8/19/2019 Valve Control

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V VALVE CONTROL SYSTEM

The position of steam supply valves of the turbine is controlled by a piston cylinder arrangement called oil-driven engine in which theEH oil enters into the cylinder of oil driven engine beneath the

piston. The hydraulic force of EH-oil on the position is balanced by strong cylindrical spring on the upper part of the piston. Thesteam of the piston is connected with the he level of the steamsupply valves.Piston moves up or down due to the unbalanced force of hydraulicforce of EH-oil and elastic force of spring to open or close thesteam supply valve respectively.There are two kinds of oil driven engine;1. ne is to control the main steam governor valve!s proportional

piston.". ther is to control the man steam stop valve# reheat mainsteam valve and reheat governor valve which are wide open or cutoff valves.Oil Driven engine for Main Steam Stop ValveThe main steam stop valve is either fully open or fully close by themovement of oil driven engine whose steam is connected with thelevel of main steam stop valve.$hen hydraulic force of high pressure EH oil at the bottom head of the piston of oil-driven engine is greater that the spraying force atthe upper part of the piston# the unbalanced for tends to move the

piston upward resulting the opening of steam valve.

$hen the hydraulic force of EH oil is less than that of the sprayingforce than the piston moves down which closes the steam valve.Main Components1. il driven engine". flooding oil valve.%. &solation valve'. (heck valve.). Electro magnetic valve.*ig on page %Isolation valve&solation valve is used for cut off the high pressure oil supply to theoil driven engine during maintenance while the EH-oil pumps are inservice.Chec Valvethe check valve installed on the oil scavenger pipe prevents the high

pressure oil back flow from oil scavenger header of the oil driven

engine during on line maintenance.the check valve installed on the emergency trip header prevents thehigh pressure oil back flow from emergency trip header duringtesting and maintenance on any one of the oil driven engine andkeeps the pressure in emergency trip header.!loo"ing valve*looding valve installed on oil driven engine.&t is connected with the oil flowing line of the oil driven engine.Emergency trip deader presser is made e+ual to that of the high

pressure oil ma,imum pressure by ad usting the pressure settingstem.The core of the pressure setting stem covers the oil hole with theforce provided by the spring.The slide valve acted by the spring hydraulic force makes if move

down ward and prevent the oil from oil driven engine toleak off to the return line.

$hen the oil in emergency trip header is relived then there is a pressure drop at the upper part of the slide valve and hydraulic pressure of high pressure oil over comes the spring force acted uponthe slide valve. this moves the slide valve upward to let the workingoil flow to the oil scavenging tank through return line.

ain steam stop valve can also be closed by manually operatingflooding valve.Electro Magnetic valve*or remote closing of main steam stop valve to perform periodictesting in valve steam test.Chec Valvesa/ (heck valve installed on the oil scavenger pipe to prevent the

back of low of oil from oil scavenging header to the oil drivenengine during maintenance.

b/ (heck valve installed on the emergency trip header to preventdepressuri0ation of emergency trip header during maintenance of one of the oil driven engine while the others are working normally.!loo"ing oil valve• *looding oil valve installed between the oil driven engine and

oil scavenging line.• during normal operation pressure selecting ad ust the pressureto the ma,. value i.e.# emergency trip oil header pressure is e+ual tothe line pressure oil pressure.•

The core of the slide valve covers the oil hole with the springforce and prevent the oil from oil driven engine to flow to the oilscavenging line.• $hen emergency trip oil relieved the oil hole covered by thecore is open by upward movement of slide valve and drain theworking oil from oil drain engine.Electro magnetic valve• This valve is used for remote closing of main steam stop valve

to perform periodic valve steam testingInterr#pti$le g#i"e valve• &nterruptible guide valve is closed by the high pressure oil• $hen this valve opens reduces the steam force on the mainsteam stop valve shaft by releasing some amount of steam to theatmosphere/ to close at minimum resis tanceDRIVEN EN%INE !OR %OVERNOR VALVE

il driven engine for governor valve performing proportional

position controlMain componentsa/ il driven engine

b/ EH converter EH servo valve/c/ *looding oil valved/ 234T 2inear variable differential transformer/e/ &solation valvef/ il filter g/ one-way valve.• $hen the control system of oil driven engine for governor

valve is in service automatically# the control signal from thecomputer will operate the valve.

• The high pressure oil EH- il/ inters the oil driven engine viaisolation valve# oil filter and EH converter respectively.• The rotation rate of turbine or the given valve of load andevery feedback signal of turbine will send out a signal operates theEH-convector.VALVE CONTROL SYSTEMIM&ORTANT &OINTS '

ain steam valve# 5eheat steam valve and the reheat governor valveare either full open or full close# so they don!t need the EHconverter and the 234T 2inear 3ariation 4ifferential Transducer/like for 6overnor valve.Emergency trip control block installed on the right side of the front

bearing pedestal consists of two electromagnetic valves for theoverspeed protection control P(/# four electromagnetic valves for the accident safety trip 78T/ and two check valves. see fig'/

ain steam valve and reheat steam valve are attached with 78Theader.6overnor valve and reheat governor valve are attached with P(header. &nfect this is the difference between reheat steam valve andreheat governor valve.

&f 78T header is depressuri0ed then P( header will also bedepressuri0ed due to the two check valves mentioned above# butdue to these two check valves reverse case do not accrue.Two P( electromagnetic valves receives signal from 4EH. $henthe load increase to more than %9: and rotation rate reaches

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