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What Is a Locking Pulley?
A locking pulley is a type of pulley that will lock the cord in place when the cord is manipulated correctly. This pulley is primarily found on household window blinds in the consumer market, but it also has some limited commercial and boating uses. The locking pulley is a simple pulley, except with two wheels instead of one. When the cord is pulled outward, it moves one of the wheels, causing the entire mechanism to lock. This enables the user to keep the blinds, or whatever object is attached to the pulley, in place without holding the cord.
A simple pulley consists of one wheel with a cord threaded through the wheel. When the operator pulls one end of the cord, the object on the other end lifts. The main difference between the locking pulley and simple pulley is that the second wheel enables the locking function.
With a locking pulley, the same basic mechanics are used, but the operator can lock the cord in place and can walk away, leaving the object suspended. This is done by pushing the larger of the two wheels out of place by pulling the cord toward the right or outside. When this wheel comes out of place, the smaller wheel falls forward and the wheels pinch the cord to trigger the lock.
Unlocking a locking pulley is done in reverse. The operator pulls the cord toward the inside, or left, of the pulley. This pulls the small wheel back into alignment and the larger wheel falls back to its original position, releasing the cord.
The use of locking pulleys has mostly been in the consumer sector. Common household blinds use this mechanism so operators can lift the blinds to let the sun in. There has been some limited commercial and boating use of locking pulleys, but other pulley types are usually used for those purposes.
While a locking pulley is convenient because it allows the operator to keep the cord in a certain position, it also has a few problems. If the locking mechanism is used frequently, it can shred the cord, because the large wheel has teeth on it. They have more moving parts and require force to lock the pulley into place, so they can fall apart quicker than other pulleys. Some people also may find locking and unlocking the pulley to be difficult, because the cord has to be pulled in a certain way to get the mechanism to work.
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Discussion Comments
@cloudel – It is good to know that products with locking pulleys are being tested like this. My dad has a locking rope pulley on his boat that he uses to anchor it, and the company he bought it from put a warranty of fifteen years on the label, so I'm assuming they test their pulleys, as well.
The anchor pulley is metal with rope running through it. It has springs and a locking slat that snaps in position when you are ready to anchor.
I've never used it personally, but I have watched him work with it many times. It seems like a great, easy way to secure the boat. He goes fishing a lot, and he makes good use of that pulley.
I have an engineering friend who works for a company that designs window blinds. They use a robot to test the locking pulley on their products, because the job is monotonous but very necessary.
The robot pulls the cord on each set of newly designed blinds all day long, up and down and left and right. The purpose of this is to see how durable the product is, and how long they should claim that it will last.
Of course, this is an estimate, since it will depend on how often the blinds are open and closed. However, it lets the company know if there is a defect in the product and if it should be redesigned.
Window blind cords last for a long time. I just recently had one break that has been used for twenty-five years, so I think I got my money's worth!
It is amazing that it was able to last that long with all the friction placed on it every time I pulled it to one side or the other. When it broke, it shocked me. I guess I just assumed it would last forever.
The cord broke off about three inches from the top. Luckily, I had just locked the blinds in place when it happened.
I believe it is time to get new window blinds. I hope the new ones last as long as my old ones did.
I have always had trouble remembering which way to pull the cord on my window blinds in order to lock it. You would think that after twenty years of using it, I would have it memorized by now!
I usually just do a trial and error run. I gently pull it in one direction while keeping a grip on the cord so that the blinds don't come crashing down, and if they continue to slide downward, I know that I should pull it in the opposite direction.
I do this carefully now, because I have had blinds crash down before. Since they are too long for my window and I have them stacked on the sill, when they fall down quickly, they fall all the way to the floor.
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