Proportional Valve Ignores Small Commands? Separate Deadband from Hysteresis
Small command changes may fall inside a valve deadband, while direction-dependent response may indicate hysteresis. Distinguishing them improves the diagnosis.
Original offline characteristic example; use valve-specific compensation guidance.
What is happening?
Deadband describes an input region with little or no intended response. Hysteresis means the response at a given input depends on the direction or history of approach. Valve design, electronics, fluid conditions, and wear can influence both.
Check these five things
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Read the valve characteristic and electronics configuration.
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Compare command and response using an approved test method.
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Identify the onset of response around neutral.
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Compare rising and falling command paths.
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Check temperature and load before comparing separate tests.
Worked example
In an offline characteristic plot, flow remains near zero from 0 to 8% command. At 20% command, the rising and falling traces differ. The first observation illustrates deadband; the second illustrates hysteresis. They need not share one corrective action.
Quick diagnostic reference
| Pattern | Interpretation |
|---|---|
| No response near neutral | Possible deadband |
| Different return trace | Possible hysteresis |
| Random variation | Investigate other conditions |
The mistake to avoid
Do not add arbitrary software offsets or dither settings. They can change neutral behavior and must follow valve-specific application guidance.
How to verify the fix
Compare reviewed characteristics in both directions and confirm neutral, low-speed control, and fault responses remain appropriate.
Field-work boundary: These are educational diagnostic guides. Use the exact equipment manuals and approved site procedures. Electrical testing and machinery changes belong to qualified, authorized personnel; control hazardous energy and validate affected functions before release.
Technical reference
Parker: Hydraulic valve characteristics and applications. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.