TECHNICAL REFERENCE
filters or active venting systems usually provide adequate removal means. For large quantities of water, vacuum dehydration, coalescence, and centrifuges are appropriate techniques for its removal. However, as each of these techniques operates on different principles, they have various levels of water removal effectiveness. The chart below provides comparative information on these techniques and their relative effectiveness. Care should be taken to apply the best technique to a given situation and its demands for water removal. Chemical Removal Removal of acids, sludge, gums, varnishes, soaps, oxidation products and other chemicals generally requires an adsorbent (active) filter with Fuller Earth, active type clays, charcoal, or activated alumina. Heat Removal Removing heat is important to maintain viscosity and prevent fluid breakdown. Usually performed with heat exchangers, including air-to-oil and water-to-oil types, finned coolers, or refrigerated units. Heat Addition Added heat is used for cold temp start-up to get fluid viscosities within operational limits. Use heaters, immersion or in-line. Kidney Loop Filtration One very effective way of ensuring thorough fluid conditioning is with a dedicated off-line circulation loop, or “kidney” loop. This system uses a separate circulation pump that runs continuously, circulating and conditioning the fluid. Multiple stages and types of filters can be included in the circuit, as well as heat exchangers and in-line immersion heaters.
Fluid Conditioning Fluid Conditioning is the term for the overall
conditioning of the fluid in the hydraulic system, and encompasses particulate removal via filters along with other various methods for removing silt, air, water, heat,
acid, sludge or chemicals. Particulate Removal
Particulate removal is usually done with mechanical filters. A well designed reservoir that allows settling will also help in keeping particulates out of the mainstream fluid. For ferrous particulates and rust, reservoir magnets or strainer band magnets can also be used. Other methods such as centrifuging or electrostatic filtration units can also be used, particularly in continuous batch processing and fluid reclamation. Removal of Silt Silt, defined as very fine particulate under 5 m in size, requires very fine filtration or “oil polishing.” Air Removal Getting air out of the system is best done by adding 100 mesh screen in the reservoir, approximately 30° from horizontal to coalesce entrained air and allow larger bubbles to rise to the surface when reservoir velocities are low. Water Removal A number of techniques exist to prevent water or moisture ingression or to remove water once it is present in a hydraulic or lube oil system. The best choice of technique for removal is dependent on the whether or not the water exists as a separate phase (dissolved or free), and also on the quantity of water present. For example, the presence of water or moisture can be reduced or prevented from entering a fluid reservoir through the use of absorptive breathers or active venting systems. However once free water is present in small quantities, water absorbing
Water Prevention and Removal Techniques
Prevents Humidity Ingression
Removes Dissolved Water
Removes Free Water
Removes Large Quantities of Free Water
Usage
Limit of Water Removal
Adsorptive Passive Breather
prevention prevention and removal
Y
n/a
Y
Y
Y
down to <10% saturation
Active Venting System
Water Absorbing Cartridge Filter removal
Y Y Y Y
only to 100% saturation only to 100% saturation only to 100% saturation down to ~20% saturation
Centrifuge Coalescer
removal removal removal
Y Y Y
Vacuum Dehydrator
Y
18 • Hydraulic Filters & Accessories
Powered by FlippingBook