• Controls or Helps to Eliminate Cavitation Damage—Cavitrol III trim can lengthen valve service life and reduce maintenance downtime. The shape and spacing of holes in the cage wall circumference helps prevent cavitation in a properly sized valve, effectively controlling or helping to eliminate (depending upon service conditions) cavitation damage and resulting valve failure.
• Rangeability—Many special characterizations are available in Cavitrol III cages to match rangeability requirements of specific systems.
• Resistance to Erosion Damage—Standard hardened trim materials provide excellent wear resistance, resulting in long trim life. The contoured valve plug seat reduces fluid separation, helps direct fluid away from trim, and helps protect against erosion damage.
• Versatility—Available in NPS 1 to 24 globe or angle valves with weld-end or flanged-end connections.
• Easy Maintenance—Cage-type trim allows removal and inspection of parts without taking the valve body out of the pipeline. Fine particles very seldom cause the accumulation problem associated with labyrinth-type trim.
• Efficient Operation—A low inlet pressure to the final stage is maintained by the flow-down configuration and the successively larger flow area of each stage. At the third stage inlet (see figure 7), about 85% of the total pressure drop has already occurred and the vena contracta pressure remains above the liquid vapor pressure. This helps to prevent cavitation in a properly-sized valve.
• Trim Interchangeability—Cavitrol III one-stage trim is interchangeable with standard trims. Quick trim changes can be made with no additional parts, such as spacers, longer bolts, and special gaskets for valve sizes greater than NPS 1.

Cavitrol® III One-Stage Trim

The Cavitrol III one-stage trim (figures 2 and 3) can effectively eliminate cavitation damage in a properly sized and selected control valve. Each cage hole is shaped to create a small flow stream with a vena contracta pressure higher than that typically present in the flow stream of a standard cage. This higher vena contracta pressure reduces the fluid's tendency to cavitate. Each hole in a Cavitrol III one-stage cage is also designed to reduce fluid turbulence, and the holes are spaced diametrically around the cage circumference; both features dissipate fluid pressure and help to increase capacity.
Cavitrol III one-stage trim can also be used to control cavitation damage. When selected and sized for this type of service, the radius edge on the valve plug and the diametrically opposed cage holes direct the cavitating fluid flow away from metal surfaces into the valve body cavity void. In this manner, damage from cavitating fluid flow is controlled.
Service conditions of each application govern whether cavitation damage is effectively eliminated or controlled.

Cavitrol® III Two- and Three-Stage Trims

The Cavitrol III two-and three-stage cages are concentric cylinders (or stages) (figure 4) with specially-shaped orifices. The choice of cage depends on the inlet pressure and the required pressure drop. In operation, liquid passes through the orifices in each stage, undergoing a portion of the total required pressure drop. This partial pressure drop in each stage of a properly-sized valve normally prevents the liquid pressure from falling to or below its vapor pressure, eliminating the formation of vapor bubbles.
A characterized Cavitrol III two-or three-stage trim can be specified on those applications where the pressure drop across the valve decreases with increasing valve plug travel. Characterized Cavitrol III two- or three-stage trim consists of two or three stages at the beginning of valve plug travel. Then, as the valve is required to take less pressure drop, cage sections with fewer stages are used.

Note
Neither Emerson, Emerson Process Management, nor any of their affiliated entities assumes responsibility for the selection, use and maintenance of any product. Responsibility for the selection, use, and maintenance of any product remains with the purchaser and end-user.

Application Information

1. Process liquid—State particle size and type of entrained impurities, if any.
2. Specific gravity of liquid
3. Temperature and vapor pressure of liquid
4. Critical pressure
5. Range of flowing inlet pressures
6. Pressure drops

Valve Body Information

To determine what information is needed for ordering the valve body and trim, refer to the Specifications section. Review the description at the right of each specification or in the referenced tables, figures, and bulletins, and indicate the desired choice wherever a selection is to be made. Always specify the body design being ordered as selected from table 1 or 3.

Actuator and Accessory Information

Select the specific actuator and accessories from the appropriate bulletins. Typically piston actuators must be used where the required valve plug travel is greater than 102 mm (4 inches). Typically diaphragm actuators may be used for 102 mm (4 inches) or less required travel. Specify any additional ordering information as required from actuator or accessory bulletins.
If operating below minimum published Cvs (see tables 2, 3, and 4), added trim reliability may be obtained through use of low travel cutoff features available with DVC6000 Series digital valve controllers.

Available Valves

One-stage: See table 1.
Two- and three-stage Cavitrol III: See table 3.
Two- and three-stage Characterized Cavitrol III: Consult your Emerson Process Management sales office

End Connection Styles

Refer to appropriate valve bulletin

Shutoff Classification

Class IV (standard for one-stage trim only): [0.01% of valve capacity at full travel tested with air at 3.4 bar (50 psid)] per ANSI/FCI 70-2 and IEC 60534-4
Class V (standard for two- and three-stage trims, optional for one-stage trim): [5x10-12m3/sec/bar/mm of port diameter (0.0005 mL/min/psid/in) of water at service pressure drop] per ANSI/FCI 70-2 and IEC 60534-4
TSO (Tight Shutoff Trim) (optional for one-, two-, and three-stage trims): Valves with TSO trim are factory tested to a more stringent Emerson test requirement of no leakage at time of shipment using ANSI/FCI Class V procedures. Consult your Emerson Process Management sales office for additional information. See figure 6

Maximum Inlet Pressures(1)

Consistent with applicable ASME B16.34 pressure/temperature ratings as shown in tables 1 and 3 up to 232°C (450°F)

Maximum Pressure Drop(1)

One-stage: 99.3 bar (1440 psi) but do not exceed the maximum pressure and temperature for the class rating of the valve body material used
Two-stage: 149 bar (2160 psi), but do not exceed maximum allowable inlet pressure
Three-stage: 207 bar (3000 psi), but do not exceed maximum allowable inlet pressure
Pressure drops are valve size and trim stage dependent. For additional Cavitrol trim application guidelines, contact your Emerson Process Management sales office.

Construction Materials

See table 5

Temperature Capabilities(1)

One-stage: -29 to 232°C (-20 to 450°F)
Two- and three-stage: See table 5 and figure 8

Flow Characteristic

Standard Cage: Linear
Characterized Cage: Consult your Emerson Process Management sales office

Flow Direction

Flow down (in through cage openings and out through seat ring as shown in figure 3)

Flow Coefficients(2)

Values given in tables 2 and 3; also see Fisher® Catalog 12

Valve Recovery Coefficients(2)

F L of One-Stage Cage: See table 2.
F L of Two-Stage Cage: 0.98
F L of Three-Stage Cage: 0.99
These values define the maximum allowable pressure drop that is effective in producing flow as shown in the following equation:

∆Pallowable = FL [P1(flowing) - rc Pv]
Where
∆Pallowable =maximum allowable pressure drop that is effective in producing flow, bar (psi)
P1(flowing) =flowing inlet pressure, bar, absolute (psia)
rc =critical pressure ratio from Catalog 12
Pv =vapor pressure of liquid at inlet temperature, bar, absolute (psia)

Port Diameters and Circumferences

See tables 1 and 3

Maximum Valve Plug Travel

See tables 2 and 3

Minimum Seating Force

Refer to figure 5 to determine minimum seat load per unit of port circumference; multiply that value by the port circumference from table 1 or
Catalog 14

Valve Plug Stem and Yoke Boss Diameters

See tables 1, 6, and 7 and figure 9

Valve Plug Unbalance Area

See tables 1, 3, and 4

Noise Level

Use Emerson Process Management liquid noise prediction methods available in the Emerson Process Management sizing program

Options

■Cage with Special Characterization or ■Valve Plug for applications over 232°C (450°F)

Note
Neither Emerson, Emerson Process Management, nor any of their affiliated entities assumes responsibility for the selection, use and maintenance of any product. Responsibility for the selection, use, and maintenance of any product remains with the purchaser and end-user.