Optimised performances and integration of the greatest number of functions are the objectives planned and achieved through the development of the HPV valves, a range of the latest generation of proportional directional valves that perform two simultaneous functions: directional control and flow control that is unaffected by load variations.
Their operation is based on the proportional hydraulic principle, i.e. keeping pressure loss constant through a variable section. The HPV spool can assume an infinite number of positions making the crossing areas infinitely variable, thus regulating the flow in relation to the pressure difference (Δp) throughout the entire operating range. By means of logical selection, an LS signal (feedback) is taken from the highest pressure ports and it’s sent to the flow-pressure regulator in the inlet section (if the circuit operates with a fixed displacement pump) or directly to the Load Sensing pump (for a closed centre circuit). As long as the circuit senses the Δp, the valve will maintain its proportionality properties.
Instead, if Δp tends to decrease, for example if actuator flow demand exceeds the overall pump flow (multiple simultaneous operations), the flow to the ports will be completely random, and in any case will tend to flow toward the actuators which will work at the lowest pressure values. The baric compensation provided by the two-way pressure compensators installed on each element, allows multiple operations to be performed at the same time without reciprocal effects. On the other hand, operating at the same time elements without compensators, the flows will vary in relation to the work pressure values.
Technical features
The main hydraulic features of the HPV valves are summarised below:
• Flow control (metering) is independent from load, therefore the flow provided at the ports does not change with a variation in work pressure of the utilities they control.
• The flow of each function is independent from the simultaneous work pressures, thus allowing simultaneous operations to be carried out without reciprocal effects.
• Electrical unloading of the LsA and LsB signals on each element.
• Excellent flow control characteristics, without dead bands.
• Symmetrical distribution, that allows the position of the manual control to be reversed with all servocontrols.
• Precise and safe remote controls (hydraulic, proportional electrohydraulic) that are easy to install.
• Funzionamento sia con pompe a cilindrata fissa che a cilindrata variabile con regolatore load sensing.
• Operation with both fixed displacement and variable displacement pumps with Load Sensing regulator.
• Remote control of operating pressure of each port.
• Internal pilot line supply.
• Externally fed hydraulic manipulators.
• Possibility of lowering the stand-by pressure of the pump (only with the open centre version).
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