This fast guide is designed to provide an easy reference to the most commonly used crane controls. It lists the function of each component in a control system, with explanations and examples of how that component operates during everyday operation of the crane. Changes in technology have made some components obsolete – these are noted by an asterisk (*) after their description. The function of a control system in a crane is to ensure that the load being lifted by the crane is positioned at the required location, safely and securely.
The systems described have evolved from manual operations, where the operator could see how much load was being lifted and could easily keep it within safe working limits. In many cases today’s cranes are used in closed cabs, sometimes at a distance from the load. The system therefore has to provide an indication of the load weight and position before the operator can fully assess the safety of operating conditions.
The Main Components in a Crane Control System Are:
- Operator’s control station (manipulator)
- Load indicator (gauge or load indicating device)
- Limit switch(es)
- Load line (cable, wire rope and/or chain hoist and/or auxiliary equipment), including auxiliary equipment such as tensioners, locks etc.
- Control valves (throttle valve, power demand valve and auxiliary valves)
- Differential (throttle) valve
- Brakes and auxiliary brakes
The Operator’s Control Station
The Manipulator includes the operating levers, switches and/or joysticks which allow the above systems to be controlled. The load indicator is usually a load cell or load indicating device which measures the force exerted by the load on the crane hook, load line or other components. The limit switch(es) are used to stop the rotation of the load line when the required position is reached. The load line should be checked before raising or lowering any loads – it must not exceed its safe working limits at any time.
The auxiliary equipment consists of all parts which are required to keep the load under control. The auxiliary equipment includes tensioners, locks etc. which are used to lock or hold the load in position once it has arrived at its destination.
The power demand valve modulates power between the rotating equipment and the stabiliser legs (if fitted) to control pitch; this also accommodates for sling sag. The differential (throttle) valve varies the flow of oil between the engine and main transmission to control idling. Auxiliary valves, such as load line lock-off, tensioner release or auxiliary locks are used to provide additional control of the load on its way up or down. If there is more than one auxiliary valve they operate independently; therefore it’s important that movement of controls (for example brake band release in the auxiliary valves) is completed before moving to another set.
The brakes are applied automatically when an overload or drum rotation is detected. Operators should not, therefore, rely on the overspeed brake to stop the load line in an emergency – they must use their experience to judge when it is safe to bring the load under control by applying the auxiliary brakes.
The load line (wire rope, chain and sling) should be checked before raising or lowering any loads – it must not exceed its safe working limits at any time. If the load line is reversed so that appears on both sides of the crane it will become slack and overloaded on one side. In this case a drum brake can get locked on, causing the load to overspeed and possibly create an accident.
This fast guide is designed to provide an easy reference to the most commonly used crane controls. It lists the function of each component in a control system, with explanations and examples of how that component operates during everyday operation of the crane.