Honking

When we say a valve "honks", it means that it vibrates open and closed; the cycle is like this:

• The diaphram/piston unseats, and due to the increase in differential force caused by the "new" area, is pushed back rather quickly.
• Air pressure in the pilot volume starts to build, as the piston/diaphram moves, compressing it.
• The momentum of the diaphram/piston keeps it going past the point where the pressures on both sides of the diaphram/piston are equal.
• The higher pressure in the pilot volume now accelerates the piston/diaphram back to where it started... and you can folow the steps from #2, but with the pressure in the pilot volume dropping.

(Note the upwards trend in the valve position.)

Honking is often interpreted as a sign that you are using a pilot valve that is too small.