Friday, April 26, 2013

Pilot valves and pneumatic amplifying relays

A plain baffle/nozzle mechanism may be made extremely sensitive by reducing the size of the
orifice. However, a problem caused by decreasing orifice size is a corresponding decrease in the
nozzle’s ability to provide increasing backpressure to fill a bellows of significant volume. In other
words, a smaller orifice will result in greater sensitivity to baffle motion, but it also limits the air flow
rate available to fill the bellows, which makes the system slower to respond. Another disadvantage of
smaller orifices is that they become more susceptible to plugging due to impurities in the compressed
An alternative technique to making the baffle/nozzle mechanism more sensitive is to amplify its
output pressure using some other pneumatic device. This is analogous to increasing the sensitivity
of a voltage-generating electrical detector by passing its output voltage signal through an electronic
amplifier. Small changes in detector output become bigger changes in amplifier output which then
causes our self-balancing system to be even more precise.

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