INTRODUCTION TO ELECTRONIC INSTRUMENTATION Chapter 11 INTC 1305 – 01 CONTROL VALVES AND REGULATORS Vern Wilson

PREVIEW of CHAPTER 10 Defining controller terms Bumpless transfer Switching from Auto to Manual Operating various loops Describing loops from drawings Various final control elements

PREVIEW OF CHAPTER 11 Valve description Fail open / close Purpose of actuators Gauge functions – 3 pressure gauges Troubleshooting Reverse the operating situation Globe, three way and butterfly valves Intro to P&ID’s and PFD

INTRODUCTION Final control element is the last device in the loop Accepts the manipulated PV info Control valve is most common There are a variety of actuators Instrument air is commonly used – regulated, clean and dry

LOOP Transmitter Input Signal Conditioner SP - Comparator Process Determine Amount  Determine Direction Send Signal Final Control Element

The Control Valve Control valves provide a differential pressure across valve Regulate the flow of fluids May open to add more or close to add less Control valves have actuators The actuator changes the controller signal into a linear or rotary motion The motion opens or closes the valve

Fisher Pg222

IDENTIFY ALL PARTS Diaphragm Spring Transducer Bonnet Body Plug Seat Packing Controller

FAILURE CONDITON If power or air failure – move to a safe position Fail open, closed or last Valves without springs fail in last position Solenoids and air tanks can be used in emergency to return valve to last point Indicated on P&ID by FC

CONTROLLER

ACTUATORS Responds to an applied instrument signal Consider safety in design Either DIRECT acting or REVERSE acting Direct – pressure extends the stem – means stem goes down to close Reverse – pressure retracts stem – stem pulled up to close Look at ID plate

PNEUMATIC DRIVEN Two main types: ◦ Spring and Diaphragm ◦ Piston Type Most Common: ◦ Spring and Diaphragm ◦ Single Diaphragm ◦ Diaphragm Plate ◦ Stem ◦ Low cost ◦ High mechanical advantage ◦ Provides a mechanical fail safe

PISTON TYPE Single or double

POSITIONERS Makes valve position match the controller output

VALVES Globe Three way Butterfly Ball

REGULATORS Self actuating device to control pressures