Crane Development origin: history. Slightly, difficult to operate. To the 15th century, Guangdong 20 tons crane, Italy invented the jib crane 20-ton crane factory, to solve this problem. This crane boom root tilt 20 t crane manufacturer, the arm top is equipped with a pulley, can lift can be rotated. It was not until the 18th century, a variety of lifting machinery are also used by humans to human, animal powered on starting weight, range and efficiency is very limited. Crane safety devices: the height limit device. For special occasions, such as still need to make small amounts of over-winding operation, press the release button on the meter box, this time limit will be lifted action, but this time the operation must be very careful to prevent accidents. Telescopic crane safety device: When unexpected accident, telescoping boom cylinder circuit of high-pressure hose or pipe burst or cut off, the hydraulic circuit balancing valves on the work, the lower chamber of the cylinder lock from the working oil to make hanging retract on their own, so as to ensure the safety of operations. 20 tons crane price | Yongchang Machinery (certified) | 20-ton crane provided by the Henan Yongchang Engineering Machinery Co., Henan Yongchang Engineering Machinery Co., Ltd. (www.tadanocrane.net) is Anyang, other leaders, over the years, the company is implementing the scientific management, innovation and development, the principle of honesty and trustworthiness, and satisfy customer needs. In Yongchang machinery leadership with the staff warmly welcome all inquiries negotiations to create a better future Yongchang machinery.