Valve & Automation South Africa presents the features and advantages of the TRI-SHARK Throttling Trim Cartridge valve from Zwick, a valve that combines the advantages of leak-free triple-offset valves (TOVs) with high-performance control valves into a single valve solution.
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When choosing zero leakage valves for open/close functionality, triple eccentric valves, also known as triple-offset valves (TOVs), are becoming increasingly popular. This valve type provides many advantages, including zero leakage, compact design, frictionless functionality and maintenance-free operation – and all these reasons contribute to their popularity increase.
Within fixed limits, TOVs can also be used for control and/or throttling applications. To extend the range and to transform these valves into efficient, high-performance control valves, however, Zwick has further developed the triple-offset TRI-SHARK valve range.
The TRI-SHARK Throttling Trim Cartridge valve
The combination of Zwick’s Throttling Trim Cartridge and its TOV TRI-CON series to create TRI-SHARK has resulted in a very high-performance, zero leakage shut-off and triple-offset control valve. The latest design offers control performance equal to that of globe or rotary plug valves, but incorporates much better shut-off capabilities while having a much lighter weight.
This valve combination provides numerous advantages. On one hand, it includes all the advantages of triple offset valves, while on the other, it features all the special qualities of an excellent control valve. It enables one single style of valve to be used for both on/off and control applications.
The Throttling Trim Cartridge is designed to be fixed into the valve body while the valve disc pivots, enabling the flow between the disc and cartridge to be as low as possible. Furthermore, the cartridge is manufactured with multiple, optimised slots, which divide the flow and clear an exact calculated cross section while opening or closing the valve.
Equal percentage flow characteristics
With the TRI-SHARK Throttling Trim Cartridge, the valve ́s characteristic is changed to equal percentage flow, which is the preferred characteristic for the majority of flow applications. TRI-SHARK’s flow characteristic makes sure that the valve is able to provide an effective control range from 5 to 30° of opening, which is the control area where traditional high-performance butterfly valves seem to reach their limits. Typical TOVs and ordinary high performance butterfly valves have good control limits between 30 and 70° of travel. TRI-SHARK valves extend this range as a result of the characteristics of the Throttling Trim Cartridge. With respect to streamed flow, the cartridge and valve design are engineered for ideal flow in this control area.
TRI-SHARK control valves have an effective control range that extends from 1% at 5.0° of travel to 100% at 90° degrees of travel, and its equal percentage flow characteristic fits the vast majority of control loop requirements.
Low to high flow capability
The TRI-SHARK Throttling Trim Cartridge eliminates the low angle instability inherent in most quarter-turn control valves. Ordinary high performance butterfly valves exhibit poor control at angles of opening that are less than 30°, for instance. TRI-SHARK technology greatly extends the control range of quarter-turn valves to as low as 3.0° of valve opening, while also providing noise attenuation and anti-cavitation benefits.
As the TRI-SHARK disc turns within the cartridge, the flow is first controlled via the clearance between the disc edge and the solid, tapered portion of the cartridge; then through the multiple, optimised slots; and finally through the additional open area of the valve.
Anti-cavitation properties: Further advantages of TRI-SHARK valves include anti-cavitation properties. TRI-SHARK’s 25% higher incipient cavitation index allows for higher pressure drops than ordinary high performance butterfly valves, while exhibiting much less noise, cavitation and damage. Even if cavitation does occur in higher pressure drop situations, the shorter vapour jets produced by the slots will avoid ‘super cavitation’ damage that would normally be caused by larger vapour jets.
The flow is divided through the slots, which reduces cavitation because the stream bubbles occurring in the cartridge slot area are smaller because of the lower flow rate within each channel. Therefore, less energy is released when the stream bubbles implode. Furthermore, especially at small opening angles, TRI-SHARK valves are able to keep water jets concentric to the pipeline ́s centreline, thereby reducing their kinetic energy to a lower level prior to contacting the pipe wall.
Flow laboratory tests have verified that individual water jets impinge upon each other at approximately one pipe diameter downstream from the TRI-SHARK control element, thereby transferring kinetic energy to the fluid prior to contacting the pipe wall, which significantly reduces the pipe wall damage that can occur.
In addition, since the mass flow is divided into smaller streams through TRI-SHARK’s throttling slots, the sound frequency rises, with the result that sound can be absorbed more easily through the pipeline, and at a frequency in the range where the human ear notices it less – and optional resistance plates can be added for even more sound attenuation.
More control with less torque: Another important aspect of the throttling trim cartridge is that the dynamic torque is reduced by the changed pressure field. With regard to the necessary dynamic torque, this means that at critical opening angles and flow conditions, a smaller actuator requiring less power can be used.
TRI-SHARK’s dynamic torque requirements are 60% less than ordinary high-performance butterfly valves, even at high end CVs. This provides exceptional stability throughout the valve’s control range.
The valve’s triple-offset metal-to-metal valve seat requires lower breakaway torques than either high-performance butterfly or rotary plug control valves, and its extended torque reversal point allows for an expanded range of control.
Standard types and applications
TRI-SHARK valves can be supplied in standard body styles including wafer, lug and double flanged versions, in sizes up to DN900 (36-inch).
By combining Zwick’s Throttling Trim Cartridge and TOV technologies, a single valve style can accommodate on/off and control applications. This solution is the smart choice for today’s control systems’ engineers delivering on applications for chemical and synthetic fuels, oil and gas production, power generation, pulp and paper, water treatment, mining and metals, and shipbuilding.
In comparison with other control valves, TRI-SHARK offers realisable benefits with respect to acquisition costs; weight and geometrical dimensions; and leak tightness and control characteristics, especially in larger diameter piping systems.
Ultimately, this valve makes it possible for plant operators to reduce their total costs of ownership (TCO) and improve sustainability and profit margins.