Montshire Minute: Construction Vehicles

Originally aired during the week of May 7, 2001

Monday

Montshire's 110-acre museum consists mostly of forested land, and visitors have reported sightings of fox, deer, bear, and many other animals on the trails over the past year. Visitors this spring and summer may begin to see some other "creatures" temporarily prowling the perimeter of the building. So this week on the program, we're offering a field guide to some amazing construction vehicles. The bulldozer is often the first piece of heavy equipment to appear at the construction site. Its job is to prepare the ground by pushing big obstacles out of the way and clearing away piles of debris. The dozer's "ripper," located on the back of the vehicle, is made for tearing up boulders or tree roots.

Tuesday

The backhoe is a very versatile machine. It can dig. It can pick things up. And it can put them back down again. The backhoe, a hydraulic attachment that can be fitted onto the back of a loader, is meant for digging holes and trenches for foundation work. Its front end is equipped with a bucket loader that can lift up a load of soil and deposit it into a dump truck. Four wheel drive helps it get around the rough, rutted surface of the construction site. The backhoe's long digging arm operates by hydraulic rams. These are long cylinders fitted with pistons. Hydraulic fluid is pumped into the cylinder and the piston moves up or down depending on which end of the cylinder the fluid is pumped. It's the pressure of the fluid, carried through circulation hoses, that produces the tremendous force the backhoe uses to dig, lift, and carry.

Wednesday

Wouldn't you love to drive a dump truck to work? You could sit way up above all the other traffic. And if anyone gets in your way-you'd have an air horn! The dump truck is the workhorse of the construction project. One truck can carry away a load of earth weighing twenty tons. When the truck is ready to release its load, the operator activates hydraulic "rams" which tips the body up. The reinforced steel floor of the body has a very shallow v-shape, so the load slides out easily. In cold weather, the body is often heated by exhaust gases so the load does not stick. The trucks have two rear tires on each hub to support the huge loads they carry. Join us tomorrow as we continue our field guide to construction vehicles. Tomorrows' feature . . . well, see if you can answer this riddle: "What goes around in circles but moves forward at the same time?"

Thursday

"What goes around in circles but moves forward at the same time?" The cement mixer, of course. Dry materials in cement are funneled into the rear of the round "drum" through a hopper. The operator of the mixer can automatically pump in water and start the drum rotating. Inside the drum are giant blades called "flights." The flights are spiral shaped and can push the cement mixture to the back or the front of the drum, depending on which direction they turn. An adjustable extension chute can deposit the cement mixture right where it needs to go. Oh yeah, after the concrete has been delivered, the drum has to be thoroughly washed out. Otherwise it becomes - you got it - a big round blob of cement.

Friday

Later in Montshire's construction project, you may see a mobile crane lifting steel beams into place. The boom, or long arm of the crane, is telescopic. No, it can't chart the course of Jupiter. But it has three or four rectangular tubes that slide in and out of each other, like a telescope. So the whole thing collapses into a neat package that can be driven to and from the site. The base of the mobile crane serves as the counterweight. The counterweight balances the load - the weight of the crane arm along with the beams it lifts up - so it doesn't topple over. The crane also needs a stable platform to function, so the operator activates hydraulically operated "outriggers," or legs along the sides of the truck. The outriggers help distribute the weight of the vehicle, giving it a more secure base.