MOOG 744 Series Servo Valves

The 744 Series Servovalve is a two-stage design which flows up to a maximum

of 70 gpm at 1000 psi valve drop.The output stage is a closed center, four-way,

sliding spool.The pilot stage is a double-nozzle and flapper, driven by a double

air gap, dry torque motor.The valve design is simple and rugged for dependable,

long life operation.

Specific design features include a first stage field replaceable filter,

an internal null adjust which acts as an electrical failsafe, and a second stage

failsafe in the event of a loss of hydraulic supply pressure.

The valves are FM approved for non hazardous locations and are

primarily used on steam turbine applications.

SPECIFICATIONS

Fluid Supply: 744 Series Servovalves are intended to operate with constant

supply pressure.

Supply Pressure:

Minimum: 500 psi (35 bar)

Maximum:2000 psi (140 bar)

Proof Pressure:

150% of supply pressure at P port

100% of supply pressure at R port

Fluid:

Compatible with common hydraulic fluids. Recommended viscosity range:

60-450 SUS @ 100˚F (10-97 cSt @ 38˚C)

Cleanliness Level:

ISO DIS 4406 code 16/13 max.

14/11 recommended

Operating Temperature:-40˚F (-40˚C)

(maximum fluid viscosity: 6000 SUS)

Maximum:+185°F (+85°C)

Rated Flow Tolerance: +10%

Hysteresis: < 3%

Threshold: < 0.3%

Null Shift: with supply pressure

1000 psi change: < 2%

Frequency Response:

Typical response characteristics

are shown in Figures 1 and 2.

Step Response:

Typical transient responses are shown in Figure 3.The straight line portion

of a response represents saturation flow from the pilot stage which will

increase with higher supply pressures.