Tuesday, 25 November 2014

Making A Water Powered Cider Press - A Failed Prototype!

 My friend Brian and I have been on about building a cider press for ages. 
There are many simple designs we could build using screw threads or bottle jacks, but Brian is an engineer - so that would be far too simple for him! 
He talked me into trying to make a press that uses mains water press for the power to press the apples. This idea is nothing new as you can buy them on-line but they are rather expensive, our idea was to make one using cheap materials and then have the plans available for anyone that wants to make them. 
We decided to build press out of 3/4" ply (18mm) and use a wine bladder from a box of wine as the pressing part. We built the ply box to the size of the wine bladder, we knew we were taking a risk with this method as the bladders aren't designed to work under lots of pressure or if they are we have no idea what that number is.
 Brian adapted the screw cap on the front of the bladder to take some 1/2" copper pipe, this would make filling the box easier. Not shown on the pictures is the corner fillets we fitted in all the corners so the bags wouldn't be going into a sharp corner.
 Our mashing of fruit was pretty basic - a mallet and a plastic bag!
 The finished prototype! We added second side pieces so that dowels could be inserted to hold the top on and Brian fitted a pressure gauge so we could see the pressure we were working to.

And now the Science bit, straight from the brain of Brian :-

"So,

When we were pressing on the "traditional press" the "cheese's had an area of about 600 x 600 and the max force we could apply was 20T.  We probably applied less as we bent the frame before maxing the jack out.  Say we applied 10T of force.

So max force was 10,000kg or in engineering speak 100,000 N 

The area was 0.6 x 0.6m so 0.36m2

Therefore the max pressure we could achieve would be Force/Area or 100,000N/0.36m2

which we can round to about 300,000 N/m2 or 300,000 Pascal (a Pascal is 1N per m2, i.e. bugger all)

There are 100,000 Pascal in a bar of pressure.  A bar is also known as 1 atmosphere.  So the max pressure we were applying to press in a traditional way was 3 bar.  THe important thing to take away is the pressure in in the order of a couple of bar and not hundreds of bar which is used for olive oil presses.

Mains water pressure varies between 1 and 5 bar in the UK and I happen to know that we get around 2 bar at our place.

This is because you can also calculate pressure in "head" terms, which is essentially the pressure generated by a vertical pipe of water.  The important thing is that the static pressure (the pressure when there is little or no flow) is only dependent on the height difference between the water supply and the delivery point.  For every 10m of height difference the pressure will be 1 bar.  I happen to know there is at least 20m of height difference between the back shed and the water tanks, so there is at least 2 bar of pressure available to squeeze apples (assuming the bladder doesn't pop)!"

Goggles, we decided, were essential!
We had the science sorted, we had the box built and we had some pears to squeeze.
Juice!
Early signs were good, and juice started to flow. The pressure was making all the ply bend  and there was some serious creaking going on. 
We added straps around the outside as extra support, and then increase the pressure, then there was a small hiss and we decided to stop the experiment.


Unfortunately the bag failed. A small hole formed where the bag creases in the corner.
Unfortunately the bag had failed. It was only the smallest of holes, but we knew we were working with a bag that wasn't designed to be taken to this sort of pressure. 
It was good fun to design and build something like this even though it didn't work properly. 
I'm ever the sceptic and I couldn't quite believe the pressures that I was told we'd get off the tap (Theirs is from spring water with a header tank), but when we were pressing with it and the ply was trying to form the shape of a ball I understood the forces we were working with!
So although it's back to the drawing board I learnt a lot from this project and the next one will be even better! Although I don't think we'll bother until next year now though!
Anyone else spent time designing and building things only for them to fail?

14 comments:

  1. Sounds like an interesting project, I haven't pressed fruit but know people who do and I think they made one out of steel and a hydraulic jack but I don't know how the did it. We use small electric pumps at the brewery and they will blow a hose apart on occasion so I can see how you would get enough pressure to press fruit. You guys have a while to think about it and be ready for another try next year.

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    1. We used a hydrauilic jack last time but my friend wanted to try something a little different. It's amazing the pressure you can get.

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  2. The science bit lost me Kev. Sounds like you will crack it though. Good luck!

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    1. That's my friend for you! I imagine it being a bit like the old lorel advert "Here comes the science bit!"

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  3. Kev - i will make sure that jambaloney sees this post...he's been dying to build a cider press because our friend D has an apple orchard and grows the best apples ever. jambaloney will try to come up with something by next fall as this fall we are too busy with other things - like figuring out how to grade this stupid driveway!!! arghghghgh!!! but he will love to see this post! thanks for sharing. it is always good to share both successes and failures...it helps other people in so many ways!

    your friend,
    kymber

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    1. I'd just go with a jack and frame if I was him as that's tried and tested. This way was just a bit of an experiment to try something a bit different!

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  4. Interesting. So the water goes into the wine bag and that in turn creates the pressure to force the juice out? Or am I seeing it backwards or something?

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    1. Nope that's how it works. The pressure was unreal, it just started bending all the ply. I was quite impressed!

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  5. Um, I thought we were supposed to call them "experience" not failures. ;) I think the trial and error period is the frustration of all inventors and designers. Very interesting post, though and you've got me thinking and hoping you'll press on with the project (and the apples :). We don't have enough apples yet to make cider, but Dan would like to plant more so that we someday can. Maybe you'll have it perfected by then!

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    1. I think it's important to show when I fail as well as succeed. A man (or woman) who has never failed has never done anything! We've a possible different joint project first and I've got lots of Christmas presents to make before I start back on this one but hopefully we should have something really for next Autumn.

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  6. Part of the problem is your mashing the apples. A scratter is better. There were plans fora drill powered plywood and timber one in permaculture magazine last year. Using a scratter means less pressure is required and gives a far higher yeild of juice. Btw give the pressings to the chickens of pigs if you have them.

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    1. This was only an experiment and if we were to do more we definitely wouldn't be smashing them like this! We got a small quantity to a pulp just to test the bag in the box with something in. A scratter was one of our next projects but the professional one we used last year did such a good job I'm tempted to go and buy one as an investment.

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  7. It was in the spring 2013 issue if that helps!

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    1. Thanks, I'll have a look on their website and see.

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