When air is introduced into the placing line, the crew must stand back from the placing hose until the air clears and a steady flow of concrete is being discharged through the hose. A placing hose should never have any type of metal at its end, such as s-bends, rams horns, or even a metal connector for another placing hose. If the hose was to whip, metal devices could cause serious injury or loss of life.Henan Daswell Machinery Co., Ltd,is a professional manufacturer and trader specializing in the research, development and production of construction machinery for nearly 30 years. Our main products are as follows:concrete block making machine,mobile concrete mixer,etc. We will provide you with the best product and service. The crew should have only one person giving direction to the pump operator, communicating movement of the boom, speed of placement, or the starting or stopping of concrete delivery. The ACPA recommends a set of hand signals for communication between the person giving directions and the pump operator to help ensure a safe placement. When an operator can’t see the placement, they must have contact with the placing crew via a relay person or radio contact. When a concrete pump operator is located at the point-of-placement, away from the pump, an oiler must be at the hopper to ensure that the proper level of concrete is maintained in the hopper, to direct backing-up by ready-mix trucks, and to make sure the pump and outriggers are working properly. This person should be trained by the operator to know the locations of the emergency stops and the dangers of the pump itself; the hopper, water box diesel engine concrete mixer, the lifting or sinking of outriggers, and any oil leaks.