INTRODUCTION TO ELECTRONIC INSTRUMENTATION Chapter 11 INTC 1305

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

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

�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 PREVIEW OF CHAPTER 11

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

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

�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 The Control Valve

Fisher Pg 222

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

�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 FAILURE CONDITON

CONTROLLER

�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 ACTUATORS

�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 PNEUMATIC DRIVEN

�Single or double PISTON TYPE

�Makes output valve position match the controller POSITIONERS

�Globe �Three way �Butterfly �Ball VALVES

�Self actuating device to control pressures REGULATORS