5. Ответьте на следующие вопросы по содержанию текста:

1. What fluid properties are required for functioning of any hydraulic power system?

2. What are the advantages and disadvantages of water as hydraulic fluid?

3. What good properties do mineral oils have in comparison with water?

4. why is the application of petroleum oil limited?

5. How can we select the proper fluid for a particular hydraulic system?

Text 2

1. Переведите текст письменно со словарем:

Change of Viscosity with Temperature: Rate of change of viscosity with temperature is expressed as viscosity index, or VI. This viscosity index is calculated from actual viscosity measurements at 100 and 210 F. The higher the VI, the less the change in viscosity with temperature. Paraffinic oils as a class have higher viscosity indexes than do naphthenic oils.

In either case the VI is affected by the treatment given the oil in the manufacturing process. For example, the index can be increased by the use of additives. Disadvantages of viscosity-index improver additives include their tendency to lose effectiveness under high shear rates and their relatively high cost.

Viscosity index is important only in applications subjected to a wide temperature range. In such cases it is important that a high-viscosity-index oil be used. If not, viscosity may be so high when the equipment is started cold that the fluid won’t flow properly. Or it may be too thin at operating temperatures. If the equipment is not subjected to low temperature, and if oil temperature is controlled within reasonable limits, viscosity index is less important.

Normally oil temperature during operation should not exceed 160 F. Minimum starting temperature is determined by the maximum viscosity which can be tolerated by suction system of the pump. Minimum starting temperature can be obtained by comparing pump capability against plot of the viscosity-temperature characteristics of the oil. The most satisfactory normal operating temperature for a hydraulic system is usually about 120 F.

Change of Viscosity with Pressure: Lubricating oils increase in viscosity as pressure increases. Even though only small differences exist in viscosity of oils at atmospheric pressure, there may be large differences at high pressure. Oils which show the greatest change in viscosity with temperature also show the greatest change in viscosity with pressure. 1923

Text 3

1. Прочтите текст, разделите его на абзацы, озаглавьте каждый абзац и составьте реферат: Filtering water-based fluids

Because HWCF do not behave like standard hydraulic fluids, established filtration guideline may not apply. Two main considerations when selecting a filter for HWCF are media efficiency and filter construction. Media efficiency controls the rate of contaminant removal versus the rate at which contaminant is added to the system, often stated as the beta ratio.

Primary sources of contaminants are ingression and particles generated from system wear; in both cases HWCF systems deserve special attention. Often lower lubricity results in increased component wear. A higher level of system generated contaminants means more filtration capacity is necessary. Additionally the lower viscosity of some HWCF requires better seals and leakage control; every leak provides a path for contaminants to enter the circuit.

Another concern is fluid compatibility. Compatibility problems with circuit components could result in the formation of precipitate that collects in the filter. Early warning of incompatibility and possible component failure can be predicted by contaminant monitoring and ferro graphic analysis.

The use of HWCF also presents the possibility of additional contaminants such as algae and microbes. These form slime if the fluid is not properly maintained and can clog the filter. Also when a circuit requires ultra-fine-filtration to protect a particularly critical component, the fluid manufacturer should be consulted to ensure that suspended additives are not removed.

Filter media must be tolerant of HWCF. Water causes cellulose fibers to swell, clogging the element. In some cases resin-impregnated cellulose fibers of stainless steel wire mesh for suction strainer applications are used. A fiberglass- synthetic medium with epoxy bonding and sealed seams is preferred for all fine filtration applications of HWCF.

Other parts of the filter housing should be checked for compatibility with the particular HWCF used. Generally no anodized aluminum, magnesium, zinc and cadmium should not be present. Polyurethane seals also are not compatible with HWCF.

Proper filter sizing is always necessary to avoid excessive pressure drop in the circuit. Factors that affect pressure drop, like flow rate and viscosity at a given temperature, are usually provided by the filter manufacturer for a specific medium based on mineral oil hydraulic fluid.

HWCF – жидкость с высоким содержанием воды

UNIT 3

Text 1

Слова и словосочетания для запоминания:

1. cause - заставлять, приводить

2. sludge - осадок

3. soluble - растворимый

4. breakdown - поломка, ухудшение, распадение

5. breakdown products - продукты распада

6. moisture - влажность

7. close-tolerance valve - клапан