:: 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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Water. This drives every compressed air user nuts!!! Every time they use an air tool, blow-off gun, or even fill the inflatable air mattress, water appears along with the compressed air.

The water is a problem if the compressed air is moving through a tool that can rust or be negatively affected by airborne particles, and, given enough ‘fill-ups and empties’ a significant amount of water will appear in anything which you inflate or run with compressed air.

Why?

Well, we know that relative humidity is the measure of water moisture in the air expressed as a percentage. At a relative humidity of 90% for example (really hot and sticky) the atmosphere is holding 90% of the total amount of water vapour it can hold. When the relative humidity in the air exceeds 100%, it usually rains.

That, unfortunately, seems to happen mostly on weekends!

Now, let’s take some of that atmosphere with it’s 90% relative humidity and compress it. What do we want the final air pressure to be; 30 PSI, perhaps 45 Pounds per Square Inch? We will use 45 PSI as an example.

Free air, the atmosphere we breathe, has a normal PSI of 14.7 (or 15 PSI to make it easier math). So, we’re going to take free air at 15 PSI and make it 45 PSI by compressing it. We will take three cubic feet of air at 15 PSI, and cram all three into the space of one to make one cubic foot of compressed air, now at 45 PSI.

If the relative in the atmosphere humidity is 90%, and we are cramming three cubic feet of atmosphere into one cubic foot, then the relative humidity of the compressed air will almost instantly exceed 100%. As a result, as long as the relative humidity of the air in the compressor tank is over 100%, it will rain in your compressor’s receiver. That water will gather on the bottom of the receiver, and will ultimately fill it unless it’s drained.

Then, every time compressed air is drawn from the compressor tank to your application, free water will follow it down your lines to your air tools, your workplace, your air mattress etc.

To make matters worse, compressing air generates heat. Air that would normally be saturated and not be able to hold any more water vapour at one temperature, can actually hold more than 100% humidity when it gets hotter. When the air inside the tank is hot, the compressed air that is flowing out of your compressor tank has a higher than normal humidity level.

What happens to air as it flows? It cools! What happens to the water vapour in the air as the air cools? It converts (condenses) back into free water.

More water!

The water generated by your air compressor, along with the water vapour carried along in the compressed air itself, both contribute to the water problem for the compressed air user.

And that’s why you have water with the compressed air, streaming out of your air line every time you open the air line valve.

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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