Binding vs Free Movement Diagnosis Tree

Why this matters

When something that should move freely drags, sticks, or jams, the failure could be mechanical (the part itself), electrical (the driver), or load (something fighting the motion). Techs waste hours replacing motors that were never bad because the real problem was a binding shaft. This tree separates "the thing is physically stuck" from "the thing is fine but not getting power or is overloaded," which sends you down completely different repair paths. It applies to any moving member: a damper, valve, actuator arm, door, pump shaft, or gear drive across every trade.

Start here: remove the power and feel it

The single most important test costs nothing. Safely disconnect the driving force (motor, actuator, air, or hand crank) and move the part by hand through its full travel.

• Moves freely and smoothly by hand: the mechanism is good. Your fault is electrical, pneumatic, hydraulic, or a control issue. Stop chasing the mechanics.
• Stiff, catches, or jams by hand: the mechanism is binding. Continue down the mechanical path below.
• Moves but with one tight spot: localized binding (a bent shaft, a bad bearing, debris). Note where in the travel it tightens; that location is your clue.

If it is free by hand but will not move powered

The mechanism is fine, so the problem is the driver or its supply.

• No motion at all: confirm the driver is getting its input (voltage at the motor, air at the actuator, signal at the control). No input means trace upstream. Input present but no motion means a failed driver.
• Hums or strains but does not turn: an electric motor humming without turning is often a failed start capacitor, a single-phasing supply, or a stalled rotor under a load it cannot break free. The mechanism passed the hand test, so look at the start components and the supply.
• Moves weakly or slowly: low supply voltage, weak air pressure, or a tired driver. Measure the supply at the device, not at the panel.

If it binds by hand: find where and why

Now you know it is mechanical. Work from the simplest cause out.

1. Debris or obstruction. Look first for the dumb stuff: a screw, a chip, packaging, scale, or ice jammed in the travel path. Pool and outdoor gear collects grit; appliances collect lint and food.
2. Dry or gummed lubrication. A shaft that turns stiff and gummy needs cleaning and re-lubrication, not force. See the lubrication tree.
3. Corrosion or scale. Valves and dampers seize from corrosion at the stem. A valve that will not turn may have a frozen stem, not a bad actuator.
4. Misalignment. A coupling or shaft forced out of line binds at certain rotation points. Loosen the mounts and see if it frees; if so, re-align.
5. Bent or damaged part. A bent shaft, warped damper blade, or distorted linkage binds at the same spot every cycle. Replace or straighten.
6. Bearing failure. A seized or spalled bearing locks rotation. Confirm by isolating the bearing.

The "tight spot" rule

Where in the travel it binds tells you what is wrong:

• Binds at the same point every time: something physical and fixed - a bent member, a high spot, an obstruction at that position.
• Binds everywhere, uniformly: lubrication failure, overall corrosion, or over-tight assembly.
• Binds worse when hot: thermal expansion closing a clearance, or a lubricant thinning and a part swelling. Note that this one is intermittent and only shows at operating temperature.

Do not force it

Forcing a bound mechanism with a cheater bar or by jumping the motor turns a small fix into a broken shaft, stripped gear, or burned-out driver. If the hand test says it is bound, fix the bind first. The driver is almost never the right first replacement on a true binding fault.

Decision summary

References

• OSHA lockout/tagout practice before manually moving powered equipment
• Manufacturer general maintenance guidance on actuators, valves, and dampers
• See related: Lubrication: Too Much or Too Little Decision Tree
• See related: The Control Isn't Responding Decision Tree