Thursday, April 30, 2009

Keeping Your Compressor Quiet

Air compressors are noisy machines. The two most commonly used ways to quiet them down are to locate the air intake outside (not good for the neighbors) or to build some type of enclosure with sound deadening material inside; that usually causes overheating problems due to poor circulation.

The best solution is to construct a silencer that uses the same principles as a gun silencer. But isn't that illegal? Only if you use it on a gun. We're using it on an air compressor. Still, this topic seems to be controversial, mostly by people who have a bury-your-head-in-the-sand approach to security and safety.

Here are the materials:

  • Pipe the same size the air compressor port will use, 16"-18" long.
  • Some exhaust pipe, the same length as the other pipe.
  • Some washers you have to make with a hole saw, enough to put one on each end and one every 1-1/2" that will fit around the air compressor intake port pipe and fit inside the exhaust pipe.
  • Steel wool to fit between the washers.
  • A drill and a 1/4" drill bit to drill holes in the smaller pipe between the washers.
  • A welding machine to weld the washers to the small pipe and to the large pipe at the ends.

Since the silencer will be heavy, use a 90-degree fitting and mount it vertically.

Some links to sites that describe how silencers work and how to construct silencers can help you understand how the Air Compressor Silencer is constructed. If you Google for "gun silencers", you'll find lots of sites, so we're not divulging secret, hard-to-find information and, unless you're dumb enough to build one for a gun, not breaking any laws. If you think so, the terrorists have already won and you are not thinking of the children.

What Pipe to Use for Your Shop's Compressed Air?

Many people use Schedule 40 PVC pipe and that choice is - OSHA ALERT - potentially dangerous. Under pressure, PVC can explode when it becomes brittle with age or exposure to UV light or when struck by an object. But there are a lot of shops piped with Schedule 40 PVC. If you choose to use it against all advice, at least consider the stronger Schedule 80 pipe and fittings, keep the pipe protected from things that may fall on it and don't hammer near it. PVC is smooth inside which means less pressure drop from friction.

There are ABS pipes, Dura-Plus and Chem-Aire, that are rated for compressed gas use. The cost is roughly twice that of Schedule 80 PVC. Dura-Plus comes in a metric size (colored blue) and an industrial size, colored gray; the blue pipe cannot be threaded for standard pipe threads. Chem-Aire pipe is green.

Schedule 40 black iron pipe is a popular choice and is very sturdy and durable. It's also heavy and awkward to install and will rust inside, not only adding scale to the air, but increasing friction and causing increasing pressure drops over time. Galvanized Schedule 40 is a better choice, but more cumbersome to work with and also requires some specials tools.

Copper pipe is lighter and easier to install, and comes in three types. Type L is identified with blue markings and Type K is identified with green markings; both are strong enough to use. Type M is marked red and is not recommended since it is only rated for 125 PSI; that won't leave much of a margin for error. Copper is smooth inside which means less pressure drop from friction; this matters for long runs of pipe.

Of course, you could always use stainless steel pipe and compression fittings or even the very cool (but ridiculously expensive) Garage Pak system which uses a coated aluminum pipe and special fittings. All that expense does buy a product that is easy to use.

There is also Compressed Air Systems which sells coated aluminum pipe. This looks like what I saw at Harbor Freight.

Wednesday, April 29, 2009

The Science Behind Piping Your Air Compressor

How many of us have spent hours examining compressor horsepower and CFM ratings, reading shop forum posts and comparing prices to decide what the "perfect" compressor for our shop will be, but then connect a few Harbor Freight air hoses and wonder why the tools don't run well and spit water everywhere?

A well-written article at the website delves into the science behind piping your shop's air compressor. In brief, our problems arise because we do not have a properly-sized pipe system to deliver the air to the tool.

Compressed air will lose pressure because of the friction from the walls of the pipe. This is expressed in pressure drop per 100 feet of pipe at a particular pressure for a specific diameter of pipe. Of course, designing a proper system is not simple because there are many factors that affect the performance other than pipe size.

Another point made in the article is that the velocity of the air through the system is rarely considered. Why does it matter? When the velocity is less than 20 FPS, moisture and debris are not pushed past traps and can be easily drained away. When the velocity is greater than 30 FPS, all the moisture and debris is blown out of the tool you're using. So if you have a long run of small diameter pipe or hose,the velocity is high and stuff shoots out of the tool along with the air. Does that sound familiar?

To further complicate matters, the tables are designed under the assumption that un-compressed air is being pushed through the pipe. Compressing air increases the volume of air that flows through the pipe, so some more calculations are necessary to adjust the figures and you'll need to determine the ration of atmospheric pressure to the pressure of the compressed air. You'll need to know the average air pressure in PSI where you live; at sea level it's 14.7 PSI and that will drop as elevation increases. What's yours? Remember, Google is your friend.

Generally speaking, the larger the diameter of the pipe, the better off you'll be. A table of inner and outer pipe diameters can be found here. A table showing the pressure drop per 100 feet of Schedule 40 pipe is here. You can see the problem we face: using a small diameter pipe (or hose) to reduce pressure loss will increase the velocity of the air which explains why so much water gets past those filters and traps. But if we use a large diameter pipe, we need higher pressure at the receiver (the tank) to compensate for the pressure drop. The benefit is less water and debris blown out the tool, but a more powerful compressor is more costly.

The Quick Soultion
At some point, somebody sat down and calculated a rule-of-thumb guide to piping you shop, based upon quite a few assumptions that probably aren't correct for your shop. That "rule" is 3/4" for the mains and 1/2" for the drops. That usually works OK for a small garage shop, . . .but maybe not.

Read the article, work the math (you can get your kids to help), and you'll be able to see why you have so much trouble with compressed air at your shop. Having understood well enough to have done the math, you'll be able to understand how to go about improving your own system and improve it. Better yet, it can help you design a good system from scratch.

Air Polisher by Franz©

While the Franzinator sits between the compressor and the storage tank, the Air Polisher sits, according to Franzinator developer/promoter Franz©, between the air line and the tool you are using.

According to him, "The Polisher is really a cheap and dirty copy of a piece of equipment used in the refinery business coupled with a device used in the natural gas delivery business."

Here is a crude diagram of the Air Polisher. Examine the diagram for this simple device.

The assembly instructions:

Remove the valve from an EMPTY 20# propane tank, screw in a pair of 3/4" tees, and a piece of ½" copper tube.

The tube can be brazed into a bored-out plug, or if you can't braze, get a 3/4" MPT to ½" copper compression fitting, and bore the shoulder out so you can slide the tube clear through.

You'll need a drain fitting for the bottom "tee" so you can drain the accumulated moisture from the tank.

You'll also need a suitable fitting for the copper pipe to allow attachment of an air hose to feed your air tool.

Mount the assembled tank in the bottom up attitude, connect the air supply and your air tool as shown in the diagram.

Not having actually assembled an Air Polisher myself, those are the best instructions I can provide. At some point, I will construct a Franzinator and an Air Polisher and provide a more detailed materials list and some pictures. Until that occurs, more detailed instructions can be found here.

Friday, April 3, 2009

WTF is a Franzinator?

Sometimes the most useful things have the oddest names. Take the Franzinator, for instance. Named after Franz©, its curmudgeonly inventor, the Franzinator is a device used to separate moisture from compressed air. Having moisture in compressed air is not a a good thing, especially in painting where it contaminates the painted surface, or in media blasting where it causes the media to clump and not work as well. As well as causing rust in the air tanks and air tools, moisture is best removed.

A number of methods have been developed from expensive refrigerated driers used to pre-condition air before it gets to the compressor, to simple mechanical separators that sit in the air line between the tanks and the air tool. Here is a tank that uses a chemical desiccant to dry the air. There are also ways to install the air lines that are intended to either cause moisture to condense or collect before it is sent to the air tool.

A non-mechanical separator causes the moisture in the hotter compressed air to condense when it comes into contact with a colder surface, must like the moisture that forms on the inside of your single-pane windows on a cold winter day.

A common example of this is a section of two- or three-inch black iron pipe assembled in an inverted "J" shape with the compressor line attaching at the bottom of the long leg and the supply line being run horizontally off the short leg. The pipe needs to be run vertically and should be as high as practical, so a 10-foot rise and an two-foot drop would be OK. The problem is that many shops, especially home shops, don't have that kind of overhead room. Here's another approach from woodsy, using a copper coil between the compressor and tank.

The Franzinator is designed to take advantage of the part of the system that has the highest temperature differential with the environment to achieve the best efficiency. It sits between the compressor and the holding tank and looks like this.

Here's the inventor's description of how it works (and here) and here's a diagram to explain it. He feels that it is optimally sized for a 2-1/2 HP compressor and larger compressors should use two or more in parallel.

Here, Franz© elucidates some more on the principle as involved in the Franzinator. He also goes into more detail on the mysteries and secrets of the Franzinator, and discusses active cooling and considers a feed tube through the top versus the side entry.

The original design called for the 90-degree feed tube to be welded in the side of the pipe. Because the Franzinator is a high-pressure vessel, the welds must be done properly; weld failure could be catastrophic and even deadly. Consequently, Franz© developed a non-welded design using JB-Weld (or similar) which is described here , including a materials list.

Some Franzinator Examples:

This fellow built one with slightly changed dimensions, with a picture here. Here's one variant with a coil that allows coolant to be circulated around the Franzinator. Finally, here's a Franzinator built by HossCat.

Does it work? Numerous forum posts attest to it. It looks affordable enough to experiment as long as you feel comfortable doing the fabrication. Or get a friend to do it.

More to Come

Franz© also has developed an "air polisher" made out of a 20-lb. propane tank and some fittings. I'll post another blog entry when I collect the links for that.

For the Eager Student

Want some more interesting info from Franz©? He has lots of knowledge to share.

Wednesday, April 1, 2009

Soda Blasting

Soda blasting has many benefits over traditional blasting media in certain circumstances, but the equipment has been expensive prompting many to seek a Do-It-Yourself approach.

There's a discussion thread at that looks at the adapter kit offered by Eastwood as well as others. It also provides links to the search engine of the USPTO for soda blasting patents.

Here's a soda blasting blog and a site that sells blasters and offers some useful info.

The jury is still out, but some knowledgeable input might help.


A friend had $20,000 in resto work done on her mother's 1954 Desoto Firedome. The work was done by FantomWorks in Norfolk, VA. You may be aware of this shop since they currently have a show on the Velocity cable TV channel.

They still show this car in their Completed Projects area, but I'm surprised they do. (Archived in case they take it down.)


They soda-blasted the body to prep it for a complete re-spray and failed to neutralize the soda before painting. The result? The entire car now has rust bubbles under the paint. The FantomWorks owner, Daniel R. Short, refused to make good on his shop's mistake (it was admitted to by his paint shop manager), but they still keep my friend Ginny J's glowing testimonial up on their site. (Archived in case they remove it). What a guy that Dan is!