Basic hydraulic question - enerpac vs "regular" hydraulic system
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  1. #1
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    Default Basic hydraulic question - enerpac vs "regular" hydraulic system

    Hey all, I have a hydraulic question, which I realize isn't specifically machining, but I think will be a simple one for someone here.

    One of the projects I work on is a drinking water filter factory over in West Africa. They use a press to turn blobs of clay into rough filter element shapes. It's basically like a normal H press. The press was shipped from the factory set up to use a mechanic's bottle jack as the power source. It was a 20T jack and worked fine, but wore out quickly.

    I switched it to an Enerpac system, and with the better Enerpac gauge as part of the system, know that we press the filters at around 15 tons.

    Now, I want to electrify the system. I know enerpac makes electrics, but I'm anxious to get away from their expensive ecosystem and move to a more standard setup. I have the hydraulic power pack. Now, I'm trying to figure out what size ram I need in order to accomplish this. However, in order to get the calculator up to a push force of 15t, it's requiring a 4.5" bore cylinder @ 2000 psi. It seems huge compared to the size of the bottle jack that was doing the job just fine before. Am I misconverting some units here, or do I really need a cylinder that big to get up to this force? Maybe bottle jacks operate at much higher pressure, which is why they can get the same force with less diameter? I know that's why the enerpac can do it, obviously less diameter is required at 10k psi - but I've had to rebuild that cylinder twice already, and want to switch to something lower pressure that presumably will have better longevity. You don't have to rebuild the cylinder on your tractor every year, lol.

    The other thing that I'm excited about in the process of electrifying this machine (in addition to saving arms getting tired out running the pump) is the ability to install some limit switches to get repeatability in the stop point - which right now is being eye balled, which doesn't lend itself to much consistency.

    img_20181018_100902.jpg

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    Your dropping from 10,000 psi to 2,000 psi.

    Yup, the cylinder will get that much bigger.

    FWIW I would place the cylinder under the press, pushing up. I can't see if your already doing it this way or not)

    When (not if) the cylinder leaks, you won't get any oil on the product.

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    Quote Originally Posted by digger doug View Post
    Your dropping from 10,000 psi to 2,000 psi.

    Yup, the cylinder will get that much bigger.

    FWIW I would place the cylinder under the press, pushing up. I can't see if your already doing it this way or not)

    When (not if) the cylinder leaks, you won't get any oil on the product.
    Yes, that is the configuration currently. Thanks for the input!

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    In my opinion, probably the best thing you can do is upgrade your wiper. Looks like your working environment is pretty harsh from the amount of clay (read: abrasive dust) present around the cylinder. If you don't have a good wiper on the rod, that clay contamination is likely to be a huge factor in reducing the life of the seals.

    If you can figure out the current configuration, I'll take a look to see if I can find a compatible upgrade, and maybe I can sweep a few up off the floor for you

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    No advice hear but I do like the picture that you provided. It provided a lot of perspective about what and how you are making these items. Definitely worth more than a thousand words.

    Bill

  6. Likes atomarc, digger doug, Garwood, Cole2534 liked this post
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    Jason,

    I also find the work you're doing interesting and probably quite 'humanitarian'..if it's OK to say that these days.

    On your press, while I can't see it real clearly, it appears there is a foot lever thing that allows for a wide opening and closure of the mold halves and I'm not sure how that locks to resist the 15 ton pressure..otherwise it would seem the hydraulic cylinder must have a huge travel.

    Your math is correct on the PSI and cylinder bore specs and that means the pump should have a very healthy GPM rating which most Enerpac systems don't have..to my knowledge.

    Do you require a double acting setup?

    My first thought would be to get out of the Enerpac arena and start looking at simple log splitter stuff. They have pumps with adequate GPM as well as two stage pumps that will extend quickly then go into a power mode for maximum push.

    These are just casual ideas..don't know exactly what you are working with so take them a face value.

    Just to add to my confusion..are you sure the process takes 15 tons, as the construction of that press, to my eye, doesn't look like it's capable of safely handling that force. How did you come up with that figure?

    Stuart

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    I like the idea of going with lower pressure. If you use parts that are common in agriculture your costs should be lower and readily available.

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    Press looks fine to me.

    Even better than a HF "20 ton" unit.

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    Thanks for the input, all.

    Stuart, the gauge on the enerpac dial, at the peak of the forming, reads in pressure and tons, and it's saying between 15 and 18 tons.

    The press frame has been through several thousand press cycles, and you're right - it wasn't up to the task. The top horizontals were bolted to the verticals and were moving all over over time, creating alignment issues. After a few passes of 7018, they don't move anymore.

    I'm sorry I don't have better pics of the press. Basically, the moving lower element has about 12" of travel from a long lever, which lifts it up to being within range of starting to press, and then they slide the ram under that bridge, then start pressing. So in the current application, the lower 12" of travel happens with the ram removed (slid forward out of the way) so they can load and unload - and then once they use the long lever to lift it up, then they slide the ram under the bridge and start pumping. For the replacement, I'm planning on doing it all with hydraulics for simplicity - even though I realize that it's going to be a slower cycle. I did the math on the volume, and a 24" throw cylinder will be 80 seconds up and 80 down with the 1.3gpm hydraulic pack I picked up at an auction (which included wired upper and lower limit switches, so that'll be nice and easy). I realize a 3 minute cycle time sounds ridiculous here in the States, but if the guys can keep up with generating the slugs and finishing the pressed filters so that the machine becomes the bottleneck, then I'll happily upgrade to a more powerful hydraulic pump, but we're not there quite yet.

    Yes, all kinds of crap is getting dumped into the top seal of the ram, because both water and clay powder are pressed out as the slug is being formed, and some of it drips down. I made a metal sleeve to protect the enerpac, basically a metal can sitting upside down on the ram end, but it obviously isn't stopping everything. I think a rubber wiper like a motorcycle fork has will be the eventual solution.

    To be honest, I don't know if I need DA or not. The reason is that right now we don't have it - it's just spring and gravity return - but we have all kinds of problems with the mold wanting to stick on start of the downstroke, and we're hoping that a DA cylinder will "unstick" them without tearing the filters apart. It's a cast aluminum mold and we use a plastic trash back over the top and another over the bottom to try to help, but even so, after reaching the top of the stroke, the guys have to beat on the top of the press frame for 10 seconds or so with rubber mallets to get it to let go. DA will be an experiment, but I know other factories doing this same thing in asia don't need the bags, and theirs let go, but I don't know if it's because they have DA presses (they do) or if it's some other voodoo they're doing.

    I also went straight to the idea of cannibalizing a log splitter, but didn't know if their hydraulics would be "industrial" enough, or just consumer grade.

    The hydraulic power pack that I have is 1.5hp. I bought it used and it's frozen, so either the motor is bad or the hydraulic pump is bad (seems more likely). I suppose if I need to replace it anyway, I could just look for an appropriately sized 2 stage pump, and turn what I already have into a log splitter kind of arrangement. The pack is nice since it already has the valves, solenoids, and limit switches all wired up for me - so I'd like to use it rather than starting over with a log splitter - but maybe just swapping the pump would be a great way to get there?

    Enerpac makes great stuff, but at $50 a gallon for their fancy oil, their system is too twitchy for this kind of application where there's dust, heat, and duty cycle. Getting to something that's more like a tractor is going to let this be a lot more repairable in the field.

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    I used to make presses like what you want........the simple way to make a ram is to get one from a dozer or loader,and use the gland end ,which is complex,and cut the cylinder and rod short. ...... there is always a bad wear area somewhere in the cylinder,which you want to eliminate..........If water and dirt are problems,use the ram rod downwards,and maybe put a rubber boot on it.....You can make a suitable ram from a longer one without any lathes or mills...just welding and cutting.

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    Jason,

    Sent you a PM.

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    Jason,

    I'll bet you have this figured out already and have made your decision but I'll throw in a bit more info to cloud the situation. I have enclosed a link with a neat calculator so you can see the relationship between cylinder speeds, GPM and their horsepower requirements and many other handy things when doing a job like this.

    There really is no free lunch. A big bore cylinder takes lots of oil to extend or retract in a reasonable amount of time, this means a high GPM which in turn means more horsepower..all these things are related.

    I would imagine in your situation that high production (cycle time) isn't a huge concern but if you peruse the charts I enclosed you can plan your project with more clarity.

    Surplus Center

    Stuart

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    Can you drill some tiny release holes to allow air in ?

    Or use some sacrificial plastic sheeting, one piece for each part.

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    I'd love to learn more about the entire operation if you care to share. Properties of clay and water filtration kind of fascinate me.

    Lowering the operating pressure will definitely help long term.

    When I work on something like this the limiting factor is usually the size of the motor you can use to power it and the budget.

    Hydraulics don't seem to do anything impressive until you get into the 20+ HP range and then things start happening faster.

    There are ways you can plumb the cylinder to add a lightening fast return stroke.

    like already mentioned, 2 stage pumps kick it up a bit too.

    Hydraulic accumulators can make things way, way faster if that's what you need.

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    Don't forget to remove the volume of the rod from your return stroke cycle time calculation! 80 seconds up is generally not 80 seconds down. But you have some "tool open time" where you are reloading the clay, so maybe 3 minutes is still a decent estimate.

    Enclosing the ram in a boot would be helpful, but if you're planning on using anywhere near the full stroke of that 24" cylinder it's going to be tough to manage something like that. A scraper seal out front will greatly increase the life of your rod seal, and since you know it's a demanding environment, we could plan for it to be easily serviceable. Some kind of scraper is pretty much standard on a lot of hydraulic designs, but they are not all created equal and if you're sourcing the system bit by bit from whatever you can get inexpensively, I would bet that the original designer did not predict the kind of ass kicking this thing is going to get out there.

    Don't know if you are still in MI for now, but if you are still around I'd love to help out if I can.

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    You want Farm duty hydraulics, see Northern Hydraulics for one source. Two speed pump for sure, high volume flow at low pressure typically around 500 psi and a pressure operated valve switches to high pressure automatically. Forget scrapers or shaft seals use a long square shetmetal can over the cylinder fastened to the rod end. Square so there is room in a corner for the return fitting to get out. No better way to protect against abrasives at lowest cost. Double action for sure to make it smooth and positive. Ball joints top and bottom on cylinder reduces side loading on the seals which is what really causes wear. Guide the mold slide not the cylinder. Large rod diameter gives you a faster retract too. Use a larger hydraulic tank, so the oil doesn’t heat up and make sure you have a good oil filter in the valve return line to the tank. Put a very fine air filter on the tank vent too, dusty air gets sucked in with every stroke.

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    Quote Originally Posted by JasonPAtkins View Post
    Yes, all kinds of crap is getting dumped into the top seal of the ram, because both water and clay powder are pressed out as the slug is being formed, and some of it drips down. I made a metal sleeve to protect the enerpac, basically a metal can sitting upside down on the ram end, but it obviously isn't stopping everything. I think a rubber wiper like a motorcycle fork has will be the eventual solution.
    Like john.k said above, I also think you should put the new cyl "upside down" so the ram comes out the bottom. Might be a little more tricky allowing the hoses to flex every cycle. I have one hyd cyl (double acting) that has the ports in the end of the ram, NOT on the body like most do.

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    I think one of the rich shop owners should sponsor these people a suitable ram and hoses....Someone on the eastern seaboard ,freight to W. Africa should be reasonable.Id give em a press ,but its on the wrong side of the world.

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    do not rely on the rod seals to keep crap out. put something like a coffee can around the entire rod and cylinder. basically an umbrella to prevent anything from contaminating the rod.

    on a bottle jack this can be a coffee can or 2 liter bottle etc....
    on an enerpack ram this can be a smaller soup can, piece of tubing etc...

    for reference, the blue shield here.
    AJ-USA | Bilstein | 24-197434 | B6 4600 - Shock Absorber


    bottle jacks are high pressure. they have no hoses. Their reservoirs are around the cylinder such that any high pressure ram leaks right back into the tank. fairly safe design. I would not be surprised they run at at 10k psi

    $1000 10k psi portable power packs are not very high duty cycle machines. You get a motor screaming along with a very tiny gearotor pump for the high speed stage and a tiny eccentric ball bearing smacking the end of a tiny cylinder rod for the high pressure stage.

    I would definitely look for a lower pressure solution, and a larger cylinder with a rod seal shield or even a bellows, cloth, leather, rubber etc...

    Don't rule out seemingly low tech solutions. A toggle press can develop serious pressure due to the mechanical advantage as it nears going over center. and you only really need serious pressure at the last bit of the travel so it seems well suited.
    toggle press design - Google Search

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    We need to know more about this power pack you have. Limit switches? They would be on the cylinder, not the power source. The Enerpac gage is accurate for "tons" with only perfectly matched cylinder rod and tube. If they don't match or you don't know what they should be then disregard that entirely.


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