Static Pile Driver Crane Overload Protection System

The crane arm of the hydraulic static pile driving machine can be damaged or even broken while working because of overloading. The problem of crane overload protection of the hydraulic static pile driving machine is originally solved by a full hydraulic project through comparison and demonstration in advance in this paper. A specially designed relief valve, i.e., mechanical and hydraulic proportional relief valve is used as pressure regulating valve and safety valve to control the highest oil pressure of the radius changing cylinder and hoisting motor in order to accord the pressure value with the crane's hoisting capacity corresponding to certain radius changing angle of the crane's arm. Once overload, the pressed oil overflows through the relief valve so as to result in the crane can't work with the overloading weight thereby achieve to prevent the crane from overloading. The crane overload protection system is a open-loop control system. Imitating the project of electrical and hydraulic proportional valve, a cam mechanism is adopted to input and convert the signal of crane arm's radius changing. According to the control signal the cam mechanism controls the regulating spring of the pilot valve.As the core of the full hydraulic crane overload protection system of the hydraulic static pile driving machine, the study and design of the mechanical and hydraulic proportional relief valve is creative. First, combining cam and lever with relief valve to replace the pressure regulating device of the relief valve or the proportional electrical magnet as the input and pick set of control signal is the key to achieve the function of the system. Second, the pilot valve of difference pressure structure is also the key part of the mechanical and hydraulic proportional relief valve. It makes the design of the pressure regulating spring more easy, the elastic factor smaller, the linear degree of the spring's peculiarity curve better, the number of the pressure regulating spring fewer, and then makes the system can automatically and proportionally adjust the radius changing security oil pressure or hoisting security oil pressure between the range of 3-18MP_a decided by the crane's hoisting capacity curve withonly one pressure regulating spring. Furthermore, the pilot valve of difference pressure structure improves the dynamic stability of the relief valve.The result of computer digital emulation and experimentation about static and dynamic peculiarity shows that the study and design of the crane overload protection system of the hydraulic static pile driving machine is effective and workable. And it can solve the problem of the crane overloading successfully.