:: Air Compressor Parts ::

If you are one of the many folks that have purchased or are considering purchasing a home compressor, you do want to have a bit of information about compressed air filters.

Compressing air generates a reservoir (receiver / air tank) full of wet, dirty, hot compressed air.

As the air leaves the tank, it carries the crud and free water along with it. It also carries a great deal of water vapour. As the compressed air travels to your appliance (air drill / air grinder / blow gun / air brush - what have you?) the compressed air in the air line cools, and some of the water vapour will condense into free water.

That’s why just having a small compressed air filter at the discharge of the compressor tank may not be enough. Even though the unit at the compressor will take much of the debris and free water from the air there, it can’t remove the vapour. Even though you think your air is being filtered, by the time the air gets to your application, water may flowing out of the exhaust ports and onto your work piece, along with the used compressed air.

Of course, if water flowing or blowing onto your work bothers you just a tad :~} , you’ll want to add another compressed air filter just before you use the air.

Many standard compressed air filters have 5 micron filter elements. If you want to know how big that is, check out the details in the Filter page on my web site.

You can purchase compressed air filters with much finer elements, and you can purchase elements that are coarser, allowing much larger particulates through. Much larger is a relative term. We’re still dealing with pretty small bits here.

If you decide that your application needs extensive air filtration, get a micro-filter element for the additional air filter you will need. The new one might filter particulates down to .005 micron, and if you don’t have a 5 micron unit upstream from it to take out the larger bits, the finer element will plug up really quickly, which is why you’ll need the additional filter housing.

You can purchase compressed air filter elements that will strip oil from the compressed air, these known as coalescent filters. Some piston / reciprocating, and other types of compressors too, let oil “blow by” the piston seals into the compressed air tank, and this oil will get blown downstream as you use compressed air. Compressor oil is not good for most tools that have Buna-N type seals. The compressor lubricating oil might ‘eat’ the seals.

Each compressed air filter you install has a negative affect on the available air pressure at your tool. Pressure drop is a reality in compressed air plumbing. You could supply compressed air at 100 PSI into the discharge air line from your tank, and by the time it gets to your tool, all you have available might be 85 PSI. The flow of compressed air through the air lines, the elbows, the ‘T’s and yes, the air filters, all create pressure drop.

If you are using your compressor a lot (make sure you know it’s duty cycle so that you don’t burn it out) then it would be beneficial to have an auto-drain of some sort on the air filter. A float type will open up and let water and crud flow out when the water in the bowl gets to a certain level. An electric auto-drain will be plugged into a 120 Volt outlet, and will open the bowl drain at preset intervals for a preset length of time. You set the electric auto-drain to the interval necessary to keep the filter bowl fairly empty.

If the water and debris in the filter bowl gets above a certain level in the bowl of the filter, it floods the element, and now your compressed air supply is pumping water and debris through the element downstream to your tool.

Did you know that water rusts metal air tool innards, and that water droplets on your work piece will not allow the beautiful paint job you are air brushing on to it to adhere? Of course you did! That’s why you need a compressed air filter.

One more thing. If your air consumption is great enough then even a filter at your tool may not stop the water vapour streaming along with your compressed air from condensing onto your work piece or in your air tool as the air cools. If that is a problem for you, you will need an air line dryer.

Drop me a email from my site if you have any questions. I’ll be happy to respond.

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.

Share This

Recently, I published an article on this site titled: What’s a 2/2 compressed air valve? Here, in the next installment in this series, is information on a slightly more complex air valve; the 3/2 style.

The first number in the 3/2 air valve, the three, 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 3/2 valves will have numbers or letters etched, cast or painted near each of their three “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.

The third port in a 3/2 air valve is an “exhaust” port and if numbered, it could be a 3 or a 5. If the port designations in a 3/2 valve are letters, then port ‘A’ would be the supply port and port ‘B’ the working port, with the third port normally being an ‘E’.

As in the 2/2 valve there may be one or two additional ports in the ends of the 3/2 valve to allow an air signal line or lines to be connected. If this is the case, this 3/2 valve will either be single, or double air piloted.

The 2 in a 3/2 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 and air will either flow to the application upon actuation, or it will be prevented from flowing.

Most 3/2 compressed air valves will be NC, or normally closed. When the valve is not actuated, it’s normal state is closed, and compressed air cannot pass through it.

If your application calls for air to flow through the valve when it’s not actuated, that the circuit needs air to be flowing through this valve when it is at rest, then a NO or normally open configured valve would be selected.

All 3/2 valves have actuators that will operate or ’shift’ the air valve. An external button, or toggle, or perhaps a solenoid actuator would be the visible actuator. Inside, there will likely be an internal actuator - a spring - which will shift the valve to the off position when the external actuator is not being used.

If the external actuator is ‘detented’, then when the valve is operated, it will stay in it’s last selected position until an operator changes it. Detented means it will stay where it’s put! This is useful when an operator needs to actuate the valve, and then manually perform another operation while the air valve feeds air to the application.

Unlike it’s less complex 2/2 valve cousin, the 3/2 valve is used when a compressed air supply is needed to an application or device that uses compressed air to power it, yet in itself has no integral air pathway to atmosphere. Therefore, when the device has performed it’s function, and it’s time to ‘deflate’ it or to let the compressed air back out, the third port in the 3/2 valve comes into play.

When the compressed air supply through the valve is shut off internally, a pathway back through the valve to atmosphere will be opened, to allow the compressed air to escape. The air supply is shut, so the compressed air flowing to the valve cannot flow through it, and the compressed air that was formerly in the device or application can now bleed back down the air line through the valve to exhaust.

So, what type of devices are these?

Usually they are single acting type actuators. One comes to mind immediately; “Air springs”.

Both Firestone and Goodyear (among others) manufacture “air springs”. These are devices that look like tires, but rather than have an opening in the middle of the doughnut where the rim goes, they are closed on both sides with steel plates. In one side there will be an air port to which an air line from a 3/2 valve can be connected. These “air springs” are mounted on their sides, picture a tire lying flat after you’ve taken it off your car, and can generate huge actuation forces. Force equals pressure times area, and the “piston” size inside an air spring can be huge. The application of air springs mirrors that of typical air cylinders, yet offer large capacity at a fraction of the cost of an air cylinder of a necessary size to generate the same force as the air spring.

Another application for 3/2 valves is single acting air cylinders. Whether they are spring extend or spring retract, an air supply is required to operate the SA cylinder. A 3/2 valve is designed to do just that.

A couple of more points; the 3/2 valve can have the exhaust port plugged, and voila, you have a 2/2 valve.

If the cost of the valve is the same, you can use a 3/2 air valve anywhere you might use a 2/2 valve. Since 2/2 valves always have to have the “working port” ultimately plumbed to atmosphere, that there is an exhaust port in a 3/2 valve offers no obstacle to it’s use.

If you have a double acting air cylinder, and you don’t have a 4/2 or 5/2 (more on these valves next article) available, you can use two 3/2 valves to operate any cylinder that requires two supply lines in order for it to extend and retract.

At ABOUT-air-compressors.com my e-book entitled All About Air Valves - Volume One is now available. If you are interested in more information about air valves, do visit the site and download a copy. This first e-book is an introduction to air valves, and focuses on the 2/2 iteration. Future volumes will focus on 3/2 valves, and then the 4/2 & 5/2 configurations.

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

Share This

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.

Share This