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BULLETIN 135APRIL 2002

Numbered Cascade Trim - 34699 NUMBERED CASCADE TRIM

Application

Copes-Vulcan’s Numbered Cascade Trim assemblyis used in control valves where low flow rates and high turndown requirements prevail such as in desuperheater cooling water control, fuel oil control, blowdown and chemical feed.The cascade trim can be applied when differential pressures are as high as 5000 psi (34,450 kPa) with service temperature as high as 1050°F (566°C).Exceptional tight shutoff can easily be maintained.

Function

A series of labyrinth grooves along the throttlingsurface of the plug provide a cascading effect so that the pressure drop is equally divided among the grooves, thereby reducing the seat wear that would normally be experienced if the entire pressure drop is taken across the seat. The cage guided tapered plug, in conjunction with the tapered cage bore, provides for maximum trim rangeability. The plug and cage are designed so that metal-to-metal contact is made on beveled seating surfaces and the clearance between plug and cage tapers in the labyrinth groove section is held to .001" (.0254mm) for proper cascading effect. For those applications where valve pressuredecreases with increased flow, Numbered Cascade Trim is ideal. At light loads when pressure drop is maximum, the plug is close to the seat and the cascading has optimum effect. As load increases and pressure drop decreases, the need for cascading diminishes. Since the total pressure drop is broken down intostages, erosion is held to a minimum, assuring that Numbered Cascade Trim will have a longservice life.
©SPX Valves & Controls, April 2002