Pilot Controlled Proportional Pressure Relief Valve
Pilot controlled valves are used for applications involving higher How rates.
The valve consists of the pilot valve (1) with proportional solenoid (2), optionally with integrated max. pressure safety control (3) and main valve (4) with main spool (5).
The basic function corresponds to that of the “normal” pilot controlled pressure relief valve. The difference lies in the pilot control section. In this case, the compression spring has been replaced by the proportional solenoid. II is a “force-controlled” proportional solenoid A proportional lorce acting on the pilot poppet (6) therefore corresponds to a certain current, specified by the electronic control. A higher input current signifies a greater solenoid force and therefore higher pressure setting; a lower input current signifies a lower pressure setting. The pressure applied by the system (port A) acts on the main spool (5). At the same time, the system pressure is applied to the spnng-loaded side of the main spool (11) via the pilot line (10) equipped with the orifices (7,8,9). This system pressure acts on the pilot poppet (6) via the orifice (12) against the force of the proportional solenoid (2). The pilot poppet (6) opens when the system pressure increases above the set value corresponding to the solenoid force. The pilot oil can flow to the tank via the port Y (13). It should be noted that flow from port Y is always at zero pressure.
Due to the orifice combination in the pilot control line, a pressure drop now occurs at the main spool (5) such that it is raised from the seat and opens the connection from A to 0 (pump – tank).
To safeguard the system against impermissibly high currents at the proportional solenoid (2) which would inevitably result in impermissibly high pressures, a spnng-loaded pressure relief valve can be installed as an additional option in the form of a max. pressure safety control (3). This valve can also be used to safeguard the pump.
When setting the pressure for the max. pressure safety control, a certain setting clearance with respect to the max pressure setting must be maintained at the proportional solenoid to ensure that it really only responds at pressure peaks.
As a reference value, this “safety range” should be approx. 10 % of the max. operating pressure.
Categories: Hydraulic Servo | Tags: Pilot Controlled, Pressure Relief Valve | Leave a comment