What is the Purpose of Bourdon Tube Gauge Spiral Spring?

Some bourdon tube gauges are equipped with a very small spiral spring attached to the pointer shaft:

Bourdon Tube Gauge

Bourdon Tube Gauge Spiral Spring

Now, this spring is much too weak to have any detectable effect on the span of the gauge.

In other words, it does not measurably resist the bending action of the bourdon tube, as a “range spring” would in another design of instrument.

Given its weakness, what possible purpose does this spring serve in the gauge mechanism?

Answer:

It is an “anti-backlash” spring, supplying enough torque to rid the sector/pinion gear set of any “slack” or “play,”

so that the pointer always responds to the slightest change in bourdon tube position.

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Credits: Tony R. Kuphaldt

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What is the Purpose of Bourdon Tube Gauge Spiral Spring?

 
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