Bucher Hydraulics has introduced the newly designed excavator pipe-rupture valve CFS-EF, or “CFS-Flat.” Reportedly an innovative extension of the company’s family of CFS pipe-rupture valves, the new version is based on proven technology and, with a flat design, allows for ready installation on lift cylinders without a sandwich plate.
Bucher developed the series CFS (Compact Flow Control and Safety Valve) excavator pipe-rupture valves to prevent uncontrolled lowering of an actuator in the event of a pipe or hose rupture. The valves can used wherever required by standards ISO 8643, EN 474 and DIN 24093 for excavators with a lifting device (for example, a load hook on the bucket). That generally applies to lift, stick and adjusting cylinders. The valve is also suitable for machines in which a pipe-rupture on the actuators could produce a dangerous situation, such as in materials handling and demolition applications.
In addition, the CFS valve holds an actuator in position when the main valve is centered. The valve also includes a secondary pressure-relief function, which protects the actuator against overload. Inlet and actuator ports on the CFS are standard SAE flanged ports, and the valve can be readily retrofitted to existing equipment.
Thanks to its almost load-independent, pilot-operated principle, variations in load pressure — even right up to the maximum — have no effect on fine-metering characteristics and the hydraulic performance of the valve. The innovative design means very small lowering pressures are necessary to operate the valve. Valve adjustment is integrated into the hydraulic circuit in a manner that ensures that the excavator pipe-rupture function has no effect on the machine’s other hydraulic systems.
The CFS-EF is a pilot-operated seat valve in a flat design. Maximum flow rate is 350 l/min (92.5 gpm) and maximum operating pressure is 420 bar (6,092 psi). Actuation is hydraulic-proportional with an opening pilot ratio 480:1; opening pressure range is 4.4 to 16 bar (63.8 to 232 psi). For surface protection, all external parts have a zinc-nickel coating according to DIN EN ISO 19598.
Functions of the valve are as follows. In the neutral or rest position, the excavator pipe-rupture valve is held closed by a spring, which acts on the control spool, and by load pressure acting on the back of the control spool.
Lifting involves volume flow in direction A to B. To raise the actuator, pump pressure is applied via port A to the valve-seat area of the control spool and causes the control spool to open, pushing against the light pressure spring.
Lowering functions (volume flow direction B to A) include:
1. Decompression. The pilot pressure at port X moves the pilot piston in opposition to the pressure springs and opens the pilot spool at the set pressure. The load pressure behind the control spool now decays as it escapes past the pilot spool to port A. The progressive characteristics of the decompression phase ensure that the actuator motion begins smoothly and without jerks.
2. Main opening. With further increase in the pilot pressure at X, the pilot spool opens further and the reduced pressure behind the control spool falls still more. Load pressure acting on the differential area of the control spool now pushes the spool off its valve seat in the opening direction until the pressures of the oil flows into, and out of, the control spool sufficiently to produce a situation of force balance.
The pilot pressure acting on the pilot piston therefore controls the open metering area of the control spool, and consequently the flow rate from B to A. The pilot valve is compensated and operates independently of any backpressure in port A.
Opening point of the pipe-rupture valve is precisely matched to the particular make/model of excavator and is set to the required value on the test bench using an adjusting screw. With optional stroke limiter, the pilot spool can be restricted additionally and thus influence the lowering speed. Other options include a balance valve (for parallel applications) and mechanical emergency lowering.
The valve has a high opening pilot ratio and the control assembly is guaranteed to close — even with a broken spring. It has little or no impact on the existing hydraulic system and is easy to retrofit. There is constant calibration due to low hysteresis, the valve is independent of backpressure, and there are no dynamic seals in the main spool and in the pressure-relief valve.
For machine builders, the excavator pipe-rupture valve is tailored to the main spool valve and easy to retrofit for optimal operation. It offers consistent valve functions, reliably meets ISO 8643 safety requirements, and is built for long service life under varying operating conditions.
Users enjoy load-independent travel behavior, increased safety for people and equipment even in the event of malfunctions, and cost savings thanks to better energy efficiency. Typical applications for the CFS-EF are crawler- and wheel excavators.