Hydraulic and Pneumatic Knowledge
Fluid Power Equipment
Liquid / Fluid Filtering Systems
Liquid / Fluid Filtering Systems
The greatest danger to liquid / fluid systems is, foreign contaminants. Liquid / Fluid systems will not be or remain contaminant free, a liquid / fluid filtering system will be required. Contaminants within a fluid / liquid system are caused by many factors. The simple process of assembling and handling the fluid system parts and components may introduce undesirable contaminants. The act of turning a threaded pipe or fitting into their mating component often shears off thread burrs, freeing them to circulate through the liquid / fluid system. Small pieces of weld slag, grains from the foundry or cast core sand may be present. Foreign matter may be deposited during storage and the use of hand tools during assembly may contaminate the liquid / fluid system. Component wear and tear will introduce contaminants into the system. Anywhere there is metal-to-metal contact and motion, there is the potential for fine metal particles breaking free into the liquid system. For these and many more reasons, a liquid / fluid system requires a filtering system in place and maintained.
The ideal liquid / fluid filtering system will remove all foreign contaminants from the liquid / fluid, permit the full required fluid flow through the system as demanded by the pump with any significant restriction during any normal operational mode. Other considerations include: maintainability, cost, capacity and size. In general, filtration systems are available in three basic types: mechanical, adsorbent, and absorbent. Note, a liquid filtering system may include several types of filters, such as, an absorbent and a mechanical filter used in series to capture contaminants in stages.
Mechanical filters are probably the most widely used in industrial liquid / fluid systems. The liquid is forced by pressure through the filter element which is composed of micro-openings, pores or tortuous passages that trap larger sizes particles. This type of filter is commonly a surface type, which is normally composed of closely woven fabric or specially treated paper. General considerations for a mechanical filter type system are: liquid capability, fire resistance (as applicable), resistance to collapse (due to pressure differential), and system temperature compatability. Filters may be constructed of pleated stainless steel and monel wire cloth.
Adsorbent Filters are generally constructed of porous materials, such as cotton, paper, wood, cloth, asbestos, etc. In general these type filter systems are used to filter fine soluble's and may be designed to allow selected dirty liquid / fluid through relatively thick layers with an increase in compactness of the filter material in the direction of flow.
Absorbent Filters are constructed of material, such as fuller's earth, boneback, charcoal, activated carbon, activated clay, or chemically treated organic mediums. This type of liquid / fluid filtering system may be in the form of gravity feed bed or even a cartridge type installation. This system presents a large surface area for the liquid to flow through. The insoluble oxidation products and solid contaminants are removed by size filtration and absorption.