Valve Design, Selection,

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H HS Hr HC H 1,081 HS 1,622 Hr
?H 0,15H HC 0,5(Hr ?H)
Valve Design, Selection, Sizing, Specification.

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Slide Valves
A flat gate like member slides across the passage
to intersect the flow. The closure element
reaches from wall to wall and in the open
position is completely out of the flow path.
Particulate matter can accummulate in the closure
member guides and thus prevent tight closure.
They are best used for the on/off service, but
they may be used for flow regulation when
accuracy is not important. The gate and wedge
gate valves belong to this group.
Open
Closed
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Ball Valve Bodies
The ball valve body design must allow for the
insertion of the ball and of the seats. Bodies
may have a top entry (fig 1) or a side entry (fig
2). Split body designs can be affected by pipe
stress in relation to resistance to stress, valve
tightness and ease of operation-opening /closing
. There are one piece body designs. They have
one port with an inside diameter large enough to
accommodate the ball. Once the ball is installed
a suitable insert secures the ball and seats and
ensures correct flow path. If the valve seats
are good electrical isolators an internal
antistatic connection has to be made for valves
in flammable fluid service.
Fig 1
Fig 2
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Packing and Gasket Selection

S
Size
T
Temperature
A
Application
M
Media
P
Pressure
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Resistance Coefficients for Typical Flow Ranges
Resistance Coefficient 5.0 to 13.0 1.5 to 3.0 0.1
to 0.3 0.1 0.3 to 0.5 0.2 to 0.3 0.2 to 1.5 0.6
to 1.0 2.0 to 3.5 3.0 to 10.0 1.0
Valve Type Globe Valve-Full Bore Forged Globe
Valve - Angle Pattern Forged Gate Valve - Full
Bore Ball Valve - Full Bore Plug Valve -
Rectangular Full Bore - Circular Full
Bore Butterfly Valve (thin to thick
disc) Diaphragm Valve - Straight Through -
Weir Type Check Valve - Lift Type -
Swing Type
The flow resistance coefficient is based on water
at ambient temperature and a specific pressure
differential of 1bar. The valve is assumed fully
open.
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Valve Sizing and Selection
Virtual Head Loss ?H
Pump Head Capacity Characteristic
Valve Loss
Head
Total System Resistance
Loss across CV when fully open
System Frictional Losses
Pressure Head
PD
VD
Static Head
HRE
Qmax
Capacity Q
HRP
Ps
zD
HC

H
zs
HRP total frictional head loss in the piping HRE
total frictional head loss in equipment HC
Control Valve head loss H total head developed
by pump P pressure in the suction (s) or
discharge (D)vessels
-zs
Ps
Vs
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Incipient Cavitation Characteristics of Various
In-Line Valves
These characteristics are based on water as a
flow medium Cavitation Index C is typical for a
particular valve type. It indicates the tendency
for the valve to cavitate C(Pd - Pv )/(Pu -
Pd) Pd press 12pipe dia. down- stream the
valve seat Pu press 3pipe dia. up- stream
the valve seat Pv Vapour press of liquid