Being fed by 4.8 volts, that servo can produce an output torque = 15.27 oz-in

A direct linkage connected to ~0.3" arm will see a lineal force of:

15.27 oz x 1 inch = Linear force x 0.3 inch

Then, Linear force = 15.27 oz x 1 inch / 0.3 inch = 52.3 oz = 3.2 lb

Hang that weight from your valve until you find out how much force it needs to operate.

Double that force value and do the math in reverse to find out the minimum torque needed at an arm lenght that provides the linear movement that the valve needs without binding the servo.

Then do the math to calculate the rated torque for one inch arm, which is how servos are specified.

I have learned here in RCU that any servo smaller than standard size suffers from vibration in planes with combustion engines.
Even for electric power, always isolate your servos from the plane structure.
The electronics inside the servos are delicate regardless the output torque.