Clean air is crucial for optimal pneumatics

Liquid water, water vapor, particulates and oil can all interfere with proper compressed air operation. Removing moisture and contaminants ensure that the system does not experience premature wear or damage.

For optimal pneumatics performance, it is usually necessary to reduce the pressure of air leaving the compressor and filter out water, oil and contaminants. For some applications, clean oil needs to be added to the air to lubricate downstream equipment. This unit shows, left to right, a combined filter/regulator for general filtration/air pressure regulation, a coalescing oil removal filter and a lubricator.

Pneumatics is a versatile, proven technology for powering or controlling the operation of an amazing number of applications, from neo-natal respirators to building-size industrial equipment. The range of pneumatics capabilities is illustrated by the variety of typical systems, their uses and requirements.

• General pneumatic circuits (e.g. directional control valves and cylinders in machine cleaning, air motors and high-speed tools)
• OEM machines
• Breathing air
• Heavy duty lubrication
• Direct injection lubrication, such as required for conveyor chains
• Oil-free applications like paint spraying or film processing
• Critical pressure control and instrumentation
• Motion control for industrial automation or equipment operation
• Continuous processes like those in paper mills or chemical plants

While the configuration of pneumatic components for each of these systems varies, they all require air of the proper quality, temperature and pressure to function most productively. The air leaving a compressor is hot, dirty and wet, and is generally at a higher pressure than desired. Before this air can be used, it needs to have contaminants removed, pressure reduced and, in many cases, oil added to lubricate downstream equipment. This article examines the first requirement: removing moisture and contaminants.

Liquid water
Air exiting the compressor outlet will contain water vapor, but as the air cools, the moisture condenses. The amount of water vapor in any given volume of compressed air is directly proportional to the air temperature and inversely proportional to the pressure, so there is more liquid water when the temperature is lowest and the pressure highest. This is the point where removing it is the most efficient. An aftercooler should be used to cool the air coming out of the compressor to within 8º C of the temperature of the water entering the after cooler for most efficient water removal.

At this point, the outgoing air should be piped to a receiver in the coolest location available, definitely not within the compressor house itself. Further cooling—and condensation—may occur in the distribution mains. These should be laid out with a pitch in the direction of air flow, so gravity and air flow will carry the water to drain legs. Except for these drain legs, all other air take-off points from the distribution mains should be taken from the top of the main to prevent water from entering the take-off lines.

As discussed earlier, water condenses (and is most efficiently removed) at high pressure, so anything that produces a pressure drop in the distribution system should be avoided. Filters should be located upstream of any pressure-reducing valves.

Maintaining consistent pressure also conserves energy, helping to control costs. Make sure to properly size piping and eliminate complex flow paths with undue bends.

Water can be removed using drip leg drains, automatic drain valves or filters. These devices should be located where liquid water is present in amounts large enough to be removed. Because air may cool as it passes through distribution mains and branch lines, it is more effective to install smaller individual filters as near to the actual point of air usage as possible, rather than rely on one large filter at the air receiver.

Water vapor
A system properly designed to remove liquid water will still not remove moisture from the air, and this moisture can condense later in the process. If the application requires complete freedom from water contamination, then the water vapor content must be reduced to the point that the dew point is lower than any temperature to which the air in the system will be exposed.

To remove water vapor from a compressed air system, air dryers must be employed. Dryers are most efficient at the lowest possible temperatures, and performance is diminished when air is contaminated by water, oil or water/oil emulsions, so dryers should always be used in conjunction with filters and coolers.

There are three types of dryers: refrigerant, regenerative adsorbent desiccant and deliquescent absorbent. (See Table 1, Dryer Comparison.) Here are some considerations for making the most cost-effective dryer choices.

Does your process truly require dry air? Air dryers are most commonly needed in general industrial applications where high ambient temperatures exist.

Do not specify extremely low dew points if the process does not warrant them.

Limit the volume of air being dried to that actually needed for the particular process, plus some capacity for expansion. For example, only one area of a process plan may require a dryer.

General recommendations for air drying can be difficult, since this depends on the temperature of the compressed air main adjacent to the operation, the level of pressure reduction and air flow rate. It also depends on the relative humidity and ambient temperatures of the local environment.

Solid particles
Particulates enter every compressed air system, either through ambient air intake, corrosion, or carbon build-up. Dirt particles can range in size from a fraction of a micron to several hundred microns, (See Table 2) but generally fall into two categories: coarse (40 microns and above) or fine.

Most normal airline filters will remove coarse particles. Fine filtration in the region of 10-15 microns is normally required for high-speed pneumatic tools or process control instrumentation. Filtration of 10 microns or finer is essential for air bearings and miniature pneumatic motors. Even finer filtration may be needed for paint spraying, breathing air or food-related applications. These require high efficiency (oil removal/coalescing) filters. Standard airline filters should be used as pre-filters to avoid overburdening the finer filters with coarse particles and triggering premature failure.

Oil as a contaminant
The principle source of oil contamination in a compressed air system is the compressor. Oil lubricates the compressor, but by the time it emerges with the compressed air, it has lost any lubricating capability and in fact is an aggressive contaminant that must be removed.

Normal airline filters will remove enough oil to leave the air suitable for most pneumatic tools and cylinders, but certain applications require completely oil-free air. Oil-free compressors eliminate oil but not water and dirt. So it can be more economical to use lubricated compressors with after coolers and standard airline filters and fit high efficiency oil removal filters only at the points in the system where oil-free air is absolutely required.

A general airline filter to remove water and large particles should always be located upstream from a coalescing filter to prevent clogging filtration media. On this general purpose/coalescing filter combination, when the filter elements become saturated to the point that air pressure drops, the green indicator on top shows red, signaling the operator that the element needs to be changed.

Oil in compressed air systems can exist in three forms, oil/water emulsions, aerosols or oil vapor. While emulsions can be removed by standard airline filters, more sophisticated filtration is required for aerosols or vapors.

Aerosols are small oil particles suspended in the air. Approximately 90% of these are between 0.01 and 1 micron—too small to be removed by the centrifugal action of standard airline filters. Special coalescing filters are required, and these should be protected against particulate and water contamination by airline filters mounted immediately upstream.

For most processes, removal of oil vapor is unnecessary, since quantities are minute. Exceptions include food or beverage processing, pharmaceuticals or breathing air applications.

The most common method of removing oil vapor is to pass the air through an adsorbing bed, usually comprised of activated carbon, after it has been through a pre-filter and a coalescing filter. Note: this system will not, as is sometimes thought, remove carbon monoxide or carbon dioxide.

Filter selection
Once all the contaminants have been considered, the degree of cleanliness of air for each part of the industrial plant or process can be determined. Table 3 shows the levels of contaminants allowed in each class of air quality as defined by ISO 8573. Employing the correct filters in the right locations can keep energy and maintenance costs to a minimum.

Table 4 shows typical air quality class requirements, and thus recommended filtration levels, for various applications. Also, selecting a filter rated for volume of air required is critical because undersized, inappropriate filters drive up energy costs.

When designing filtration to clean compressed air, be sure:

• The correct type of filter and element rating is selected for particle removal.
• Liquid removal is efficient and re-entrainment is not possible.
• It is easy to maintain the filters and remove liquid condensate.
• There is easy visual monitoring of condensate or filter elements for proper function or prompt maintenance. This may be a pressure drop device, liquid level indicator or transparent bowl.

With the system in place to remove contaminants from compressed air, designers can move on to the challenges of optimizing pressure and adding lubrication. Correct air preparation is the best way to get maximum performance from any pneumatically controlled system.

Norgren, Inc.

Humphrey Products Receives ISO-13485 Accreditation

Kalamazoo, MI — Humphrey Products is proud to announce that it received the accreditation for ISO 13485: 2003 in addition to its continued accreditation of ISO 9001 status. ISO 13485 represents the requirements that medical device manufacturers must incorporate into their management, engineering, distribution and quality systems.

Adding to all the normal benefits that the ISO 9001 registration provides customers and distribution, ISO-13485 certification provides the system controls, serialization, process change controls and notification that are currently required for products used and sold within medical markets.

“The medical market is a huge and all encompassing category and can cover many and varied applications,” said Robert Humphrey, President and CEO of Humphrey Products, “anywhere from process equipment used in the automated preparation and evaluation of biopsy materials on test slides, to those applications such as oxygen concentrators used by the patient within their own homes, or all the way into the ER, and patient invasive devices used by surgeons to assist with various medical procedures.”

Humphrey Products
www.humphrey-products.com

Clippard Releases New Full-line Catalog

Clippard Instrument Laboratory, Inc., manufacturer of the industry’s most complete line of miniature fluid power products, has just released the all-new 356-page catalog.

This full-line catalog includes features, specifications, technical drawings, color photographs, and application highlights throughout. Products can be found in six main categories, including Cylinders, Electronic Valves, Control Valves, Modular Valves, Fittings and Hose, and Air Preparation equipment.

Clippard Instrument Laboratory, Inc.
www.clippard.com/catalog

PRG 2-Finger Radial Gripper

The new PRG 2-Finger Radial Gripper from SCHUNK combines high gripping moments with small dimensions. The integrated pneumatic oval piston drive guarantees maximum power density.

Radial gripping motions are often achieved by integrating a slotted link gear. Existing links cause an extreme reduction in the gripping moment, if the opening angles are rather small. SCHUNK has found a solution for such an application; the patented Single-Pin guide rail which ensures a constant closing moment throughout the gripping range. The new PRG did not change in dimensions and can reliably grip larger workpieces or workpieces with a larger tolerance range. In addition, innovative dampening, which is directly integrated in the drive rod, allows short cycle times and a much longer admissible finger length.

The multifunctional PRG has an adjustable stroke to fit the individual application and is also available with a gripping force safety device, in a high-temperature version and with three different opening angles (30° / 60° / 90°). The end position can be optionally monitored by inductive proximity switches or magnetic switches.

SCHUNK Inc.

www.schunk.com

Bimba Introduces its First Rod-Type Electric Actuator

Monee, IL — Bimba announces the introduction of its first ever, rod-type electric actuator, the Original Line Electric (OLE).

OLE actuators are designed, built, and tested to provide the longest life, greatest durability, highest speed, and most thrust per dollar. With speeds up to 22 inches per second, strokes to 18 inches standard, and thrusts up to 350 pounds, these new actuators can address a wide range of applications. The unique modular design can be ordered with or without motors and drivers’ from Bimba, enabling engineers to use their preferred stepper or servo brand.

The OLE product line is available in 1.5, 2, and 3 inch diameters with standard options including trunnion, block front, clevis, pivot, and foot mounts, reverse parallel motor mounts with rear pivot or clevis, step motors, drivers, encoders, brakes, washdown ratings, female rod threads, and switches.

Bimba Manufacturing
www.bimba.com/ole

Enfield Technologies Makes Proportional Pneumatic Control More Affordable

Thanks to some innovative engineering, Enfield Technologies has reached an important goal – making a complete proportional pneumatic control system much more affordable.

A basic positioning system includes a proportional valve and control electronics manufactured by Enfield Technologies paired with a pneumatic actuator and a position sensor provided by a variety of highly regarded partner companies. The same valves and control electronics used in motion control are also used for proportional pressure, flow, and force regulation applications.

During the last 18 months, Enfield Technologies has revised its sourcing and manufacturing processes. They have also reengineered several key products, adding new features, improving performance and reducing costs. This has allowed the company to offer price reductions averaging 42 percent on its primary components. For example, the LS-C10 controller dropped 70 percent, from $564 to $169.20, and the LS-V25s proportional valve dropped 45 percent, from $721 to $396.60. Enfield Technologies has also implemented volume discounts and an additional 5 percent bundle discount (bundle kits include a controller, valve and cable).

Enfield Technologies has added more than 35 technical resellers and integration partners over the last year. The company has also launched several new products, including the Enfinity System (C2 controller and M2 valves).

For more information, visit http://enfieldtech.com/affordable/

Enfield Technologies
www.enfieldtech.com

Sealed Two-Finger Parallel Gripper

The successful DPGplus series of sealed 2-finger parallel grippers has been extended with sizes 240 and 300. The pneumatic drive with oval pistons and the multi-tooth guides ensure precise and reliable gripping. This ensures a high level of machine up time and high returns from production and assembly applications.

The DPGplus sealed 2-finger parallel gripper is an expert at handling rough or dirty workpieces. It is suited for loading and unloading in harsh environments, like grinding machines, lathes, and milling machines. It is also suitable for use in painting systems, powder coating systems, or underwater.

The sealed grippers of the DPG-plus series feature sealing class IP 67 for the highest sealing in its class, with moments between 30 Nm and 160 Nm, (22 Ft-lb-118 Ft-lb) depending on the direction of load and size of the unit and grip forces up to 11,700 N (2,630 lbf). The high sealing class and performance are made possible by combining a multi-tooth guide with a round sealing surface of the base jaws toward the outside.

SCHUNK Inc.

www.schunk.com

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DUAL SENSOR FOR C-GROOVE CYLINDERS

BIM-UNR Dual Sensor (High-Res) TURCK’s BIM-UNR line of compact magnetic cylinder position sensors now includes a dual sensor designed for detecting short and long stroke C-groove cylinders. BIM-UNR dual sensors provide a distinct advantage by combining two sensors through one cable connection to speed installation, as well as lessen wire costs and connection points. This design makes the sensor particularly beneficial in areas where multiple cylinders are used, as it only requires a single cable. With dimensions of 2.9 x 4.6 x 18 mm, Delivering reliable performance and high EMC immunity, thisl sensor provides an exceptional alternative to ordinary cylinder position sensors. The sensor mounts within C-groove cylinders with no accessories required. Plus, it can be inserted into a C-groove from the top rather than from the side, further simplifying installation. On the sensor’s side is a built-in tab that keeps the sensor in place to facilitate one-handed mounting. As the mounting screw is located near the cable exit, the sensor remains fastened even if the cable is pulled. TURCK www.turck.us