Compressed Air Made Simple - Part 2

(To Part 1) (To Part 3)

A Pneumatic Tinker-Toy Set for the Home Imagineer

Updated 11/20/07

Note: In this article, part numbers from Grainger are supplied. Please note that cheaper parts may be found elsewhere. One source we recommend is They have most of the air components you will read about in this article and the next and at very reasonable prices. Be sure to have a look!

Most beginners dread pneumatics because of the bewildering array of devices, connectors, and parts that require wiring to a power source and switching equipment. Indeed, if you begin putting together an animatronic device without doing some homework first, you'll be calling and driving all over the place, wasting time and money. Instead, we offer you a method of selecting and connecting air components that is simple. This chapter will cover the basics of these components, and the upcoming chapters will go into detail about specific applications.


You must develop a respect for the power of pneumatic actuators (cylinders, etc.) Even a low air pressure on a device can make it powerful enough to injure you! When experimenting with with air, don't hook up to your main supply unless you are clear of the device and everything is safely positioned away from you. Be sure your connectors are snugly fastened, and will not fly apart. Do not activate your electrical supply until everything is safely secured. Stay by your shutoff valve just in case. (You have officially been warned now: don't hurt yourself by being too eager!)

Let's assume you've bought a compressor, and have tested it. The output of your compressor should have a quick disconnect fitting attached to it. It's a metal (usually brass) gadget that is universal for air tools. Let's look for a moment at a typical oil-sump compressor.

This is my current setup - rather underwhelming, but it has all the parts it needs to be useful. Let's start at the pump and look at the unloader/check valve. This keeps the air in the tank from pushing its way back into the pump after it stops. It also bleeds (unloads) the brass tube between it and the pump so that the pump can start easily. There are basically two types of unloader - this dual-duty version, and another that is fired by the pressure switch when the compressor shuts off - the kind seen most often. My rig was in pieces (and rust powdered) when I got it, so instead of going to the expense of adding a switch fired unloader, I got the combo version from Grainger.

On top of the unloader fitting is the pressure relief valve (see tips below.) I believe mine blows at 150 PSI.

Note the typical gauge pair - tank pressure (my pump stops at 120 PSI) and regulator/filter/trap with gauge for settting the working pressure. Note the water draincock at the bottom of the filter. Out of sight under the belly of the tank is another water draincock.

All compressor rigs should have these parts in some form.

Compressor tips:

- Drain the tank after each session of use.

- Change the oil every few months of light use, and immediately before and after October's show. Use synthetic oil - it's worth the extra cost, and will keep your pump clean inside!

- Check the pressure relief valve regularly - just pull on the brass ring. Push it back down to stop the loud exhaust.

- Keep the belt modestly tightened. It should flop just a bit while running. Too tight, and it will wear out prematurely.

- Listen regularly for odd noises and stop the unit immediately if a loud and irregular noise occurs.

- Keep kids away from the compressor and operating devices.

- DO NOT run a compressor-driven setup without someone home to supervise it!

Using Plastic Tubing for Pneumatics

By using nylon pneumatic tubing and quick-connectors to hook up your devices, you will have a set of components that plug together as quickly as Tinker-Toys. This tubing can be cut with a razor knife to any length desired - just be sure to make your cut clean and straight. Remember, the measurement given for this tubing is the inside dimension, not the jacket; and that is also true of the fittings and adaptors discussed below. This is often confusing to first time air users, but you'll soon get used to it. For our purposes, the easiest-to-find supplier for short lengths of this nylon tubing is Home Depot. This tubing can safely handle up to 100 PSI - more than you'll ever need for a haunt prop. It's stiff, and somewhat pricey - about $4 for 25' of 1/4", but you'll need it. The 1/8"seems only to be available in this ice maker plumbing kit, which goes for about $5.50 - 6.00 (it's about 43 cents a foot at Grainger, and must be bought in 100' rolls: # 4HM08.) That doesn't keep you from looking for it on the internet, of course.

Nylon tubing is rather stiff, and must not be bent too severely or it can kink and damage itself. If you need greater flexibility, you can use Polyurethane tubing, which can handle even more pressure (140 PSI). Grainger has it - it's $85 a roll in 1/4" (# 4HL94) and $39 a roll in 1/8" (# 4HL92). Stick with Nylon to save money on long straight runs.

Below are shown two sizes of inexpensive clear PVC hose that can be used if you don't need pressures higher than 45 PSI. It comes in 100' rolls. You will need 1/4" (Grainger 4HL97) and 1/8" (4HL96).

1/8" cannot carry a large volume of air at once, so it's better for slower moving gadgets. 1/4" is better for faster, heavier pop-ups, and for filling air cannon reservoirs that guzzle.

The Kit

Let's start with a list of the rest of the parts needed for basic animatronic work:

- Quick connect 1/4" on a metal quick connect fitting for connection to compressor. This gets air to your first component, and eventually the rest down the line. 1/8" NPT can also be used, but it will restrict your entire system. The Grainger part numbers are: 4HN10 (1/8") and 4HN12 (1/4"). These two sizes should get you through your projects. Larger sizes are available, if you end up needing more volume.

The plastic quick disconnect fittings work like this: you press down on the nylon ring around the tube and hold it, then pull out the tubing. It takes one or two tries to get the technique, but once it's mastered, quick disconnect air plumbing becomes much easier than wiring electricity.

- Manifolds - one branch for each air effect you need to feed. Fit all with appropriate quick disconnects. The input to the manifold should always be as big as or preferably larger than the outlets. Here's a good place to go from 1/4" to 1/8" as you begin to branch to your devices.

Notice the use of Teflon tape to seal metal-to-metal contact. For you new air users, Teflon tape is non-sticky, very thin white plastic that comes in rolls (Home Depot, Grainger). I wrap the tape about 5-6 times around the threads on the male part, but you can use more. The easiest method is to hold the part, and turn it in the direction in which you would tighten it. As you turn it, feed the tape onto the threads. Now, screw the taped male thread into the threaded opening, and use a pipe wrench to tighten it.

Please Note! We no longer recommend the use of PVC plumbing pipe elements in compressed air setups. If you have been using PVC, please discontinue using it. Although we have been using it in our shop for years without incident, we have reliable reports that it becomes brittle with age when used with compressed air and may shatter under pressure. We are converting the manifolds in our shop to black metal pipe of the kind used in natural gas applications. This is safe for use, and we heartily recommend it. The plastic quick disconnects we show are safe, and this warning does not apply to them.

- Regulators with 1/4" or 1/8" (as needed) NPT quick connects on in and out. You will also need a filter/trap module at the regulator on your compressor, as mentioned above. It keeps water and particles out of the other regulators and the actuators they feed. Be sure to use gauges (they're inexpensive) on your regulators so you know what pressure you're feeding. (One example of a 'modular' regulator is pictured near the beginning of this chapter.)

Remember, each device in a group of varied animatronics will most likely need a different pressure to operate properly, so figure on one per device. Complex animatronic devices will often need two or more of these - so start small!

The regulator on your compressor should be used to regulate the maximum pressure required by the air-hungriest effect. Unless you're only running one effect, avoid using the compressor regulator as a setting for the whole show.

Shop for price - the best prices are at Harbor Freight, followed by Home Depot.

- Valves, electric solenoid type, fitted with 1/8" quick disconnects. This little guy is fine for anything but an air cannon or monster pop-up; one that will return itself by weight to the starting position. It has a small throat, so it can't manage massive airflow.

This is a good place to discuss the two basic valve types you will need. The first is the valve mentioned and illustrated above. Normally, the valve connects the actuator to a small exhaust port in the valve that runs through the center of the solenoid. When the valve is electrified (via 24 Volts A.C.) it connects the air supply to the actuator, causing it to operate. When off again, the air is allowed to exhaust. You can buy a connector socket for the solenoid (part # 2G505) if you wish. (It runs on either 12 V. DC or 24 V. AC.)

The second basic type of valve is designed to operate a double-acting pneumatic actuator. These have inlets on both sides of the piston, and thus they can be forced in both directions. If you need to open and close a window or move a sliding panel - for example - this is what you need to use. There's a separate exhaust port for each direction of travel on most of these, too. If you don't want to have air hissing in your scene, you can pipe the exhaust outside the room with tubing. See the image immediately below for an example.

Get one valve for every device or movement in your animatronic stable. They also come in blocks. A block is basically a manifold with valves on the outlets, and they come in all varieties (more in a later chapter. If you want to do some homework on your own, see the catalog or website.)

- Pneumatic actuators (cylinders) - These come in single- and double-acting varities. Singles have one inlet that pushes the piston and rod out; the area above the piston is exhausted continually. Double-acting versions have been mentioned above. You can obviously use a double as a single, with the added advantage of being able to push the piston back to the bottom of the cylinder, raising a prop that hangs down from above. The prop will drop when the air is exhausted. (See the article on our Coordinate Ghost System (CGS) in the main index to view two such droppers.)

A double-acting example from Grainger is shown below, with part number, and suggested uses. Grainger carries an assortment of piston diameters and rod lengths (up to about 12").

Mounting these depends entirely on how they're used. You can use the rear pivot if the entire cylinder must pivot to move a lever. You can use the front threaded mounting point around the rod opening if you're push-pulling a sliding object and the cylinder does not need to move to keep from binding. (Grainger carries a line of brackets and mounts for these Speedaire components - just ask about them.) By the way, the pivot mount for this cylinder is Grainger part # 6W163.

See the clevis (not to be confused with Butt-Head's best friend) on the end of the rod? This is one method of attaching the rod to the lever to be moved, in the pivoting scenario. It simply screws onto the threaded end of the rod. Since the end of the rod is a standard sized thread, you can easily construct your own custom bracket or clevis. Just make sure it's sturdy enough for the task.

Remember, you should not depend on the piston rod to carry a side load! In other words, dont hang a heavy object from the rod as if it were a fishing pole. It's not designed for this, and the bearing will eventually fail - or the rod will bend. (I've seen this rule violated in some expensive haunt props from big companies, with the predictable result: early failure.)

- Flow restrictors - They restrict air flow in one direction only. In other words, air can flow freely in one direction, but is restricted in the other. On unidirectional units, there is an arrow in the restricted direction, so pay attention to it.

What are they used for? Making an animatronic move at the proper speed, for one thing. Pop-ups often reset as violently as they pop unless a flow restrictor is used on the exhaust cycle. Sometimes one is needed on the activation as well. Remember, violent action is what kills props ahead of their time, so here we have a means to avoid it. Grainger has them, as shown in the image above.

A lot of beginners confuse a restrictor with a regulator, so let's look at the difference. A regulator sets maximum pressure. A flow restrictor allows the pressure to enter the line, but more slowly than it would otherwise. The line will eventually reach the full regulated pressure, despite the presence of the restrictor.

- Check valves - Part # 6D914 from Grainger is perfect for keeping full reservoirs from backfeeding (that is, losing pressure into the rest of the feeding system should it fail or fall low.) It has the same thread size as our 1/4" quickie connector, but is male on both ends. Use one on the inlet of any and all reservoir tanks you use. As with flow restrictors, be sure to look at the air flow direction on the case - don't install it backwards!

- Shut off valves (ball type) - To begin with, you may want one on your compressor, just before the brass quick disconnect. Also, fit one or more with plastic QD's to provide yourself with a local shutoff for any given device. Ball valves are positive, washerless, and tend not to fail. They also require only a quarter-turn to open or shut, and the handlle shows the condition of the valve. If the handle is in line with the tubing, it's open. If it's at a right angle to the flow, it's shut. (See Harbor Freight or Home Depot for these at better prices.)

- Reservoir tanks - these keep a large volume of air close to a hungry effect, such as an air cannon. You'll need to fit a check valve on the inlet so it won't back-feed. If it's going to be used to make an air cannon, you'll need one with an opening of 1/2" to 1" diameter, and a large throat valve to fit it. (We'll talk more about this in the next chapter.)

Where does one get reservoirs? Burned out oil-less compressor tanks show up from time to time in household garbage, and are often in good shape - the user merely burned up the pump, and ditched the tank as junk. Make sure the drain valve on the bottom operates, and that an ocean of rusty water doesn't come out when you open it. Examine the outside of the tank for rust carefully, and keep the working pressure down to about 45 PSI if you're uncertain of its interior condition. Now it's a useful reservoir - at least to you - with as many as 3 or 4 inlets and/or outlets.

You can also get small tanks intended to carry air for filling tires at Home Depot or Wal-Mart, and these can be refitted for use with a bit of plumbing work.

- Low voltage (24 Volts A.C.) transformer for valve solenoids - For safety, we recommend firing effects with low voltage, although 120 V. valves are available. A small one (Grainger #3TZ67 - about $8-9) will fire a few of these valves adequately. For large numbers of valves, get a larger unit.

- Timers or show controllers - More on this in an upcoming chapter, but for now, to set off a device, you need a means of either detecting a passing guest or making the prop cycle repeatedly. Both and have timers with and without passive infrared motion detectors just for this purpose. To make a timer cycle endlessly, you just hard-wire the trigger input closed, and adjust the knobs as show in the instructions.

Why not just a PIR (Passive InfraRed) detector or switch mat? Because the effect needs to stay up long enough to be seen, and it needs to be buffered from constant re-triggering. Timers provide this capability.

Here's a simple example circuit for those who want to try their hand at a finished pop-up controller:

Inside the timer is a circuit controlling a relay, which is nothing more than a 'switched switch.' Normally open means that until the timer is activated, the switch is open (or off.) When the timer activates, the relay closes (turns on) and provides a completed circuit to the solenoid on the valve, which then opens, and the pop-up jumps. On this particular timer, we can set a Pre-Delay - that is, a period after triggering during which nothing happens. This can allow more patrons to be close to the pop-up when it goes off. The On Time setting allows us to tell the unit how long we want the pop-up to be seen. The Off Time lets us specify how long the timer will rest before once again allowing a trigger.

The trigger is either a simple switch closure or a special accessory infrared detector provided with a special hookup. For automatically repeating firings, you'd simply short these switch trigger contacts with a piece of wire.

If we're dropping a prop down, we wire to the normally closed contact, which applies voltage to the solenoid to allow the air pressure to hold our prop up in the air. When the relay fires, the valve goes to exhaust mode (turns off), and our prop drops. Simple, really.

Here's a complete pneumatic hookup for moving a bi-directional cylinder:

Once again, CAUTION! Be careful when testing a cylinder under no load. Use flow restrictors in both directions so it doesn't get slammed at the end of its travel. It can also hurt YOU by stabbing or pinching ! Since we had to use over 50 PSI to make this valve work properly (part of the valve is actually moved by air pressure) the reaction of an unloaded actuator can be quite violent. Start with the restrictors screwed shut, then open them cautiously until you get safe motion. Remember, though it's moving slowly now, it still moves with considerable force, and your hand cannot stop it!

We'll talk more about a specific application in the next chapter...

To Part 3 - Building a finished Pop-Up - The Grave Popper

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