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Hydraulic Oil Usage

Hydraulic System Pressure (Setting)

Hydraulic Pump Operation

Hydraulic System Operation

Hydraulic System Design

Pneumatic System Design

 

 


Hydraulic Oil Usage


Temperature Guidelines
For normal operation (0-1500 psi, 130¼ F), use oil with a fluid viscosity of 150 SSU @ 100¼ F.

For higher pressures and temperature (up to 150¼ F), use oil with a fluid viscosity of 225-325 SSU @ 100¼ F.

For cold startup applications down to 0¼ F, ATF Type A fluid will prove satisfactory.



Hydraulic Setting System Pressure


System pressures should be set as low as possible to prevent unnecessary fluid heating; on some applications, this setting may be from 50 to 200 psi above necessary working pressures to overcome dynamic pressure drop or to achieve proper acceleration.

If system is equipped with a pressure compensated pump, adjust the pressure using the pump compensator.

If system is equipped with a fixed displacement pump, adjust the pressure using the system relief valve.



Hydraulic Pump Operation


Eliminating Pump Noise
Pump noise (crackling) is often caused by air entering the pump suction. The tightening of fittings on the suction side of the pump will usually eliminate such problems.



Pump Won't Prime
If pump fails to prime, vent pump discharge to atmosphere by loosening a discharge fitting until you see a steady stream of flow, then tighten.



Hydraulic System Operation


Power Unit Cleaning after Startup

After the first few hours of operation of a new power unit, foreign material from the system plumbing will be flushed back to the reservoir.

It is good practice to drain and replace the initial fill, then clean the reservoir and suction strainer, followed by replacing with new hydraulic fluid.

As an alternative, an offline re-circulating pump and filter can be used to accomplish this task.


Beware High Temperatures
For most industrial applications, an operating temperature of 150¼ F is considered maximum.

At higher temperatures, difficulty is often experienced in maintaining reliable and consistent hydraulic control, component service life is reduced, hydraulic fluid deteriorates, and a potential danger to operating personnel is created.

If system is running at 150¼ F or higher, shut down the system, and determine the cause of the elevated temperature.



Maintenance Intervals
At least once a year or every 4,000 hours of operation, the reservoir, suction strainer, and air vent filter should be cleaned. At this time, check the entire system for possible future difficulties.

Some application or environmental conditions may dictate such maintenance be performed at more frequent intervals.

If system is equipped with filters having visual or electrical indicators, service the filters whenever the indicators show a by-pass condition.


 

Hydraulic System Design


Pump Sizing
Size the pump to the average oil flow plus 10%. There is no need to size the pump for peak load when using an accumulator.


Reduce System Pressure Drop
Use adequate pressure and return lines with a minimum number of 45¼ and 90¼ joints. These joints induce unnecessary pressure drops.



Accumulator Sizing

When designing for multiple components and operations, use an accumulator. It should be sized at least 10 times larger than the change in volume of oil.



Accumulator Pre-Charge
Pre-charge accumulators to 80% of system pressure. Any oil in the accumulator that is not being used is reducing its effectiveness.

The gas bubble should be as large as possible as long as there is always some oil in the accumulator.


Maximizing Cylinder Control
Locate valves as close as possible to cylinders to maximize control.


Maximize Cylinder Control

Locate accumulators as close to the valve(s) as possible.


Cylinder Control in Proportional Circuits

For maximum control of the cylinder (in proportional systems), do not use flexible hose between the valve and the cylinder.


Maximizing Hose Life
Never bend hose past its listed bend radius (can be found in manufacturer's catalog).


Maximizing Hose Life
Bend hose in one plane only to avoid twisting its wire reinforcement, which would reduce the hose's pressure capability.

If you must bend a hose in more than one plane, install hose clamps between bends, and provide enough length on both sides of the clamp to relieve strain on the hose's reinforcement wires.



Maximizing Hose Life
80% of hose failures are attributable to external physical damage, with abrasion cited as the major culprit.

To prevent abrasion, use clamps to secure hose in place and keep it from rubbing against adjacent surfaces.

Additional protection can be provided by sleeves. Sleeves can be metal to prevent crushing, or fabric to keep abrasive particles way from the hose.

And always use a hose with an abrasion-resistant cover if at all possible.



Maximizing Hose Life
Excessive heat can dramatically reduce hose life, so it is important to keep hose away from any external sources of heat.



Pneumatic System Design


Sizing Pneumatic Motion Systems
To correctly size pneumatic motion systems, every component must be taken into account. Using only the flow coefficient (CV) is not enough. Every component in the system must be considered to ensure high performance and minimal losses.

A good rule of thumb for sizing a cylinder for speed is to make it large enough to provide two times the calculated force requirement.


Sizing Pneumatic Cylinders
A good rule of thumb for sizing a cylinder for speed is to make it large enough to provide two times the calculated force requirement.


Sizing Pneumatic Valves

You want to size pneumatic valves by determining the average flow rate through the exhaust port, and likewise, through the supply port during motion. These exhaust and supply flows will be used to estimate all other component pressure drops in the circuit.

You want a pneumatic valve that has a pressure drop between 2 psi and 10 psi. A valve that has a lower the pressure drop provides a more efficient circuit.

You also need to determine pressure drops across the exhaust valve fitting, exhaust air line, exhaust and supply flow controls, cylinder exhaust fitting, cylinder, cylinder supply fitting, supply air line, supply valve fitting, and the valve supply port. Please call or e-mail for the necessary equations.

With this information, you can calculate the delay time before motion begins when retracting/extending the cylinder. This will also give you an initial time estimate when combined with the valve shift time, PLC scan time, and the valve solenoid time. Then you can resize and adjust components accordingly to give you the proper system response you need.

Using this type of method to determine valve and cylinder requirements may result in space and cost savings as opposed to using the old CV style of pneumatic component sizing. Also, cylinder times are more predictable, and cylinders and valves can be sized to minimize air consumption.

Pneumatic Dryers

Eliminating the cost of replacement parts, labor, standby inventory, and downtime can offset the cost of installing and operating air dryers.

Dryers remove water vapor from the air and lowers the dew point of air (the temperature to which air can be cooled before condensate forms). The four basic types of compressed air dryers are deliquescent, regenerative desiccant, refrigeration, and membrane.

Deliquescent dryers contain a chemical desiccant that absorbs moisture in the air. This chemical desiccant is consumed in the water-removal process and must be replenished periodically. The solution that must be drained from this type of dryer contains both water and the chemical, so disposal may be a problem. Due to differing environmental regulations in each area, these dryers are the least popular of the four types.

Regenerative desiccant dryers work much like deliquescent dryers. The main difference is that a porous desiccant, usually silica gel, is used instead of a chemical. The porous desiccant does not react chemically with the water, so there is no need for replenishment or disposal of the chemical. The desiccant has to be dried, or regenerated, periodically for this dryer to function properly. This type of dryer is further divided up into two types, the heatless regenerative dryer and the heat regenerative dryer. The major difference between these two is the cycle time, and amount of energy consumption to complete a regenerative cycle.

The refrigeration dryer types condense moisture from the compressed air by cooling the air in heat exchangers chilled by refrigerants. These types can only produce dew points in the 35-50 at normal operating pressure (compared to -100 to 65 for the previously mentioned dryers). There are three types of refrigeration dryers. Tube-in-tube dryers operate by cooling a mass of aluminum or bronze that in turn cools the compressed air. Water-chiller refrigerators use a mass of water for cooling. An extra heat exchanger is needed to maintain chilled water if cold water is not available on-site. Direct-expansion refrigerators use a refrigerant-to-air cooling process to produce dew points as low as 35. No recovery period is necessary with this type, so direct-expansion dryers can run continuously.

Membrane-type air dryers are gas-separation devices. They consist of miniature tubes made of plastic compounded to allow water vapor to pass through when there is a pressure differential. This type of dryer is very rugged, with some lasting years while drying continuously. This type of dryer also delivers the most consistent level of drying protection that follows the change in inlet dew point temperature. The membranes of the dryer never become saturated, so there is no need for regeneration. The also contain no moving parts to wear out. They also are non-electric, use no refrigerant in the cooling cycle, make no noise, and can be mounted in any orientation. This is probably the best type of air dryer for most applications among the four.

The two questions to ask yourself in determining what dryer is right for you is 1) How dry must the air be? and 2) What type of dryer should be used?. For more information in determining these two criteria, please contact Indiana Fluid Power.



Filters, Regulators, Lubricators

Air is a simple medium to use for motion control. It's clean, ready available, and simple to use. However, it can be the most expensive form of energy in your facility. A good rule of thumb to use is that for every 2 psi increase in operating pressure, there is a corresponding 1% increase in the energy cost to compress this air. FRL's are needed in your pneumatic system to ensure that every tool, cylinder, or process is receiving a clean, lubricated supply of compressed air at the proper pressure to provide peak performance to decrease your energy cost.

Filters are used to maximize reliability and longevity of your supply of air and components in your motion control system. Filters are used to clean out condensed water, oil carryover from compressors, solid impurities, and wear particles from your air supply. The most likely component in your system to be affected by dirty air is pneumatic valves.

The manufacturers of pneumatic valves normally require certain air ratings in order for the valve's to perform effectively. You want to match your point of use filters to your most demanding component of clean air. Filters are rated according to the minimum particle size that their elements will trap. Finer filter ratings will increase the pressure drop through the filter, which equates to higher energy cost to compress the air. That is why it is extremely important to match your filter to your application to keep your energy costs in line. Finer filtration over what is needed isn't necessarily better. These filters should be selected based on required air flow, acceptable pressure drop, and pipe-connection size.

A pressure regulator is used to reduce supply pressure to the level required for efficient operation of downstream pneumatic equipment. Once you have determined a minimum suitable operating pressure for your application, it is essential to supply the air at a constant pressure, regardless of upstream flow and pressure fluctuations. Selecting the best type of regulator for a specific application first requires a choice among regulator styles (unbalanced poppet, diaphragm, balanced poppet). The next consideration becomes primary (supply) pressure versus secondary (output) pressure. Finally, desired airflow rate must be selected. Although several models may appear to be acceptable for a given airflow and pressure, a larger body size regulator will produce better setting sensitivity and less pressure drop than a smaller body model under the same set of operating conditions.

Many system components and almost all pneumatic tools perform better when lubricated with oil. Injecting an oil mist into the air-stream which powers them can continuously lubricate for proper operation and longer service life. Correct application of most airline lubricators requires mounting close to a single component or tool. Too little oil can allow excessive wear and cause premature failure. Excessive oil in the pipeline is wasteful and can become a contaminant in the ambient area as it exits out of tools and valves by the air exhaust. Finally, intermittent lubrication is the worst condition of all because oil film can dry out and form sludge or varnish on the internal surfaces of your equipment. Lubricators are generally selected based on pipe connection size, oil reservoir capacity, and acceptable pressure loss versus flow rate. Remember to account for this added downstream pressure loss when setting the pressure regulator.

If you need any explanation on how F-R-L's work and how to properly size them for your application, please contact Indiana Fluid Power.


 

 

 

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