The valve types 2WR are 3-stage high response valves.
They control the rate and direction of a flow and are primarily used in closed loop control circuits.
Design
They comprise of the following sub-assemblies:
- A pilot control valve (1) as a 2-stage servo directional valve (pilot)
- Low friction jet / flapper amplifier and
- Mechanical feedback of the spool position
- A main control spool (2) for flow control
- An inductive position transducer (3) whose core (4) is attached to the spool (2) of the third stage
- And integrated control electronics (5) for 2WRCE orseparate electronics for the 2WRC version.
Function
Within the integrated control electronics (OBE) the command and actual values are compared and the pilot control valve solenoids are controlled via a currrent proportional the closed loop control deviation.
The pilot control valve asumes a proportional control position and controls the flows into or from control chambers A (6) and B (7), that actuate the main spool (2) by means of the closed loop control valve until the system deviation is 0.
The stroke of the main spool is thus controlled in proportion to the command value. It must be noted herethat the flow also depends on the valve pressure drop.
Valve features
Flow can be passed through the valve from A to B or from B to A.
The poppet spool closes or opens with a command value of approx. 2 %. With smaller command values the valve‘s closed loop control circuit trys to correct the spool position and thereby presses the spool, with up to the full system pressure, onto its seat and closes the connection leak-free.
The stated switching times are only valid for the closed loop control range of the valve. With command value jumps from the seat to small opening values, additional delay times occur.
The 2 % opening point (= 0.2 V) is factory pre-set. When replacing the pilot control valve or control electronics the opening point can be calibrated by adjusting the position transducer (3) by using the 13A/F nut.
When carrying out an exchange no adjustments to the control electronics and pilot control valve (= closed loop controller, controller or control electronics), other than the zero calibration at the position controller may be carried out.
Only the filter element can be replaced on the pilot control valve (see data sheet „Servo directional valve“)
Due to the diameter differences in the seat area, the spools are not pressure balanced. To compensate for the force differences for spool „K001“ 6 %, and for spools „D001“ and „S001“ 22 % of the system pressure is required as the control pressure, and then by adding reserves for flow forces and dynamics, the recommended minimum control pressure can be obtained (see technical data).
Attention:
A loss of power at the pilot control valve results in the spool being in an undefined position (2).
| 1) |
Preferably, port B is to be connected to the actuator. |
