HAPP Principle
A hydraulic activated pig consists of three units (Fig. 3): a brake unit, a seal unit and the cleaning head.
All units have openings that allow the entire fluid flow through the pipeline to bypass. The brake unit ensures that a hydraulically activated pig is held back against the fluid flow in the pipeline. The fluid pushes against the following seal unit, which channels it into the openings of the cleaning head. Seal unit and cleaning head pose a flow restriction resulting in a pressure difference across the pig. Thus the fluid is accelerated in the cleaning head's nozzles creating extremely powerful liquid jets. These jets are directed onto the pipe inner wall and remove any kind of deposits.
The brake unit ensures that the travel speed of the pig is many times slower than the fluid velocity thus allowing it to entirely remove deposits from the pipe wall before it travels across the cleaned surface. The deposits removed are immediately flushed downstream the pipeline with the main jet of the cleaning head which is directed in the middle of the pipeline. With all deposits removed from the pipe wall and transported downstream by the fluid flow there remains no risk of the pig getting stuck in debris accumulated in front of it.
Read more about this topic: Hydraulically Activated Pipeline Pigging
Famous quotes containing the word principle:
“The principle of fashion is ... the principle of the kaleidoscope. A new year can only bring us a new combination of the same elements; and about once in so often we go back and begin again.”
—Katharine Fullerton Gerould (1879–1944)