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Forbes Marshall Pilot Operated Pressure Reducing Valve
5.11 Position in relation to other control valves
Figure 9: FMPRV41 position in relation to other control equipment
*This is a typical representation of FMPRV41 position in relation to other control
equipment.
Line or system stop valves, either remotely actuated or manually, should be installed on the
upstream side of the Forbes Marshall Pilot Operated Pressure Reducing Valve FMPRV41.
Where there is downstream control equipment, particularly temperature control valve,
ensure the control equipment is atleast 50 pipe diameters away from the FMPRV41 to
prevent pressure pulses being transmitted back causing unstable operation and premature
wear or if this is impractical an intermediate vessel can provide a similar benefit.
Where a safety valve is required to protect the process system downstream of a FMPRV41
and where a temperature control valve is also being used downstream of the FMPRV41, it is
recommended that the safety valve is fitted downstream of the temperature control valve
rather than in between the FMPRV41 and the temperature control valve. If any slight
leakage occurs this will avoid any pressure build-up causing nuisance operation of the
safety valve but provide complete protection for the downstream system.
Where valves are installed downstream of the FMPRV41 the intermediate downstream
pipework must be properly trapped to ensure no condensate can build up on the
downstream side of the FMPRV41.
