FAQ'S

1) WHY DOES OIL GET CONTAMINATED?

Oil gets contaminated by

·         Particles entering the oil

·         Thermal degradation forming polymer products, resinous matter and sludge

Sources for Particles to enter the oil are:

·         Initial load when system is assembled – like dust and debris in pipes, reservoirs, and first fill of oil itself(from barrels at NAS 10-12)

·         From breathers, since systems are air compensated

·         Wear particles from moving parts – fine metal, rubber.

·         Repair of parts and break-in of systems for replacement of parts, filters, seals etc.

Oil undergoes a thermal cycle, where local temperatures at the work may rise to 60 deg C and it is later cooled in heat exchangers. This leads to polymerisation, especially in the presence of catalysts like fine metal particles and moisture.. the table shows how much moisture and wear particles contribute to degradation of oil, measured as the Total Acid Number.

Note:
1. Time: hours for reaching a certain level of acid value.
2. Test oil is turbine oil with viscosity of 32cSt/100°F (37°C)
3. Tested oil temperature is 200°F (93°C)

Acid value indicates formation of “Sludge” and sticky resinous matter which forms hard deposits on valves, pipes.

---

2) WHY DOES MACHINE BREAKDOWN OCCUR?

Breakdown can be due to:

·         Increased clearances between mating parts. (Due to wear).

·         Blocked oil passages especially at bends, valves and orifices.

·         Clogged filters leading to cavitation (suction side), pressure and flow surges (pressure side) and consequent vibration and jerky operation.

·         High acid value (see above table)leading to corrosion, degradation of rubber parts.

---

3) WHY DOES OIL LEAK?

We have discussed above how contaminants like wear particles are generated and contribute to increasing formation of sludge and resinous matter.

Sludge, being acidic, attacks and reduces life of oil seals. Sludge has an electrochemical attraction to metal surfaces and will deposit on oil coolers, reducing heat transfer efficiency. This hard scale is just the same persistent grime in ovens and pans (like blackening of pan or tawaas) This leads to increased operating temperature, reduced viscosity & consequently higher leakage.

It is generally thought that oil leakage is independent of oil contamination. Our studies prove that leakage is mainly due to oil contamination, with sludge being the prime contributor.

---

4) WHY DOES OIL TEMPERATURE INCREASE?

Generally, 10-15% of electrical energy input from motors gets converted to heat energy.

This percentage can increase when contamination increases, say by increased pumping energy required to push oil through choked filters. When suction side filters are choked, there is pump cavitation and aeration. Pumping energy is still higher as suction pressure drops while final pressures still have to be maintained. Moreover aeration contributes to an effect known as “dieseling” whereby oil ignites at high pressure side when air is available.

This leads to build up of oxidation products, like sludge. Sludge in turn deposits on heat exchange surfaces on oil coolers reducing heat transfer and increasing operating temperatures on both oil and water sides. Higher water temperatures lead to increased scaling on water side…. and a chain reaction is set in place.

Running machines at oil temperature between 43°C – 48°C is important. The focus has hitherto been to keep oil “cool”. It is however pertinent to understand what “cool” implies.

Below 43°C is too cool and above 48°C 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 50°C is critical.

---

5) WHY IS OIL CHANGE NECESSARY?

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.,

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.

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.

Use of our Vacuum Dehydration equipment LVDH-600 is the method which can perform water removal on line.

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.

---

6) WHY IS OIL CHANGE NECESSARY INSPITE OF USING MECHANICAL FILTERS? 

(FILTERS AND CENTRIFUGES)

Both filters (see comparison) and centrifuges (see table) have a limitation that they cannot adequately remove smaller particles. Yet , it is contaminants below 5 microns, known as “Silt” 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.

Silt particles exist in much larger numbers(see graph) and over time, as these particles remain in the oil they contribute significantly to build up of sludge and resinous matter and act as catalysts to increase the acid number of the oil (see table above).

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 oxidised we have to change the oil… only a few dozen Parts Per Million of oxidised matter and contaminants can dictate the need to change oil.

Only Electrostatic cleaning removes fine particles, the cause of sludge formation, and also the oxidised matter. Oil cannot be maintained with mechanical filtration, at the level necessary to prevent costly oil change and downtime.

7) WHAT IS OIL DETERIORATION?

An analysis of “deteriorated” oil proves that when oil is contaminated, its physical characteristics are not changed. Only a tiny percentage of oil molecules chemically react in the oxidation process and produce a resinous matter, which is generally referred as “sludge”. (Mud in water indicates that water is contaminated, it does not however alter the basic molecular structure of water.)

Oil is said to have deteriorated when a few dozen PPM of resinous matter exist in the oil. A relatively high acid value is measured in such oil and resinous matter of light brown colour is deposited on a 0.8-micron membrane patch, when oil is checked by membrane analysis method. Resinous matter is soluble in oil at temperatures higher than 60°C. And remains insoluble at temperatures lower than 60°C.

Resinous matter is also measured as benzene insoluble.

This resinous matter or sludge passes through filters when its concentration is small but clogs filters when its concentration increases.

This is Deteriorated oil – and it affects the hydraulic system because,

sludge is sticky in nature and is easily deposited on metallic surfaces of valves oil coolers, and pipes leading to Malfunctions or sticky valves; increased machine working temperatures and oxidation of oil, and decrease in viscosity.

---

8) WHAT ARE THE PROPERTIES OF OILS USED IN HYDRAULICS AND LUBRICATION?

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.

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.

Viscosity of oil is temperature dependent and the standard of measurement is at 40°C. This value is used in design of systems and using oil at temperatures far above or far below 40°C are both “Off Design” situations.

The other properties required to be monitored are…

Total Acid Number
Contaminants
Moisture

Acid number is a measure of the oxidation the oil has undergone (table)

Contaminants in oil are measured by

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.( How clean is your oil?)

c) Turbidity Measurement: The turbidity of an oil sample is measured by an electric meter and compared with that of standard purity. This instrument is very easy to operate and is inexpensive.

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 (See Table above). Moisture is the biggest enemy of oil, specially emulsified water.

Our LVDH 600 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.