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In the full open position, the flow is straight through and operates as
a true venturi with inherent high flow and high pressure recovery
characteristics. The cage straddles the flow stream and supports the
ball on four inclined pads holding it on the edge of the stream. The
force holding the ball firmly against the cage is caused by the
pressure differential created by the high velocity fluid in the flow
stream, compared to the relatively static state of fluid in the valve
body. This dynamic characteristic is commonly referred to as the
Bernoulli effect. The presence of a pressure differential at full open,
and during all positions of the cage and ball, prevents suspended
particles in the stream from settling out in the body, thereby keeping
the valve clean and free of any material deposits. Also, in the full
open position, any suspended particles flowing through this venturi
configuration tend to concentrate in the center of the diverging cone
and through the orifice. This obviously helps in lessening the erosive
action of the fluid on the valve surfaces, in particular the seat face.
In
the close throttling position, the ball is supported in three-point
suspension by the two forward inclined pads on the cage and the seat
face. In the intermediate throttling position, the ball rests on the
four cage pads. The seat face acts as a load bearing surface,
permitting the ball to cam in and out of the seat. This three-point
suspension, with the ever present pressure differential, keeps the ball
in a very solid and stable condition during all positions of control,
therefore preventing the ball from spinning and/or chattering. This
same stable three-point suspension also permits extremely close control
throughout the stroke, even at minute openings of the valve, down to
only a few thousandths of an inch.
In the closed position, the
ball sits freely on a conical seating surface and is held there by the
system pressure. The line contact between the ball and the seat yields
a high unit loading for exceptionally tight closure. Due to the ball
seating with pressure, the higher the pressure, the higher the closing
or seating force. This high seating force, along with slight rotation
of the ball during the initial opening travel, results in a new seating
surface contacting the seat each time the valve is closed. Due to the
freedom of movement of the ball in the conical seating surface,
temperature changes will not affect a tight shut-off.
In the
fully-closed and locked position, a wedging surface inside the cage
applies a light mechanical load to the ball, assuring positive
shut-off. This function should only be used in low pressure or low flow
applications where there is insufficient flow to create an adequate
pressure differential. When the valve is operating with a sufficient
differential pressure across the valve, the guide pin has no function. Applications: - Abrasive slurry control
- Amine service
- Ammonia slurry control
- Attemperator spray control
- Bottom ash control valves
- Condensate drain
- Drum emergency blowdown
- Feedwater bypass
- Feedwater level control
- Feedwater re-circulation
- HP sampling valve
- Heavy oil upgrading
- Nuclear turbine bypass valves
- Pitch blending control
- Power operated relief
- Pressure reducing
- Reheat/superheat spray
- Soot blower control
- Sour water service
- Steam service
- Super critical water oxidation
- Superheater bypass
- Water/coke slurry
Industries:- Aerospace
- Petrochemical
- Pulp & Paper
- Chemical
- Pipeline
- Refining
- Government/Military test
- Power
- Steel
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