The LKV is attached to a stationary rope part on a hoisting system or crane. The rope is deflected trough a slight angle between the two wheels and the clamping jaw. When loaded, the rope tends to straighten. The resultant force is applied to the pull rod. When the pre-set switch value is reached, the pull rod operates a micro switch and a close/open circuit is made. The spring element of the load cell is pre-loaded, reducing pull rod movement to the last 25% of full load.
For the best possible accuracy, the LKV is equipped with hardened wheels with carefully designed rope grooves. To ensure correct fitting on the rope diameter, the wheels and the clamping jaws are provided with line tracks at intervals of 4 mm. The wheels should not be regarded as wheels but rather as moving support points, as the peripheral movement on the wheels at full rope load is only about 0.6 mm (incl. the elasticity of the rope).
The LKV Overload Guard /Load Guard / force control switch / crane guard / load limiter is installed “parallel to the hoisting system” and therefore not directly included in the rope system and does not affect the construction of the lifting equipment. The locking device prevents unauthorized interference with the switch setting. In spite of the changes that normally take place on the rope diameter, the LKV maintains its set switch value even after fitting to a new rope. As the LKV is fully pressure tight (IP 67), it is well protected against dust, dirt, moisture, frost and other environmental conditions. The power-absorbing element consists of specially made Belleville washers dimensioned to resist fatigue. The spring washers cannot be overloaded.
The micro switch has alternative contact functions. When the LKV is used as an overload guard, the “normally closed function” should always be used. The micro switch has self-cleaning, gold-plated, silver contacts, suitable for operation on low current voltage (under 10 V and/or 60mA). The hysteresis between contact at rising and falling load is 5-8%. This difference is somewhat reduced at lower loads and slightly increase at higher loads. To avoid “chatter” of the contacts and contactors if the load should start to sway, a time delay relay can be connected to delay the re-connection of the hoisting movement.
The LKV is ususally delivered with a factory pre-set switch value, thus eliminating time consuming and expensive installations.