 
 <prompt> How you fit show say these elevators get small capacity? Given di last question, write one context wey contain di answer. E fit be 1 - 20 sentences. Context: <response>: ```One kind elevator wey dey use vacuum for top of the cab and valve for top of the "shaft" to move the cab up and close the valve to keep the cab for the same level. Dem dey use diaphragm or piston as "brake" if pressure increase suddenly above the cab. But to go down, e dey open the valve make air pressurize the top of the "shaft", make the cab fit go down by im weight. E mean say if power fail, the cab go automatically go down. The "shaft" dey make of acrylic, e dey always round because of the shape of the vacuum pump turbine. Dem dey use rubber seals to keep the air inside the cab. Because of technical wahala, these elevators get low capacity. Dem dey usually allow 1-3 passengers and up to 525 lbs.``` 