Metso Flow Control Inc.
Europe, Vanha Porvoontie 229, P.O. Box 304, FI-01301 Vantaa, Finland. Tel. +358 20 483 150. Fax +358 20 483 151
North America, 44 Bowditch Drive, P.O. Box 8044, Shrewsbury, M A 01545, USA. Tel. +1 508 852 0200. Fax +1 508 852 8172
South America, Av. Independéncia, 2500-Iporanga, 18087-101, Sorocaba-São Paulo, Brazil. Tel. +55 15 2102 9700. Fax +55 15 2102 9748
Asia Pacific, 238B Thomson Road, #17-01 Novena Square Tower B, Singapore 307685. Tel. +65 6511 1011. Fax +65 6250 0830
China, 11/F, China Youth Plaza, No.19 North Rd of East 3rd Ring Rd, Chaoyang District, Beijing 100020, China. Tel. +86 10 6566 6600. Fax +86 10 6566 2583
Middle East, Roundabout 8, Unit AB-07, P.O. Box 17175, Jebel Ali Freezone, Dubai, United Arab Emirates. Tel. +971 4 883 6974. Fax +971 4 883 6836
www.metso.com/valves
8
Jamesbury 3-Piece Ball Valves, Series 4000, Threaded End, Socket Weld, Butt Weld, Rev 2.0, Safety Manual
Series 4000 3-piece ball valve with VPVL Series actuator, equipped with solenoid valve control for safety action
Appendix 2.
Equations to calculate PFD for 1oo1 and 1oo1D final elements.
These equations correspond to IEC 61508 and ISA TR-96.05.01.
An average value of probability of failure on demand for 1oo1D architecture with diagnostics is given by the
equation
PFD
AVG
= DC * λ
D
* TI
PST
/2 + (1-DC) * λ
D
* TI
FST
/2 + λ
D
* MTTR
where
DC
is diagnostic coverage (fraction),
λ
D
is dangerous failure rate (failures / hour),
TI
FST
is full stroke test
interval (hours),
TI
PST
is partial stroke test interval (hours) and
MTTR
is mean time to repair (hours).
Diagnostic coverage provided by a typical partial stroke device is applicable to the valve, actuator, quick ex-
haust valves and volume boosters. Diagnostic coverage for a solenoid or air operated valve is not available.
The Neles ValvGuard device itself uses diagnostic coverage provided by the internal pneumatic diagnostic test,
and / or the partial stroke test.
The PFD equation for 1oo1 voting without diagnostic testing is similar to 1oo1D except that the diagnostic
coverage is equal to 0. Thus the general equation becomes:
PFD
AVG
= λ
D
* TI
FST
/2 + λ
D
* MTTR
