Valve used to control the movement and locking of the actuator in both directions by realising the controlled descent of the load that does not escape dragged by its own weight, as the valve does not allow any cavitation of the actuator. It is insensitive to back pressure and is therefore used where normal overcenters do not function properly at load control, allowing the pressure set by the system to be used to operate several actuators in series. Flange connections allow the valve to be mounted directly on the actuator.

The BOST valves of the  series are double overcenter valves: they perform the function of supporting and controlling the descent of a load in two directions. The double counterbalance valves are used in applications with bidirectional loads of which it is necessary to guarantee stability in the working position and to control their movement  valves are flangable valves, ie they can be applied directly on the actuator (generally a hydraulic cylinder). Through the flanging the back lines from the cylinder are connected to the controlled line, fed in the delivery phase by free flow through two check valves. Counterbalance valves are pilot operated valves. Powering the line on the opposite side to the load, the pilot line is operated and manages the partial opening of the descent line to allow movement control even in the presence of gravitational loads and avoiding the cavitation phenomenon. Thanks to a reduction ratio between the load line and the hydraulic pilot line (pilot ratio), the pressure required to open the valves is lower than the setting pressure. The  double counterbalance valve can also perform the function of protecting the hydraulic system and the mechanical structure connected to it, acting as a shock-proof valve when pressure peaks occur due to excessive loads or accidental impacts. This function is only possible if the return line on the distributor is connected to the drain. The  is a semi-compensated counterbalance valve: the setting of the valve is not affected by any residual pressure on the return lines, counter-pressures which instead increase the pilot pressure required to open the valve. This type of valve is therefore suitable for installation in systems that include distributors with closed-center sliders, with uses closed in neutral.

The key feature for supporting the load is the hydraulic seal. To guarantee the best performance in terms of sealing, BOST pays particular attention to the realization of the components, from their construction in high-strength, hardened and grinded steel, to the dimensional and geometric verification, as well as to the testing of the assembled valve. The  counterbalance valves are parts in body valves: all the components are housed inside a hydraulic manifold, a solution that allows managing high flow rates while keeping the overall dimensions down. All manifolds are made of steel, this allows the BOST counterbalance valves to work with pressures up to 350 bar (5075 PSI) and guarantees a high resistance to wear to the benefit of the valve's useful life. For an adequate resistance to the action of corrosive agents, valve body and external components are not subject to zinc plating treatment. The valve body is leveled on all six surfaces for better treatment efficiency. For applications exposed to particularly aggressive corrosive agents (eg marine applications) the zinc-nickel treatment is available on request.  valves are available in sizes from BSPP 1/4 "to BSPP 1/2" for working capacities up to 60 lpm (15,9 gpm). Furthermore, various setting ranges and different piloting ratios are available to better adapt to all types of applications. For optimal operation it is advisable to calibrate the counterbalance valve at a value 30% higher than the maximum work load.