Rotary Servo Valve

The hydraulic servo valve has five ports: Supply, two Control Ports, Over Board

Drain (OVBD), and Drain/Tank. With the hydraulic valve in its middle position,

both control ports are blocked. As the valve rotates, supply pressure is

connected to a control port while simultaneously connecting the drain to the other

control port. The combined action of the servo position controller and cylinder

position controller modulate the power cylinder position as necessary to match

the input demand. OVBD is permanently connected to drain and can (optionally)

be connected to the OVBD connection on Hydraulic Power Cylinder to drain any

leakage pass the primary rod seal.

A unique function of the software is a periodic, symmetrically opposed impulse

(called “Silt Buster”) which flushes silt and debris from the servo valve without

causing undue wear. At the interval and amplitude selected by the user, this

function provides a very rapid motion of the hydraulic valve, allowing any silt to

be flushed to the drain passage. This motion is followed immediately by a step of

equal amplitude in the opposite direction. The opposing symmetry of the impulse

results in no net change in fluid volume to the controlled servo valve, and thus

does not interrupt the control of the turbine. This unique function provides a

higher degree of stability, reliability, and silt resistance.

If the unit detects any diagnostic shut down condition, or if the detected

diagnostic condition prevents reliable control, or if a loss of power occurs, the

servo valve return spring forces the valve to connect the appropriate control

pressure to drain, causing the cylinder to move to the fail-safe position.