Calculation 2 (Maximum allowable stem torque in round section)
Where Mc = Max allowable torque on rectangular section area, Nm B= (2a) Rectangular section length, mm h= (2b) Rectangular section width, mm
Calculation 3B (Maximum allowable stem torque in Circular section with opposite flattened side)
Valve MA! " Min (MC#$ MC2$ MC3$ MC%)
Vale M!"# shall be the lowest alue maximum allowable torque in drie train com$onent i%e M&', M&2, M& M&* ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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/ome 5 6ntroduction 5 Maximum !llowable "tem #orque (M!"#)
Maximum Allowable tem !orque (MA!) ' &omment
MA! (Maximum Allowable tem !orque) We 3now ball ales (rotar1 ales) are used as 7"8Vs-B8Vs in critical serices li3e shutdown, isolation and blow down a$$lication%
!s an engineer we alwa1s ensure reliabilit1 and integrit1 o actuator and its com$onents%
/oweer as ar as stem com$onents are concerned we either gie little attention to mechanical integrit1 o stem or sometimes we leae it to ale endor and assume 9"tem design is suicient enough to withstand actuator torque:% !lwa1s it is not true, "tems do ail;;; 6 stem 3e1 o an 7"8V is ailed 6t will not close when there is a close command and this ma1 lead to disastrous situation
MA!& 'efinition its importance 6t is maximum allowable torque a stem o a quarter turn ale can be sub?ected to without mechanical ailure% 7ngineering unit m
MA! value& 'efinition its importance
#his is ale manuactures res$onsibilit1 to calculate and $roide ale M!"# during engineering stage and ensure torque deliered b1 actuator is alwa1s less than the ale M!"#% 8uring oer stage ale M!"# urnished in $erormance table shall be considered as basic alue% 8uring engineering stage ideall1 +* wee3s ater 0<, Vale manuacture must submit Vale M!"# calculation same shall be reiewed and a$$roed b1 res$onsible engineer% Requirement o ale M!"# calculation shall be indicated in "8R@ #o stud1 the conce$t o M!"#, irst we need to 3now ew o the ale internals and the stresses deelo$ed during the ale o$eration%
'rive train its component 'rive !rain& 8einition as $er !06 A8 9!ll $arts o a ale drie between the o$erator and obturator (Ball -8isc), including obturator but excluding the o$erator% 'rive !rain components in a ball ale are
'% "olid round stem 2% "tem 3e1 e1s are used to transmit torque rom actuator to stem % Ball "tem ?oint (there are two t1$es o Ball "tem ?oint) a) Ball stem ?oint with dowel $ins C #1$e ! b) Ball stem spliced +oint Crectangular section o stem its into matching grooe in the Ball+ #1$e B
Ball valve desi,n - .ound (solid) bar tem with Ball connection usin, drive / dowel pin (!0pe A)
Ball ale design
Round (solid) bar "tem with Ball connection using drie - dowel $in (#1$e !)
Ball ale design #1$e B Ball valve desi,n - .ound (solid) bar tem with rectan,ular cross section at the end of stem for connection with Ball pliced +oint (!0pe B)
Actuator Couplin,
!ctuator &ou$ling
tresses in different drive train tem components are sub+ect to followin, t0pes of stress when operatin, torque is applied b0 an actuator to achieve desired operation (openin, / closin, /runnin,)
"tem+ torsional shear stress "tem 3e1 C torsional shear stressD bearing stress 8owel -drie $in Eoint or s$liced ?oint+ torsional shear stressD bearing stress tem under !orsional shear stress
"tem under #orsional shear stress
1e0 under shear stress
e1 under shear stress 1e0 under Bearin, tress
4orces are generated at the contact surace between the member and the connecting element% &onsequentl1 stresses are $roduced on the common contact surace (bearing surace)%
e1 under Bearing "tress Bearing "tress = Resultant orce at the contact surace
0ro?ected !rea o the contact surace normal to the resultant orce
Valve torque calculation& !ssum$tion or the calculation a) Ball ale with solid circular stem connection to ball b1 dowel $ins C (#1$e !)% b) Ball ale with solid circular stem rectangular cross+section at the end o stem or connection to ball+(#1$e B) (Vale - !ctuator mounting brac3et design 6"< F2'' and stress calculation Not coered in this $resentation)% c) #his guide is a$$licable to trunnion mounted ball ales onl1% d) #his guide is limited to maximum allowed torque calculation or ale stem its com$onents onl1% e)#he torsional and shear stress limits used or calculation o maximum allowable torques are based on !"M7 code "ection V666, 8i2, 0art !8+'2 and same is in line with section G%2H%2 (!llowable stresses) o !06 A8% ) Iield strength (I")+ 9 #/7 !B6@6#I <4 M7#!@ #< #<@7R!#7 #/7 "#R7"" W6#/
ASME code Section VIII, Div2, Part AD-132
!"M7 code "ection V666, 8i2, 0art !8+'2 API6D /ISO 14313 De!i"n !#eci$ication $or %a vave!) 'e$erence
Calculation for tem desi,n with Ball +oint usin, .ectan,ular / Circular cross section
Calculation #A (Maximum allowable stem torque with # 8e0 )
Basis .oar8:s formula 24 (!able ##)
Calculation #B (Maximum allowable stem torque with 2 8e0)
!his portion of calculation can be alternativel0 done based on ;olar movement of inertia or an0 other method$ same needs to be reviewed case b0 case basis Calculation 2 (Maximum allowable stem torque in round section)
Where Mc = Max allowable torque on rectangular section area, Nm B= (2a) Rectangular section length, mm h= (2b) Rectangular section width, mm Calculation 3B (Maximum allowable stem torque in Circular section with opposite flattened side)
Calculation % (Maximum allowable torque on tem 8e0s)
Where, a = width 3e1 @ = length 3e1 n = number 3e1 r = stem radius b = grooe 3e1
Vale M!"# shall be the lowest alue maximum allowable torque in drie train com$onent i%e M&', M&2, M& M&*
Calculation for tem desi,n with Ball +oint usin, 'owel pins
Calculation 6& (Maximum allowable torque at dowels)
Where != 8owel cross section area, mm2 cd=center to center distance between dowels , mm d= dowel diameter, mm I"= Iield strength o dowel M<&, N-mm2 Calculation 9& (pecific loads at dowels)
"@= Mt - (cd-2)-'HHHO Calculation >& (pecific pressure on dowels)
"0d = ("@-(dL@d-2))-NsO "0dP I" o dowels Where Mt = Max actuator out$ut torque, Nm "@= "$eciic loads on dowel, N ?d max = maximum allowed stress on dowel , N-mm2
"0d= "$eciic $ressure on dowel, N-mm2, Bearing stress on dowel Ns= Number o dowels d= dowel diameter, mm @d= dowel length, mm I"= Iield strength o dowel M<&, N-mm2 Who will $roide M!"# alue> #his is ale manuactures res$onsibilit1 to calculate and $roide ale M!"# during engineering stage and ensure torque deliered b1 actuator is alwa1s less than the ale M!"#% What stage we should get M!"# alue>
8uring oer stage ale M!"# urnished in $erormance table shall be considered as basic alue% 8uring engineering stage ideall1 +* wee3s ater 0<, Vale manuacture must submit Vale M!"# calculation same shall be reiewed and a$$roed b1 res$onsible engineer% Requirement o ale M!"# calculation shall be indicated in "8R@
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