What is Cage-guided Globe Valve - Inst Tools

A more modern version of the globe valve design uses a piston-shaped plug inside a surrounding cage with ports cast or machined into it.

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These cage-guided globe valves throttle flow by uncovering more or less of the port area in the surrounding cage as the plug moves up and down. The cage also serves to guide the plug so the stem need not be subjected to lateral forces as in a stem-guided valve design.

Cage-guided Globe Valve

A photograph of a cut-away control valve shows the appearance of the cage (in this case, with the plug in the fully closed position). Note the “T”-shaped ports in the cage, through which fluid flows as the plug moves up and out of the way:

An advantage of the cage-guided design is that the valve’s flowing characteristics may be easily altered just by replacing the cage with another having different size or shape of holes.

By contrast, stem-guided and port-guided globe valves are characterized by the shape of the plug, which requires further disassembly to replace than the cage in a cage-guided globe valve.

With most cage-guided valves all that is needed to replace the cage is to separate the bonnet from the rest of the valve body, at which point the cage may be lifted out of the body and swapped with another cage.

In order to change a globe valve’s plug, you must first separate the bonnet from the rest of the body and then de-couple the plug and plug stem from the actuator stem, being careful not to disturb the packing inside of the bonnet as you do so.

After replacing a plug, the “bench-set” of the valve must be re-adjusted to ensure proper seating pressure and stroke calibration.

Cage-guided globe valves are available with both balanced and unbalanced plugs. A balanced plug has one or more ports drilled from top to bottom, allowing fluid pressure to equalize on both sides of the plug. This helps minimize the forces acting on the plug which must be overcome by the actuator:

Unbalanced plugs generate a force equal to the product of the differential pressure across the plug and the plug’s area (F = PA), which may be quite substantial in some applications.

Balanced plugs do not generate this same force because they equalize the pressure on both sides of the plug, however, they exhibit the disadvantage of one more leak path when the valve is in the fully closed position (through the balancing ports, past the piston ring, and out the cage ports):

Thus, balanced and unbalanced cage-guided globe valves exhibit similar characteristics to double ported and single-ported stem- or port-guided globe valves, and for similar reasons.

Balanced cage guided valves are easy to position, just like double-ported stem-guided and port-guided globe valves.

However, balanced cage-guided valves tend to leak more when in the shut position due to a greater number of leak paths, much the same as with double-ported stem-guided and port-guided globe valves.

Technical Specifications

SPECS Cage Guided Control Valves have large Cv value, and of excellent dynamic stability. It is suitable for heavy duty services. Only a small operation force can achieve stability control due to the balanced fluid pressure structure on plug. For those severe fluid conditions that cannot be covered by this series, please select Specs Valve multi stage type Control Valves.

Applicable Standard

Design & Manufacture Standard: IEC -

Face to Face: ISA-75.03-

End Connection: ASME B16.5, EN-1, GOST, ASME B16.25

Test Standard: IEC-4

Products Range

Size: 1 1/2"~24"

Pressure Rating: ASME CLASS 150~

Material: Carbon steel, Stainless steel, Alloy steel, Duplex stainless steel

End: Flanged (RF, RTJ), Butt Weld, Socket Weld.

Temperature Range: -196℃~550℃

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Seat Leakage: ANSI Ⅳ(0.01%) or Ⅵ(bubble-tight)

Bonnet Type: Standard, Fin-Extension, Long-Extension, Bellows, Steam Jacket

Design Features

1. The third generation of S-type smooth casting body cavity gets greater circulation ability to reduce the initial investment, as it is now with more efficient average flow velocity by improving the second generation through CFD (Computational Fluid Dynamics)

2. In accordance with ASME, valve body and the upper bonnet are pressed together by the double-head stud bolt

3. The stability of plug movement are improved due to the strong cage guide and the unique balanced sealing ring (GF TFE structure for room temperature, graphite & Graph-lock structure for high temperature), so that the vibration and mechanical noise are reduced

4. With the solid cage, valve body are protected from steam and cavitation damage. There was a S streamlined channel and this makes small loss of pressure drop, high flow, wide range of control.

Benefits

1. Compared with un-balanced single seated straight through valve, the equipped actuator can be smaller for the balanced structure plug, however, it can overcome higher pressure difference and with better price

2. The flow characteristics can be changed by different cage window shape, and this promote the parts commonality.

3. Noise can be reduced by 10dB compared with the ordinary single/double seated control valve

4. Easy and fast replacement for valve parts even when the valve body is in the pipeline, this makes maintenance easier. The valve parts of  standard cage can be easily replaced by the multi-hole cage in order to apply for different conditions, and this can ensure the out flow is within the security range to prevent cavitation and reduce the noise.

The GA Of Cage Guided Control Valve

Body part selection map

Various flow characteristics are optional

Soft seat structure

Control valve packing

Most control valves use packing boxes with the packing retained and adjusted by a flange and stud bolts. Several packing materials can be used depending on the service conditions expected and whether the application requires compliance to environmental regulations. There are 3 common packing types as follows:

PTFE V Ring Packing

Molded in V-shaped rings, packing lubrication not required.

Resistant to most known chemicals.

Recommended working temperature range:−40 to +230°C

Graphite Packing

This packing system is designed primarily for high temperature applications。

Recommended working temperature range: +230 to +450°C

Low Fugitive Emissions Live Loading

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