Conveying Systems Flashcards
<p>Vertical transportation includes</p>
<p>passenger & freight elevators, escalators, dumbwaiters, vertcial conveyors, moving ramps, wheelchair lifts, platform lifts, stairs, ramps, ladders</p>
<p>Hydraulic elevators</p>
<p>car is lifted by a plunger/ram set directly below the car in the shaft</p>
<p>ram operates in an oil-filled cylinder the same height as the car must travel (shaft goes into ground)</p>
<p>limited to 2-6 stories, lower speed</p>
<p>in holeless or roller chain version, the shaft stands alongside next to car in shaft</p>
<p>Electric elevators</p>
<p>all operate by using counterweight over a sheave on cables (called ropes), driven by motor, traction of ropes on sheaves drives car (so called traction elevators)</p>
<p>gearless traction: motor directly connected to sheave, higher speed</p>
<p>geared traction: slower, but more flexible config., where ropes are pulled more remotely</p>
<p>ropes can be in double or single wrap, indicating loops over the sheave; double is faster, but shortens life span of ropes</p>
<p>1:1 roping:Ârope is attached to counterweight, 2:1 roping is when rope loops around counterweight on a second sheave, makes counterweight travel twice as far, but doesn't require as much weight to lift - smaller motor needed</p>
<p>Â</p>
<p>Elevator operations</p>
<p>operations means user interface</p>
<p>types: single automatic - single call button on each floor, single button for each floor in car, car can only be called if no one's using it, person using it gets exclusive control</p>
<p>selective collective operation: car remembers and answers calls in one direction, when done, switches to other direction, not in use defaults to lobby (ok for light use)</p>
<p>group automatic operation: many elevators in one bank, deploys mult. cars in most efficient manner</p>
<p>destination floor guidance system: AI who puts people going to same/near floor in same car, riders select floor at central kiosk</p>
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<p>Elevator controls</p>
<p>controls means motor/machine interface</p>
<p>unit multivoltage or Ward-Leonard: old school, three motors (AC motor drives DC generator, drives DC motor), noisey, low efficiency, one one avail. til 1980s</p>
<p>silicon-controlled rectifier (SCR) or thyristor: just variable DC generator to DC motor, lower power output, still inefficient</p>
<p>variable-voltage, variable frequency (VVVF): AC uses rectifier and inverter to make DC power, that drives an AC motor able to make 3-phase AC currents, is solid state, fast, dependable</p>
<p>Elevator safety devices</p>
<p>main brake on sheave comes on when power is cut off</p>
<p>a governor tracks car speed, applies brake if too fast</p>
<p>safety rail clamps also brake in an emergency</p>
<p>car buffers stop a car if it travels too low (but not from a dead-fall)</p>
<p>hoistway door interlocks prevents elevator from operating if hoistway doors aren't closed/locked</p>
<p>safety edges on auto doors activate a switch to reopen if something touches them</p>
<p>proximity detectors (maybe photoelectric) do the same when obj. is present in door path</p>
<p>weight sensors prevent overloading</p>
<p>telephones, alarm buttons, escape hatches & ropes for emergency exiting</p>
<p>backup power sometimes required so at least one car can operate at a time, return all to lobby</p>
<p>firefighters can override emergency mode with a key</p>
<p>all must be ADA compliant</p>
<p>Elevator design considerations</p>
<p>capacity, speed, number of cars, roping method, machine room layout, control system</p>
<p>Âbased on handling capacity ofÂ5 min. peak period</p>
<p>speed determined by number of floors served + capacity</p>
<p>car capacity + speed determines number of cars, along with max. wait times (for offices, 30-35 sec., for hotels, 70 sec.+)</p>
<p>doors speed counts: center opening, single speed is commonest, side opening doors move telescopically to make faster; bigger clear space means faster entry/exit times</p>
<p>Very tall buildings + elevators</p>
<p>not economical or wait time efficient to have all cars serve all floors</p>
<p>max = 15 floors for a car to serve</p>
<p>can have separate shafts for elevators serving different floor levels (space inefficient)</p>
<p>sky lobby: high-speed elevators go to intermediate floor lobby, then to floor-serving elevators;Â shafts do not extend full height of building</p>
<p>stacked or double stacked cabs: two cars attached, go to upper floor for odds, stay on main level for evens</p>
<p>Elevator hoistway/pit</p>
<p>hoistway allows car travel, has guiderails, control machines, is a dedicated, fire-rated, enclosed space (1-3 floors, 1 hr; 4+ floor, 2 hr)</p>
<p>emergency illumination required throughout</p>
<p>can't have more than 4 cars in shared hoistway & if they serve the same floors, must be divided further</p>
<p>pit for controls, car buffer, needs lighting, ladder, poss. sump</p>
<p>Machine rooms</p>
<p>best place = ab. hoistway, usu deeper than hoistway bc of all the machine clearances</p>
<p>must be held off from top floor alot, and be tall, so they poke out of roof a lot</p>
<p>machine-roomless elevators have controllers in hoistway itself, not separate room, only work in low/midrise, are more efficient, quieter</p>
<p>Â</p>
<p>Freight elevators</p>
<p>five classification groups: A (general), B (motor vehicles), C1 (trucks), C2 (load of truck only), C3 (smaller increments of truck loads)</p>
<p>Non-public stairs</p>
<p>Winders (tapering must be equal), circular (inside arcÂcannot be less than twice width of stair), spiral (greater allowable riser ht, so you get a 6'6" headspace, but not more than 9.5")</p>
<p>Stair minimums</p>
<p>min width = 36", or if > than 50 occupants, 44"</p>
<p>handrails max project 4.5" both sides (9" total)</p>
