Thread: Starting with the right compressor

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Hi, I've been saying for years that I must do some pneumatic props but this year I'm actually going to buy some stuff and attempt it. My main concern is getting the compressor right as it could turn out to be an expensive mistake if I get it wrong.

The plan (maybe not all for this year):-

An air canon (set off every few mins)

A treasure chest with opening/closing lid (2 cylinders)
A barrel with a pirate popping out of it

Moving arms for the Grim Reaper (possibly 2 cylinders per arm)

Jack-in-the-box style clown. 2 cylinders to open the lid and a cylinder to raise the clown.

I was planning to have an accumulator tank for the chest/barrel props, 1 for the grim reaper and 1 for the clown.

First off, will a single compressor be able to handle all of those props?
Does it have to be a big compressor as everything has an accumulator tank?

I've been looking at a few compressors. This one looks quite good but the specified dimensions seem a little small and it's very expensive. Theres also this one which is a LOT cheaper but the specs don't look that much different. Is there something I'm missing? I don't want to buy a huge compressor if a small one is more than enough.

The second link is to an airbrush type compressor and would not meet the needs or demand.

The first compressor from Airlines with 8 bar pressure (116 psi) with a tank of 25 liters (6.6 gallons) would be on the small side and would be running quite often to meet the air supply demand.

Instead of the quiet series, I would lean towards the Super Cosmos 50 myself or the Jupiter 20/50 for the tank size, little higher max pressure, and mainly for the higher CFM
http://www.airlines-pneumatics.co.uk...ctCode=S020103

I've remembered there is a Machine Mart near where I live which is great because a lot of people in other threads have been saying to try it out before buying to see how loud it is.

I found this one. It has double the tank size and a higher CFM but it has a lower working pressure.

I'm assuming the CFM is the amount of air that the compressor can put into it's tank. I'm sure the required CFM could be calculated based on the size of the rams and how often they trigger but I haven't found any rams yet. Is there a general rule that says something like "each ram would use roughly 1CF per actuation"? (I'm not very good with Imperial measurments by the way)

The pressure should be in the range for the props you are going to use. I would doubt you would use over 50 psi for the props. The cfm is how much air can be delivered at a set pressure. Usally a lower pressure equals a higher CFM. I do believe you can calculate the CFM per actuation , but it will depend on piston diameter,rod diameter, length of travel ,etc. I might have some information that can help, I'll check. You might be able to check with the manfacturer of the cylinder to get that information.

I've had a look at some big compressors online and they look good but I don't think I would be able to store them anywhere. Would it be alright to get a smallish one and add an extra air tank as long as the CFM is enough? Almost all of our halloween stuff gets put in the loft. We have the space but only a small hole to get things through.

Am I right in thinking that a 50L compressor with an extra 50L tank is the same as a 100L compressor? It seems obvious but you'd be supprised how many times things like this don't work how you expect.

If you do as what you are proposing ........here is what will happen you will run a small compressor longer to fill all of the auxillary tanks due to the fact the compressor "looks" for a pressure to shut off at , this is volume . If you look at it like a garden hose trying to fill a bucket I think you will understand. If you have a 5 gal. bucket and open the garden hose at full open it will fill quiclkly, if you start adding more 5 gal. buckets it will take longer to fill ALL of them.Same pressure ,different volume.Hope this helps If you want some more help PM me and I'll be more than happy to help you out.

You basically want the the compressor with the most CFM's you can afford or have room for. The air cannon will use a lot of air. The cylinders may or may not use a lot depending on what cylinders and how they are set up. I'd imagine you'd need a minimum of 5cfm maybe 10cfm would be better depending on the frequency of activations, unless you want your compressor to be running constantly.

You're looking at 10 cylinders and an air cannon, that can potentially be a lot of air. An air cannon activation can easily dispurse 1-2 Cubic feet of air per activation. An air cylinder depending on the size and way it is set up can use from 1/10 to 1/2 a cubic foot per activation.

That sounds alright. I don't mind it taking ages to charge all the tanks for the first time but I will try and get one with a high CFM. The one I'm hoping to buy is 14CFM but only has a 50L tank.

I'm going to see if theres anywhere else in the house I could store it. If possible I will get a bigger one.

All of our props are integrated so if I find that the compressor doesn't quite meet the demand then I can time certain props to trigger alternately and less frequent.

Do pressure gauges exist that can be connected to a PC or some kind of electronics? It would probably help if the PC can monitor the current pressure so it doesn't activate big props when theres low pressure.

It depends on what type of input you are looking for, for your computer software. There are many sensors out there though that can measure air pressure electrically. Boost sensors and MAP sensor for cars/diesel trucks would work. I'm sure there are a bunch of different industrial options as well. You just need to know what type of output you are needing from the sensor. Most automotive sensors run on a 5 volt reference signal, and then send back a voltage from 0-5v which is then correlated to a software logrhythm which can give a pressure value to the voltage signal. From there you'd need your software to recognize a range that is acceptable to trigger in, and a range that is unacceptable.

I'm sure it's pretty simple, but I couldn't tell you how exactly to do it, more the theory behind making it work. I don't have much experience with computer controls as I like being the puppet-master and have a good feel for the capability of my system.

The PIC chips I use run on 5V so one of those sensors would be good. I would prefer something that changes its electrical resistance in relation to the pressure. I can measure that with an ADC pin on the PIC and the programming would be easy. I'm not sure if this is how the 5V sensors you mentioned work but they sound similar.

I'm going to machine mart today and hopefully I will end up buying a compressor. By re-arranging some stuff I think I'll have room for this one. Its 14CFM and a 150L tank so I'm sure it would be more than enough for the props I'm planning. I just need to check its not too noisy.