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Shell Advanced High-Water-Based Fluids
Shell Advanced High-Water-Based Fluids
Keywords: Shell, Water based, Fluid
Shell Advanced High-Water-Based Fluids are a new generation of fire resistant emulsions specially designed for use in critical fluid power transmission systems. Their enhanced stability, lubrication and anti-wear characteristics are achieved by the application of Shell's unique formulation technology, proven in demanding operations in the metal processing and mining industries.
The ability of these advanced emulsions to perform as lubricants is due to the combination of their excellent stability towards variations in temperature, pressure, shear and bacterial attack. In addition, they provide excellent protection against corrosion and wear, possess low foaming characteristics, can be finely filtered and are broadly compatible with construction materials and seals commonly found in modern hydraulic systems.
The availability of these advanced fluids now provides the operator with greater flexibility when choosing the best hydraulic medium for applications under his control.
The minimum requirement of a hydraulic medium is that it should be virtually incompressible and sufficiently fluid to permit efficient transmission of power. These characteristics alone are possessed by many liquids and selection of a hydraulic medium would be a simple matter if no other requirements had to be considered. Water or fluids containing significant proportions of water have been used satisfactorily in certain applications and, despite shortcomings, they proved to be the only practicable hydraulic medium for massive equipment requiring large volumes of fluid. The apprehension of operators to use hydraulic fluids having a high water content is understandable when the disadvantages of water are considered. Water has negligible lubrication properties, has relatively high volatility characteristics, promotes corrosion and can only be used in a relatively restricted range of temperatures. However, water has some distinct advantages when compared to mineral oil which include fire-resistance, natural abundance, convenience of high purity supply, cost effectiveness and its harmlessness with respect to toxicity and environmental pollution.
Fluids which comprise high concentrations of water are not suited for all applications and only specially engineered systems are capable of operating reliably on water alone. The growing demand for fluids which combine the desirable features of water, particularly fire-resistance, with lubrication performance superior to that of conventional HFA 5:95 emulsions has given considerable incentive to the development of a new range of high-water-based fluids. Shell Advanced-High Water-Based Fluids are at the forefront of these advances and offer the potential for users to convert from mineral oil and certain other types of hydraulic fluids to fire resistant, high-water-based fluid without sacrificing system reliability or efficiency. In addition it may not be necessary to vary the performance ratings of equipment originally designed for operation using mineral oils, thereby maintaining system efficiency and simplifying the change-over process.
Of prime importance to the success of smooth transition to Shell Advanced High-Water-Based Fluids and subsequent long-term reliable operation of systems is close collaboration at all stages between the system user, the various hydraulic component manufacturers involved and Shell.
Shell Irus Fluid A
Shell Irus Fluid A is a stabilised, concentrated oil-in-water emulsion which requires dilution with water prior to use. A 5:95 HFAe fire-resistant emulsion can be readily formed by diluting one part by volume of Shell Irus Fluid A with five parts by volume of appropriate water.
The composition and cleanliness of the water used to dilute Shell Irus Fluid A can have a pronounced effect upon the performance and longevity of the finished emulsion. Potable water of low total hardness should be used and particular care should be taken to rigorously exclude solid debris, microbial contamination and general organic matter. The introduction of micro-organisms, notably bacteria and fungi, can be particularly troublesome as such infestations can develop extraordinarily quickly giving rise to problems including sludge formation, unpleasant odours, filter deposits and corrosion. Water supplies of less than 200ppm total hardness (as CaCO3 equivalent) are preferred for dilution.
The 5:95 emulsion of Shell Irus Fluid A can be easily formed by the use of a paddle or appropriate positive displacement mixing device. Care should be taken not to agitate the emulsion vigorously as excessive air entrainment and foaming may result. It is recommended that Shell Irus Fluid A should be gradually added to the total required quantity of water and the resulting emulsion homogenised by gentle and continuous agitation.
Shell Irus Fluids AT10 and AT37
Shell Irus Fluid AT10 and Shell Irus Fluid AT37 are supplied ready for use and do not require dilution with water. The finished emulsions have a typical water content of 84 percent and 70 percent respectively and meet the requirements of the ISO 6071 HFAe classification.
Shell Irus Fluid AT10 and Shell Irus Fluid AT37 display enhanced lubrication performance and stability characteristics compared to conventional oil-in-water emulsions. Compared with Shell Irus Fluid A, Shell Irus Fluid AT10 and Shell Irus Fluid AT37 exhibit additional performance features because of their higher viscosities. Their excellent resistance to breakdown in the high shear environments experienced in pumps and valves, reduced pump wear, improved pump volumetric efficiency due to lower internal leakage, longer valve life from reduced cavitation damage and more efficient sealing within hydraulic systems are some of the proven advantages of using these ready-made emulsions.
Another benefit of using Shell Irus Fluid AT10 and Shell Irus Fluid AT37 is that they enable systems to be converted from mineral oil to a fire resistant high-water-based fluid with relative ease, the high capital cost normally associated with the provision of specialised hydraulic components being avoidable in many circumstances. Depending on design and component selection, it is possible to retain system efficiency when converting to Shell Irus Fluid AT10 and Shell Irus Fluid AT37 as their use permits the down-rating of system operating conditions to be kept to a minimum or eliminated completely.
Shell Advanced High-Water-Based Fluids are recommended primarily for:
hydraulic systems operating in high fire risk areas such as mining, iron and steel making, rolling mills and foundries;
very large ram pumps used to circulate large volumes of fluid at a given pressure;
systems employing rotary pumps at pressures up to 70 bar, e.g. machine tool systems;
systems employing rotary pumps at pressures up to 200 bar and beyond, e.g. applications in the metal processing industries;
injection moulding, die-casting machinery and motor-vehicle assembly equipment.
Shell Advanced High-Water-Based Fluids have been tested extensively in a wide range of hydraulic pumps in the laboratory and their performance has been proven in long-term applications in the metal processing industry. In addition, considerable practical experience has been gained at relatively high system pressures well beyond 70 bar, successful conversion under these conditions to high-water-based fluids being generally considered an impractical proposition a few years ago.
The performance limitations of conventional 5:95 HFA emulsions became readily apparent for systems operating well above 70 bar, reliability and efficiency often being sacrificed where fire resistance was of paramount importance. Difficulties associated with filterability, emulsion instability and bacterial degradation of these conventional emulsions were not uncommon and contributed to limiting the growth of high-water-based fluids outside the serious fire hazard situations.
In conventional hydraulic pumps a loss of volumetric efficiency is to be expected whilst operating with a fluid similar in viscosity to that of water (approximately 1mm/s at 40°C). Internal leakage will depend upon the pump configuration. Axial and radial piston pumps generally offer the maximum efficiency although certain internal gear pumps designs are also suitable. Standard vane pumps and motors are not usually recommended for use with high-water-based fluids although modified designs are capable of operating satisfactorily at system pressures of around 70 bar. Advice should be sought from the pump manufacturer regarding the suitability of existing equipment with Shell Advanced High-Water-Based Fluids and the expected magnitude of the internal leakage should be established also. It is important that this is taken into account as, depending upon circuit design, there may be a shortfall in pump capacity as components wear normally. Relative to Shell Irus Fluid A, Shell Irus Fluid AT10 and Shell Irus Fluid AT37 provide improved volumetric efficiency, due to reduced internal leakage.
The negligible lubrication properties of water have already been stated. The limited viscosity increase with increasing pressure is a major disadvantage and results in poorer lubrication and consequently higher rates of wear compared to mineral oils. Shell Advanced High-Water-Based Fluids are formulated with a unique combination of base fluids and performance additives chosen for their ability to build and maintain effective boundary films to reduce wear and corrosion. The mechanical performance of Shell Irus Fluid AT10 and Shell Irus Fluid AT37 is superior to that of Shell Irus Fluid A due to the improved lubrication and sealing properties of the higher viscosity fluids. In addition, the careful selection of materials used for rubbing interfaces, surface finish and design geometry aimed at achieving hydrodynamic lubrication all contribute to improving component life.
The comparatively low viscosity of water at high pressures is a major contributor in limiting the life of rolling bearing elements by fatigue damage. Solutions to the problem include the selection of rolling bearings sized considerably in excess of those normally specified for mineral oils, isolating the bearing from the fluid whilst providing an external source of lubrication and the use of plain or composite bearing bushes. Ball and rolling bearing elements should be avoided wherever possible when using Shell Advanced High-Water-Based Fluids; however, experience has shown that satisfactory life can be achieved with certain types.
The operation of directional spool valves on very low viscosity water-based emulsions can lead to premature failure by erosion processes. These problems can, to some extent, be overcome by the selection of more resilient construction materials, such as stainless steel, and designs which avoid impingement erosion by high velocity jets. An alternative approach is to select more viscous fluids, and experience has shown that the use of Shell Irus Fluid AT10 and Shell Irus Fluid AT37 can avoid costly modifications due to the marked reduction in cavitation damage. It has generally been found necessary to use poppit-type valves with Shell Irus Fluid A emulsions.
Characteristics of Shell Advanced High-Water-Based Fluids
As a hydraulic medium, water has markedly different properties compared to those of mineral oil and it is important that these variations are appreciated prior to formulating plans for conversion to high-water-based fluids.
The density and vapour pressure of Shell Advanced High-Water-Based emulsions are notably higher than those typical of mineral hydraulic oils. It is important to note that the conditions at the pump suction port, which have a strong influence on pump longevity, are affected by fluid density temperature, vapour pressure, pump speed and the static fluid head. The pressure existing at the pump inlet must not fall below the minimum permissible level specified by the pump manufacturer and attention should be paid to the following aspects:
A positive static fluid head of at least 0.5 metre, obtained from a reservoir located above the level of the pump, is usually adequate to provide sufficient suction port pressure, i.e. not less than zero gauge pressure or as required by the manufacturer. Alternatively, a secondary inlet boost pump may be used to obtain the desired conditions. The higher density of water-based fluids compared to those of mineral hydraulic oils can be problematical where the pump is situated above the fluid level in the reservoir and negative head conditions exist.
The pipework between the reservoir and the pump suction port should be as short as possible with the minimum number of elbows, bends and restrictions. The bore of the pipework may need to be enlarged if the pump suction port pressure losses cannot be reduced to acceptable levels.
The recommended pump speed specified by the manufacturer should be strictly adhered to. Increasing pump speed reduces pressure at the suction port and consequently a higher inlet pressure is required if acceptable pump life is to be realised.
The fitting of fine porosity strainers in the suction line should be avoided as they can contribute significantly to inlet pressure losses. Alternative fluid filtration arrangements should be considered, e.g. filter location in the high pressure line and in the return line to the reservoir.
Failure to maintain the required pump suction port conditions can promote cavitation, erosion and excessive noise. Accelerated wear and malfunction of the system components can result. High-water-based fluids are less compressible than mineral oil, they are more "rigid". As a consequence, faster acting pressure relief valves should be used in order to avoid excessive pressure peaks.
Compatibility with system components
Shell Advanced High-Water-Based Fluids are formulated with carefully selected corrosion inhibitors to protect primarily ferrous construction materials from the strong corrosion potential of water. Excellent protection is afforded to surfaces which are constantly submerged in the fluids. However, in reservoirs constructed of mild steel, rusting can occur above the fluid level where condensation can form. Ideally, reservoirs should be constructed of stainless steel although mild steel can be used if suitably protected by a two-pack, chemically-cured epoxy coating. Conventional paint, enamel and varnish finishes invariably show limited compatibility with high-water-based fluids and should be avoided. Shell Advanced High-Water-Based Fluids are generally compatible with the construction materials used in hydraulic systems although magnesium, zinc, cadmium and aluminium metallurgy should be avoided wherever possible.
High nitrile and neoprene seals and packings recommended for use with mineral oils are generally satisfactory for use with Shell Advanced High-Water-Based Fluids. Fluorinated elastomers, e.g. viton are also suitable. Polyurethane, butyl, ethylene-propylene, silicone and natural rubber elastomers should be avoided. Packing materials containing asbestos, leather and cork are not recommended since they absorb water. Board and paper materials should not be used for flange and cover seals. Fluid packing compounds or mastics should be used sparingly to avoid system contamination and possible blockage of valves and filters.
The presence of contaminants in a hydraulic circuit, particularly those which can cause abrasive wear, can have a significant impact upon the reliability and service life of the system components. Efficient filtration and rigorous contamination control is of great importance when using Shell Advanced High-Water-Based Fluids; ten micrometer or 15 micrometers nominal filters should be used, as normally recommended by equipment manufacturers. These should be located in the high pressure line and in the return line to the reservoir after the load valve, or as recommended.
The surface of the filters should be large enough to avoid a high pressure drop and the volumetric capacity of all filters should be such that they are able to pass at least three times the output of the pump at the operating viscosity. By-passes are not recommended in the high pressure line, and a pressure drop in excess of 3.5 bar is to be avoided.
Many types of filter are suitable for use with Shell Advanced High-Water-Based Fluids. Users should refer to individual manufacturers' recommendations. Inert metal mesh or glass fibre filters are preferred. Active clay or absorbent filters should not be used. Frequent filter changes are recommended, particularly during the initial stage of operation with Shell Advanced High-Water-Based Fluids.
The pump suction strainer should be relatively coarse, sizing in the range 150-300 micrometers with a flow rating of greater than twice the pump output flow rate being satisfactory. Inert metal mesh strainers are preferred.
Fire resistance properties
Hydraulic fluids vary widely in their resistance to fire and the materials they produce on thermal decomposition. Possible incidents which could lead to hydraulic fluid ignition are contact with incandescent surfaces, a high pressure fluid jet spraying on to an ignition source and ignition of fluid soaked material. Shell Advanced High-Water-Based Fluids display excellent fire resistance in the recognised wick and spray tests and also when poured directly on to a metal surface at a temperature significantly above the auto ignition temperature of conventional mineral oil. Shell Irus Fluid A emulsions and Shell Irus Fluid AT10 and Shell Irus Fluid AT37 display superior fire resistance to most HFB (water-in-oil emulsions) and HFC (water-glycol solutions) fluids and generate thermal decomposition products of significantly lower hazard than HFD (phosphate-ester) fluids.
The fluids represent a significant advance in fire resistant, high-water-based emulsion technology and Shell Irus Fluid AT10 and Shell Irus Fluid AT37, in particular, set new standards of system performance, reliability and life expectancy compared to that achievable with conventional 5:95 HFAe products.
Change-over procedure to Shell Advanced High-Water-Based Fluids
Shell Advanced High-Water-Based Fluids display very limited miscibility and compatibility with most hydraulic fluid types including mineral oils and other fire resistant fluid categories such as water-glycols (HFC) and phosphate esters (HFD). Great care must be exercised during conversion to reduce contamination to the absolute minimum otherwise performance and longevity of the fluid may be impaired. It should be noted that systems previously filled with phosphate ester (HFD) fluids should be flushed with the minimum quantity of mineral oil prior to undertaking the procedure detailed below.
The following change-over procedure is recommended:
Drain the oil from the system completely. Particular attention should be paid to the reservoir, fluid lines, cylinders, accumulators, filters and other equipment where residual oil may be trapped. Low points of pipework and dead-legs should not be overlooked.
Physically clean the system of any wear debris, residual sludge and deposits. Remove the paint from the inside of the reservoir unless it has been tested and found to be resistant to Shell Advanced High-Water-Based Fluids. Apply a compatible protective coating to the internal surfaces of the reservoir. Make provision for a suitable breather arrangement to prevent the ingress of airborne contamination and ensure that the reservoir lid can be tightly sealed. Consideration should be given to replacement of the existing reservoir by one fabricated in stainless steel. Open top reservoirs must be replaced by an enclosed design.
Undertake any necessary modification to the reservoir, pump location or sizing of the suction line. Fit an appropriate suction line strainer. Check with the equipment manufacturers that the pump, valves and other components are suitable for use with high-water-based fluids. Modify pump speed and system pressure according to recommendations.
Discard the old filter element and replace by a type compatible with Shell Advanced High-Water-Based Fluids. Replace filter elements having zinc or cadmium-plated parts with appropriate substitutes. Do not use a highly absorptive filter medium such as activated clay or Fuller's Earth since these filters may alter fluid composition by removing essential additives.
Clearly identify reservoirs and systems which are undergoing conversion to minimise confusion and errors, particularly during fluid maintenance.
Close the system and fill with a quantity of Shell Advanced High-Water-Based fluid. Flush initially by operating at no load or at minimum pressure, then bring the fluid up to normal temperature and operate all parts. Many users follow the practice of operating all hydraulic functions on the flush fill for several hours in order to ensure complete circulation.
Drain the flushing charge as completely as possible while it is still warm and without allowing it to settle. Discard this fluid. Install a new filter element.
Examine pump parts, O-rings and auxiliary equipment. Worn pump parts should be replaced. Leaking pipe joints should be repaired and deteriorated gaskets, seals and packings should be replaced in order to minimise mechanical fluid losses. Cork shaft seals should be replaced.
Reconnect the system and tighten all joints and connections.
Refill the system with the selected Shell Advanced High-Water-Based fluid. Operate the system at reduced pressure to ensure proper lubrication of the hydraulic pump, then bring up to design operating conditions.
During the first few weeks of operation, particular attention should be paid to filters and inlet strainers. They may become blocked by sludge and deposits that have been loosened by the excellent wetting properties of Shell Advanced High-Water-Based Fluids. Such blockages may cause pump starvation, noisy operation and component damage. Therefore, filter cartridges should be replaced and inlet strainers cleaned as often as needed. Any residual oil found floating on the fluid in the reservoir should be scooped or sucked away.
Maintenance of Shell Advanced High-Water-Based Fluids
As with all emulsion hydraulic fluids, care should be taken to ensure that the operating temperature remains within strict limits. The operating temperature should be in the range 5-55°C, the ideal temperature being approximately 40°C. The emulsion should never be subjected to sub zero temperatures or temperatures in excess of 65°C as deterioration in stability and performance is likely to occur. Systems converted to Shell Advanced High-Water-Based Fluids have a tendency to operate cooler than with mineral oil due to the difference in thermal properties of the fluids. A reduction in bulk fluid temperature of circa 10°C is not uncommon.
Excessive evaporation of water from the emulsion can be prevented by maintaining the fluid temperature at the optimum value previously stated. In the event that significant evaporation has occurred, water can be gradually added into the system header tank or reservoir at a point of high turbulence and away from the pump suction line; in the case of Shell Irus Fluid A emulsions, addition of further quantities of concentrate should be unnecessary. Additional quantities of 5:95 Shell Irus Fluid A emulsion or Shell Irus Fluid AT10 and Shell Irus Fluid AT37 can be added to the system as and when required and should be introduced into the header tank or reservoir at a point remote from the pump suction line. Pre-filtration is recommended to reduce particulate contamination.
The concentration of water in Shell Irus Fluid A emulsions and Shell Irus Fluid AT10 and AT37 should be monitored in service by the use of a refractometer. It is recommended that stream samples are taken at regular intervals, say once or twice a month, to check the following characteristics: appearance/colour, emulsion stability/homogenity, water concentration, viscosity at 40°C, pH, microbial contamination and total insoluble matter.
Correctly maintained emulsions of Shell Advanced High-Water-Based Fluids should be stable to microbial attack. However, in a very few systems, particularly those which have not been adequately pre-cleaned or where water added has a high bacteria or organic matter content, an increase in bacteria level may occur. The level of bacterial contamination can be assessed using a simple dip-slide technique. Suitable dip-slides can be recommended on request.
Levels up to 106 total bacteria are unlikely to affect emulsion stability. Bacterial contamination in excess of 106 will probably be accompanied by an unpleasant odour, blackening of the emulsion and a significant lowering of the pH. If this occurs, the system should be drained and flushed with a suitable system cleaner and a fresh charge of fluid added. If required, an effective, compatible biocide is available.
Shell Advanced High-Water-Based Fluids should be stored in a cool, dry place within a covered building and away from direct heat, strong oxidizing agents and sources of ignition.
The fluids must not be subjected to temperatures below +5°C or above 30°C during handling and storage and situations where cooling and warming cycles occur frequently should be avoided.
Containers must not be stored in the open or exposed directly to adverse weather conditions such as frost and cold winds. Shell Advanced High-Water-Based Fluids are likely to be damaged irreversibly if subjected to temperatures below 0°C. Containers should be kept tightly sealed when not in use.
Shell Advanced High-Water-Based Fluids must never be discarded into drainage systems or water-ways after use. Waste emulsions should either be removed by a licensed waste contractor or, in the case of large scale use, separated into constituent oil and water phases to facilitate safe disposal. Used emulsions can be split by the commonly recognised techniques, e.g. by the addition of ionic salt, and the oil phase recovered by allowing the treated emulsion to stand in settling tanks and then either removing the separated oil from the surface or by centrifuging. The recovered oil phase should be disposed of to a licensed waste contractor. The water phase may need further treatment to remove solids and residual oil phase, or require neutralisation of acids used for splitting, prior to disposal. Treated effluent may only be discharged in strict accordance with the requirements of the local authority.
If spillage occurs in a high fire risk environment, the emulsion and any material which has absorbed fluid should be cleaned away without delay as evaporation of the water phase is likely to leave oil-rich residues which present an increased fire hazard.
The emulsions are unsuitable for direct combustion as fuel as they contain in excess of 30 percent water. Empty barrels should be returned to specialist drum renovators and labels should not be removed until the containers have been cleaned prior to reconditioning.