:: Air Compressor Parts ::

Many industrial machines using compressed air as an energy source, use air cylinders or other pneumatic actuators to do the actual work.

Compressed air is ‘explosive’ as it moves from high pressure to low pressure on it’s way back to atmosphere. That means when the air valve shifts and air flows to the cylinder, the cylinder piston and rod moves extremely quickly. A high speed cylinder rod may not be best for your application, and you will want to reduce the speed and the impact.

One easy method of controlling the speed of an air cylinder is installing flow controls in the air lines between the valve to the air cylinder, in the cylinder ports themselves, or even in the exhaust ports of the air valve, though the latter is least desirable.

In the ‘valve exhaust’ type flow control the controls themselves may be far enough away from the cylinder that the piston and rod may have traveled the full stroke before the exhaust flow control can start back-pressuring the line to slow the cylinder. Cylinder control reaction time is always negatively affected depending on the distance from the cylinder to the flow control.

Some folks opt for needle valves to throttle the flow of air into and out of the air cylinder, thereby reducing it’s speed. The problem with using a needle valve to control the speed of an air cylinder is that it throttles the compressed air flow equally in both directions.

If you are using a larger cylinder, by throttling the air into the cylinder, you are actually preventing the smooth cylinder stroke desired. As air pressure builds in the cylinder it will reach the point where it overcomes the friction of the piston and rod seals and the piston will start to move. As it moves, it increases the volume of the air space inside the cylinder behind itself. The piston moves toward one end of the cylinder creating a larger area behind than in front of it. This is an area into which air has to flow quickly to ensure that the piston keeps moving. If the air inrush cannot keep up with the increasing cavity size there will be insufficient pressure to keep the piston moving, and it will stop. So too will your piston rod, and whatever tooling you have installed on the end of it.

The rule of thumb for using a flow control to reduce and smooth air cylinder piston travel is to only throttle the exhaust air from the cylinder. The air flowing into the cylinder port should never be reduced.

How is this accomplished?

Use a “cylinder flow control”. This is a device that may not look any different from the needle valve. Inside, however, there is a “needle bypass” which allows the air to bypass the needle which is throttling the air achieving full flow of air unidirectionally.

The “free flow” of compressed air through the cylinder flow control allows the unit, when it’s installed in the correct orientation, to provide full and un-throttled inrush of air to the cylinder, yet, when the valve has shifted and the double-acting air cylinder has reversed, the air that is now flowing out of the cylinder is throttled to the level necessary to achieve the cylinder speed desired.

There will be a second cylinder flow control on the other line too, and this works exactly the same way.

As a result, air flow into the cylinder ports at either end of the cylinder is totally unencumbered providing high-force piston movement. The piston is trying to go fast and at full power, but since the exhaust flow of air is impeded by the cylinder flow control, the piston moves with full power, but at a controlled and desired rate.

Most cylinder flow controls will have a schematic on the side showing the flow paths to ensure that they are installed correctly.

Some cylinder flow controls are equipped with sealant coated male threads for screwing into the cylinder port, and with an “instant” type fitting into which the cylinder air line can be quickly fitted, features that save time and money.

Bill Wade’s experience in compressed air and other industries spans decades; from field sales positions through to the corporate presidential office. His sales agency represents a select group of industrial firms. Mr. Wade writes about all facets of compressed air at http://www.about-air-compressors.com.

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It’s really easy to pick up a low cost air compressor at the local store anymore. But, how do you get the air from the compressor to your application? Folks that are plumbing up compressed air lines for their garages or workshops at home, as well as the professional plant person, have a variety of options with which to do connect the various air-lines available to them.

Usually the air compressor will come with a rudimentary kit which will include a PVC (Polyvinyl Chloride) or RVC (Rubber Vinyl Chloride) air hose. If not, these kits are available as accessories.

Rather than having a clutter of air hose running across the floor (a trip hazard) consider emulating the factory installation. Have the discharge air line from the compressor run up to the ceiling in the garage or workshop, and then install “drop lines” down to the various locations on the bench where compressed air might be used.

The discharge from the compressor should have, at the very least, a compressed air filter where the air exits the receiver / tank, and the smaller home-compressors will often have a regulator there as well. Compressing air causes water problems, and you can read more about this in my article in this E-zine entitled “Why does water run out my compressed air lines…”. The regulator is necessary too, and you can read about this in an article titled “Why use a compressed air regulator” also on this site.

Commercial installations of compressed air will have a large general purpose compressed air filter at the compressor discharge, and then a filter, regulator and sometimes an in-line lubricator (oiler) at each of the points where the compressed air is to be used, to help deal with compressor generated water.

The regulator will provide the ability to control the pressure of the air to that particular application. You might want 90 PSI of air to run a grinder at one drop line, but farther along the bench you might only want 12 PSI for an air brush paint set up. Individual regulators give you this capability. If you are installing a regulator at each drop location, remove the regulator at the compressor to ensure you have full pressure and flow to the air main overhead and the drop lines.

The oiler use is dependant on what it is that the compressed air is running.

On your work bench, at the bottom of each drop line, you can install a coupler. A coupler is a device into which you can insert a connector. The coupler will be “checked”, meaning that compressed air is trapped at that point until a connector is inserted into the coupler which opens the “check” and allows air to flow.

Compressed air can then be supplied to the air tool or whatever you wish to drive with compressed air via an air-line extension cord. You can purchase ready made or you can make your own. They are lengths of air hose or tube with a connector at one end and a coupler at the other. The air tool will have a connector in it’s air port. When ready to supply compressed air to your tool, you simply insert your air-line extension cord connector into the drop line coupler, and the other end, which will be a coupler, has the air tool connector inserted into it.

Connectors and couplers are not all the same. Different manufacturers have differing styles and they are not usually interchangeable. When you first start purchasing couplers and connectors for your air line, make a note of the brand first purchased, and purchase the same brand as your needs continue.

I remember the difference between a coupler and a connector by making a mental image of a “cup” into which I insert the connector. The “cup” is the coupler.

If it were me installing an “air main” and drop legs down to my workbench in my garage, I would use soldered copper pipe. Copper pipe won’t rust, and there are more than sufficient adapters available to convert from the soldered (sweated) copper to a thread.

If opting for an overhead main, know that the longer the supply line to the application, the more pressure loss there will be. Each elbow and every turn creates a loss in available pressure at your application, so make the air main as large as practical. How big? Why not 3″‘ copper pipe at the ceiling and 3/4″ copper drop lines for the home workshop?

Remember that PVC or RVC air hose size is measure on the I.D. A 1/2″ air hose will have a 1/2″ I.D., regardless of the O.D. of the line. Different air line manufacturers will have hose with different wall thickness, so the outer diameters will vary.

To connect PVC or RVC air hose together, you can use the aforementioned couplers and connectors. Usually the coupler and connector has a “barbed” male protrusion, though other styles are certainly available. Make sure the “barb” size of the coupler / connector corresponds with the internal diameter of your air hose. A gear clamp (do yourself a favour and purchase stainless steel clamps over carbon steel. A few pennies more, but much longer life) is installed on the hose first, and then the barb is inserted into the I.D. of the hose. After insertion of the “barb” the gear clamp is brought up the air hose, over the area where the “barb” is inserted, and tightened firmly. Using a small wrench to tighten the clamp is preferable over a slotted screw-driver which have a tendency to distort the nut.

There are a variety of other fittings available to join air hose. “Barb” to “barb” connectors, “barbed” elbows, “barbed” T’s, and so on.

If you are planning on using a lot of compressed air, hours worth of tool use at time for example, your drop legs should have a manual valve at the bottom of them and the supply to your tool should be taken about six inches from the bottom. The manual valve will allow you to drain the water that will accumulate there. See ABOUT-air-compressors.com for more extensive information on plumbing for compressed air.

As to the smaller air lines themselves, perhaps running to an air valve, joining an air valve to a cylinder, or even a small air brush or air tool, P.E. (polyethylene) is the air tube of choice. It is chemically inert, won’t rust with air-borne water, has a variety of fittings available, and is inexpensive.

P.E. tube has a variety of fitting styles available.

It can be connected with compression-ring (ferrule) type fittings. A nut, and then the ring fits over the tube, and once the tube is inserted into the fitting, the compression-ring is brought down over the tube and then the nut is tightened onto the thread, compressing the ferrule and created a seal. This type of fitting is available in many configurations including straight fitting, elbow, ‘T’ and so on.

The easiest fitting for plumbing P.E. tube is the “instant” variety. There will be a hole, correctly sized for the O.D. of the tube, into which the tube, after it is cut squarely, can be inserted into the fitting. Inside the hole will be an “O” ring type seal, and then a collar of small metal fingers through which the tube passes. When the air is turned on, the P.E. tube swells a bit, and these “fingers” dig into the surface of the tube, holding it in. The “O” ring prevents escape of the compressed air. There will be a small ring on the exterior of the fitting which, when depressed, will “bend” the fingers out of the way, allowing the tube to be removed from the fitting when necessary. This should only take place if the air is off.

“Instant” type fittings may not work on soft air-line tube, such as polyurethane. Copper tube may present a problem too, as the “fingers” cannot easily grab the smooth surface of the tube.

There are some manufacturers that offer a line of miniature barbed fittings for tube. If you are installing many fittings in your application, they may offer a lower cost solution. The downside is that they significantly reduce the air flow through the smaller I.D. plastic tube.

For a good selection of air line couplers, connectors, hose, tube and fittings, consider locating and visiting your local industrial supplier of fluid power or compressed air components, rather than your local hardware or department store. Not only will the industrial supplier likely have everything you need in one location, undoubtedly, they too will have the expertise to provide the advice that will not necessarily be available at the other retail outlets.

If you have questions, please don’t hesitate to visit my site and send me an email through the contact page there.

Bill Wade’s experience in compressed air and other industries spans decades; from field sales positions through to the corporate presidential office. His sales agency represents a select group of industrial firms. Mr. Wade writes about all facets of compressed air at http://www.about-air-compressors.com.

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