Air Compressor Unloader

Here’s information on the simplest type of air valve; the 2/2 style.

The first 2 in the 2/2 air valve refers to the number of “working” air ports that are found in the valve body. That is, the number of ports that supply air to the valve, and channel the compressed air to whatever it is that the valve is supposed to do.

Most 2/2 valves will have numbers or letters etched, cast or painted near each of their two “working” air ports. If there are numbers near the ports, the number 1 would be the supply port to bring the compressed air to that valve. Port number 2 would be the working port from which air would flow to accomplish whatever task that you wanted that valve to do.

If the port designations are letters, then port ‘A’ would be the supply port and port ‘B’ the working port.

If the 2/2 valve is to be “air operated”, that is an external air signal is to be used to shift the 2/2 valve, there will be another port. That port may not have a designation or it might say ‘12′. No, that’s not a twelve, but rather indicates that air will flow from port 1 to port 2 when an external air signal operates that valve.

The second 2 in a 2/2 air valve indicates the number of positions that the internal valve mechanism has. In this case, two. When this valve is operated or actuated, it will either open or close. At rest, that is when the external valve operator has not been activated, the internal valve mechanism will either stay open or closed.

Most 2/2 compressed air valves are classified as NC. NC stands for normally closed. This means that when the valve is not actuated, it’s normal state is closed, and compressed air cannot pass through it.

There are some applications for 2/2 valves where the flow of air through the valve when it is not being operated is desirous. A NO or normally open valve would then be selected. When this type of 2/2 valve is at rest, compressed air will flow through it, and it is only when the valve is actuated that the flow of air will stop.

All 2/2 valves will have actuators that will operate or ’shift’ the air valve.

A compressed air blow gun is a good example. On it there will be a push button or a trigger of some kind. When the button is depressed or the trigger is pulled, the compressed air will flow through the gun and out the nozzle to atmosphere. When the actuator is released, an internal spring (a secondary actuator) will shift the internal valve mechanism back, and the air will stop flowing. A compressed air blow gun contains a 2/2 NC air valve.

Some other 2/2 valve actuators are whisker switches, toggles, push buttons, palm buttons, roller cams, electric solenoids or compressed air.

2/2 valves can have detented or non-detented actuators. If the actuator is detented, this means that when the operator actuates the valve, the actuator will stay in the position selected until it is again moved by the operator. Toggle switches for air valves are often detented. You flick the toggle in one direction to actuate the valve, and it will stay actuated until you move the toggle back. The detented 2/2 valve may not have an internal spring, though with standardization of manufacture, even a detented valve may have a spring, since various kinds of actuators may be affixed to that same valve body.

Non-detented valves do contain an actuator spring, and the internal valve mechanism will “spring” back to the other position when the operator releases the primary actuator, similar to what happens when the button on a compressed air gun is released.

At ABOUT-air-compressors.com, an e-book entitled All About Air Valves - volume one - will soon be available (end August 06). If you are interested in more information about air valves, do visit the site and download a copy.

All 2/2 valves must, when operated, allow air to ultimately flow to atmosphere. If a 2/2 valve is selected to provide air to a closed tank or air vessel, then when the 2/2 valve is shifted to a closed position, the air will be trapped in the downstream line. You wouldn’t select a 2/2 valve to provide compressed air to an air actuator, for example.

The exception to this rule are inflatable bladders that contain their own integral 2/2 valves; a bicycle or vehicle tire being good examples. When you connect your 2/2 air supply valve to the tire valve, the tire valve - itself a small 2/2 valve - is actuated by the supply valve fitting, allowing compressed air to flow into the tire. When the supply valve is no longer actuated, as long as the fill fittings is attached to the tire valve, the line is pressurized. That’s why, when you pull the fill fitting away from the tire, you hear that characteristic “pssssst” as the air that’s been trapped between the two valves is vented. The tire valve will have shifted back to being closed by the air pressure inside the tire, thus preventing the compressed air in the tire from escaping back to atmosphere.

Other 2/2 compressed air valves commonly encountered are those push button valves on the handle of air tools, and the air-horns that are commonly heard at sporting events.

The air-horns were designed as distress sirens for small boat operators. The push button on the top of the gas canister is the 2/2 valve, and it’s the pressure of the compressed gas trapped in the canister that forces the valve shut (NC - normally closed) when the button is released.

I guess it’s better to hear an air horn at a football game than indicating some poor boater’s distress out on the lake; unless it’s blasting into your ear, of course!

And as always, if you have any questions, please send me a message from the contact screen at my web site.

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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Posted on July 3rd, 2008 by itbsuperrich
Filed under: aircompressorunloader.air-compressor-guide.info | No Comments »

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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Posted on June 25th, 2008 by itbsuperrich
Filed under: aircompressorunloader.air-compressor-guide.info | No Comments »