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Thread: Ram size vs Pressure and power

  1. #1
    Looks slow but IS fast Muz's Avatar
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    Ram size vs Pressure and power

    The log splitter that I've built and shown elsewhere on here, struggled today to split some wet cupressus so it got me thinking ... the ram on my splitter I know is too small, the rod is only 30mm and case is 60mm but it was £free and its split tonnes of stuff so far without issue. All the diggers Ive used so far generate about 210 Bar max pressure on the aux service line, would upping the size of the ram increase the work output, or will I have to multiply the power some other way ?
    Please don't PM me for plant advice.. thanks .. Post in the forum where I will gladly help, as will many of our contributors.. as the info and responses will help everyone else, which is why we exist

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    Quantity Surveyor on the up v8druid's Avatar
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    Quote Originally Posted by Muz View Post
    The log splitter that I've built and shown elsewhere on here, struggled today to split some wet cupressus so it got me thinking ... the ram on my splitter I know is too small, the rod is only 30mm and case is 60mm but it was £free and its split tonnes of stuff so far without issue. All the diggers Ive used so far generate about 210 Bar max pressure on the aux service line, would upping the size of the ram increase the work output, or will I have to multiply the power some other way ?
    Trouble with upping the ram bore and hence the piston surface area, is it'll slow the process down.
    Volume of the cylinder increases and thus takes longer to fill with a given speed of supply/flow rate.
    This would be the same if you double up on the rams too, which'd again effectively provide more power by doubling the surface areas of pistons, but would need twice the time to fill both rams.

    PSI of supply (3000lbs/sq. in. @ 210 bar), bearing on the piston's surface of 60mm = circa 7 square inches = circa 21,000lbs/10.37 tonnes - upping to say 80mm bore would give you circa 10.25 sq in and a circa 50% increase in power ........ but at a slower rate to fill the void, which is the cylinder behind that increased piston's surface area!!

    Sorry if I'm 'teaching granny to suck eggs' here!!

  3. #3
    Looks slow but IS fast Muz's Avatar
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    Quote Originally Posted by v8druid View Post
    Sorry if I'm 'teaching granny to suck eggs' here!!
    Not at all .. I just wasnt sure that increasing the bore would increase the power given the pressure would remain the same .., so it is indeed the surface area of the piston that allows a greater power output then .. I'm assuming flow wont be such a major issue as there is more flow in the diggers aux circuit than the current ram can utilise, as it fair zips in and out , does about an 18" stroke in under 2 seconds
    Please don't PM me for plant advice.. thanks .. Post in the forum where I will gladly help, as will many of our contributors.. as the info and responses will help everyone else, which is why we exist

  4. #4
    Quantity Surveyor on the up v8druid's Avatar
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    Quote Originally Posted by Muz View Post
    Not at all .. I just wasnt sure that increasing the bore would increase the power given the pressure would remain the same .., so it is indeed the surface area of the piston that allows a greater power output then .. I'm assuming flow wont be such a major issue as there is more flow in the diggers aux circuit than the current ram can utilise, as it fair zips in and out , does about an 18" stroke in under 2 seconds
    Jeez that's a quick stroke Muz!!

    Basically the more sq in.s the piston is, the more power for a given pump pressure.
    The speed at which it will work is purely down to flow rate and cylinder volume.

    To work the area of the piston it's Pi x D.
    Pi = 3.142 (or 3 & 1/7th - the magic number for circle calc.s) and D = diameter of piston/bore of cylinder!

    So for a say 4" piston/cylinder its 3.142 x 4 = 12.568 sq in

    With a 3000 psi (lbs/sq in) system for every sq in of piston, you get 3000 lbs pressing on it, so with 12.568 sq in.s, it's 12.568 x 3000 = 37,704 lbs of pressure on the piston, which divided by 2204lbs (=1 tonne) gives you the tonnage (17.107 tonnes/17,107kgs)

    For the return pressure you have to subtract from the area of the piston, the area taken up by the rod, as it doesn't get any pressure applied to it.
    So for a say 2" rod, the area of that would be Pi x 2 = 6.284 sq in.

    Subtract that from the 12.568" of the piston's flat surface area, which'd leave you with 6.284 (pure coincidence, in this example) of area, for the 3000 psi oil pressure to bear on, which'd give you (in this case) exactly half of the pressure returning the piston in the cylinder - 8.553 tonnes pull/return.

    The speed as I say is down to volume -
    to calc. the volume it's .... area x height - so for that same 4" cylinder, with say your 18" stroke it'd be 12.568" x 18" = 226.224 cubic inches or 3.707147 litres (1 litre = 61.02374 cu in)

    Therefore, if you had say a 20 ltr/min flow rate, you'd be getting 1 ltr every 3 seconds, off load, to fill the cylinder would take 11.12 seconds, which would slow slightly/vary, depending on the load it would have to overcome - the calc.s for that are real complicated

    Obviously the return rate's quicker as the volume of that side of the piston is (in this example) halved!!

    It all sounds complex, but try doing a few calc.s with varying cylinder/rod sizes and it soon becomes quite easy, with a bit of practice ...... once you have had the magic bits explained !!

  5. #5
    Looks slow but IS fast Muz's Avatar
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    Well thats excellent info and saved me a lot of googling.. thanks fella . Made a chance call to one of my machine shops who have a 40 mm rod and 80mm case ram thats gathering dust, with a decent stroke length, so I might go see them tomorrow about it, hopefully this one will have 1/2 inch BSP in /outlets which should be better than the 1/4's on this ram I have should allow more volume in and out and generate less heat too .

    I was aware of the reduction in power when returning the ram certainly, .... it always gave me concern with modern mini excavator design that the boom lift ram gets fitted on the top of the boom, and so its lift capacity would surely get reduced .. in the end it doesent seem to make much difference to the ones I have like that, because I suppose the lift still generated is greater than the stability of the machine will sensibly cope with, and also theres the benefit of it being protected from bucket damage etc

    Well it shouldnt take much modding of the splitter to fit a bigger ram .. I'll maybe add to the original thread and update
    Please don't PM me for plant advice.. thanks .. Post in the forum where I will gladly help, as will many of our contributors.. as the info and responses will help everyone else, which is why we exist

  6. #6
    Quantity Surveyor on the up ianoz's Avatar
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    Gees Druid, been talking with you for ages now , and never realized you actually had a brain and knew how to use it .
    Looks like Druid will be a very usefull little engine here Mr Fat Controller

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    Quantity Surveyor on the up v8druid's Avatar
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    Quote Originally Posted by Muz View Post
    Well thats excellent info and saved me a lot of googling.. thanks fella . Made a chance call to one of my machine shops who have a 40 mm rod and 80mm case ram thats gathering dust, with a decent stroke length, so I might go see them tomorrow about it, hopefully this one will have 1/2 inch BSP in /outlets which should be better than the 1/4's on this ram I have should allow more volume in and out and generate less heat too .

    I was aware of the reduction in power when returning the ram certainly, .... it always gave me concern with modern mini excavator design that the boom lift ram gets fitted on the top of the boom, and so its lift capacity would surely get reduced .. in the end it doesent seem to make much difference to the ones I have like that, because I suppose the lift still generated is greater than the stability of the machine will sensibly cope with, and also theres the benefit of it being protected from bucket damage etc

    Well it shouldnt take much modding of the splitter to fit a bigger ram .. I'll maybe add to the original thread and update

    Should certainly improve the flow rates Muz - there is a formula for working out the reductions in flow through various size venturi, at given pressures, but my heads too fuzzy ATM to recall it and as Ianoz'll tell yer, the Druids memory ain't what it was!

    Glad to be of help Boyo - didn't want to be "teaching granny....... ", etc., specially not as a newbie
    Know what you mean on the lift rams that retract for lift - a Jake's a classic example, but will out lift its stability

    Yer 80mm case'll probably have a 70mm piston which'd give you 11.76 T at 3000 psi on the push - most timber's gonna wave the white flag with that up its arse !! (and still be quick on the cycle)

    Most folks building a basic splitter go OTT on the cylinder size and pay in cycle time, for power they really don't need, to torture timber into submission!!

    Do you have a link to your splitter thread so's I can have a read of it please

    Gra

  8. #8
    Quantity Surveyor on the up v8druid's Avatar
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    Quote Originally Posted by ianoz View Post
    Gees Druid, been talking with you for ages now , and never realized you actually had a brain and knew how to use it .
    Looks like Druid will be a very usefull little engine here Mr Fat Controller
    PMSL Ian

    hated maths with a passion in school, then spent the rest of my life using what they'd struggled to teach me, everyday fabricating - the amount of geometry knowledge required for making stuff is immense!! - you wanna roll a circle/ring .... Pi x r x r = how long the bit needs to be for a given diameter of ring!
    Couldn't see the relevance to me of that, at 15!!

    Needed lots of geometry for building me own tilty too as you know
    Story worth sharing d'yer think???

    Gra

  9. #9
    Looks slow but IS fast Muz's Avatar
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    Quote Originally Posted by v8druid View Post
    you wanna roll a circle/ring .... Pi x r x r = how long the bit needs to be for a given diameter of ring!
    Couldn't see the relevance to me of that, at 15!!
    Aye your not wrong there .. currently trying to impress that on my 16 daughter at the moment

    Heres the link for the splitter thread .. now dont laugh



    http://www.plantandconstruction.co.u...-Log-Splitters
    Please don't PM me for plant advice.. thanks .. Post in the forum where I will gladly help, as will many of our contributors.. as the info and responses will help everyone else, which is why we exist

  10. #10
    Site Agent Wee Jim's Avatar
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    the splitters my friend Bruce makes are currntly being made with the Rams off an old ford digger so they have plenty power. The first splitter we made was both the rams from the tail door or a Massey baler we out them side by side and that was good too!



    Talking about rams. I buggered the ram on my digger today! I snapped the main ram for the boom. With the VAT I am now £550 lighter.

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