The sensitivity of this pneumatic mechanism may be improved by extending the control rod and
adding a second plug/seat assembly. The resulting mechanism, with dual plugs and seats, is known
as a pneumatic pilot valve. An illustration of a pilot valve is shown here, along with its electrical
analogue :
As the control rod is moved up and down, both variable restrictions change in complementary
fashion. As one restriction opens up, the other pinches shut. The combination of two restrictions
changing in opposite direction results in a much more aggressive change in output pressure as
registered by the gauge.
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