Unit ThirteenUnit Thirteen

Hydraulic Fluid ConditioningHydraulic Fluid Conditioning

The illustration is that of a “power unit” which includes the The illustration is that of a “power unit” which includes the reservoir.reservoir.

Hydraulic Fluid ConditioningHydraulic Fluid Conditioning

The Importance of FiltrationThe Importance of Filtration

Maintenance of hydraulic oil is critical to the service life Maintenance of hydraulic oil is critical to the service life of a machine. Clearly, over 80% of all machine failures of a machine. Clearly, over 80% of all machine failures can be traced back to contamination of the hydraulic oil. can be traced back to contamination of the hydraulic oil. Because of the costs associated with the loss of Because of the costs associated with the loss of production time, proper maintenance of the hydraulic production time, proper maintenance of the hydraulic and lubricating systems becomes as critical an element and lubricating systems becomes as critical an element in design as the selection of the components that make in design as the selection of the components that make up a system.up a system.

The Purpose of Hydraulic FluidThe Purpose of Hydraulic Fluid

Transmit PowerTransmit Power

Dissipate HeatDissipate Heat

Lubricate Moving PartsLubricate Moving Parts

Seal Clearances between moving Seal Clearances between moving partsparts

Hydraulic ReservoirsHydraulic Reservoirs

Reservoirs should be fabricated in accordance to NFPA Reservoirs should be fabricated in accordance to NFPA standards and include all the individual components above.standards and include all the individual components above.

Sizing a Hydraulic ReservoirSizing a Hydraulic Reservoir

First of all, heat from a hydraulic system is generated when First of all, heat from a hydraulic system is generated when energy is consumed and no work is being done. Relief valves, energy is consumed and no work is being done. Relief valves, flow controls, and pressure reducing valves are examples of flow controls, and pressure reducing valves are examples of heat generating devices but there are more. In sizing a heat generating devices but there are more. In sizing a reservoir it is generally a good idea to oversize slightly to reservoir it is generally a good idea to oversize slightly to ensure adequate heat dissipation. The general rule is that ensure adequate heat dissipation. The general rule is that minimum reservoir capacity should be minimum reservoir capacity should be 3 times the rated flow of 3 times the rated flow of the pump plus 10 percent extra for air spacethe pump plus 10 percent extra for air space. The extra 10 . The extra 10 percent is to ensure room for expansion of fluid level and escape percent is to ensure room for expansion of fluid level and escape of air.of air.

For more information see: “Design Engineer’s Handbook” by Parker, page H-3For more information see: “Design Engineer’s Handbook” by Parker, page H-3

Basic Parts and OperationBasic Parts and Operation

1.1. Reservoir Capacity: Reservoir Capacity: Three times rated flow of pump.Three times rated flow of pump.

2. Mounting Plate: 2. Mounting Plate: Facilitates a secure surface for mounting Facilitates a secure surface for mounting the prime mover.the prime mover.

Basic Parts and OperationBasic Parts and Operation

3. Flexible Motor Coupling: 3. Flexible Motor Coupling: Connects prime mover to hydraulic Connects prime mover to hydraulic pump. Allows for variances in alignment.pump. Allows for variances in alignment.

4. Filler Breather Cap: 4. Filler Breather Cap: Allows for adding of fluid, escape or entry of Allows for adding of fluid, escape or entry of air, and filtration of air.air, and filtration of air.

5. Baffle: 5. Baffle: Forces return fluid to travel further before suction to Forces return fluid to travel further before suction to ensure greater fall out of contamination and escape of air.ensure greater fall out of contamination and escape of air.

Basic Parts and OperationBasic Parts and Operation

6. Reservoir Legs: 6. Reservoir Legs: Allow for mounting and circulation of air.Allow for mounting and circulation of air.

7. Additional Return and Drain Lines: 7. Additional Return and Drain Lines: Allow for machine Allow for machine modifications.modifications.

8. Oil Level Indicator: 8. Oil Level Indicator: To allow monitoring of fluid level.To allow monitoring of fluid level.

Basic Parts and OperationBasic Parts and Operation

9. Cleanout Covers: 9. Cleanout Covers: Allows easy access for removal of contamination.Allows easy access for removal of contamination.

10. Drain Plug: 10. Drain Plug: Allows for draining prior to cover removal.Allows for draining prior to cover removal.

11. Reservoir Tank: 11. Reservoir Tank: Holds fluid and acts as a conduit by which heat escapes to Holds fluid and acts as a conduit by which heat escapes to surrounding air. Material is usually SAE1020 but aluminum is becoming surrounding air. Material is usually SAE1020 but aluminum is becoming popular due to its unique heat transfer characteristics.popular due to its unique heat transfer characteristics.

Reservoir TypesReservoir Types

Conventional Overhead L-ShapedConventional Overhead L-Shaped

Conventional reservoirs, also known as “flat tops,” are by far the Conventional reservoirs, also known as “flat tops,” are by far the most common designed for motors of 7.5 to 40 horsepower.most common designed for motors of 7.5 to 40 horsepower.

The overhead design allows for positive head pressure while being The overhead design allows for positive head pressure while being able to accommodate more than one pump.able to accommodate more than one pump.

The L-shape design offers positive head pressure and The L-shape design offers positive head pressure and accommodates motors of 40 to 50 horsepower.accommodates motors of 40 to 50 horsepower.

CoolersCoolers

The primary function of an auxiliary cooler is to dissipate the The primary function of an auxiliary cooler is to dissipate the heat that is not removed by the reservoir alone. Coolers are easy heat that is not removed by the reservoir alone. Coolers are easy to add to a system after initial installation and can greatly reduce to add to a system after initial installation and can greatly reduce system temperatures.system temperatures.

Basic SymbolBasic Symbol Air CoolerAir Cooler Water CoolerWater Cooler

Air CoolersAir Coolers

Water CoolersWater Coolers

Coolers in a CircuitCoolers in a Circuit

Hydraulic FiltersHydraulic Filters

Affect of DirtAffect of Dirt

1. Interferes with lubrication.1. Interferes with lubrication.

2. Interferes with heat transfer.2. Interferes with heat transfer.

3. Interferes with tiny openings and clearances.3. Interferes with tiny openings and clearances.

Micrometer ScaleMicrometer Scale

A micrometer is one-millionth of a meter.A micrometer is one-millionth of a meter.

Twenty five micrometers is equal to .001 inch.Twenty five micrometers is equal to .001 inch.

With good vision, the human eye can see down to 40 With good vision, the human eye can see down to 40 micrometers.micrometers.

A grain of salt is about 100 micrometers in diameter.A grain of salt is about 100 micrometers in diameter.

A human hair measures about 70 micrometers in A human hair measures about 70 micrometers in diameter.diameter.

Fluid CleanlinessFluid Cleanliness

The “cleanliness” of oil is a specific term, measurable, and is The “cleanliness” of oil is a specific term, measurable, and is defined by ISO 4406. Generally speaking, the human eye cannot defined by ISO 4406. Generally speaking, the human eye cannot be relied upon for determining the cleanliness of hydraulic oil. be relied upon for determining the cleanliness of hydraulic oil. Automatic particle counting is the most effective means of Automatic particle counting is the most effective means of determining the amount, average size, and type of contamination determining the amount, average size, and type of contamination in oil.in oil.

Filter ElementsFilter Elements

Filter materials used for cleaning hydraulic oil are Filter materials used for cleaning hydraulic oil are usually of the absorbent type. They are further usually of the absorbent type. They are further divided into two categories: surface and depth.divided into two categories: surface and depth.

Surface type elements, composed of stainless wire mesh, Surface type elements, composed of stainless wire mesh, are used primarily for coarse filtration such as suction are used primarily for coarse filtration such as suction strainers.strainers.

Depth type elements are usually used for fine filtration Depth type elements are usually used for fine filtration and are composed of a thickness of material in which dirt and are composed of a thickness of material in which dirt particles become trapped as they try to weave around the particles become trapped as they try to weave around the media.media.

Filter/Strainer SymbolFilter/Strainer Symbol

The schematic symbol for a filter is the same as a The schematic symbol for a filter is the same as a strainer and is drawn the same way in pneumatics as strainer and is drawn the same way in pneumatics as well as in hydraulics.well as in hydraulics.

Nominal and Absolute RatingNominal and Absolute Rating

Nominal Nominal and and AbsoluteAbsolute are terms used to describe the are terms used to describe the way a filter is constructed rather than how it filters.way a filter is constructed rather than how it filters.

A A nominalnominal rated filter simply indicates an average rated filter simply indicates an average “pore” size and that some particles bigger than the pore “pore” size and that some particles bigger than the pore size will probably get through but certainly smaller ones size will probably get through but certainly smaller ones will.will.

An An absoluteabsolute rating indicates the exact pore size of an element rating indicates the exact pore size of an element such as a wire screen and that a certain diameter particle will such as a wire screen and that a certain diameter particle will be stopped. The problem with this rating is that it doesn’t be stopped. The problem with this rating is that it doesn’t take into account a particle that is long and narrow that may take into account a particle that is long and narrow that may get through.get through.

Beta RatioBeta Ratio

The beta ratio is a filter efficiency rating that was taken from The beta ratio is a filter efficiency rating that was taken from the “multi-pass” test. In the multi-pass test, fine dust of a the “multi-pass” test. In the multi-pass test, fine dust of a certain micrometer size is sent through a filter element several certain micrometer size is sent through a filter element several times. After several passes, a comparison would be made times. After several passes, a comparison would be made between upstream and down stream contamination with the between upstream and down stream contamination with the difference being the amount of contamination trapped by the difference being the amount of contamination trapped by the filter. The two were divided(upstream divided by downstream) filter. The two were divided(upstream divided by downstream) and the result was a percentage of particles trapped. The and the result was a percentage of particles trapped. The greater the percentage of a known size, the greater the filters greater the percentage of a known size, the greater the filters efficiency at that value.efficiency at that value.

Example: Example: If 100 particles of a known size are circulated If 100 particles of a known size are circulated through a filter and 75 of them are trapped, the beta is 4 or through a filter and 75 of them are trapped, the beta is 4 or 100 divided by 25, the amount left uncaught, equals 4 or 100 divided by 25, the amount left uncaught, equals 4 or 75% efficiency.75% efficiency.

Filter Ratings in PracticeFilter Ratings in Practice

Filter ratings can be manipulated or misunderstood very Filter ratings can be manipulated or misunderstood very easily so the rating itself is no guarantee of how well a easily so the rating itself is no guarantee of how well a filter can remove a certain size particle. It is filter can remove a certain size particle. It is recommended that the component manufacturer or a recommended that the component manufacturer or a reputable filter manufacturer be consulted in reputable filter manufacturer be consulted in determining which type of filter is best suited to a determining which type of filter is best suited to a particular application.particular application.

Sources of DirtSources of Dirt

Dirt is any insoluble material circulating in a hydraulic or Dirt is any insoluble material circulating in a hydraulic or pneumatic systempneumatic system

There are three main sources of dirt:There are three main sources of dirt:

1. Built in- during manufacture or assembly.1. Built in- during manufacture or assembly.

2. Ingressed or added by dirty makeup fluid or environmental 2. Ingressed or added by dirty makeup fluid or environmental defective seals.defective seals.

3. Self-generated by failing components such as bearings or other 3. Self-generated by failing components such as bearings or other wear surfaces.wear surfaces.

Proportional Flow FilterProportional Flow Filter

Examine the filter and its connection to tank in the above Examine the filter and its connection to tank in the above illustration. Notice that part of the flow can go through the filter illustration. Notice that part of the flow can go through the filter and part would go over the relief valve. The amount of oil filtered and part would go over the relief valve. The amount of oil filtered would depend on system pressure and flow. Cylinder speed would would depend on system pressure and flow. Cylinder speed would be affected.be affected.

Full Flow FiltrationFull Flow Filtration

A full flow filtration filter is one in which all the system’s oil A full flow filtration filter is one in which all the system’s oil must pass through the filter element as it travels through the must pass through the filter element as it travels through the system. This type of filter is by far the most common in use system. This type of filter is by far the most common in use today.today.

Parallel Flow FiltrationParallel Flow Filtration

In this method of filtering, the machine runs continuously while oil is In this method of filtering, the machine runs continuously while oil is being cleaned. Even when the machine is shut down for being cleaned. Even when the machine is shut down for maintenance or repair, oil is being filtered. Notice that the filtering maintenance or repair, oil is being filtered. Notice that the filtering system incorporates its own pump.system incorporates its own pump.

Location of Filter and PressureLocation of Filter and Pressure

Location and type of filtration is determined by demand. Oil Location and type of filtration is determined by demand. Oil coming from the reservoir should have almost no restriction so coming from the reservoir should have almost no restriction so filtration will be minimal. Oil returning to the reservoir will be filtration will be minimal. Oil returning to the reservoir will be warm and contain particles picked up from the system warm and contain particles picked up from the system components. Sensitive components on the high pressure side of the components. Sensitive components on the high pressure side of the system will generally use a filter with no by-pass check valve.system will generally use a filter with no by-pass check valve.

Filter Bypass ValveFilter Bypass Valve

Most filters, except high pressure, use a by-pass valve to Most filters, except high pressure, use a by-pass valve to protect the system from running dry in the event of filter protect the system from running dry in the event of filter blockage. The thought here is that dirty oil is better than blockage. The thought here is that dirty oil is better than no oil.no oil.

Filter MaintenanceFilter Maintenance

When servicing filters, it is best to consult the manufacturer’s When servicing filters, it is best to consult the manufacturer’s recommendations but in most cases the hours of operation should recommendations but in most cases the hours of operation should dictate the replacement as this is the only reliable means of dictate the replacement as this is the only reliable means of ensuring peak system performance.ensuring peak system performance.

Although filters may come with a “by-pass” indicator, this is not a Although filters may come with a “by-pass” indicator, this is not a preferred method of monitoring filters because if the indicator is preferred method of monitoring filters because if the indicator is showing by-pass then the damage has already been done. Some showing by-pass then the damage has already been done. Some types of indicators include a needle, warning light, and sound types of indicators include a needle, warning light, and sound alarm.alarm.