Hydraulic valves

Single counterbalance valve for open center with bolt VBZB

In stock

Overcenter valve simple effect not compensated fixed setting with banjo bolt


Using the VBZB counterbalance valves it is possible to manage suspended loads and control their movement by eliminating vibrations sudden and dangerous lowerings. The banjo bolt applicable on the valve body simplifies the installation operations and makes the action of the valve more effective.

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The single VBZB series overcenter valves are suitable for applications in which it is necessary to guarantee the stability in the working position of a hydraulic cylinder with suspended load and to control its movement in only one direction (usually the descent phase), leaving the side opposite of the free-flow actuator. Thanks to the valve body designed for the installation of a banjo bolt on the load side, the VBZB counterbalance valves are installed directly on the cylinder, simplifying the circuit, reducing assembly time, and optimizing performance thanks to the containment of the phenomenon of hysteresis. The banjo bolt is on the controlled opening line and must be installed on the cylinder return. Along the same line, the oil flow in the opposite direction is free thanks to a non-return valve. Powering the line opposite to the load, the piloting is also fed, with the task of managing the partial opening of the descent branch allowing the control of the actuator movement and avoiding the cavitation phenomenon thanks to the action of contrast to the gravitational force . A reduction ratio between the load line and pilot line (pilot ratio) allows the valve to be opened at a lower pressure than the calibration one. The piloting signal is damped with a calibrated hole so that the opening and closing of the valve are progressive, avoiding load oscillations. The VBZB single counterbalance valve also functions as a relief valve: in the event of a sudden and excessive increase in pressure due to excessive load or impact, the valve protects the hydraulic structure itself and the mechanical structure to which it is applied, opening when the calibration value and discharging the excess pressure. For this to be possible, the return line on the distributor must be connected to the drain. The VBZB is a non-compensated counterbalance valve: residual pressures on the return line counteract the opening of the valve by raising the pressure and piloting value necessary to open it. For this reason this type of valve is recommended for systems with directional valves with open center spool, with users connected to tank in neutral position. The hydraulic seal of the overcenter valves is a fundamental characteristic for sustaining the load. In order to guarantee the best sealing, Oleoweb manufactures the internal components of the counterbalance valve in high-strength steel, hardened and grinded, and during the production process the dimensions and geometric tolerances of the sealing parts are accurately checked, as well as the same seal with assembled valve. The VBZB are parts-in-body counterbalance valves: all the components are assembled inside a hydraulic manifold. With this solution it is possible to manage high flow rates while keeping down the overall dimensions. The Oleoweb counterbalance valves have a steel body to reach operating pressures up to 350 bar (5075 PSI), corresponding to the fixed calibration value of the VBZB valve, and guarantee a high resistance to wear to the benefit of valve reliability and durability. VBZB valves are available in size BSPP 3/8" for recommended working flows up to 40 lpm (10,6 gpm). Body and external components are protected against corrosion by zinc plating. The valve body is machined on six faces for optimal surface treatment effectiveness. For applications exposed to particularly aggressive corrosive agents (eg marine applications) the zinc-nickel treatment is available on request.

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