Cider press

[patrickg]

OK Frantz, Lets see if I can apply the basic principles as you have described them.

Take a guy that weighs 200 lbs whose feet are 10 inches long and 5 inches wide (this is just an example not a custom boot order). With both feet flat on the ground that is 200 lbs "distributed" over 100 sq inches. Following your example that becomes 100 X 200 or 2000 lbs. When this guy stands on something it compresses the something until equilibrium is reached. Lets say he stands on a bathroom scale. Why doesn't the scale register 2000 lbs? Or better yet, since, by your approach, the scale would have to push up at 2000 lbs and he only weighs 200 lbs, why doesn't he get thrown upward with an initial acceleration of something like 10 G's???

I by no means wish to "talk down to you", but my first co-major was physics and math and while your arithmetic remains flawless your analysis is bassakwards. There is just a simple misunderstanding here. It happens to me a lot but this time it didn't.

Now then, if we had a hydraulic cylinder in a static situation (not currently extending or retracting so there are no dynamic losses) then the force on the piston (ram) would be equal to the pressure in the fluid times the area of the piston. A larger piston would "multiply" the force proportionately more, increasing as the square of the diameter. This is sort of a fair "fit" to your contention but this hydraulic cylinder example does NOT model the situation we are discussing.

The cider press doesn't care how the force is applied, by hydraulic cylinder, screw jack, or an inverted pyramid of Lithuanian acrobats with SCUBA weights on their waists. The force applied to the "sqeezing chamber" can come from anywhere, it is an issue of convenience (and my laziness) that I consider a hydraulic ram or air/hydraulic jack.

Whatever linear force is applied to the "crushing piston" is distributed (divided up equally) over the surface of the piston and then since the fruit acts essentially like a liquid (untill nearly finished pressing) the pressure in the fruit (in psi) is the same as on the face of the piston which is the area of the piston divided into the psi.

AHA, a small light came on in what's left of my brain. Something that always helped me learn and teach about solving physics and engineering problems involving lots of units was to include the units in the calculations. For example, if you divide pounds by square inches you get psi. If you expected psi as the answer then you might have worked the problem correctly. If you made a booboo and reversed the numerator and denominator or multiplied instead of divided your answer would be in units of either: square inches per pound or square inch pounds and you would know their was an oops. Getting the units right isn't proof that the numbers are right but not getting the right units is proof that the calculation was set up incorrectly. (There is still a small problem with me and units. I have a lot of left over square radians from years of physics homework and tests. I never needed these for anything and they are apparently useless surplus.)

Put the units in with your good math and see if you accept the results of how the units turn out.

Meanwhile, I still haven't found out a practical pressure for sqeezing pears but am hoping to do so soon.

Patrick

 

[Anonymous Poster]

Let me try this again; the pressure gague between the pump and the cylinder is calibrated in pounds per square inch. It reads 2000#/sq" when the pump is running.
The piston in the hydraulic cylinder is 6" in diameter.
We are not deducting for pushrod diameter because the oil is going into the end of the cylinder opposite the push rod.
Pie R squared cake are round = 3.14. The formula for finding square area of the piston is 3.14 x radius squared, radius =3.
3 x 3 x 3.14 = 28.26 square inches of piston area.
Each square inch of piston area has 2000# of hydraulic force pushing on it, because the pump is putting out 2000#/s".
The bathroom scale got thrown out years ago, and I have it hidden in the garage where the wife don't look.
So, each of the 28.26 square inches with 2000# of pressure on it, adds it's 2000# to its neighbor's 2000#, and when they get all done cypherin, the total combined push on the piston is
56,520#.
Now, about the guy weighing 200# with the feet that are 5" x 10", its good to know you know my Army bud over in Ok City.
If gary is standin in his custom army boots with square corners, he's exerting a force on the ground 2# per square inch on the ground. If he's only standin on 1 foot cause he's kickin some private, he's exerting a force of 4#/ sq inch on the ground. Remember the old analogy of a Sherman tank exerting less ground pressure than Gary's Captain in hi heals? Aw lets not go there, the thought of that critter could give me nightmares.
OK, now if we agree, so far, on the 56,520 pounds of total force at the end of the piston rod, we can go on. If not, get out the Grainger book, cause there is a section in the back that explains force the same way I just did.
Now, if you really want to have fun, we can discuss how to use an air compressor and a tank to replace the pump and simplify the system.
Remember, the bathroom scale is hidden, so don't mention it, and do you have a picture of the acrobats wearing scuba equipment, I'd love to see that.
By the way, Gary is putting in his papers end of this year, so he will be available to help press cider, but you're gonna have to feed him, an he don't like MREs.

 

[patrickg]

Franz, Your post was most amusing and as always your arithmetic was flawless. If you read my previous post you will see that I agree with you on the basics of how hydraulic cylinders work with no need to quote chapter and verse in the King James version of the Grainger catalog. You might also note that there ain't neccessarily a hydraulic cylinder involved in the cider press except as a convenience, MAYBE, so all the analysis so related can be left out so we can cuss and discuss pressin' pears.

What matters is putting force onto the piston that presses on the pears (by whatever means, hydraulic or otherwise, hence acrobat reference) That force is spread evenly and equally, like your army buddies weight on the ground, over the pear crushin' piston (platen?). The larger the piston used to crush pears the less psi on the pears if the applied force on the piston, to do the squeezin', stays the same (and it will because acrobats are most weight conscious).

I sure hope you weren't envisioning a piston with hydraulic fluid on one side and pears on the other cause that ain't happening in my shop. There will be a piston to crush pears that is mechanically pressed on with a great force (up to 20 tons) by my mechanics press. What I need to do is: 1. find out what psi is required to do a good job pressin' pears and divide that into 40,000 lbs to find the max area of the pear crushin' piston in square inches. Then I pick the PVC pipe size that has that cross sectional area or the nearest smaller standard dimension.

My interest in hydraulics is to supply the mechanical force in a more easily used manner than pumping on the 20 ton jack handle a jillion strokes per inch of movement. I thought a couple ways would be either a air/hydraulic jack that uses shop air instead of pumping a handle or a hydraulic ram plugged into the remotes on the back of the 'Bota.

The only reason I went previously into all that other stuff was I thought you didn't understand it and was trying to help. I guess I confused the issues of importance which I believe I have restated above with suficient clarity.

Any help solving the problem would be appreciated. No hydraulics lessons needed. If there actually is some part of what I said previously that you don't understand, ask a specific question and I will explain it. If you don't agree with my analysis, I would be happy to entertain a debate on the physics and or engineering as a separate item not involving pressing pears. If you choose the latter, please post a labeled sketch so we can be sure we are discussing the same thing. Often two persons will be arguing about different items thinking it is only one. A waste of time and frustrating as well. Hopefully I haven't caused that in this instance.

Patrick

 

[Anonymous Poster]

Gotcha Patrick, what we was havin there was a failure to communicate.
Now that we have renomenclatured the mush pressing piston as a platten, things get a lot simpler.
The cider press I'm most conversant with cause I got sucked into helping erect it and hook it up, had a platten that was a laminated oak square, 24" x 24" and about 4" thick, backed up by steel that attached it to the piston rod, and kept it from tipping.
Said platten traveled verticly 22" compressing the pile of mush laden cloths from a height of 20" down to a height of 2 or 3".
Now, since the total force the 6" piston pushing the platten down has been discussed adnauseum, and since way back in this thread we determined the total area of the platten was 576 square inches, I divided the total hydraulic piston force available by 576, and came up with a platten pressure of around 98 pounds per square inch asserting itself against a pile of mush.
So, if you have a totral available force of 40,000 pounds, and desire to assert a force on the mush of about 100# per square inch, you could have a platten of around 400 square inches pushing on the mushpile. Reverting to my childhood math, and using my sliderule (still have one) the mush platten would be around 22 1/2 inches in diameter. Now, just what size PVC pipe has that internal diameter I don't have a clue.
Then again, I still don't understand why you feel you need to contain the mush pile laterally inside a PVC pipe.
Given that I see a lot of antique cider presses in this part of the country, mostly screw operated, the 22 1/2" diameter seems about right based on seat of the pants engineering.
Now, comes the fly in the ointment, my bud Gary, the Army Engineer in Oklahoma claims there ain't a pear tree inthe whole windblown state over 15 feet tall cause any tree in Oklahoma more than 15 feet tall, including power poles, gets knocked out by a tornado.
However, I'm not in Oklahoma, and have no direct knowledge of pear tree height in said geography, so I'm going to assume either Gary has had too many beers, or hasn't been to your part of the state.
So, step 2 in seat of the pants engineering, the same course that gave us the system of torquing a bolt to 400 ft# without a torque wrench that went that high by dangling a 100# woman at the end of a 4 foot pipe over the wrench handle, the simplest method of determining if 100#/ sq" is sifficient to squeeze the juice out of mushed pears would be to build a test device. A 1" square peg indexing into a 1" square hole filled with mushed pear, and equipped with a series of small drain holes at the biottom of the hole, equipped with a small platform atop the peg, should provide definitive results when the same 100# woman is talked into standing atop the platform. Locating the 100# woman and convincing her to stand atop said platform is your problem.

Never use a simple explanation when a convoluted one will perform the same function.

 

[John_Mc]

<font color=blue>I topped one of the trees drastically to reduce the excessive height and it came back with a vengence with new growth but did not bloom at all. Shocked its system I suppose. Read where trees that haven't been pruned for a while shold be cut back a little each year NOT all at once. Now I know!</font color=blue>

You should also NOT prune them during the growing season. Do it after the leaves have dropped in the fall (or in the winter, before the sap starts to run again). This minimizes the stress on the trees. It also helps to trim back any other trees that are in the area competing for sunshine; most fruit trees like to be out in the open to maximixe the sun exposure (at least that's true of the apple trees up in my area of Vermont).

John Mc

 

[stovepoker]

Patrick, I wouldn't advise using PVC anywhere in your press.
Try to stay with fruitwood, but not not Cherry. If you must use plastic Polyethylene is ok. The garbage grinder is ok if it's all stainless. If not, forget it. The amount of pressure and time needed to get the juice out is directly related to the fineness of the grind. Extreme tonnage is not needed, but consistent pressure across the rack is important. Perry is best made if NO metal is contacted.

 

[patrickg]

Franz, AKA Cool Hand Luke, I'm glad this was so simple to resolve. I have never ever had much trouble getting ladies to do things for me so standing one on a peg should be easy but I may have to enlarge the peg a mite due to shortage of 100 lb ladies in these parts.

Tell Gary that I will wager 10 cases of Colorado Kool Aid against one old fashioned rootbeer float that I have pear trees (plural as in more than one) that he can't reach the top of while standing on a 20 ft extension ladder (base of ladder standing on the ground of course). I realize that this assumes Gary to be less than 8-10 ft tall but I'll take my chances.

Furthermore, published statistics for the probability of serious damage to a house have been calculated for ground zero (geographic center) of tornado alley (next county to the S-E of me). The odds are, one damaging tornadic event to hit a house in about 4000 years. Given the age of my trees, about 100 years, a tree would have a 2.5% chance that one would have been hit by a tornado in its lifetime. They don't look like they have been hit and are so old and decrepid that a good straight wind would break them off. They did lose a serious % of their leaves today in a thundershower but the leaves had been looking real poorly for a while for some reason. Pears are looking mighty good and the windfall I picked up last week was real sweet and juicy but nicely firm, not soft like a bartlet, more likke an apple.

Regarding your last statement. Rest assured, I abhor imprecision and eschew obfuscation.

Patrick

 

[RobertN]

This is a great thread! I have been toying with theidea of a ice cream maker that would run from a belt pulley on my Farmall...

 

[patrickg]

Cool, Bob. What size drum for the icecream ingredients, one of those food quality 40 gallon jobs?

Why not, I saw a weed eater type pull start motor attached to a blender and advertised, among other places, in TDR (Turbo Diesel Review) as the ultimate Margarita maker when "off-grid." Isn't a tractor, with appropriate implements and attachments, just an adult "transformer toy???)

Patrick

 

[RobertN]

I was thinking to keep it small, as a first expieriment. I thought maybe stick with one of the easily available 5 qt models, and prove the concept on that. I figured that might be a nice place to start, and would be fun to set up at a family reunion.

I am still looking for a belt pulley and gear box. I have a pto, but no pulley gear box. I know a couple places I could get one, but it is low on the priority list right now.

Before pto's came into the forefront, belt pulley's used to drive everything. So, why not an ice cream maker /w3tcompact/icons/grin.gif

I want to finish my trebuchet first anyways... I started cutting the wood for a 3' tall siege engine.

I have seen the gas powered blender at a rental shop of all places, for parties...