Hydraulic valves

Double overcenter valve for open center VBCD

In stock

Double counterbalance valve not compensated for in-line installation

Thanks to counterbalance valves it is possible to support suspended loads and control their downward movement eliminating vibrations or lowerings too fast and therefore dangerous. The VBCD series, thanks to the BSPP threaded ports, can be installed in line into the hydraulic circuit in compliance with the spaces available on the machine.



The VBCD series valves are double descent and movement control valves (also known as overcenter). Their action blocks the cylinder and controls its movement in both directions; and are therefore suitable for applications in which it is necessary not only to control the descent phase of a suspended load subjected to gravitational force, but also to guarantee stability in the actuator working position in the presence of bidirectional loads, as occurs for example in the reversible hydraulic motors. The installation of these valves inside the hydraulic system requires that the cylinder return lines are connected to the two controlled opening lines. Two check valves allow the supply in free flow during the delivery phase. Thanks to the pilot ratio (reduction ratio between the load line and the hydraulic pilot line) the pressure required to open the valves is lower than the setting pressure. Feeding the line on the opposite side that the load one, is also fed the pilot line, which has the task of managing the partial opening of the descent line. This partialization (meetering) allows the control of the actuator movement by counteracting the gravitational force which tends to lower it suddenly and avoiding the cavitation phenomenon. A further function of the double balancing valves VBCD is that of protecting the structure connected to the actuator: in the event of an increase in pressure caused by too high a load or accidental impacts, the valve also functions as a pressure limiting or anti-shock valve and opens when the load pressure reaches the setting value. For this to be possible, the return line on the distributor must be connected to the drain. The VBCD is a non-compensated counrebalance valve: any residual pressure on the return lines counter the opening of the valve by raising the setting values and piloting pressure necessary to open it. It is therefore advisable to install this type of valve in systems where distributor has spool with users connected to tank in neutral position (open center). A fundamental characteristic for counterbalance valves is the hydraulic seal, thanks to which it is possible to sustain the load. To ensure the best hydraulic seal, the internal components of the Oleoweb counterbalance valves are made of high-strength, hardened and grinded steel and during the production process the dimensions and geometric tolerances of the contact parts are accurately checked, as well as the seal itself on the valve assembled. The VBCD overcenter valves belongs to the family of parts in body valves: all the components are housed inside a hydraulic manifold (body valve). Thanks to this solution it is possible to manage high flow rates with contained overall dimensions. The body and external components are made of high strength steel. The galvanizing treatment protects the surfaces against contact with air from oxidation. The machining of the body on the six external faces guarantees to Oleoweb’s overcenter valves an optimal execution of the surface treatment to the advantage of its effectiveness. For applications exposed to particularly aggressive corrosive agents (eg marine applications) the zinc-nickel treatment is available on request. The steel body also ensures high wear resistance with benefits in terms of reliability and valve life; its shape allows easy assembly of pipes with banjo bolts. The sizes available for VBCD valves range from BSPP 1/4 "to BSPP 3/4". The maximum working pressure is 350 bar (5075 PSI) while use is recommended for flow rates up to 120 lpm (31,7 gpm) depending on the size chosen. It is advisable to set the valve at a value 30% higher than the maximum working load to achieve optimal operation. Different setting fields and different piloting reports are available to better adapt to all types of applications. It is also possible to seal the calibration with a plastic cap, protecting it from tampering.