How To In Progress - Pneumatics For Beginners

This is a work in progress - full of typos, errors and missing pics. When its all done it will be posted to the main site. Until then feel free to PM any feedback.


Pneumatics for haunters – how to get started

A little background before we begin:

The other day on the GoE email list a discussion occurred regarding using pneumatics with improvised cylinders. By improvised I mean hacking things up like a screen door closer or a bicycle pump to create a pneumatic cylinder for prop actuation. It’s easy to see why people think that’s OK. One jaunt around the various project list websites will turn up a bonanza of props built just like this.

Well, I’m here to tell you – DO NOT DO THIS.

Seriously, it’s bad. As a haunter, keeping smelling salts around as a testament to how scary and cool your haunt is should be a good thing. Hiring a combat medic for the night? Not so much.

Compressed air has tremendous explosive potential and the laws of physics are firmly against you on this one. Put another way - there are certain nicknames you may earn as you travel through life. Stumpy, Peg, Patch, or even Hook aren’t the ones you want. As a parent I do the "here's the church, and here are the people" thing with my little girl all the time. I don't want her asking me why the congregation thinned out.

Even if you only lost one finger there’s a 1 in 10 chance it could be your preferred bird-flipping finger. I don’t know about your locale, but here in Rhode Island if you lose your bird-flipping finger you actually have to forfeit your license (or go through extensive physical therapy to re-train yourself).

Me being a righty, it’s just not going to feel good telling someone they’re number one with my left hand. Don’t believe me? Try it (vice versa for you lefties).

See how awkward that felt?

Let’s just avoid the whole thing and use real cylinders. And here’s a secret *use eBay*. If your patient you can find real cylinders for about $15-20 bucks each, and you don’t need to spend two hours hacking it to make it work. It’s plug and play, and safe beyond any pressure most home compressors are capable of.

Hazzah.


So where do we start? At the beginning of course!

The compressor

As all of this magic will start at the compressor it deserves a few words. Basically, you’re going to pay for the following:

· Horsepower
· Capacity
· CFM (the volume of continuous air flow it can output)

What’s that all mean? Well horsepower is going to dictate how quickly you can fill the tank full of air. Capacity will dictate how long you can go before filling it again. CFM isn’t that important to us as home haunters. If you’re using the compressor to power an auto body style spray gun you need a certain continuous volume of air. As haunters we only need the air in spurts to trigger props.

So what to buy?

Well, what can you afford? At the time of me writing this my trusty 32 gallon upright compressor is no more so I’m in the market myself. I know from experience that I could fill the 32 gallon with 80PSI and it would power (4) 1” bore, 10-inch stroke cylinders if I paused to top off the tank a few times throughout the night. That’s with about 100 ToT’s.

So I can say that the 32 gallon worked well. Truth is, a 20-gallon would have worked fine with a few more refill breaks. Also, you can get supplemental tanks for extra storage. We’ll go into them later.

So the short answer?

Buy what you can afford, and buy big if you want to avoid paying for a 2nd compressor down the road as your obsession grows. As a side note, most of the compressors for home shops (light duty) are the oil-less variety. They are noisy, but maintenance free (one less thing to deal with) and you'll get more capacity for your buck. Unless you have some big money to spend, you'll probably go oil-less. Make sure you get a filter to keep water out of the air lines.

Now that you have your compressor, it’s time to get this party started.

First things first, you’ll notice your compressor has two regulators.

This is important. The 1st is the pressure in the tank. The 2nd is the pressure on the airline.

The first one is pretty self-explanatory. That’s storage. As you use air the pressure drops and if it falls below the pressure your props require it’s time to refill the tank. Some will turn on automatically when they fall below a certain pressure. This ensures you’re topped off, but can cause the loud compressor to turn on when you least want it to. Fill it up, and then turn it off. Keep an eye on it and if gets low turn it on and top it off.

Now the 2nd regulator, that’s the important one. That is the maximum air pressure you allow at the outlet into the airline (and onto your props). This is where we officially start having fun.


The hip bones connected to the …

The air supply to your props starts at the compressor. What do you set the master regulator at? A good rule is to set it no higher than the maximum PSI you need at your greediest prop. If you have 3 props running off air, and one needs 40PSI, and the other two need 30PSI, than the master regulator gets set at 40PSI. This is step one (more to come) to keep things as safe as possible.

So lets connect the first bit of your pneumatic setup, namely the air hose that will run out from the compressor to the props.

See the brass barrel fitting on the compressor? That barrel is a sleeve that slides back. You slide back the sleeve, insert the male end on the main air hose, and while holding it in (giggity!), release the spring-loaded sleeve. It seats itself in there and all is good. Very quick to change out, hence the reason it’s called a quick disconnect. This is a very standard setup you’ll find on most compressors, and chances are your compressor is setup like this. If not, you can get the parts at any Home Depot or NAPA.

A word of caution:
Make sure your holding the hose firmly when you go to slide the barrel back and release the airline. If not, it flies off for a second like a fire hose from the stored pressure. It won’t get far, but it will get far enough to thwack you real good on the head - or as happened to me - directly in the baby maker. Don’t be me! I ended up stumbling out of my garage doubled over like I’d been gut shot as I clutched myself and collapsed in the driveway. And yes, my neighbor was tending her plants in the next yard and saw the whole thing. I give her a lot of credit for making into her house before the laugher started. And yes Ann, I totally heard you laughing.

OK, so where were we…

You connect the airline to the compressor, and run the airline out to a central location. Now we need to get air to all the props. For simplicities sake let’s say we only have two props. Both are pop-ups, but one is pretty hefty and demands more pressure to get it working. So we need to split the air in two directions, and also deal with two different pressure settings. Now that we’re near our props, we also need to think about adapting this clunky main air hose down to the smaller airline we’ll use for our props.

There’s a very simple way to do this AND add another layer of safety to our setup. We spend a few bucks (under $10, don’t get nervous) and put another regulator here. That way in the unlikely event the main regulator failed this one will kick in upstream of our props. We’ll also stick a “press in” style quick release on the end of the regulator that will take the airline size down to the ¼” ice maker line we’re going to use. See the pics below for the general idea.

The regulator with the male main air hose connection and smaller “push in” quick disconnect connection to the props:

So now we have a redundant safety system, and we have it split. Now you run a separate smaller airline to each prop - and of course add a regulator to each prop - so you can make the pressures individual to each prop. So that’s the basic “hip bone connected the thigh bone” idea. You now have air to each prop, so lets dive deeper and learn about the basic bits involved to make all this happen.

The regulator ready to run out to two props (each prop using one cylinder):

Cylinders

This is easy. 90% of the props you see use our good old buddy the rear pivot mount cylinder. By pivot mount (see pic) I mean the rear of the cylinder has that hole through it for a bolt and pivot mount (see pics again). This is what we’re going to concentrate on because it might be the only actuator you ever use. Once you get comfy with all this you might branch out into rotary stuff, grippers, etc but chances are this is all you’ll need. I get mine by hunting on eBay, you can do the same but if you don’t mind paying a little more for new you can get them new at places like Grainger- or even better - Halloween suppliers like Monster Guts or Evilusions.

There are two main types of cylinders you’ll concern yourself with:

· Single acting
· Double acting

Single acting cylinders have one air inlet, and use a spring for return force. Double acting cylinders have two inlet ports and can have force applied in either open or close. For most props you can also use the weight of the prop for return force. That makes double acting cylinders real handy, and my cylinder of choice.

Other than that the only two things you’re dealing with are bore and stroke. Bore is the diameter of the cylinder, stroke is how envious it makes your wife when actuating. In general most props are going to be hunky dory using 1 1/16th bore with the stroke applicable to your application.

Now that you know what cylinder to use, you need to get air to it. So you’re looking at the threaded hole in the cylinder (an inlet port) and wondering what to do. You need to put a “push in” style fitting in the cylinder so you can run the airline to it. If the cylinder bore is 1 1/2” or under, its generally an 1/8 inch fitting.

“But wait”, you ask. That hole in the cylinder looks more like a quarter inch. Well it is, but if you measure the opening in the fitting that goes in it, the actual hole that lets air pass… you guessed it. It’s an eighth inch hole. If you get a larger bore cylinder and it takes a ¼” fitting then yep, the hole the fitting goes into is like a half inch. And yes, if you look at the opening on the fitting itself it’s a ¼ inch.

Some larger stuff takes bigger fittings, but it’s the same story. And don’t bother wasting time on this if your confused. If you’re not sure what fitting your cylinder takes bring it with you to home depot. It’s that simple. They’re a couple bucks apiece, the learning curve won’t kill you so don’t sweat it.

For your info, here's a pic of a 2" bore single acting (spring return) cylinder, and a 1 and 1/16ths double acting. Yes the 2" is HUGE. I can jack my car up with those. Most applications will use the smaller one.

Valves

Now then, how to switch the air on and off to our props. Again, don’t get nervous, this stuff is simple. We need a valve. But which one? Well lets list the choices that are most used:

· 3 way
· 4 way

Yep… not much to it.

A 3 way valve is used when you only need to send air in one inlet on a cylinder. This is your typical pop-up application.

It has 3 ports:
· Input from the compressor
· Output to the prop
· Exhaust

A typical 4 way valve has the following:
· Input from compressor
· Output 1
· Output 2
· Exhaust 1
· Exhaust 2

The 3 way valve is just perfect for most pop-up type props, air cannons for the like. Even if you’re using a 2 way cylinder, you just plumb the line from the compressor to the valve, then from the output of the valve to the inlet on the cylinder that makes the rod go out. When you turn the valve off the air exhausts and the weight of the prop resets it, allowing it to drop again.

Here's a diagram for the more visually minded. It assumes you want a simple pop up movement, with the weight of the prop acting to reset it. The valve is a 3 way, and the cylinder is double acting: