3.6
Steam Capacity Chart:
Note
The capacities quoted below are based on valves fitted with an external pressure
sensing pipe. Reliance on the internal pressure sensing pipe will mean that
capacities may be reduced. In the case of low downstream pressure this reduction
could be up to 30% of the valve capacity.
3.6.1
How to Use the Chart (for steam application):
Saturated Steam
A valve is required to pass 600kg/h reducing from 6 bar g to 4 bar g. Find the point
at which the curved 6 bar g upstream pressure line crosses the horizontal 4 bar g
downstream pressure line. A perpendicular dropped from this point gives the
capacities of all FMPRV41 sizes under these conditions.
Superheated steam
Because of the higher specific volume of superheated steam a correction factor
must be applied to the figure obtained from the chart above. For 55°C of
superheat the factor is 0.95 and for 100°C of superheat the factor is 0.9.
Using the example given for saturated steam, the DN40 valve would pass
1150X0.95=1092kg/hr. if the steam had 55°C superheat. It is still big enough to
pass the required load of 600kg/hr.
Upstream pressure bar g
Figure 4: FMPRV 41 Sizing (Steam application)
7
FMPRV41
