Forklift load calculations - One forklift versus two ? - Page 2
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  1. #21
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    Everybody talks about dropping the load while traveling with 2 lifts. Keep the load just high enough to clear the ground, and if one lift tips, itís no big deal. Also I train all my operators to keep a hand on the lift lever when under load. That way, if something starts to happen, you can sit it down fast.

    The worst problem when moving with 2 lifts is they can get to pulling against each other and pull one or both of them over. Best practice is to have the one in back do the pushing, and just leave the lift in front in neutral, and let the other lift push it. Also, keep your forks as level as possible when traveling. If you are tilted out too much, the weight of the machine can try to push your forks out from under the load.

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  3. #22
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    Quote Originally Posted by OldParts View Post
    There must be different arrangements out there. I've never heard a relief go off when idle or lowering, only when applying pressure, but usually anything I operate is on it's second, or third, or...., life.
    My old excavator has reliefs on every handle,, both directions.

    why ?

    Because if your knocking down a building, and the building falls on the boom,
    the first thing you do is get off the handles. If that would block off the reliefs,
    you could blow a hose, bend a cylinder, or break the boom.

    I'm pretty sure the forklifts I have used have the same relief set up on the lift cylinder.

  4. #23
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    With two lifts, assuming the machine isn't heavier on one side (eg assuming it's an evenly distributed load), the load center for each lift is at 22" (think of it as two cantilevered beams with a distributed load spanning them).

    As to whether they'll pick it up, there are two things - can the hydraulics lift the weight (regardless of load center), and will the counterweight prevent tipping (sum of moments about the front axle). If the hydraulics have the force and the counterweight has the mass they'll pick it up.

    All this is assuming it's all static so the minute you get out of sync or start moving around you're fucked unless the load is an inch off the ground, in my mind.

  5. #24
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    Quote Originally Posted by digger doug View Post
    My old excavator has reliefs on every handle,, both directions.

    why ?

    Because if your knocking down a building, and the building falls on the boom,
    the first thing you do is get off the handles. If that would block off the reliefs,
    you could blow a hose, bend a cylinder, or break the boom.

    I'm pretty sure the forklifts I have used have the same relief set up on the lift cylinder.
    I've never been on a excavator, forklift, or anything that had reliefs on the individual circuit. On everything I've ever been familiar with, you just have a main relief that only controls main pump pressure, and with the valve in hold, everything is locked solid. And yes, if a wall falls on your excavator, you can very well blow a hose, bend the boom, or bend a cylinder.

    What kind of excavator do you have that haves a relief when the valve is in the hold position?

  6. #25
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    Quote Originally Posted by adh2000 View Post
    You guys have failed statics and dynamics. The forklift can lift up to its maximum rated weight at any point along the fork. It makes no difference to the lifting cylinder or the mast. Oil pressure in the cylinder is the same regardless of the loads location along the fork. The reason the maximum lift is derated as you move out on the fork is because of the tip hazard, not because the machine can’t lift the weight. If you mitigate the tip hazard somehow you can lift more weight further out on the fork.


    Sent from my iPhone using Tapatalk
    So how is adding a second fork lift changing the tip hazard? If they are both over loaded then the rear is still trying to float in mid air except now it is 2 trucks instead of one. Educate me on all the physics that I'm failing on if you will.
    Dan

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    Quote Originally Posted by Danny VanVoorn View Post
    So how is adding a second fork lift changing the tip hazard? If they are both over loaded then the rear is still trying to float in mid air except now it is 2 trucks instead of one. Educate me on all the physics that I'm failing on if you will.
    Dan
    If side by side, you're right, limit is lift1 + lift2 at that location on the forks. As I drew it, it would take fork extensions or securing the load to the forks to even get off the ground, but really shows the front heavy problem.

    If opposed, now you can have the weight of a wide object much closer to the front wheels of each.

    They both still have to lift 1/2 (or some ratio totaling 100% if the machine is heavier on one end) the weight, and still at the respective distances. But in this case that distance should be much less, so not nearly as front heavy.

    Of course if moving, changes in slope etc can have the same effect as tilting the forks up on one of them and still bring the back end off the ground, but patient operators and good communication can go a long way. If the base is "hollowed" underneath or the desired contact points blocked up (if not done carefully though slipping off is even more of a danger), a shift in effective load location is less likely too. Yet, terrain with some twisting motion or maneuvering causing articulation can still make for other unwelcome surprises.
    Attached Thumbnails Attached Thumbnails forklift2.jpg   forkliftsxs.jpg  

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    On the forklift hyd. control valves I am familiar with, there are two relief valves.
    One for the main hyd. cyl. and one for the tilt and auxiliary functions.
    These would limit those functions, but not the pressures in those functions.

    Bobcats and excavators are a much different application.

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    Another thing to consider is, if 2 lifts are at opposite sides of a load, one or both of the lifts will have to roll backwards for the load to fall. Now I wouldnít count on this to extend the capacity of a lift, but it does help for both lifts to hold their brakes when the load is high.

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  11. #29
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    Default Cradle Concept

    cradle-2.jpg
    A model of the cradle/carrier earlier proposed; I'd put this carrier between the lifts. It was drawn as .375x3x8" tubing 103" long with 30" spacer stabilizers(3)between the 2 long members.

    This would help bring the load back to both masts and give the forks some degree of freedom within the tubes for maneuvering. Therefore you don't have to worry about sliding around on the machine base and contacting the sheet metal with the vertical section of the forks. Could also chain the machine to the carrier making sure it doesn't slip or tip. And, as said earlier-- one lift could be the driver with this carrier in place since it pushes against the other lift instead of the machine.

    If both machines have the forks inside the carrier tubes and are fully capable of lifting the load-- how could they tip over unless the forks slide so far out of the carrier that the load is no longer within the rating zone(within 24"(I'd keep within 6") out from vertical of fork).

    And, once on the ground-- the carrier would make it easy to skate as well.

    Wouldn't this also greatly improve the safety of the lift?

    Thoughts?

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  13. #30
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    Quote Originally Posted by danil View Post
    cradle-2.jpg
    A model of the cradle/carrier earlier proposed; I'd put this carrier between the lifts. It was drawn as .375x3x8" tubing 103" long with 30" spacer stabilizers(3)between the 2 long members.

    This would help bring the load back to both masts and give the forks some degree of freedom within the tubes for maneuvering. Therefore you don't have to worry about sliding around on the machine base and contacting the sheet metal with the vertical section of the forks. Could also chain the machine to the carrier making sure it doesn't slip or tip. And, as said earlier-- one lift could be the driver with this carrier in place since it pushes against the other lift instead of the machine.

    If both machines have the forks inside the carrier tubes and are fully capable of lifting the load-- how could they tip over unless the forks slide so far out of the carrier that the load is no longer within the rating zone(within 24"(I'd keep within 6") out from vertical of fork).

    And, once on the ground-- the carrier would make it easy to skate as well.

    Wouldn't this also greatly improve the safety of the lift?

    Thoughts?
    I have had thoughts of a similar setup. The cross members are a plus. For a strait lift and lower off of a truck that would be pretty safe. Both lifts still have to stay together. There's not enough free movement to travel. Bottom line for me is that one machine lifting is enough to think about without adding a second machine. Try to avoid the balancing acts of two lifts.

  14. #31
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    Heres a few pictures of my UNSAFE HACK SHIT LIFT at the farm. I didnít want anyone helping me (in case something went wrong) so I ran both machines. I let the mill hang over the trailer for a few minutes before moving it out of the way. The BH rated lift is 4000lbs & the fork truck is rated at 5000lbs.

    The K&T 3CH with the HD vertical head and vises tip the scale just over 8000lbs. Both machines picked it up on the tips of the forks with no problem. I didnít want to use the little BH but itís all I had. Once it was on the ground the old Clark was able to pick it up and drive it in to the building. We moved a 15k Cincinnati grinder around the bossís shop a few times with two 8k fork trucks side by side.

    I think youíre good to go and have plenty of head room with both fork trucks. When lifting it off the trailer, be sure to set the parking brake and block the tires front & back so nothing moves around on ya. You canít see it in the pic. but the BH boom is extended all the out and the bucket is in a 2í hole.
    Attached Thumbnails Attached Thumbnails a404e1ef-ff22-4981-a002-9e4b81ccd6cf.jpg   9f72c23a-5a47-4573-aa86-02556e0c74e6.jpg   336768bd-626e-4eac-80a7-bf7ad7cb558f.jpg  


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