hydraulics

hydraulics
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Posted by: jackmule ^®

09/28/2005, 22:23:06

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I do not know much about fluid dynamics. However I have run into a situation that confuses me and upon any close hand knowledge I get conflicting answers. It should be a basic hydralic setup 1. if you have 2 cylinders operating on the same control valve a "T" connection, like on any front end loader or set of tilt cylinders on a forklift. 2. if one of the rams or rods whatever is longer than the other will the bucket or mast try to bind, in the middle of the stroke? Do the cylinders try to contain the same volume of fluid regardless if they are attachched to the same thing, or will they compensate for a differnece in rod length?

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Re: hydraulics

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Posted by: swearingen ^®

09/29/2005, 07:35:24

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If the cylinders are the same size, the ram length differences won't matter in its operational range unless they're extremely different lengths. Connecting to the same line keeps the pressures equal which means the forces are equal, so it shouldn't bind any more than equal length rams.
If the ram lengths are extremely different lengths, you may get into some differential stiffness issues that will make it bind.

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Posted by: fluidpower1 ^®

10/01/2005, 12:28:24

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As swearingen said, pressure at both cylinders will be the same so force will be the same. That means if the load on each cylinder is the same then travel speed and distance will also be the same.
However, If the, say Bucket, is picking up a load at one extreme right or left end of the bucket, pressure will have to increase at both cylinders to meet the resistance of the loaded cylinder which means the lightly loaded cylinder will exert more force also. If the Bucket mechanism is not extremely strong the added force to the lightly loaded side will cause it to extend until enough bending of the mechanism forces pressure high enough to lift the off center load. OR until the cylinders stall or something breaks.
Always remember "Pressure is Resistance to Flow" and it will increase until something moves or maximum system pressure is reached. Pressure will also be the same throughout the circuit when no modifying valves such as Flow or Pressure controls are used.
Also as swearingen said, Stroke length has nothing to do with cylinder movement in the working range of the shortest stroke.
Many actuator applications that require equal movement use flow controls, flow dividers, mechanical means or other ways th force the actuators to move at the same rate regardless of load differences.

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