressure line and the process is repeated to complete one full-lubrication cycle.
These systems can operate in manual mode with a pull-handle pump, as well as in full automatic mode.
Pros & Cons
Because Dual Line systems can be used with oil and grease, their engineering is not demanding—and can easily accommodate the addition or reduction of system points after they’ve been installed.
As with Single Line systems, the adjustable injectors are easily tampered with and can lead to an over- or under-lubrication condition unless they are access-controlled.
A pressure-line failure is easily detected through a time-out switch located at the end of line. No secondary-line failure device is available. Users must perform system line integrity checks as part of their PM programs. LMT
Founded in 1946 in Milan, Italy, Dropsa is one of the world’s leading producers of centralized lubrication systems and components. According to Dropsa, as it has for more than 60 years, it continues to innovate in the field of lubrication technology and now offers a wide range of products in the areas of Total Loss Oil, Grease Lubrication, Re-circulating Oil and Air/Oil Lubrication. All of them are backed by a production program catering to “the most diverse lubrication applications, from small machine tools to transfer lines, printing presses, paper machines, steel mills and practically all other sectors of industry.”
Based in Sterling Heights, MI, Dropsa USA coordinates the company’s network of distributors and specialist part-ners in the United States. In addition to maintaining an experienced team to support customers, this facility houses a full-product training center for customers and distributors.