General Pulley - Mech Advantage Ques

[Brandnew]

I'm looking for some general information on pullies and advantage. It's been a LONG time since I've had to deal directly with pulleys....be gentle.

I understand that the mechanical advantage, in general, of a pulley system is the # of supporting cables. For example, the system shown in the link has an MA ~ 6.

Thus, I realize that if I'm lifting a load of say, 4000 lbs, a force of 667 lbs would have to be exerted in the system shown above.


I'm looking at a pulley system where the the two "groups" of pulleys need to be seperated at different distances. So I'm looking at putting a hydraulic cylinder in between the "groups" that can extend/retract to change the distance, as required.

Just imagine a hydraulic cylinder in between the system shown

My question is, what force do I need to design the hydraulic cylinder for (assuming it's used in the system discussed above)? Is it only 4,000 lbs or are the forces more "additive" since it would need to extend all of them simultaneously???


I'm struggling with how to look at this since I haven't looked at a problem like this for years. Just need help in the proper way to "view" this situation. Any help/suggestions appreciated??

 

[scarecrow55]

I think it will be 4667, i.e. the tension in the lines supported plus the pulling line.

 

[Brandnew]

Thanks, that makes sense.