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written by Michael Pyper

When really heavy loads have to be positioned with millimeter accuracy, valves from Bucher Hydraulics are normally used. With the LCW load-control valve (Load-Control valve for Winches), specifically designed for winch functions, the lifting, lowering, and holding operations become even more responsive and energy-efficient. The well-thought-out design reduces the pressure losses by more than 40 percent compared with other commercially available valves.

When, for example, the blade of a wind turbine has to be installed, very high positioning accuracy is essential. During installation, the load has to be held safely and exactly in position, despite the leakage that is inherent in the design of the hydraulic motors. The LCW assists the disc brake that is normally used in the winch drum.

Static disc brakes are usually responsible for holding the load in winches. The brake is opened and closed hydraulically by an appropriate valve, such as the LCW, which, in most cases, is flanged to the hydraulic motor.

Functional integration saves pipework and installation costs

Load-Control Valves are used in hoist winches, also called pulling winches, mainly for mobile and ship cranes, as well as for ship winches and cable crane masts. Because the LCW valves include the function of a pipe-rupture valve, they are usually flanged directly to the hydraulic motors without intervening pipework or hoses.

The new LCW is not only particularly responsive and efficient, but is also much easier to install. How is that possible? The load-control specialists have succeeded in integrating the pilot pressure bypass, which normally needs a separate line, into the return line of the LCW valve. Another new feature is the integration of all design options into the control cover. The additional flanges on the opposite side of the motor that were previously required are now no longer necessary. There are therefore fewer components and less piping. That reduces installation costs as well as the risk of potential leakage points. An advantage that OEMs in particular appreciate.

Crane operators are especially pleased by the particularly sensitive and responsive starting behavior and the high positioning accuracy. Operating companies, however, are likely to welcome the greatly optimized energy efficiency. This results from the reduced pressure drop during lifting and by the reduced pressure, and pressure peaks during lowering. The pilot pressure is halved from 20 bar to just 10 at 350 l/min. Especially in times of exploding fuel costs, this saves money.

LCW uses the CINDY principle for outstanding safety

The new LCW valve is based on the proven CINDY principle developed by Bucher Hydraulics. Thanks to this principle, the closing force on the control axis is guaranteed even in the event of spring breakage, because it uses the existing load pressure for closing instead of acting against it. In addition, the lowering motion can be precisely controlled. The LCW is designed for the pressure peaks that occur during an emergency stop, and it ensures safety for man and machine.

Hoist winches are in use for almost every movement. A particular challenge: the design of the winch system means that a certain starting pressure is necessary during lowering to overcome the inertia of the winch drum as well as the frictional resistance that exists when starting with no load on the hook. Due to the starting pilot pressure that is required, the valves tend to open and close. The result: there is a jerk. The integral pilot pressure bypass valve halves the resulting pressure peaks from the customary 80 bar to 40-50 bar. In addition, a higher pilot oil damping volume and stroke-dependent damping from the start to the end of travel ensure sensitive and jerk-free travel behavior at all times. An integral pipe-rupture function eliminates the need to install an additional safety valve.

Reduced lowering pressure conserves oil

In addition to reducing the starting pressure peak, the engineering designers also succeeded in reducing the pilot pressure during lowering from about 45 bar to around 33. The pilot oil pressure should be kept as low as possible to conserve oil. For example, pressure peaks heat up the oil, which ages faster and has to be replaced earlier. This wastes time unnecessarily: time during which the crane is not available and incurs costs.

During lowering operations, the LCW is controlled from the opposite side.
This ensures that loads only ever move as fast as is defined by the incoming oil flow from the main control valve. The internal opening-control prevents cavitation, i.e., the formation of vapor-filled bubbles, which could otherwise lead to sagging of the load.

The LCW valves are standard products that are available at any time. Nevertheless, Bucher Hydraulics offers customized modifications for every new crane model. An acceptance test on site with the customer ensures that each specific crane model, with its particular boom length, can be lowered precisely and without pressure peaks. Thereafter, no further adjustments are necessary for either series or replacement deliveries – in other words, a real Plug and Run.

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