 
 <prompt> Wetin dey make dis elevator get low capacity? Based on di question wey dey before, write small tori wey get di answer. E fit be 1 - 20 sentences. Context: <response>: A elevator of dis kind dey use vacuum on top of di cab and a valve on top of di "shaft" to move di cab up and close di valve to keep di cab for di same level. A diaphragm or a piston dey use as "brake" if sudden increase in pressure above di cab happen. But to go down, e go open di valve so air fit pressurize di top of di "shaft", wey go allow di cab go down by im own weight. Dis one mean say if power fail, di cab go automatically go down. Di "shaft" dey make of acrylic, e dey always round, because of di shape of di vacuum pump turbine. To keep di air inside di cab, rubber seals dey use. Because of technical limitations, dis elevators get low capacity. Dem usually allow 1-3 passengers and up to 525 lbs. 