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Lifting Techniques Part 3 – Complex Block & Tackle
This is Part 3 series by Senior Refrigeration Tech (and prolific writer) Jeremy Smith. Pay attention to this one, folks. I know rigging and safe lifting practices may be boring to some of you, but it could very well save your back or your life.
This article is written by a technician representing his real-world experiences and his advice for best practices. You MUST understand the particular application, the weight of materials, and the load strength of every item you use—from struts to pulleys to anchors, ladders, ropes, etc. HVAC School is NOT giving OSHA-approved safety advice. Refer to your managers, safety professionals, and OSHA guidelines first and foremost. Apply any and all of these practices at your own risk with the knowledge that we are trying to help keep you from hurting (or killing) yourself.
Complex block and Tackle systems
Now that we have a basic understanding of how to handle ropes, tie knots, and rig a basic pulley system, we're ready to dive into more complicated systems. I reserve these for buildings that have a roof hatch so that I can set up a gantry over the hatch. I haven’t yet figured out a system to extend a beam over the edge of a building, but I'm working on it. I'll go into the basics of how I build and what I build in the next section. For now, let's just accept as a given that we have a solid beam installed over the hatch opening to which we can connect ropes and pulleys.
For jobs like this, I keep a double pulley on the truck. Threading or ‘reeving’ these takes more time and is more complicated, but the reduction in effort is worth it. Start by fixing your single pulley to the overhead beam and connecting the double one to a light “load” like a wrench or something similar. Tie one end of the rope to our overhead beam. Start threading by running the other end through one side of the double pulley, then through the single, through the other side of the double. Now, you should have a nice mess of rope. Lower that weighted double pulley to the spot where the load is. Secure the free end of the rope with a clove hitch just to keep it from falling and to keep a tiny amount of tension on the system.
The setup shown here was used to hoist a 15-hp blower motor onto the roof. Motor weight was something like 145 pounds with 4 lines supporting the load, and the effort to hoist that motor was less than 40 pounds.
I like to stand on the roof while hoisting, so I make it a point when threading pulleys to wind up with the pull end of the rope going up. This also has the advantage of using every line to support the load and obtaining maximum effort reduction.
As before, connect to the load and hoist it slightly. Check for good balance, twisted ropes, and crossed lines. Make any corrections and hoist away. Since we're hoisting to an overhead beam, there won't be any need to take 100% of the load at any time, so this method is much safer, and when we dig into the gantry build, we'll find a great way to manage the load once it's at the top of the lift. As the loads get heavier, you'll be using heavier and heavier duty hardware to attach to them. Eyebolts, shackles, and chains are the rule here.