Answer / lenin kumar

HhHHH



Hi my dear friend the valve action depends on the
service.If the PV increasing the valve opening also
increasing, the action is direct action.If the PV
increasing, the valve opening decreasing i.e reverse action.

For example if you used one valve to fill the tank.if the
PV increasing, you have to close the valve.i.e your valve
action is reverse to the PV value.
If you used valve in discharge line of the tank.If the PV
increasing, you have to open the valve. i.e your valve
action is direct to the PV value.
SP-PV=Error=Reverse action
PV-SP=Error=direct action

Answer / hvkkumar,mtech instrumentation

for pressure increases the % of valve opening increase in
direct action .but in case of reverse actoin pressure
increases the % of valve opening decrease.

Answer / alexpandian

Hi,

We r using direct&reverse actuion in many places:

Control vlv- By giving air, if the stem of actuator moves
down then its dircet acting actutor & if stem moves up then
it is reverse acting.

Controller-
DIRECT: If the PV is less than SV then MV will
decrease.Mainly using in vent valve application.
REVERSE; If the PV is less than SV then MV will
increase.using in normal control loops.

PV-process value SV-set value MV-manipulated value

Answer / saravanan

Direct acting valve
Air to close -- Spring to open --- Failed Open (FO)
(increasing air pressure pushes down diaphragm and extends
actuator stem)



Reverse acting valve
Air to open -- Spring to close --- Failed Close (FC)
(increasing air pressure pushes up diaphragm and retracts
actuator stem)

Answer / j arumugam

if control variable(CV) INCREASES process variable
INCREASES is called Direct acting (Gain < 0)


if control variable(CV) INCREASES process variable
DECREASES is called Reverse acting (Gain > 0)

Answer / naganaresh katta

If PV>SV then MV Increases in direct action
IF PV<SV then MV Decreases in reverse action.

Answer / www.islamqa.com

For linear motion valves

Direct acting valve:
====================
valve opens when stem is drawn out of the body

Reverse acting valve:
=====================
valve closes when stem in pushed into the body

reference:
Lessons in industrial instrumentation - version 4 - page:713


Regards,

Ahmed Sabry
Control and Instrumentation Engineer
GPC - General Petroleum Company
CELL.: 00 2 0121367310

Answer / vinayak

Hi ...

Revese action normally used in AIR Fail to Close valve.

Direct acttion normally used for Fail Open valve.

It is very important to define reverse or direct action as
per process requirement.

DIRECT ACTION :
20 MA DC = 0 % VALVE CLOSE
16 MA DC = 25 % VALVE OPEN
12 MA DC = 50 % VALVE OPEN
8 MA DC = 75 % VALVE OPEN
4 MA DC = 100 % VALVE OPEN


REVERSE ACTION :
4 MA DC = 0 % VALVE CLOSE
8 MA DC = 25 % VALVE OPEN
12 MA DC = 50 % VALVE OPEN
16 MA DC = 75 % VALVE OPEN
20 MA DC = 100 % VALVE OPEN

Answer / ashish khatana

REVERSE ACTION CV = AIR TO CLOSE = AIR FAIL TO OPEN

DIRECT ACTION CV= AIR TO OPEN =AIR AIL TO CLOSE

ALL INSTRUMENTS WORKING PRINCIPLE.

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