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Turn-table manners

Discussion in 'Excavators' started by F-1.08-F.G., Sep 20, 2008.

  1. F-1.08-F.G.

    F-1.08-F.G. Active Member

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    Just a quick question for all you hoe operators... I was running our 345BL the other day and I noticed something that I figured I would ask the experts about. When you really get the machine swinging (say from 90 degrees or more), is it hurting anything to just deadstick the turntable to a stop, or should you slowly ease out of the swing with the machine?:confused: I notice that if I was in full swing and I just let the swing go to neutral it would take the 345 a little more than maybe 45 degrees to come to rest. It just seemed like a good length of time was spent 'dragging' on the turntable motor with no input. I know that with smaller excavators this condition is relatively non-existent... so if any you guys on 345's and up or mass-ex guys (or anyone for that matter) have any pointers or ideas, I'm sure everyone would like to hear from you. Thanks
     
  2. Turbo21835

    Turbo21835 Senior Member

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    Seems to me that "dragging" you felt would have something to do with all that extra weight, either in the counterweight or the bucket. That is a lot of mass to stop compared to say a 320
     
  3. Iron Horse

    Iron Horse Senior Member

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    If you ease it to a stop pushing the joystick in the other direction you are using the hydraulic drag of the swing motor , if you release the joystick to the neutral position you are using the swing motor brake . I use the ease it to a stop method and start the slowdown as you say , about 45*-90* before the stop depending on how fast i'm swinging . If i'm only swinging slowly i feather the joystick back to the neutral position . I think the way i do it there is less wear on the brake , but i have been wrong before .
     
    Last edited: Sep 21, 2008
  4. John C.

    John C. Senior Member

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    The swing motor has cross over reliefs installed that soften the stop of just letting the control handle go to neutral. It doesn't matter if you just ease up on the control or just let it go to neutral.

    The swing brake is only a parking brake. It is spring applied after none of the hydraulic functions are operated for 5 to 10 seconds.

    Some Cat excavators have a soft swing function. Maybe this is turned on in the 345B. The other possibilities include that this is normal or that the swing cross over reliefs need to be reset to factory specifications.
     
  5. F-1.08-F.G.

    F-1.08-F.G. Active Member

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    I rarely ever stop the machine by sticking in the opposite direction, unless it is absolutely required or an emergency to avoid hitting something, as I see this to be anything but helpful to the longevity of the machine. After a short time on any machine I can normally get in to a groove as to where I need to neutralize the swing stick in order to 'coast' the machine to a stop and be relatively 'on target'. I was just wondering if this 'coasting' feature is, for lack of a better term, programmed into the machine, or if I should ease off on my input gradually as the machine slows down, requiring me to act much sooner. Most of the guys at work gave me the :beatsme treatment... but I think you guys have pretty much answered my question. Thank you.
     
  6. diggerop

    diggerop Well-Known Member

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    The Liebherr 994 and probably the 996 and others need opposite swing to stop them or they will just keep coasting around and on those big machines they will do a 360 plus no worries, if you are on a bit of an angle you have to keep opposite swing on while the truck is backing under and a while dumping the load. The swing brake is switch operated on the left joystick or on the dash only to be used if you want to hold it for awhile or traveling and parking. I think the swing motors must disengage somehow as there is no resistance from them at all when the stick is in the neutral position. A bit tricky for a bit but good when you get used to it.
     
  7. John C.

    John C. Senior Member

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    It sounds like your 994 runs a free swing. Basically when shovels used frictions there was no way of stopping the house from rotating but to apply opposite turn with the other friction. I have been told that all the electric shovels made today are still free swing.

    In the woods when the transition was made from cable machines to hydraulics the older operators that felt they had to have free swing and could not get used to a house that stopped turning by just letting go of the handle. So basically the cross over reliefs were shorted over so the oil just went back to tank with no restriction on it until you applied opposite stick. This setup was very problematic as it wore out or got crap in the hydraulic system and in many cases even became dangerous as you switched operators from one machine that didn't have it and machine that did. I killed a couple of these systems for owners that didn't want anymore close calls.

    I've never been around a 994 but I image its pretty big and doesn't work an much of anything other that flat ground. A free swing is OK to run on flat ground but when you are working slopes doing shovel logging you will tend to overheat the hydraulic system real fast with it.
     
  8. 360joe

    360joe Well-Known Member

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    The slew system I have seen all operate the same. When you let go or ease off on the slew lever a hydraulic valve will temporarily provide a connection between the input and output ports on the slew motor. This connection will provide resistence to hydraulic flow slowing the slew motor down and avoiding suction in the inlet port to the motor. As stated by others, the slew brake only acts when rotation stops, it is for holding only not slowing down. The slew brake is spring loaded and normally on. It is opened or held off by pressure in the slew circuit, ie when you pull the slew lever, and will come on again as soon as pressure in the slew circuit drops to zero.
     
  9. Iron Horse

    Iron Horse Senior Member

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    When the joystick is in the neutral position and the oil pressure is relieved from the motor . The swing brake would be applied weather stationary or still moving . How would the brake know if the house has stopped moving ?
     
  10. John C.

    John C. Senior Member

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    Iron Horse,
    The swing brake is released by oil supplied from a solenoid valve controlled by a manual switch in some machines or by the computer in all the machines I have worked on in the last ten or so years. There are pressure switches connected to all the hydraulic functions on the machine that provide an input signal to the computer. When the computer receives no signal from any of the pressure switches for approximately 5-10 seconds the computer shifts the swing brake solenoid to connect the brake supply line to tank. The springs then push the disks together and lock up the output shaft of the swing motor.

    There is no connection to the swing circuit at all other than the pressure switch for that function.
     
  11. Iron Horse

    Iron Horse Senior Member

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    As i am not an expert in this field i cannot argue . How is it that if i am slewing slowly and release the joystick the machine stops imediately to a full stop , no pause for 5-10 seconds . I would think that if it was soley by way of hydralic backpressure and allowing for internal leakage through the motor etc the stop would be spongy and not sudden . And what is the method for earlier machines with no computor ?
     
  12. Haul-Pak

    Haul-Pak Well-Known Member

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    The 345 has anti-reaction valves installed to prevent cavitiation of the swing circuit when the lever is returned to neutral.

    When swinging, oil flows to the motors -

    When the lever is returned, all oil flow is blocked -

    The upperstructure continues to turn -

    Pressure builds in the circuit. This pressure is allowed to flow through a check valve -

    A replenishing Valve allows oil into the vac side to stop cavitation -

    This system allows the U-Structure to slow and stop without a shunt.

    Far Far more complicated than this but .... Basics of the system.

    Large and Ultra Large shovels use a closed swing system. The momentum forces on the oil goes back into the system and provide extra power to the machine. Oposite lever reaction causes the pumps to stroke the other way. This pressure is removed by leakoff valves. The Equlizer Valves gov this. (Depending on how many pumps / Motors are involved)
     
    Last edited: Sep 24, 2008
  13. scholzee

    scholzee Well-Known Member

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    How do lines pass through turn table to wheel motors ?

    Newbie and I cannot post a new thread, do not mean to hijack this one but I do not understand how lines and controls pass through the turn table without getting twisted from the house swinging ?
     
  14. John C.

    John C. Senior Member

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    Iron Horse,
    Older machines I have worked on had an emergency brake type lever that operated the swing parking brake. Others were a valve that operated a cylinder that pushed a lever that tighted the brake. It was all kind of a dinosaur thing but they worked to some extent.

    Haul Pak,
    You are pretty close to how it works but there are a couple of different things going on. There are relief valves on the motor, one for each direction of flow, that are set at about two thirds the system pressure of the machine. They each relieve into the up stream side of the other valve. Most people call them cross over reliefs but I have also heard them called safety suction valves. Because there is so much reduction in the gear reducer below the motor, the torque can be applied both ways, starting to swing and stopping the swing. When the swing gets mushy its usually because the seats on the cross overs are going bad and starting to leak through at a lower pressure.

    The closed loop system you are speaking of uses a dedicated pump that will pump oil in two directions. The pump is usually controlled by some sort of hydraulic actuator, I have seen cylinders and mechanical linkages in old machines and servo pistons in newer machines. This pump feeds a fixed displacement by-directional motor. Pump oil into one side and the house turns one way and simply reverse the oil flow and the house goes the other way. There are suction checks in this system so that when you let go of the control lever the oil will freely go around the loop. Koehring excavators used to use this system and I'm sure lots of really big machines still use it.

    scholzee,
    Excavators use a swivel joint by one name or rotary manifold by another name. Basically it is a tube that is stationary with the either the house or carbody and a center section, that is stationary with the other. The center section is like bar stock with what look like thick plates that fit into the tube. The outside ends of the plates have cylinder seals. Tubes connected on the outside of the barrel correspond to the spaces in between the plates.
    Once you see one you will think how simple it is.
     
  15. Countryboy

    Countryboy Senior Member

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    Welcome to Heavy Equipment Forums scholzee! :drinkup
     
  16. 360joe

    360joe Well-Known Member

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    John C
    I agree with what you said regarding typical slew brake operation. I said above that the slew brake is released by pressure in the swing circuit which is probably misleading. As you stated, a solenoid controls hydraulic feed to realise the slew brake. This solenoid will be controled by the valve computer which will take inputs from pressure sensors on all the other hydraulic circuits including the slew circuit. The valve computer will only energize the solenoid to send pressure and release the park brake when there is pressure in the swing circuit but there is no hydraulic connection between the parking brake and swing circuit. Just wanted to clarify my earlier post.
     
    Last edited: Sep 29, 2008