Physics Puzzle for the Gearheads

[onlinebiker]

A two post lift has two hydraulic cylinders. One per post. When you push the "up" button a motor starts and runs a hydraulic pump which shoves oil into the post cylinders which have a flat chain arrangement that raises the lifting arms - and if it is in the arms correctly - your car. There is a lever which bleeds the cylinder back to the oil tank and allows the arms to go down. 

If a hose or seal failed while the car was up and you were under it - the car would fall rapidly and squash you like a bug.

Two safety ratchets engage as the lift is going upwards - making a prounounced clunk with each engagement. If pressure is lost to the cylinder - the ratchets will stop the lifting arms from dropping.

If one ratchet fails - there is a system of steel cables on pulleys that make the lifting arms lift and drop in unison - so it will stay up on one ratchet.


That's the last clue without drawimg a picture.

[Rhizomorph13]

Is it because the Gremlins go to sleep once it gets hotter than 70?

[onlinebiker]

I adjusted the cables till the ratchets "clack" in unison - at 70°f.  

As little as one degree either way causes the steel cables (over 50 ft long) to expand or contract. As they are a different alloy than the lift frame - the expansion rate is different for the two. 

Thus as the temp goes higher or lower than 70°f the ratchets click at greater and greater time apart.

[Rhizomorph13]

I adjusted the cables till the ratchets "clack" in unison - at 70°f.  

As little as one degree either way causes the steel cables (over 50 ft long) to expand or contract. As they are a different allow than the lift frame - the expansion rate is different for the two. 

Thus as the temp goes higher or lower than 70°f the ratchets click at greater and greater time apart.

Yep, never would have gotten that one. Makes sense though.

[Anomalocaris]

If the rackets aren’t clacking in unison, that would mean the lifts are tilted or askew,  no?

[arewethereyet]

I had to read the explanation a couple times...but I get it. I was simply NOT going to ask husband to explain it to me. He could have, and would have, but my eyes would have glazed over before he was done.

[onlinebiker]

If the rackets aren’t clacking in unison, that would mean the lifts are tilted or askew,  no?

By a few minutes of degree. Not even close to enough to worry about.

[Fireball]

The double post hoist where I worked as a mechanic many years ago had a rack and pinion setup. The pinion gears required replacement periodically. One other gas station had the pinion gears worn enough that one side dropped fast enough ahead of the other that the car fell off. To their credit, the company immediately contacted all the users about what to look for and discontinue use until repairs could be made. Ours was worn, but they replaced the rack and pinion gears, anyway. Beats a lawsuit by a mile. I don't know if anyone got hurt in that accident.