•
clearances
• Component Clearance (microns)
• Roller Element Bearings 0.1 - 1
• Journal Bearings 0.5 – 100
• Gears 0.1 - 1
• Dynamic Seal 0.05 - 0.5
• Pump (Gear) Tooth to Side Plate 0.5 -5 Tooth tip to Case 0.5 -5
• Pump (Vane) Vane Sides 5 - 13 Vane Tip 0.5 - 1
• Pump (Piston) Piston to Bore 5 – 40,
Valve Plate to Cylinder 0.5 - 5
• Spool to Sleeve 1 - 4
oil deterioration
tiny percentage of oil molecules chemically react in the oxidation process & produce a resinous matter which is generally referred to as "sludge".
Oil is said to be deteriorated when matter of light brown colour is deposited on a 0.8 micron membrane patch, when oil is checked by membrane analysis method.
cause of deterioration :
Sludge in oil denotes deterioration. The process of sludge formation, starts with oxidation.
Oxidation of hydraulic oil :
Requires : Oxygen # Heat # Catalyst
Ø 15% of mechanical energy is converted to heat energy, that’s why hydraulic systems require oil coolers.
Ø 10% of air is always dissolved in oil. Therefore both heat & oxygen are always present in oil. Fine material particles from wear of pumps & water act as catalysts to oxidize oil & produces sludge.
Ø Wear of pumps and moving parts. These worn metal particles, along with moisture, act catalysts to oxidize oil & produce sludge.
WHY DOES MACHINE BREAKDOWN OCCUR :
Breakdown can be due to:
Ø Increased clearances between mating parts. (Due to wear).
Ø Blocked oil passages especially at bends, valves and orifices.
Ø Clogged filters leading to cavitations, pressure and flow surges and consequent vibration and jerky operation.
Ø High acid value leading to corrosion, degradation of rubber parts.
• Running machines at oil temperature between 43oC – 48oC is important. The focus has hitherto been to keep oil “cool". what “cool” implies.
• Below 43oC is too cool and above 48oC is too hot.
• It is also important to note oil oxidation (i.e. sludge formation) is accelerated when temperature exceeds 50oC. Salt release from water (leading to scale formation) is also accelerated when temperature exceeds 50oC.
• Therefore, keeping oil temperature below 50oC is critical.
WHY IS OIL CHANGE NECESSARY
Ø Oil change is necessary when oil condition indicated by turbidity, or blackening worsens enough to cause operating problems, like sticky movement, hunting, slow pressure build up, high leakages etc.,
Ø The need for oil change can also be dictated by oil analysis reports when periodic testing is done. If parameters like acid value and solid content exceed limits set by oil supplier oil has to be changed.
Ø Accidental ingress of water can also necessitate oil change as water oil mixture cannot support hydrodynamic loads and prevent metal to metal contact at moving/ meshing parts.
Ø Use of our Vacuum Dehydration equipment LVDH-50 is the method which can perform water removal on line.
Ø Use of ELC to remove solids and oxidation products can prolong intervals between oil changes. In fact, if ELC is dedicated to a system and oil condition is monitored with membrane patches or particle counts, oil life can be prolonged indefinitely and oil becomes an asset rather than a consumable.
WHY IS OIL CHANGE NECESSARY INSPITE OF USING MECHANICAL FILTERS
Both filters and centrifuges have a limitation that they cannot adequately remove smaller particles. Yet , it is contaminants below 5 microns, which are most harmful to the system. Smaller particles alone can enter the clearances in mating parts (typical clearances)and have the capacity to increase erosive wear and also catalyse oxidation.
These oxidation products are the main cause of :
Sticking of hydraulic valves,
Wear and breakdown of pumps, cylinders
Increased seal failures
Increased wear on mating parts, causing heavy leakages.
Therefore, as oil gets more contaminated and oxidized we have to change the oil... only a few dozen Parts Per Million of oxidized matter and contaminants can dictate the need to change oil.
Only Electrostatic cleaning removes fine particles, the cause of sludge formation, and also the oxidized matter. Oil cannot be maintained with mechanical filtration, at the level necessary to prevent costly oil change and downtime.
WHAT ARE THE PROPERTIES OF OILS USED IN HYDRAULICS AND LUBRICATION
Ø Hydraulics is based on Pascal’s Law applied to liquids. Lubrication is based on separation of moving I meshing parts by an oil film. Oil is used only for transmission of energy and lubrication of mating parts.
Ø The basic property of oil that is exploited for use in Hydraulic and Lubrication systems is its Viscosity. Viscosity of the oil permits the build up of a thin load bearing film of oil between moving parts, preventing metal to metal contact.
Ø Viscosity of oil is temperature dependent and the standard of measurement is at 40 oC. This value is used in design of systems and using oil at temperatures far above or far below 40 oC are both "Off Design" situations.
Ø The other properties required to be monitored are...
Total Acid Number
Contaminants
Moisture
Methods of measuring Contamination
a) Particle counting: This equipment automatically counts and records the number of particles in oil by electronic sensors. It cannot read contaminants below 5 microns in size, is expensive and requires trained personnel for operation.
b) By membrane filter: This method is very reliable and contaminants in oil can be observed by the naked eye. Membrane patches of oils to be checked can be compared with standard patches. If required, membranes can be weighed before and after the oil sample is passed to arrive at the weight of contaminants in a given oil sample. 0.8-micron membranes are used for oil analysis by this method. This equipment is inexpensive, easy to operate and is portable.
ELC is the best method of contamination control, removing all particles as well as Oxidation products.
Moisture:
This must generally be controlled within a couple of hundred ppm preferably within the saturation limit of the oil. Moisture is harmful by itself, causing breakdown of oil film at the minimum and corrosion at higher values. It also is a catalyst for oxidation of the oil. Moisture is the biggest enemy of oil, specially emulsified water.
Our LVDH 50 is the best method of on line moisture removal, and can reduce moisture content to below the saturation limit without taking the oil to high temperatures.
