🔍 Key Concepts

• Pilot-operated (pilot-controlled) regulators use a small pilot valve whose output air pressure loads the main valve diaphragm or piston. • In this type of valve, the big spring on the main valve is not used to set outlet pressure; it is used to balance or match something related to the pilot signal. • Understand the difference between system set point, manipulated variable, and pilot output (loading) pressure in a control loop.

💭 Think About

• In a pilot-operated pneumatic regulator, what actually determines the outlet (controlled) pressure: the pilot adjustment, the main valve spring, or some other element? • Look at the illustration: what does the large spring act against (diaphragm or piston), and what other force is applied there from the pilot? How do these two forces need to relate so that the valve responds correctly to the pilot signal? • In a control loop, which component sets the desired pressure set point, and which component simply follows the signal coming from that controller?

✅ Before You Answer

• Be clear which part sets the pressure set point (pilot vs. main valve spring). • Decide whether the main spring should be matched to the process variable, the manipulated variable, or the pilot loading pressure range. • Verify that your chosen option makes the main valve act as a slave device that faithfully follows the pilot output over its full operating range.