Compressed Air Basics: Vibration Isolation

A Whole Lotta Shakin' Goin' On

Your compressor shakes.  The machinery in your shop shakes.  When air goes through a pipe, it shakes the pipe.  The technical term for this shaking is vibration.  There's vibration in nearly everything you use. 

Sometimes this vibration can cause machinery to fail and cause pipe fittings and welds to leak.

Actually, I should rephrase that....It will cause machinery to fail and cause pipe fittings and welds to leak, if nothing is done about it.  That's why every compressor must be isolated from vibration.  There are two places that are a concern for every air compressor.

FLEX HOSE AFTER THE COMPRESSOR

Every compressor manufacturer says that you need to put a vibration isolator or flex hose between the compressor and the pipe system.  I'd say about half of our customers know this already, before we mention it to them.  However, it's important that we get the word out to everybody else.

The reason for this is that your compressor vibrates, the machinery that uses the air vibrates, and when air goes down the pipe it vibrates the pipe.  The vibrations from different sources have different harmonics - they vibrate at different frequencies and different amplitudes.  When you don't isolate the vibrations of different harmonics, it wears out the components much more quickly.

Not only that, but the compressor was built and tested to withstand its own vibration.  It was not built to withstand different harmonics.  There's no possible way for the manufacturer to test all the conditions that a compressor can see - there's an infinite amount of possibilities. 

You won't see it immediately.  This is a long term effect that we're discussing.  Usually it takes a couple of years for the lack of vibration isolation to cause a problem.  The problems on the compressor usually exhibits itself as a leaky oil cooler or air cooler.  For the pipe it will break welds or cause leaks.

There's a chance it may never cause a problem.  However, putting in a $20-$100 flex hose to prevent thousands of dollars in broken parts seems like a no-brainer to me.   You can just use a rubber hose.  Make sure it meets the pressure, temperature, and flow specifications.  Most of the time we use metal flex hoses.

VIBRO-PADS WHERE THE COMPRESSOR IS MOUNTED

The other place where you have to worry about vibration is where the compressor is mounted.  There should be a rubber pad or foot at the bottom of the compressor.  Sometimes the compressor will come with these already installed; sometimes you'll have to add them yourself.

If you don't do this, the weld where the foot of the tank meets the tank will crack.  Again this could take several years, but why make a tank that should last decades only last a few years?  For $20 worth of parts (we sell vibro-pads for $4.95 each), this can be avoided.
 

Every Kaeser Rotary Screw Compressor comes with mounting feet that vibrationally isolate it from the floor.

 SO LITTLE TO INVEST; SO MUCH TO LOSE

Manufacturers can void your warranty if you don't install the compressor properly, and they would be correct to do so.  If you don't isolate your compressor from vibration, the problems with the compressor would be your fault.  They weren't caused by manufacturing defects; they were caused by a bad installation, which was out of the manufacturer's control.

You can't drive your car into a lake and expect the dealer to fix everything for free because the car is under warranty.  In the same way, you can't install your compressor the wrong way and expect the problems caused by the installation to be covered under warranty.

A flex hose is $20-$100 and vibro-pads are about $20 total.  The amount that we're talking about is nothing compared to price to fix a compressor.  If your compressor doesn't have a flex hose between it and the air system, go fix that now.  If your compressor mounts directly to the floor (or whatever else you mount it to, like a truck bed) without rubber pads, go fix that now.  It's quick and easy and will prevent thousands of dollars in problems.

Taking a Break From the Basics - Air Flow Through An Orifice

We're taking a small break from the Compressed Air Basics Series, but we'll be back to it next week.  I noticed something - a certain page on our website that draws a lot of traffic and I wanted to discuss it.

When looking at a list of our most visited web pages, this one is always the most popular or in the top three:  http://www.aircompressorworks.com/airflowthroughorifices.html.

It is just a chart of how much air can flow through a hole at different pressures and different hole sizes.  It seems simple, but this chart it very important to many compressed air applications.  As a customer, this chart can mean a lot to you.

LEAKS

The first reason is leaks.  Leaks in a compressed air system can cost you a lot of lost money in electrical bills, maintenance, and wear and tear on the compressor.  I've seen customers who needed a 20 hp air compressor just to keep up with leaks. 

Looking back at that chart, if you just have a tiny 3/32" hole - that's less than 1/10th of an inch - it will leak out about 17 CFM if the pressure is 125 psi.  That's 5 hp worth of compressor right there just to keep up with a tiny 3/32" hole.  At the average Florida electrical costs and a 60 hour work week, that's about $1200 per year.  If you have a large air system it's common to have several of these leaks.  That tiny hole doesn't seem so tiny once you do the math.

That chart gives you a great idea of how much air is coming out of your leak.  You might notice that for the same size hole, the lower the pressure is then the less CFM the leak is.  It's a great example of how turning down your system pressure can save you money.  Not only do you get the energy savings of running the compressor at a lower pressure, but because the air lost from leaks is reduced, then the compressor runs less.  It's a positive feedback loop:  Lower the pressure and your leaks are smaller;  the leaks are smaller so you need less CFM; you need less CFM so you can lower the system pressure a little, which then reduces the leaks even more, ect. 

BLASTING

Another way that chart comes in handy is with abrasive blasting.  Abrasive blasting is sandblasting,
bead blasting, soda blasting, and some other media blasting applications.

We have customers that use a lot of air for sandblasting, and yes, a lot of that air is justified - they really do need it.  However, there are many other customers who waste tons of air and media by using too much pressure or nozzles that are too big.

The blasting is just a leak, and the size of the leak is the bore size of the blasting nozzle.  A very common thing to do is just use unregulated air from the compressor and blast away - whatever's coming out of the compressor, that's the psi they're using.


Well, look again at that chart.  With an 1/8" bore and 125 psi, you need about 31 CFM.  However, if you regulate the pressure down to 90 psi, then you only need about 23 CFM.  The price difference in a compressor that can do 23 CFM at 90 psi and one that can do 31 CFM at 125 psi is between $1500 and $2000.  Also, the electrical cost to run the bigger one is more.  The majority of sandblasting applications need 90 psi or less, and some can go as low as 40 psi.  It all depends on what you're blasting and the media that you're blasting it with.  If you could blast at 40 psi, then you'd only need about 12 CFM.

Another way to reduce the CFM needed is to reduce the bore size.  Let's say you had an 1/8" bore, but you could use a 3/32" bore and still do the job just as fast or nearly as fast.  At 90 psi, you'd need only about 13 CFM.  So we started out at 125 psi and an 1/8" bore needing 31 CFM.  However, reducing the pressure down to 90 psi and using a smaller tip, we now only need about 13 CFM.  That's a $2000-$3000 difference in the initial price of the compressor, and you save money in electricity and maintenance. 

Also, as the nozzles get used, they get worn down.  What happens is that the hole gets bigger and bigger.  If you're compressor is running more than it used to or can't keep up anymore, then it's time to get new nozzles.

If you can reduce the pressure and use a smaller bore, not only does it use less compressed air, but it also uses less media.  So there is even more savings to be had.

So how do you figure out what you need?  If you have a set-up already, regulate down the air to the lowest psi and still get the job done.  What media you're using, the material you're blasting, and what you're trying to remove will determine the pressure you need.  Once that's done, try a smaller tip size and see if you can do the job in the same amount of time or really close to it.

 CLEANING

In a lot of plants, the personnel used compressed air for cleaning.  They blow dust off machines, they knock the debris off radiators, and they even use the air to clean themselves.  Sometimes they just use the air from an open hose hooked into the air system.  Looking at the chart again, you can see that blowing air from a 3/8" hose at 125 psi is about 284 CFM!  That's a ton of air. 

This is why the air needs to be regulated, and blowguns need to be used.  Regulating down to about 30 psi and using a blowgun will knock that 234 CFM down to under 20 CFM.  Some applications require larger blow guns and a little more pressure.  However, even with a huge blowgun used at 90 psi, it's still less than half of just an open hose using unregulated air.

OTHER APPLICATIONS

The power of that chart is that it tells you the CFM needed for any application where compressed air blows through a hole and onto something else.  There are thousands of applications out there that this applies to.  Using it that chart you can see how manipulating the size of the hole or the pressure can affect your compressed air usage. 

We didn't make that chart - it was made by some engineer ages ago.  The name of the person who came up with it has been lost in antiquity, to the best of our knowledge.  You can see the equation that's used at the bottom of the page.  We put it on our website, because it comes in handy so many times for us.  We're glad so many people are finding it as handy as we do.

Compressed Air Basics: Clean Air Treatment Part 2

Last week we looked at removing the liquid water out of your compressed air system.  However, if you are using more than just shop tools, then there are other things in the air that you need to be concerned about.

Particulates

In layman's terms particulates are dust.  They're little particles suspended in the air.  You'll also hear this term when it comes down to the cleanliness of your oil.   The oil filter in your car is used to trap the particulates that get into the oil.  In the same way, you often need to trap that particulates in your compressed air. 

Particulates, and the filters that trap them, are measured in microns.  A micron is another word for micrometer, which is one millionth of a meter. 

To the right you can see a perspective on how small a micron is. Human hair is 50-70 microns wide.  When we talk about filtering out particulates in compressed air, we start out at "big" particles, which are 3-5 microns.  Filtration down to .01 micron is common.  Special applications can often demand filtration beyond that.

Think of how small that is.  A human hair is 50-70 microns, basic filtration traps particles 20 times smaller than that, and common advanced filtration can trap particles that are 5000 to 7000 times smaller than with width of your hair, or 9000 times smaller than a typical grain of sand.  The largest particle a human eye can see is in the range of 40 to 50 microns.

Just in the air around us there are thousands of different types of particulates suspended in the air.  In industry, there are many other contaminates as a byproduct of what the company does.  Obvious examples are sawdust in a cabinet shop, concrete dust at a concrete plant, or grain dust at a mill.  However, there are much smaller particles that you can't see in high concentrations, and there are too many to list here.


The first line of defense against particulates is your compressor's inlet air filter.  Many of the things we have mentioned will mess up your compressor if allowed to continually get in.  Most compressor inlet filters will be between 1 and 25 microns.  The manufacturer will put on the air filter that they think will protect the compressor.  Make sure you check in often and keep it clean.


The second line of defense is lubricant. The oil in your compressor (assuming it's oil-lubricated) will trap a large amount of particulates.  If your compressor has an oil filter, then many of these will get trapped in oil filter.  Again it's important that you keep your oil (and oil filter if applicable) changed on a regular basis. 

Filters are the last line of defense for particulates.  When talking about particulates, filters will have a micron rating.  That will tell you what size particles it traps.  If you have a 5 micron filter, then it will trap a large majority of particles 5 microns and above, usually around 99% or greater.  The filter may also have a ppm rating, and that tells you how many parts per million of particles of that size (the micron rating) or greater will pass though the filter.  Filters have changeable elements inside of them.  You need to change them on a regular basis as part of your maintenance plan.  For the most part you need to change them every 6 months to a year, depending on how many hours you run per year.

Vapors & Mists

Particulates are solid particles suspended in the air, but there are also vapors and mists suspended in the air around us.  Most of it is water, which we discussed last week, but that's not all. 

A mist is liquid suspended in the air.  A vapor is a gas mixed in with the air.  Whether a substance will be a particle, mist or a vapor is determined by pressure and temperature of the air it's in.  Every substance has a pressure and temperature thresholds where it changes states. 

Many processes are sensitive to mist, such as painting.  A few are sensitive to vapor, such as breathing air.  A good example is oil mist and oil vapor.  A common misconception is that the oil mist in compressed air is solely generated from the oil in the compressor, and that using an "oil free" compressor will give you oil free air.  While an oil-lubricated compressor will have a small amount of oil carryover, there is already a higher hydrocarbon concentration in the air around us and, if you want oil-free air, you must filter that out even with an "oil-free" compressor.

An oil-lubricated compressor that is well maintained will pass hydrocarbons downstream in the amount of 1-3 parts per million (ppm).  However, in relatively clean atmospheric air, there is already 6-10 ppm of hydrocarbons.  If you're near a well-traveled road, an airport, or an industrial area, then the air will average 10-30 ppm of hydrocarbons in the air.  You're breathing that in right now as you're reading this.

So remember, it's not the compressor that gives you oil-free air or even clean air.  The filtration after the compressor gives you clean air; nothing else does.  The junkiest, nastiest compressor that's passing a lot of oil, with just a moderate amount of filtration, will give you cleaner and dryer air than the most pristine "oil-free" compressor with no filtration.  Also if you put that same exact moderate amount of filtration after the pristine compressor, the quality of air will be the exact same as the quality of air after the junky compressor.
 
Filtration for vapors and mists will have a micron, ppm rating, or an ISO rating.  The manufacturer of your equipment will usually specify a micron rating and they should specify whether that applies to particulates, mist, vapor or all three.  If it's a real concern to the equipment, they should specify an ISO rating.

ISO 8573.1:2010

ISO is the International Organization for Standardization.  They publish standards about many different things in all different types of industry.  ISO 8573.1:2010 is the ISO standard about compressed air quality.  There are actually other parts to this standard and there is another standard that has to do with how the air and filters are tested.  However, when you buy filters ISO 8573.1:2010 is what you need to look at.

There are three parts to this standard:  Particulates, Water, and Oil:

The ISO rating will have 3 digits with a period between each number.  Let's look at a common ISO rating:  2.4.2. 

The first "2" represents the particulate requirement.  It basically means a .1 micron filter.  The chart above shows you how many particles are allowed to pass by of different sizes.

The "4" represents the water requirement.  This is the simplest one.  4 means you need a dew point o 38F (or 3C).  A properly sized refrigerated dryer will meet this standard.

The last "2" represents oil.  Now this one is the trickiest....sometimes manufacturers need you to meet only the oil mist standard and not the oil vapor standard.  An oil mist filter is different from an oil vapor filter.  For breathing air and medical air you need to meet the complete standard (mist and vapor).  For painting you'd only need to meet the mist standard. 

Beyond ISO Ratings

Some processes require filters that go beyond the above ratings.  There are even compressed air filters that are designed to filter out bacteria.  Going into the "other" category is beyond the scope of this post.  99% of you reading this will never need or even encounter that level of filtration.

FILTRATION ORDER

If you're going beyond just standard shop air, you'll need more than one filter.  You can't just stick an ISO 1 oil vapor filter in line and call it a day.  A filter that gets out oil mist is different from one that filters out water, and they're both different from one that takes out oil vapor.  An oil vapor filter will be ruined if it gets wet.  A oil mist filter (a coalescer or coalescing filter) will get won't work properly if used to catch water.

The basic order is:
1.  Catch the big particulates.
2.  Filter out the water (can sometimes be combined with #1 above in the same filter)
3.  Catch the smaller particulates and mists (if needed).
4.  Filter out the vapors (if needed). 
5.  Bacterial filter (if needed).

The exception is if you have a desiccant dryer or a membrane dryer.  Those dryers will filter out the water, but if any oil gets on the desiccant or membranes, it will ruin it.  If you have a desiccant or membrane dryer, then order is this:

1.  Filter to catch big particulates and most of the water.
2.  Coalescing filter
3.  Desiccant or membrane dryer to lower the dew point.
4.  If you have a desiccant dryer, after it you need a particulate filter to catch the desiccant dust.
5.  Vapor filter (if needed).
6.  Bacterial filter (if needed).

You have to gradually step up the filtration as you go down the line.  The filters that catch the smaller particles will get destroyed or clogged up by bigger particles or water.  Thing of trying to catch cannonballs with butterfly net - it won't work. Catch the bigger particles first (the cannonballs), then catch some of the medium sized ones (basketballs maybe?), and then you can catch the small ones (your butterflies).

Consult an Expert

If you need advance filtration you need to talk to your local compressed air salesperson.  If you just have shop tools, most of the time you can just stick in a water filter and go.  However once you go beyond that, it gets complicated.  There is a wide variety of filters available for you to buy.  Even sizing filters is not always simple. 

Just like the dryers we looked at in the last post, filters have correction factors, and you must take those into consideration when sizing them up.  You can get your compressed air thousands of times cleaner than the air you breathe, and you can dry your air well beyond the driest any desert on earth has ever been.  However, excessive filtration causes large pressure drop, additional maintenance, and greater energy costs.  It's not recommended to go far beyond the level you need; you'd just be wasting your money and running up your electricity bill. 

Your local compressed air salesperson should have hours of training and years of experience on filtration.  They'll take into account the level of filtration you need, the flow you need it at, the correction factors based on the ambient conditions, the pipe size you have, and do all this while taking into account that you want to have the least amount of pressure drop possible.  They should also take into account your duty cycle and maintenance considerations for later.  Let them guide you toward the right decision.