LIFE OF HYDRAULIC & LUBRICANT OIL
It is an open secret that oil never wears out but the contaminants make it discard-able. The contaminants act as catalyst in oxidation of oil and that degrades the oil to lead to discarding. Although the oil can not last forever, even under the best conditions, and a chemical reaction, of oxidation takes place and inevitability ultimately the oil loses it properties and it becomes discard-able.
Generally speaking, the hydraulic & lubrication oils have indefinite life when protected from excessive heat, moisture, air & particles. These all are considered to be contaminants and their control is part of programme for systemic contamination control. In fact, some companies have achieved service life more than ten years.
Hence we should have an effective Contamination Monitoring and Control program, to minimize the oxidation, by keeping the oil as far as possible clean and thereby prolonging the service life of the oil, reducing maintenance costs, machine downtime and providing better protection for equipment.
The Effects of Oxidation:
- Formation of sludge, varnish and other deposits
- Increased viscosity
- Decreased lubrication properties of oil
- Decreased film strength
- Decreased load-bearing capability
- And damaging of various system elements and filters itself.
The contaminations in the oil not only harm and damage the parts, components and systems but it also cause the damage in chain reaction process. You know that the contaminants not only damage the system but also act as a catalyst in oxidation which produces sludge and varnish to reduce the lubrication and also choke the filter element.
The other factors responsible for degradation of oil are many but water, heat and air are more important.
Where from the contamination enters into the system?
There are five primary sources of contamination:
- Built-in during manufacturing and assembly process.
- Ingress from outside the system during operation from Reservoir Vent Ports, Power Unit Openings, Maintenance Events and Cylinder Rod Seals etc.
- Contaminated New Oil Although hydraulic and lubrication fluids are refined and blended under relatively clean conditions, the fluid travels through many hoses and pipes before it is stored in drums or in a bulk tank and it doesn’t remain clean. Hence an efficient filtration unit like Systemguard® should be used to remove the contamination from new fluids before filling it into the hydraulic or lubrication system.
- Air contamination either ingresses from leakages or generated due to Cavitations which occur when the volume of oil demanded by the hydraulic system is more than the supply of oil.
- Internally Generated contamination is contamination generated during operation due to wear and tear of following types which in turn generates more finer particulate contamination to damage the parts and components as chain reaction, and act as catalyst in the oxidation process, which is shown below in a figure under the Abrasive wear:
a) Abrasive Wear – Hard particles bridging two moving surfaces, scraping one or both as shown in figure below and generate more and more contamination as chain reaction.
b)Aeration Wear – Air bubbles in the fluid implode breaking away surface material.
c) Adhesive Wear – Loss of oil film allows metal-to-metal contact between moving surfaces.
d) Cavitation Wear – Restricted inlet flow to pump causes fluid voids that implode causing shocks that breakaway critical surface material.
e) Corrosive Wear – Water contamination in the oil causes rust that degrades the surface.
f) Erosive Wear – Fine particles in a high speed stream of fluid eat away a metering edge or critical surface as shown below:
g) Fatigue Wear – Particles bridging a clearance cause a surface stress riser or micro-crack that expands into a spall due to repeated stressing of the damaged area.
Steps to Implement systemic approach to protect oil and system from variousContaminants like particulate contamination, Water Contamination, Air contamination and Heat Control
Contamination monitoring is the operative element for achieving the goal of extended life of Oil as well as the life of system. Contaminant levels, as affected by ingress and filtration, are extremely dynamic. It is not unusual for levels to vary two or three orders of magnitude over a period of days or even hours. Accordingly, contaminant monitoring closes the loop by providing the essential feedback and therefore control. Attempting maintenance without monitoring is like driving a car without knowing the direction or flying an aeroplane in storm without direction finder and altimeter.
Fluid contaminant monitoring can be accomplished in the field or plant by extracting samples of fluid into bottles for lab analysis or by portable instruments used right at the machines.
Systemguard is a complete oil management machine equipped with a state-of-the-art Laser Particle Counter for Contamination Monitoring and complete Contamination removal including water removal and is easy to use. The Laser Particle Counter allows maintenance and service departments to monitor and maintain the fluid cleanliness of hydraulic and lubrication systems and take action to ensure the long oil life associated with the reliability and proper operation of their equipment.
A systematic approach to Contamination Control starts fromsetting a target of cleanliness for the system followed by achieving the target cleanliness by an efficient and reliable machine like Systemguard and maintaining it by proper monitoring.
Referring to the Nippon Steel report, they state that the influence of a systematic contamination control practice contributed to a reduction of oil consumption of 83 percent.
It is established that by improving fluid cleanliness, oil change intervals can be extended by manifold times. Due to significantly lower wear rates (particle generation), filter change intervals can be extended to a factor of two or even more.
Taking steps to restrict the entry of contaminants into the fluid can further extend this. An additional savings can be achieved by additional routine filtration by a good quality Off-Line Filtration unit like Systemguard® with H2O-Pro Water removal Filter, Magnetic filter and Particle removal filter.
Heat or Temperature Control
Temperature of oil plays an important role in the system performance. At elevated temperatures the viscosity of oil is reduced. An extreme system duty cycle, aeration, cavitation, over-pressurization and contamination are all factors that contribute to excessive heat. Excessive heat, in turn, accelerates oxidation in the system fluid, deteriorating its viscosity. This creates a chain reaction. Therefore, the root cause of excessive heat must be eliminated to effectively cure the problem and an oil cooler is to be installed for removing the excessive heat generated due to the various obvious conditions.
Normally Shell & Tube type Heat Exchangers have been installed for cooling the Hydraulic Fluid. The main disadvantages of Shell & Tube type Heat Exchangers are as under: –
1) Laminar Flow of water in the tubes result in falling of the heat transfer surface. A hard layer is deposited inside the tubes resulting in narrowing the passage. The layer deposited in the tube also act as insulating material and do not allow the heat to be transfer from oil to water.
2) When the water passes through the tube this highest velocity is at the cavitation and the velocity near the walls of the tubes is reduced to almost zero creating a stagnant water film (which is bad conductor of heat) near the heat transfer surface. Therefore the efficiency of Shell & Tube type Heat Exchangers is very less.
3) Very after the leakage start in the Heat Exchanger and the water is mixed into the oil, it deteriorates the hydraulic fluid, which damages the fluid power systems, machines and components.
The better alternative solution is Honeycomb Type Compact Brazed water oil coolersconsisting of unique pattern-embossed plates of acid resistant stainless steel AISI-316offering minimum risk of corrosion and the smooth surface quality minimises the possibility of particles to adhere to the surface as the fluid passes through the unique channels and it is regularly changing the direction, disturbing the boundary layer to ensure the turbulent flow.
The embossed pattern in the Honeycomb type heat exchangers is so designed that the ridges on adjacent plates intersect with one another creating a lattice of contact points, which are subsequently joined together to create a compact and Pressure resistant oil cooler in which virtually all the material is utilised for heat transfer.
AVOID CAVITATIONS AND AERATION
Cavitations / Aeration is localized gaseous condition within a liquid stream, which occurs when the pressure is reduced to the vapour pressure. Put more simply, cavitations occur when the fluid doesn’t entirely fill the existing space. The noise from cavitations is similar to that heard from aeration. Cavitations can be caused over speeding of the pump, a restricted or excessively long intake line, dirty or insufficient capacity suction strainer in the inlet line of pump or too high fluid viscosity of oil.
The presence of dispersed bubbles of air in a system’s hydraulic fluid cause an implosion effect when the compressed air bubbles are subjected to system pressure at the pump outlet. This implosion can cause metal to be removed from the pressure plates, wear plates, etc. near the implosion point and result in extremely high local temperatures.
Pump aeration makes a loud, crackling noise like marbles being pumped. The noise is higher pitched at higher pressures. Excessive aeration makes the fluid look milky. It also causes components to operate erratically because of the compressibility of the air trapped in the fluid. Possible ways that air could be sucked into a pump are through faulty shaft seals and leaky inlet joints.
A sudden violent, inward collapse or Implosion of air bubbles when subjected to hydraulic system pressure cause severe pump damage.
A most common factor resulting the cavitation of the pump is suction strainer without any anticavitation by-pass valve. A low capacity of suction strainer is very injurious in the system. Therefore normally a suction strainer of 3 to 4 times of the pump capacity should be installed in the inlet line of the pump.
Even when a proper size of suction strainer is installed and it is choked, cavitation starts in the pump. Therefore to protect the pump against cavitation, an anti-cavitation suction strainer should be used. The anti-cavitation suction strainers are provided with a by pass valve to protect the pump against cavitation. The integral by-pass relief valve, present to open at 3 psi pressure drop.
Any queries or suggestions from readers are invited by:
Er. Ashok Kumar Gupta
G H Media Business Private Limited,
Global Media House, A-57, Sector-16,
Noida-201301, Delhi-NCR, U.P. INDIA,