LKV Overload Guard

The Piab LKV Crane Overload Guard is designed for easy installation without
disturbing the crane, particularly on overhead travelling cranes, container
handling equipment and haulages where operators may not know when they have
an overload condition.

The Piab LKV is intended for use as an overload guard or as a slack line switch in lifting equipment and is made for forces up to 35,000 lbs. (16,000 kg) in single line part and for maximum 1.47/64″ (44mm) line diameter.

The Piab LKV is attached to a stationary line part. The rope is deflected through a slight angle between the two wheels and the clamping jaw. When loaded, the rope tends to straighten. This applies a force to the clamping jaw and so directly to the pull rod. When the set switch value is reached, the pull rod operates a microswitch and a close/open circuit is made.

The spring element of the load cell is preloaded, reducing pull rod movement to the last 25% of full load.

For the best possible accuracy the LKV is equipped with case-hardened wheels with carefully designed rope grooves. To ensure correct fitting on the rope diameter, the wheels and the clamping jaws are provided with tracks at intervals of 5/32″ (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 line load is only about 1/64″ (0.6 mm) (including the extension of the rope).

The Piab LKV is fully pressure tight. Each instrument is tested under pressure. The Piab LKV fully conforms to the international protection specification class IP 67 acc. to IEC 529.

Externally it is zinc coated and yellow chromated. The wheel bearings are sealed with 0-rings and lubricated with MoS₂.

If the LKV is to be used in a very corrosive environment, it may be polyester-lacquered.

The LKV Overload Guard is 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 Piab LKV maintains its set switch value even after fitting to a new rope.

As the LKV is fully pressure tight, it is well protected against dust, dirt, damp, frost and other atmospheric conditions.

The power-absorbing element consists of specially made Belleville washers dimensioned to resist fatigue. The spring washers cannot be overloaded.

The Piab LKV can be overloaded by 100% without affecting the repeatability.

Install the Piab LKV directly to the static line part close to the anchor point or close to a compensating pulley. The line need not be unloaded.

Set the switch value with the spanner provided for this purpose. (The LKV can be delivered with the switch value set to trip at the value you require.) Check the switch value with a buzzer or similar device.

Connect the LKV electrically, e.g., to the control circuit of the hoisting movement or the top limit switch.

Test-load for control and possible readjustment. Seal the set value with the locking clamp and the padlock provided.

The microswitch has alternative contact functions. When the Piab LKV is used as an overload guard, the normally closed function should always be used.

The microswitch has self-cleaning, gold-plated silver contacts, suitable also for operation on low current/voltage (under 10 V and/or 60 mA).

The difference between contact at rising and falling load is 5-8%. This hystersis is somewhat reduced at lower loads and increases slightly at higher load values. To avoid “chatter” of the contacts and contactors if the load should start to sway, a time relay can be connected to prolong the reconnection of the hoisting movement.

The price of an LKV Overload Guard and Slack Line Switch varies according to model. Choose the LKV model that has a switch range that will accommodate the single line part value of the crane or hoist. To obtain the single line part value when used as an Overload Guard, divide the rated capacity of the crane or hoist by the number of line parts. To obtain the single
line part value when used as a Slack Line Switch, divide the tare value by the number of line parts.

Example: The single line part value of a 10 ton crane with 4 line parts is 2.5 tons or 5000 lbs.

The appropriate LKV would then be set at 5000 lbs. when used as an Overload Guard.

The appropriate LKV model for a 10 ton crane with 4 line parts is an LKV 4, with a switch range of 880-8,800 lbs. for a single line part to accommodate the single line part value of 5,000 lbs. An LKV 2 is unsuitable since it has a maximum switch value of only 4,400 lbs. versus the required 5,000 lbs. The same LKV 4 can also be used on a crane with 4 parts of line to a maximum of 16 tonne or 35,200 lbs., or a maximum of 24 tonne or 52,800 lbs. with 6 parts of line, etc.

All LKV models are guaranteed to be free from defects in material and workmanship for 5 years from the date of shipment to the customer.

When ordering please specify:

1. The rated capacity of the crane or hoist in tons or tonnes (pounds or kilograms) when used as an Overload Guard
2. The tare value or the weight of the hook block and tackle, when used as a Slack Line Switch.
3. The number of wire rope line parts (falls) including the stationary line.
4. The nominal wire rope size in inches or millimeters.
5. The shut-off value if to be set for a value other than for the rated capacity, or for the tare value.
6. Rated capacity of the wire rope if the crane or wire rope has been modified from the original installation.
7. The general application, including minimum headroom available.