HYDRAULIC - (Symbol of hydraulic, Hydraulic fluids & Properties, Hydraulic filters, Cavitation, Safety precautions)

Hydraulic

Symbol of hydraulic components 

1- It is a graphical representation of the hydraulic components in a hydraulically operated machine. 

2- It gives us an idea how control valves, actuators, pumps etc., are interconnected.

Example of hydraulic circuit 

1- This hand pump has been designed for use on machines which require emergency lowering, or for pilot supply on access platforms and lubrication circuits.

Hydraulic fluids 

1- A hydraulic fluid power system may be defined as a means of power transmission in which a relatively incompressible fluid is used as the power transmitting media. 

2- The term fluid has come into general use in hydraulics to refer to the liquid used as the power transmitting medium. 

3- The hydraulic fluid has the following primary purposes 

I)- To transfer power 

II)- To lubricate parts 

III)- To avoid corrosion 

IV)- To remove impurities 

V)- To dissipate heat 

VI)- To seal clearance between parts

Properties of hydraulic fluid 

Viscosity 

1- Viscosity is the measure of the fluid's resistance to flow. 

Physical and chemical stability 

1- The fluid characteristics should not change during long use and during storage.

System compatibility 

1- The hydraulic fluid should be inert to those materials which are used in or near the hydraulic equipment. 

Good heat dissipation 

1- The hydraulic fluid should carry away the generated heat away and dissipate to the cooler or atmosphere. 

Adequate low temperature properties

1- The hydraulic fluid should be able to operate in low temperature environment or at high altitudes. 

Inflammability

1- The hydraulic fluid should have low inflammability. 

Low foaming tendency 

1- A liquid has the property to absorb a portion of the gas or air with which it comes in contact. 

2- It doesn't cause any problem if absorption is within limits. 

3- But it may cause problems in functioning of the system if the limit is crossed. 

Fire resistance 

1- The hydraulic fluid should have high fire resistance. 

Prevent rust formation

1- Moisture is present to some extent in hydraulic systems. 

2- Fluids with rust inhibitors help to minimize rust formation in the system. 

Low volatility 

1- The hydraulic fluid should not evaporate at low temperatures.

Contamination in oils and its control 

1- One of the main cause of failure or poor functioning of a hydraulic system is contamination of hydraulic oil or fluid. 

2- Hydraulic filters are used for handling and removing contamination from hydraulic oil. 

3- Contaminants of hydraulic fluid are broadly defined as any substance that impairs the proper functioning of the fluid. O Contaminants are classified as 

I)- Solids 

II)- Liquids 

III)- Gaseous 

IV)- Bacteria 

V)- Organic

Hydraulic filters 

1- There are four types of filters generally used in hydraulic system. 

I)- Mechanical filter 

II)- Absorbent filter 

III)- Adsorbent filter 

IV)- Magnetic filters 

Mechanical filter 

1- Mechanical filters contain closely woven metal screens or discs. They generally remove only fairly coarse particles. 

2- Mechanical filter is known as strainer in hydraulic system.

3- These filters are located in the suction line of the pump, hydraulic oil is drawn from the reservoir through the filter.

4- Grade of Mechanical filter: 60-100 µm 

5- um is the micron which is 1/1000 part of 1 mm. 

Absorbent filter 

1- Absorbent filters, such as cotton, wood pulp, yarn, cloth, or resin, remove much smaller particles; some remove water and water-soluble contaminants. 

2- The elements often are treated to make them sticky to attract the contaminants found in hydraulic oil.

3- These filters are installed in the pressure line of a hydraulics system at the pressure port of the pump. 

4- Since this filter is subjected to the maximum operating pressure, it must be of robust design.

Adsorbent filter

1- A filter used for trapping various sizes of particulate matter. Adsorbent filters consist of clay, chemically treated paper and desiccant. 

Magnetic filter

1- Magnetic filters are basically used to remove the ferrous material from oil along with contaminants. 

2- Magnet are geometrically arranged outside or inside the filter which produce a strong magnetic field that help to arrest the ferrous particles from oil.

Hydraulic filter typical installation location 

Filter types on the basis of location 

Suction Steiner 

Pressure line filter 

Return line filter 

Off line filter 

Suction Steiner 

1- Suction filters serve to protect the pump from fluid contamination. 

2- They are located in the upstream of pump's inlet port. Inlet strainers are submersed in fluid in the tank. 

3- Suction filters have relatively coarse elements, due to cavitation's limitations of pumps.

Return line filter 

1- Return line filters may be the best choice if the pump is particularly senssitive to contamination. 

2- In most systems, the return filter is the last component through which fluid passes before entering the reservoir. 

3- Therefore, it captures wear debris from all of the system's. 

4- Working components and any particles that enter through worn cylinder rod seals before such contaminant can enter the reservoir and be pumped back into the system. 

5- Because this filter is located immediately upstream from the reservoir. 

6- Its pressure rating and cost can be relatively low.

Pressure line filter 

1- Pressure filters are located downstream from the system pump. 

2- They are designed to handle the system pressure and are sized for the specific flow rate in the pressure line where they are located. 

3- Pressure filters are especially suited for protecting sensitive components, such as servo valves, because pressure filters are located just downstream from the pump. 

4- They also help to protect the entire system from any pump-generated contamination. 

Off line filter

1- An off-line filtration circuit includes its own pump and electric motor, a filter and Off line filter the appropriate connecting hardware. 

2- These components are installed off-line as a small subsystem separate from the working lines, or they may be included in a fluid-cooling loop. 

3- Fluid is pumped continuously out of the reservoir, through the off-line filter and back to the reservoir.

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Cavitation 

1- The inter-locked air bubbles and pockets in the hydraulic pipe lines and components is called cavitation. 

2- In cavitation the static pressure falls below vapor pressure. 

3- The vapor formation condenses resulting in pressure jerks and noise, and heating-up the oil resulting in a turbulent flow. 

4- Therefore resulting flow of oil should be a stream line or laminar in the pipe lines.

Safety precautions and related hazards for hydraulic system 

Safety precautions 

1- There are numerous hazards involved, like skin irritation, fires, explosions, environmental damage and a slippery workplace. 

2- But hydraulic fluids are required for many machines to function. 

3- Therefore it is necessary to follow certain precautions while using these fluids. 

4- With proper knowledge of these hazards, working with hydraulic fluid can be safe. 

I)- In order to avoid skin irritations, it is necessary to wash contaminated skin immediately. 

II)- It is also necessary to keep you clothing clean. 

III)- Wearing masks and gloves while using hydraulic fluids is also helpful. 

IV)- To avoid environmental dangers, there is biodegradable hydraulic fluidwdo option, though it is more expensive.

5- To avoid fires, materials and fluids soaked in hydraulic fluid should be stored in sealed metal containers and disposed of at proper places. 

6- To check for leaks, use cardboard. 

7- Never use hands or fingers to search for hydraulic leaks. 

8- Maintain a clean work area free of slipping hazards. 

9- Use chemical resistant gloves, splash goggles and a chemical resistant apron to avoid prolonged or repeated skin or eye contact. 

10- Never begin work on a hydraulic system until fully trained. 

Related hazards 

Health problems while using hydraulic fluids 

1- People can become exposed to the chemicals in hydraulic fluids. 

2- The exposure to chemicals may be due to inhalation, ingestion or touch.

3- There are instances of people suffering from skin irritation or weakness in hands while handling hydraulic fluids. 

4- There are also cases of intestinal bleeding, pneumonia or death through hydraulic fluid ingestion though no serious hazards are reported with hydraulic fluid inhalation. 

5- Similar to ingestion, fluids can be accidentally injected into the skin as well. 6- This takes place when the high pressure hydraulic system hose is disconnected and toxic fluids are leaked and injected into the skin. 

7- If there is a small leak in the hydraulic pipe and someone runs there hand along it, at 2000 psi, they can easily incur an injection of hydraulic fluid and may not even be aware that it happened until gangrene begins to set in. 

Fire dangers associated with hydraulic fluids 

1- When working with hydraulic fluid, there is every chance that the hydraulic fluid

gets heated to high temperatures.

2- And it is evident that most petroleum - based hydraulic fluids will burn and thereby create explosions and burns. 

Environmental problems related to hydraulic fluids 

1- Another hazard of hydraulic fluid is that when the hydraulic hose or pipe leaks, the chemicals of the fluids can either stay on top of the soil or sink into the ground. 

2- If the chemicals get mixed in a water body, they will sink to the bottom. 

3- In fact in such cases the chemicals can stay there for more than a year. 

4- Aquatic life can absorb the toxic hydraulic fluid, leading to illness or death to the animal or anything higher on the food chain. 

5- For example, a hawk that eats a fish that has been contaminated by hydraulic fluid that was mixed in water could become ill as well. 

Fluid texture problems 

1- Although the slimy texture of hydraulic fluids may not seem like a danger problem, a spill can cause a person to slip and fall.

2- Also when there is fluid on the hands of a person, it can cause him to slip while climbing on a machine. 

3- It can also cause the operator to lose steering control. 

Injuries from loose hydraulic hoses 

1- Due to high pressure with in a hydraulic system, the impact force of a disconnected and flailing hydraulic hose can cause abrasions, temporary unconsciousness, bruise, fractures and lacerations. 

2- Proper maintenance and good pre-shift equipment inspections can minimize these hazards.

Hydraulic reservoir 

1- The storage space for the fluid is the reservoir. 

2- The fluid is kept clean by using strainers, filters, and magnetic plugs.