Multiple speed hoisting system with pressure protection and load control

A control system for hoisting loads comprising fluid operated means having opposite sides operable at either a low speed or a high speed in response to alternate fluid pressure differentials between opposite sides of the fluid operated means;

• a source of pressure fluid;
• a fluid circuit interconnecting the fluid source and the fluid operated means;
• said fluid circuit including a valve for controlling the speed of the fluid operated means, said valve including a low speed position blocking connection between opposite sides of the fluid operated means and a high speed position connecting opposite sides of the fluid operated means, means biasing said valve to said low speed position, and means for shifting the valve from the low speed position to the high speed position, said valve shifting means including a solenoid for maintaining said valve in the high speed position when energized, an operator's switch, and an electrical circuit interconnecting the solenoid and the operator's switch, a pressure switch within the electrical circuit, said pressure switch being connected to the fluid circuit for sensing the pressure therein near a pressurized side of the fluid operated means, said pressure switch being operable in response to a predetermined pressure level within the fluid circuit for breaking the electrical circuit to the solenoid, whereupon the valve biasing means shifts the valve controlling the speed of the fluid operated means.