JIT
INDUSTRIES
Watchdog Fail-Safe Actuator Calculator
▸ Design Inputs
Input Pressure
psi (line / supply)
Required Seating Force
lbf
Stroke Length
inches (used / actuation)
Max Extra Length
inches (for optimization)
Calculate
Results — Four Configurations
Lowest cost option highlighted
Enter inputs and click Calculate
Calculation basis (matches Excel Watchdog calc)
Concentric annular air reservoir (tank tube around cylinder tube). Volume uses tank ID, cylinder OD (= bore + 2×wall), and total length = stroke + extra.
Isothermal expansion (Boyle): P
final
= P
init
× V
tank
/ (V
tank
+ V
cyl
). Fail-close force = P
final
× piston area.
P
init
= line pressure (no booster) or 2× line pressure (with 2:1 amplifier).
Only standard VA bore/tank sizes. Cylinder must also satisfy Operating Force (area × line pressure) ≥ Required Force.
FSF = 1.00. Cost = tank base (0.7 × VA cyl base) + total stroke × tank $/in (0.3 × VA) + $1000 Watchdog (no booster) or + $1500 booster.
Rod diameter taken from tank size data; female rod thread from acting cylinder bore data.