Introduction to Pneumatics for Home Haunting

Lesson 4
Air Compressors

So you have your air cylinder, valve and all the necessary fittings and tubing. Now you need an air compressor to put all that valuable equipment to use.
The more common air compressors use a tank, piston (like that in a car engine) and valves to achieve air pressure. An electric motor (usually) powers the piston. When the piston is on the downstroke, air is sucked into the piston chamber through the inlet valve. On the upstroke, the trapped air closes the inlet valve and is compressed and forced  through the outlet valve before entering the tank. With
each upstroke, more air is added to the tank, increasing the air pressure.
Air compressors come in many shapes and sizes. Pictured below are but a few of the many styles of compressors available. There are as many brands as there are style of compressors.  Compressors can get expensive, and if you want a compressor only for your haunt and do not plan on operating it the rest of the year, affordability should be a key issue. Ultimately, it is up to the consumer to do his or her research before making a purchase.
The compressors shown above are only a few of the many available on the market. The two most common compressors tailored to the home owner are the compressors at the far left and right sides of the picture. The one at the far right, known as a pancake compressor, has seen increasing popularity in the home workshop thanks in part to brands like Porter-Cable offering affordable package deals that include the compressor, a pneumatic nail gun, hoses and fittings.
Now that we know a little about how compressors work and what some look like, let's break down other features.
When setting out to buy a compressor, either new or used, you will first need to decide on electric or gas powered.
Gas powered compressors really have no use in a haunt, unless you operate a haunted trail and there is no way to run conventional power to a pneumatic prop in a remote location. Gas powered compressors are loud, and typically used on job sites when no other power source is readily available to operate power tools.  In the above picture, the yellow compressor at center is gas powered.
Electric compressors are far more common than gas powered. When it comes to electrical compressors, you need to choose either 110 or 220 AC (Alternating Current). The receptacles in your walls where the TV, microwave and your computer plug into are all 110 AC. This is common household current. 220 AC is what you could consider industrial strength, and as the number implies, twice the amount of current as 110 AC. 220 requires special outlets and plugs which most likely you won't find in your home. For the typical haunter, 110 AC is all that is needed.
Now that we know what kind of power requirements are needed, the choice to be made is oil or oilfree compressors. Oil compressors have oil that lubricates the internal workings of the compressor. These require some maintenance, and there is a chance of the oil passing into the line. For haunting applications, this may not be a bad thing. But if you plan on using pneumatic tools in the off season, it may cause problems as many newer tools are oil free tools. If using a pneumatic paint sprayer, this would be problematic, since oil mixing with the paint could affect the coat.
Oilfree compressors have no need of oil, giving the consumer a practically maintenance free purchase. When shopping at home stores such as Home Depot, the majority of the compressors available are oilfree. The Porter-Cable pancake combo mentioned earlier is oilfree.
Oil compressors are typically more expensive than their oilfree cousins, but tend to be quieter.
When choosing an air compressor, there are several features to consider. Horsepower is a term often overemphasized. The typical range of a garage air compressor is 1.5 - 3 horsepower, and usually that is all that will be needed for a haunt. Unfortunately, many manufacturers inflate these numbers, claiming 2 hp for a machine that only achieves 1.5 hp.
Tank volume is another key feature. Naturally, the larger the tank, the more air it will hold, the less the motor will cycle. There is a trade-off to this however. While you may not want a noisy compressor motor triggering every few minutes and distracting patrons from your props, to achieve that means spending more money on a larger compressor that may take up excess room in your garage in the off season.
P.S.I. or pounds per square inch is the pressure of air the compressor exerts. When shopping for a compressor, look for one that has at least a 100 psi rating, as many props function at or below this range. With psi, it is better to have more than needed instead of not enough.
Of the features many compressors list, cubic feet per minute (c.f.m.) may be the most important. You can have a powerful motor and a huge tank but it will do no good if the cfm's are low. Basically, cfm is the amount of air that the compressor moves. The higher the cfm, the better.  A rule of thumb is that per true HP, compressors will deliver about 4 true CFM at 100 psi. So a 2 hp compressor will give 8 cfm at 100 psi.
Most compressors come with a regulator.
Moisture builds up in compressor tanks. It is an inevitable nuisance due to atmospheric pressure and compressed air meeting. It is advisable to drain the tank after each use to remove as much of this moisture as possible.

We hope this lesson was helpful. This is by no means an exhaustive lesson, there is much more to learn in pneumatics. Do a search on the web if you would like to learn more. If you are considering using pneumatics for haunting for the first time, do not be intimidated. Though it may seem daunting at first, once you master the fundamentals of pneumatics, you'll wonder why you didn't start this addictive form of haunting sooner.