Application of MOOG G77x servo valve

Flatness: 0.05 mm/100 mm (0.002 in/3.94 in)

Surface roughness: better than Ra 0.8 μ m (0.000032 in)

Non compliant surfaces can cause valve body deformation, seal failure, or valve core jamming.

2. Oil ports and seals

G771: Port diameter 4.85 mm, using O-ring (section 1.78 mm, inner diameter 6.07 mm, size -010)

G772: Port diameter 6.60 mm, O-ring inner diameter 9.24 mm (dimension-012)

G773: Port diameter 7.92 mm, O-ring inner diameter 10.82 mm (dimension-013)

Material recommendation: Fluorocarbon rubber (FKM, Viton) ®  B）90 Shore， Compatible with mineral oil and various synthetic oils.

3. Electrical connection

Standard connector: MS3106F14S-2S (4-pin), Moog P/N：-49054F0145002S

The coil leads are all connected to the connector and can be configured externally as series, parallel, or differential connections.

For explosion-proof environments, intrinsically safe valves and corresponding safety barriers should be used.

4. Zero adjustment steps

Disconnect the electrical signal (zero current).

Use a 3/8-inch angled wrench to loosen the self-locking screw sleeve (usually less than half a turn), do not remove it.

Use a 3/32 inch hex wrench to rotate the zero pin clockwise to provide flow output to port B, and counterclockwise to do the opposite.

After reaching the required zero bias flow rate, tighten the self-locking screw again to a torque of 57 in · lbs (approximately 6.4 N · m).

Matching electrical parameters with coils

G77x offers multiple coil specifications to accommodate different servo amplifier outputs. The coil is wound with copper wire, and the resistance changes significantly with temperature (the temperature coefficient of copper resistance is about 0.4%/℃). Therefore, it is recommended to use a current feedback servo amplifier (high output impedance) to eliminate the influence of coil resistance changes on valve characteristics.

Standard coil parameters (at 25 ℃):

Recommended ordering code: rated current (single coil), coil resistance (Ω/coil), power consumption (single coil)

H ±15 mA 2060 0.023 W

L ±40 mA 800 0.128 W

Inductance value (measured at 50Hz, under pressure conditions):

H coil: single coil 0.72 H, series 2.2 H, parallel 0.59 H

L coil: single coil 0.22 H, series 0.66 H, parallel 0.18 H

Wiring configuration and valve opening direction:

Series connection: Coil B is connected to coil C, and A+and D - → currents flow through both coils, generating a large inductance and suitable for high impedance amplifiers.

Parallel connection: A is connected to C, B is connected to D, A is connected to C+, B is connected to D - → The total resistance is half of a single coil, suitable for low-voltage driving.

Single coil: Only use A+/B - or C+/D -, with the other pair of coils suspended.

Valve opening phase: When connected in series or parallel to allow flow from port B, the corresponding input current polarity is as shown above.

Engineering suggestion:

Priority should be given to valves with ± 40 mA (L coil), as they have lower resistance, better noise resistance, and most industrial servo amplifiers can be directly driven.

If using an old-fashioned voltage type amplifier, it is necessary to ensure that the amplifier has sufficient output voltage to overcome the influence of coil inductance.

Performance characteristics and dynamic response

The core advantage of the G77x series lies in its high dynamics and low nonlinearity, which are crucial for closed-loop position/pressure control systems.

Key static indicators:

Threshold: ≤ 0.5% rated signal. The minimum input signal required to initiate the movement of the valve core reflects the friction and viscosity characteristics of the valve. A low threshold means higher resolution.

Hysteresis: ≤ 3.0% rated signal. The maximum difference between forward and reverse outputs under the same input signal. Low hysteresis loop helps improve repeatability accuracy.

Zero shift (Δ T=38 ℃): ≤ 2.0% rated signal. The impact of temperature changes on the zero position is crucial for a wide temperature working environment.

Dynamic characteristics:

Step response time (0-100% travel):

4 L/min, 10 L/min, 19 L/min specifications: typical value 4 ms

38 L/min specification: 10 ms

57 L/min specification: 17 ms

This indicates that small flow valves have extremely high response speeds and are suitable for high-frequency applications.

Frequency response (can be estimated from the performance curve): At ± 40% of the rated signal, a -3dB bandwidth can typically reach over 100Hz (depending on the model).

Traffic calculation:

Due to the sharp edge throttling of the valve port, the flow rate is proportional to the square root of the pressure drop:

Q=QN×ΔpΔpN

Q=Q N× Δp N Δp

Among them, Q_n is the rated flow rate (corresponding to pressure drop Δ p_N=35 bar/valve port), and Δ p is the actual working pressure drop. For example, if a valve rated at 10 L/min is subjected to a pressure drop of 70 bar/port, the actual flow rate is approximately 14.1 L/min (70/35).

Valve core zero cutting options:

Standard Axis Cut: default option, used for most position control systems.

Open Center Spool: Used in hydraulic motor circuits, allowing for a small amount of leakage to cause the motor to coast.