Single stage vs. 2-stage air compressor - advantages at ...
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Single Stage vs. 2-Stage Air Compressor - Advantages
Heating the air in compression can actually help. If you start with room temperature air and compress it, the heating makes it expand so it has a larger volume and lowered viscosity, making it push out the exhaust valve faster. If the tank is large enough that the air in it is reasonably cool, that air temperature defines the back pressure, not the air going through the exhaust port. If the heat conduction between the intake and exhaust ports is high enough to significantly heat the incoming air, then the compression stroke starts with a smaller charge and resultant loss in output. Cool in, hot out improves the throughput.
The manufacturer only listing displacement (swept volume) is just dodging the issue. A good spec sheet gives the actual output at various pressures. These compressors never deliver the full swept volume. Running at slow speeds and against low back pressure, they may come close, but all drop off when they have to work hard. Configured as a two-stage where the low-pressure cylinder was only working against about 15 PSI in the manifold between the cylinders, at 62 CFM swept volume and 100 PSI it actually delivered 56 CFM. That is about the best you could expect. I sized the orifice in the bead gun to match and sent the air through the cooler and to it, only feeding the 200 gal. tank when not blasting. With the large storage, other people in the shop never noticed.
Another factor usually neglected is the force needed to open an atmospheric intake valve. Running my Gardner Denver ACR as a vacuum pump, it would rapidly go up to 25 in hg gauge and stop. The approximately 4-5 in difference between that and atmospheric pressure was the differential needed to actuate the valve. That difference is also subtracted from the fill pressure when it is used as a compressor, although that is mitigated a bit because once the valve snaps open, it will tend to stay.
The viscosity of the air can have a surprising effect. I once repaired some huge heaters for an aluminum annealing oven big enough to handle truck loads. The operator commented that even though he had the blower motors rewound for the maximum performance possible, he had to start with the blowers off and heat the air until it got thin enough to avoid overloading them.
All these factors get in the equation, which isn't simple.
Bill
Advantages And Disadvantages of Air Compressor Types
Air Compressor Type Advantages & Disadvantages
Which Air Compressors type is right for you?
There are several types of air compressors to choose from. Choosing the right type of air compressor is very important for your needs as it will save you money and trouble in the long run. You will learn on this page the advantages and disadvantages of the different kinds of Air Compressors.
It all depends on what you use it for! You will find here a short list of the most popular types of Air Compressors and we will discuss the pros and cons of each one, including some typical examples and common uses.
After reading this page, you should have a fairly good idea of what kind of compressor is best for you. The difference between these Air Compressors is both the PRESSURE and the FLOW (cubic meters per minute, or cubic feet per minute). The most common pressure is 7 to 8 bars.
Strap yourself in, because air compressors differ in many ways depending on job demands. Deciding between each option below is a matter of looking at needs, the tools being used, how many users, and budget. The major differences between air compressors are listed and explained below in terms of options, advantages, and disadvantages.
Mounted / Unmounted Options
The first major difference between air compressors is mobility, so, naturally, you have a choice between portable air compressors and permanent mount air compressors.
But be careful, because there are major differences when it comes to the advantages and disadvantages of each. The type of place where the air compressor is needed will often do the deciding for you.
Permanent Mount:
The best use for mounted air compressors is obvious. Mounted compressors are typically for permanent shops, for working out of a truck, and for longer-term job sites.
Most mounted compressors are electrically powered, but mounted, gas-powered compressors can be found for trucks and job sites as well.
Advantages:
- They tend to be less expensive
- Upgrading permanent mount compressors with air filters, water filters, and in-line lubrication is easier.
- There is a much broader selection of electrical power options for mounted units.
- Generally, they are more powerful.
- Generally, they have greater air capacity (CFM output).
Disadvantages:
- Not portable.
- More air hose must be run when distance is an issue, and that means some additional cost.
Portable:
The real advantage of portable air compressors is their portability. The good news is that portable compressors are versatile, and most jobs that need air compression can be handled just fine by fairly-priced, portable units.
Advantages and disadvantages for portable compressors are the reverse of the advantages and disadvantages for mounted compressors.
Advantages:
- Portability and versatility.
- No additional air hose needed.
Disadvantages:
- They tend to be more expensive (the biggest drawback).
- Upgrading for filtering and lubrication is more difficult, but usually not needed for jobs where portable units are used.
- Most portable units are designed to be electrically powered by standard wall current (but, again, that's usually plenty for mobile projects).
- Air capacity (CFM output) and overall power tend to be less.
- High-powered portable units are available, but they are almost always gas-powered, heavy, and expensive.
- The general idea is that if you don't need a portable unit, buy a permanent mount compressor.
- But when mobility is a must, finding a good portable air compressor at a decent price shouldn't be hard.
Stage Options
Air compressors are designed with one or more "stages" (cylinders) where the pistons compress the air.
Single Stage:
The "single" in "single stage" means that they only have one cylinder for compressing air. For most air tool jobs (requiring 120 PSI or less), especially jobs around the house, single stage air compressors perform nicely.
Multi-Stage:
For pneumatic tools and jobs that need more pressure (above 120 PSI, generally), multi-stage compressors measure up to meet the demand. Multi-stage compressors have two or more cylinders. After air is compressed in the first cylinder, it is passed to the second cylinder for more compression, and so forth.
Multi-stage compressors create much more heat than single stage compressors, and usually require a radiator. They are needed most when more than one person will be using the same air compressor, and when high demand air tools are in use. Examples: grinders, air nailers, air sanders, and tire changers.
Advantages/Disadvantages:
The advantages and disadvantages for these options are simple. As the air pressure (stages) and power increase, so do power requirements, cooling requirements, cost, and weight.
Bigger, more powerful machines weigh more, need more cooling, cost more, and need more power. The opposite is true of smaller, single stage machines.
If you need a multi-stage compressor, you'll know by the tools you plan to use with it and how many people will be using it at once. If you're not sure if a multi-stage compressor is for you, giving one a "test lift" will usually provide all the missing information you need (make sure to "bend the knees").
Power Options
Choosing between a gasoline or electric air compressor can be made easier by making other choices first, like choosing portable or mounted. Considering both mobility needs and the demands of the job usually narrow the choice down.
Other considerations play a part as well, such as what type of tools will be used, air pressure needed, and number of users.
Gasoline:
Most gasoline compressors are portable, but mounted gasoline-powered compressors for trucks and job sites are available too. There are two basic kinds of gasoline compressor motor designs. Some power electric generators, which then drive the cylinder(s) with an electric motor. Others drive their cylinder(s) directly using a clutch.
If you need a multi-stage compressor (portable or mounted) it will probably have to be a gasoline unit to meet the power demand. Portable compressors grow heavier with increased power performance. This is especially true since gas compressors tend to be heavier anyway. Portable, multi-stage, gas-powered compressors can easily grow to be monsters in the 200 lb.+ range.
The real benefit that gasoline compressors offer is an alternate fuel source when electricity isn't an option. That usually means the work site is remote, so the extra noise they make usually isn't a problem.
Advantages:
- Alternate source of power.
- Usability in remote areas.
- Power, in the case of high-performance portable machines.
Disadvantages:
- Hassle of buying, transporting, and keeping gasoline on hand.
- They tend to be noisier.
- Powerful, multi-stage portable units must be gas-powered and are heavy.
- A little extra maintenance if you choose to clean the gas tank now and then.
Electric:
Easy, convenient, and the most common way to run a compressor. Most operate on standard wall current, but the bigger, powerful models offer additional higher-voltage power options. This way, the mounted electric units can keep up with the performance of the powerful portable units, and then some.
Choosing the right electric compressor is very important. As with gas compressors, undershooting your performance needs with an electric compressor will have you replacing your weaker unit in no time. But, if you overshoot on an electrical unit, you may end up paying way more for your power bill than you'd like.
Additional reading:
Brewing Beer with Honey - BeerSmith kapa Horizontal Two-Stage Air CompressorElectric compressors are best for most users when the right one is selected. There are some portable electric units which are best when you need a compact model. One of the biggest drawbacks is having to run lots of air hose, since using extension cords is not recommended.
Advantages:
- Easy, hassle-free power source.
- Best choice for permanent mount compressors.
- Best choice for most jobs.
- Portable units are more compact and weigh less.
Disadvantages:
- Additional cost to run extra air hose is recommended to reach a work area, not extension cords.
- Powerful electric units require heavy-duty electrical wiring to meet power needs.
- Portable units are less powerful than gas compressors.
- Powerful units can have expensive energy demands.
Like the other options discussed here, the best course of action is to examine your needs. A lot of choices make themselves if you can really pin your needs down first.
Lubrication Options
This might be the easiest decision to make when buying a compressor. Oiled compressors outperform and outlast oil-less compressors at the expense of extra care and maintenance. If your compressor is going to see a lot of use, oiled compressors are a must, and the required maintenance will be worth the effort in every way.
Oil-less compressors are only recommended if you're planning to use your compressor now and then. If that's the case, an oil-less compressor will perform well for a long time without extra care.
Oiled:
In an oiled compressor, the cylinders are thinly coated with oil as the machine operates. This makes them much more durable. This also means that, like a car or lawnmower, the oil must be changed from time to time. Also, oil compressors cost more than oil-less compressors, but it's almost always worth it to go with oil.
Buy an oil compressor if it's going to see a lot of use. Oiled models are absolutely necessary for high power compressors, because a tighter cylinder seal is needed as pressure increases (even more so for multi-stage compressors).
Checking the oil level with each use and scheduled oil changes are strongly recommended, because an oil compressor will outlast oil-less models by a long shot if cared for correctly.
Advantages:
- Oiled designs make powerful compressors possible.
- Oiled compressors last longer.
- Oiled helps cool the unit.
- Oiled compressors are best under all circumstances, except in the cases of occasional use and budget limits.
Disadvantages:
- Extra care and maintenance with oil changes/checks.
- Oiled units weigh more in general.
- Oiled units are heavier in general.
- Oiled units are more expensive in general (but they're almost always worth it).
Oil-less:
These compressors are "permanently" lubricated, usually by coating the cylinders with something like teflon. You might hear that oil-less models are more advanced. They cut down on care and hassle at first, yes, but the fact is that they wear out, and having to buy a new one is a big hassle. There's just not a good substitute for doing it the old-fashioned way.
But, if you just need an air compressor for jobs here and there that won't demand a lot of pressure (up to about 120 PSI), oil-less might be just the thing for you. They are less expensive (because it takes fewer parts to make them), and they are lighter (from having fewer parts).
Big heads up though--on average, oil-less compressors are not built as well as oiled compressors, but there are a few notably good oil-less designs here and there. So if lighter use is what you're looking for, then an oil-less compressor could be the perfect buy.
Advantages:
- Less expensive.
- Oil-less machines are lighter.
- Convenience. Oil-less machines don't need the maintenance that oiled machines do.
Disadvantages:
- Less durable, because the "permanent" lubrication eventually wears down.
- Oil-less compressors run hotter.
- Oil-less units have a power cap, and generally are not as efficient as oiled compressors.
- Oil-less air compressors only offer a good return on their purchase value if you don't plan to use it heavily.
Pressure & Flow Options (Reciprocating Vs. Rotary)
Reciprocating Piston Air Compressors