Here I sit while a monsterous pile driver about 50 feet from my building BANGS away at a pile every 1.5 seconds by my watch, causing my entire floor to vibrate & making ripples in my coffee.
***BANG…
BANG…
BANG…***
Gravity causes the weight to BANG down on the pile, okay that’s easy enough. But what causes it to fly back upwards again? I was imagining a steel cable & a pully drawing the weight back up to the top of the driver, and an operator who is in charge of pressing the “release” button so the weight can BANG down on the pile. But this isn’t the case. Nothing as far as I can see is attached to the weight. It appears to be simply “bouncing” up and down. But what keeps it in motion? Are they feeding fuel into the chamber beneath the weight and then igniting it, causing an explosion which sends the weight back up into the air? Then why don’t I hear a second BANG after the weight hits the pile?
Pile drivers, like a great deal of large construction machinery, are hydraulically powered. Fluid is pumped into a piston to raise the weight. Alternatively, I think some pile drivers might use air or steam in a piston.
The simplest piledriver is a rock.
Well, you have to lift it up to drop it down. Add a rope and a pulley, and better a guiding rail. If you don’t have slaves at hand (according to my tech-lexicon, the piledriver is 4000 years old, bet it was easier to get slaves back then) add a mechanism to lift the weight. It can be hydraulic, pneumatic (air or steam), or electric. We can omit the pulley by integrating the weight into the cylinder. The weight makes BANG!, and whatever gets it up again makes the ‘shhhck’-sound. (You hear no shhhck? Read on, there’s another kind.)
But we waste half of the energy.
The falling weight stops on the pile, exerting a force. Note that we can achieve the same result again by accelerating a mass upwards, pushing off on the pile. The weight does not have to rest on the pile, so we can join the two (de-/ac-)celeration phases. By accelerating it up to the same speed it had when falling down the weight will return to it’s previous height.
Put a spring on the pile and drop a weight on it. Ignore friction and it would bounce forever.
But we have friction, and we want some energy ending up in the pile, remember? And the pile is kinda stuck in the ground, so we have to exert a big enough force to get it moving. Force is mass * acceleration. As our mass is already as heavy as anyone cares to carry around we try at the acceleration. To achieve high acceleration, we need to change the velocity of the weight in a short time and distance.
Replace our spring with a closed, air-filled piston - same principle.
The weight comes down, cushioning on the air. Now inject some fuel into the piston and ignite it. Note that the weight would bounce on the air without the fuel anyway. The combustion just replaces the energy lost to pile and friction elsewhere.
You hear no second bang because stopping the weight and getting it up again is one continuous motion, thus doubling the energy available to put into the pile.
What you have is nothing but a stomping piston engine. (stomping, get it? :))
You start by putting your opponents head, face-down between your legs (you are standing) then you pull them up in such a way that their legs are up in the air, then you drop to your backside.
Pile drivers used in construction are pretty simple really.
A large vertical structure contains a heavy weight. At the top of the structure is a pulley. A cable attached to the weight goes over the pulley and down to a winch. The winch lifts the weight a bit, then lets it drop (by freewheeling down). The freewheeling is controlled so the winch drum doesn’t just spin free and unwrap all the cable into one big mess. This is the “bang bang” type pile driver commonly in use. Cable-tool oil drilling rigs work on a similar principle.
Vibratory and hydraulic types tend to make a bit less noise.
All I can say is I hope they’re driving concrete or wooden pilings. I had to sit in an office 150 feet from a combustion-type driver hammering I-beams into the ground, once.
Shhhkk… as the piston rose to full height…
WHAAaaannnggggg… as the piston came down and fired itself back into the air…
I know your pain.