We are often told about the dangers of construction sites and the unacceptable accidents that occur every year. Diggers and excavators are regularly used not just for moving great shovelfuls of earth or rubble but as a cranes. Failure of hydraulics as the digger is lowering a load, say into a trench where men are working, can be disastrous. Accidents of this type resulted in a requirement that all excavators/loaders manufactured after 1 July 1987 and used as cranes as specified by the FMCEC (Federation of Manufacturers of Construction Equipment and Cranes)and the CPA (Construction Plant Hire Association) must be fitted with a controlled lowering device. Excavators manufactured before this date cannot be used as cranes without the fitment of a CLD `as soon as practicable’.
The minimum requirement is currently for a CLD to be fitted to the boom and outward reach side of the dipper services provided that lifting is done with the dipper in the outward reach mode only. If a CLD is not fitted, the safe working load for all excavators and loaders used for craning is limited to 1tonne. There is a strong case for the provision of CLDs but they must not interfere with normal operation.
Husco specialises in hydraulic devices for agricultural, materials handling and off highway construction, and works very closely with its customers getting involved with the design of new products very early on in the process.
Although most products start life as specially designed devices many end up as standard products. The requirement for the CLD however was universal.
Husco’s CLD is connected in series between the control valve and the cylinder it is protecting. The connection from the CLD to the load supporting side of the cylinder must be of rigid construction capable of withstanding four times the normal working pressure of the system so it cannot burst or rupture under pressure.
The CLD is a flow sensitive device, with input flow controlling flow out of the cylinder. Since it is not like a counter-balance valve, traditionally used in such applications, it does not affect the machine performance or controllability.
In operation the valve is `invisible’ to the system and control is always retained by the operator. In the event of a hose failure the operator can choose to stop the machine movement by returning the main control valve to the neutral position, or if he thinks it safe to do so he can lower the load under full control. If for any reason the hydraulic power supply has been interrupted, or it is not safe to use it, the load can be lowered under full control using the manual over-ride.
The Husco CLD meets and exceeds all the requirements of the international standard ISO/DIS 8643 Earth Moving Machinery – Hydraulic Excavator and Backhoe Loader Boom Lowering Control Device. And it meets and exceeds the requirements of the FMCEC as outlined in Guidance for Excavators used as Cranes.