Chapter 1 – The Basic Stuff
This is the basic information that most every buyer will prefer to have in front of them when they purchase an industrial vacuum. This stuff will help give you an idea of what to read through in order to make an educated choice as a buyer.
The duty cycle of a machine is determined by the length of time it will be operating. It’s imperative that you match the capabilities of the vacuum system you’re looking to buy with the duty cycle that the machine will be expected to have.
As a rule, most of the smaller canister or shop-type vacs use high speed vacuum producers, which run at about 20,000-25,000 rpm! This is a death wish for the vacuum, since it will cause the carbon brushes or bearings to wear out in as few as 800 hours. There are some high-rpm vacuums of European design that you may be able to run for 2,500 hours, but you’ll pay dearly for the extra hours.
This means if you only use your vacuum for about three hours each day, one of the typical standard canister vacuums will not usually last longer than 18 months or so.
Most vacuum systems on today’s market that are over five horsepower use motors that are capable of running continuously for years. There are various differences in the vacuum producer types that will be a determining factor in their longevity. Some will last for five years or so, and some will last for 40 years. This will be fully discussed in our Central Vacuum section, under Types of Exhausters.
If you’re looking at systems that are smaller than five horsepower, be sure that you buy a model that won’t self-destruct if you would like your vacuum system to last.
The Filter System is something that you might not pay much attention to, up front. But it will get a lot of attention after you begin using a vacuum system! You may be reading this information now because of the time that is wasted when you have to clean and maintain the filters on your current system. There’s an easier way to use a vacuum system without a lot of downtime…
The filter is one system that you’ll have to choose, among several various types of filter media. This is usually based on how fine the dust is that you work with.
Consider how the filter system will be cleaned, too. Many filters on portable units are called “shaker type”. For some models, especially canister vacuums, this means just what it sounds like… you have to remove the filter and physically shake it!
Larger vacuum systems with shakers utilize various methods to accomplish the cleaning of the filters. Side to side shaking is generally accepted as being more effective than up and down shaking, but it’s more difficult to accomplish. Some vacuums have cleaning systems that are almost worthless, but others work extremely well. Feel free to ask us for more details.
Shaker filters will need you to power off your system before you can clean the bags. Unless the filters can remain working efficiently until your material canister is full, you’ll need to periodically turn off the system and clean the filters. This is the number one complaint from owners of vacuum systems, if the system is under-sized and uses a shaker design, since it causes the most down time. A cleaning system can work automatically, either by automatically shutting down the system, shaking and the restarting the system or by using pulse jet cleaning or reverse air. We only know of one portable vacuum that still uses reverse air filter cleaning, and it isn’t automatic. The technology of reverse air cleaning is older in terms of today’s technology, but it’s effective in some systems.
Pulse jet cleaning uses dust collecting technology that allows the filter to be cleaned while the vacuum system is running. It seems like it would be a useful way to clean filters, but in actuality it’s not that useful if your system has limited storage capacity. Plus, you have to connect it to plant air.
The majority of the time, pulse cleaning systems are used in portable vacuums with cartridge type filters. This is due to the fact that these filters are very easily clogged, and they have to be cleaned quite often. Many cartridge units are marketed as having pulse cleaning, but that’s a misleading “fact”, since it’s not a continuous type of cleaning. You have to shut the system down, connect it to plant air and then manually pulse clean it.
In our knowledgeable opinion, if you have very fine dust in your work areas, don’t look to cartridge systems to keep the areas clean. At least get references from people who use a model before you buy – some cartridge systems do work well, but many more don’t. Some vacuum manufacturers’ models even require that you physically take the cartridge out, and clean it however you can!
You also need to be aware of “can velocity” in a vacuum. This refers to the upward flow of air through a filter cartridge. It should not exceed 125 fpm, or you may wonder how it works – until it doesn’t. If can velocity is too high for the unit, the filters will be easily clogged and they usually aren’t easy to clean, either.
It’s important for you to determine how much material storage will be feasible for you to handle. It all depends on the material your system will vacuum and store. If you are vacuuming steel shot at 375 pcf, then even small storage containers will need to be handled by someone using a machine. On the other hand, if your vacuum material is paper “fluff” at 5 pcf, you’ll want to ask about the best ways to compress that material.
There are many equipment standards, and a variety of optional types of equipment to help you handle many different materials. Ask a few different manufacturers for any ideas they might have.
Portable machines, even by name, need to be easy to move. If you get a unit with larger wheels, they will help you push the unit over uneven floors, cables and mats. Systems with smaller wheels are harder to work with. Some models come equipped to be lifted by forklift or crane, so they can still be moved, even if they are larger in size.
The vacuum system you select should be easily handled in your working environment. Allow for any odd areas your plant layout may have. If you’ll need to move the unit in narrow aisles or through doors, or if you want yours to fit in an elevator, check the weight and dimensions of various units, before you buy.
You’ll also want to check the material gauge, and whether the unit is constructed in a way that gives it heavy duty usage. You’ll be sending your vacuum system out into your company’s war zone, so to speak, and you’ll want it to be built like a tank – but to handle better in tight quarters than most tanks could.
As a rule, if a system has over two horsepower, it will use three phase power. Be sure that you have distributed appropriate power sources in any areas where you will be using your vacuum unit. If you don’t already have power sources wherever they are needed, you’ll want to budget for that cost, in addition to the unit cost, Be sure that each connection point has a disconnect, because portables only rarely feature disconnects, if they are under 20 hp.
Finally, you’ll have to consider what electrical type you’ll need. Many plants require an electrical enclosure that is dust tight (NEMA 4), but many portables only will offer you NEMA 1 or NEMA 12, standard. These are more for general usage, and not sealed.
As a last consideration, you’ll need to look into costs for delivery for your unit, and what kind of warranty you get. Check over any warranty very carefully. Will it pay for the cost to ship you any parts that are defective or need replacing? What specifically does it cover, and how are you reimbursed if you must pay for replacement parts yourself, first? You would be amazed, and not always in a good way, at the various service levels after you make your purchase.
Chapter 2 – A different CFM
This is the lesson in “air flow” that’s eventually covered in just about every vacuum system sale. There is more confusion over the terms “SCFM”, “ICFM” and “ACFM” than any other topic in the wonderful world of compressed air. So, for the layman, here are a few definitions:
Standard Cubic Feet of air per Minute. For our purposes, this is the volume of air standardized at 68 degrees F. at sea level pressure. We tend to disregard the “sea level” part when talking to you about systems. But we do take site elevation into account in the design calcs.
Actual CFM. Air is compressible. When pressure is applied to a standard cubic foot of air, it gets smaller. When vacuum is applied, it expands. The volume of air after it is pressurized or rarified is referred to as its actual volume.
nlet CFM. Just to make things more confusing, blower manufacturers use charts that specify their volume performance based on conditions at the inlet of their equipment. And because air system designers have to read these charts, we tend to use the term. No one else does; but since we do, you need to, too. Sorry ’bout that!There are many equipment standards, and a variety of optional types of equipment to help you handle many different materials. Ask a few different manufacturers for any ideas they might have.
The system diagram beside shows three different points in both a vacuum and pressure type system. Note that the location of ICFM changes with pressure and vacuum applications Note that in a vacuum system, the volume of air expands (is rarified) as it travels toward the air pump inlet (and thus travelsfaster in a fixed size pipe). In the pressure system, air expandsin exactly the same way as it travels from the compression side of the air pump to the system end point. And as a final small note, the only difference between a vacuum producer (or exhauster) and a blower is the side of the process connection.
Chapter 3 – Let’s Discuss Pressure
This is a quick lesson in pressure and vacuum terminology. There are a few common pressure terms that need to be understood if you’re going to talk vacuum with those of us in the business. Here they are:
|W.G.||Water Gauge (plus a height dimension)|
|W.C.||Water Column or Column of Water|
|Inches H2O||Inches of Water (Column)|
|S.P.||Static Pressure (usually in inches)|
|Water Lift||Water Lift|
These are all the same thing. They can reference pressure or vacuum, but is normally associated with dust collector fan performance. In vacuum systems, it’s most often used when talking about pressure differential across a filter media.
Pounds per Square Inch. Most commonly used as a pressure term, but it can be a negative (vacuum) number. PSI = ” Hg./2 thereabouts.
Only used by the ultra-high vacuum people. Equals one millimeter Hg.
Inches of Mercury or Column of Mercury in inches. A measurement of vacuum, rarely used for pressure indication. The most common vacuum designation for the industrial class of vacuum systems. For those really interested, 1 inch Hg. equals 14 inches of water. (okay, so it’s 13.5951 inches with a water temperature of 39.2 degrees F, but who can remember that?) “Full” or “Absolute” vacuum is 29.92″ Hg. Most common high vacuum type conveying systems top out at 27″ Hg. (And if you can’t convey with that, think of some other way!).
Chapter 4 – The Dreaded @
Marketing is a competitive business, and there are always some vendors who feel the need to over-emphasize the positive things about their vacuums, and perhaps even to exaggerate beyond what their units can really do. Performance claims are often boastful for many types of products, but there are really a lot of extremes seen in the vacuum business. And you rarely hear about a unit’s limitations. Hey, every unit has some limitations. Here is your reality check!
Almost every vacuum company states their performance figures at either end of the performance spectrum, since those figures will always be the largest for each typical scale.
For example, when making claims about volume performance, many companies use what’s known as the “open condition volume”. This is the volume that is achieved by a vacuum producer when pulling 0 vacuum. They also use conditions you would only find at zero flow to make vacuum performance claims.
Combining those two figures is simply meaningless. It’s like measuring your car’s mileage while it’s running in your driveway. Worse than this are companies whose marketing copywriters get confused and use the two performance claims together, with the @ symbol.
Here is a chart developed from the published performance figures for a vacuum producer that is used in popular shop-vac type vacuums. It’s the model 116472-00, by AMETEK. They supply those little high speed centrifugals for nearly all the canister vacuums made in the USA! Note that the maximum flow for this unit is 112.0 cfm (that’s the red line) and the maximum vacuum is 106.6 water lift (that would be the blue line).
Chapter 5 – Horsepower Stories
As we mentioned in our last section, marketers love to exaggerate their units’ productivity beyond reality. The retail vacuum business is likely one of the areas where the most grievous infractions occur. But if our customers have already tried shop vac units, we usually need to explain to them the ins and outs of horsepower – we’ll even explain it to people who already should know.
As you might know, you can easily find vacuums that state their horsepower with wide, bold numbers, like 5.0 Hp or even 6.0 Hp. But they still plug into standard 15 amp electrical outlets. What’s up with that? Turns out, if you read the really, really fine print, you’ll see something like “10A” on the nameplates.
|Amps x Voltage = Watts|
|Watts / 746 = Horsepower (electric)|
It means that those little 10A motors plugged into a 110V outlet draw 1100 watts. Wait, that’s only 1.47 Hp!