T riple Eccentric valves, also known as Triple-Off-Set valves (TOVs) provide advantages including zero leakage, compact design, frictionless functionality and maintenance-free operations. Within fixed limits, TOVs can also be used for control and/or throttling applications.
Zwick designed and patented the Throttling Trim Cartridge to transform TOVs into control valves as well. The revised design is equal in control performance to a globe or rotary plug valve, but incorporates better shut-off capabilities while being significantly lighter in weight. By combining the Throttling Trim Cartridge with the TOV series TRI-CON, Zwick created TRI-SHARK, a zero leakage shut-off and control, Triple-Off-Set valve.
The Throttling Trim Cartridge is designed fixed with the body while the valve’s disc pivots, enabling the flow between disc and cartridge to be as low as possible. 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 Charactristic
With the Throttling Trim Cartridge, the valve’s flow characteristic is changed to an equal percentage flow, which is the preferred inherent flow characteristic for the majority of control applications. TRI-SHARK’s flow characteristic provides an effective control range from 5 up to 30 degrees of travel. Typical TOVs and ordinary high-performance butterfly valves have good control limits between 30 and 70 degrees of travel. The Throttling Trim Cartridge and valve design, with respect to streamed flow, is engineered for ideal flow control in this area.
TRI-SHARK control valves have an effective control range that extends from 1% at 5 degrees 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. TRI-SHARK technology extends the control range of quarter-turn valves to as low as 3 degrees of valve opening, while also providing noise attenuation and anti-cavitation benefits.
As the TRI-SHARK disc turns within the Throttling Trim Cartridge, the flow is first controlled through 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.
Further advantages of TRI-SHARK valves are the 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 the damaging effects caused by larger vapour jets, referred to as “super cavitation”.
The flow is divided through the slots, which reduces cavitation because the stream bubbles occurring in the cartridge slot area are of a smaller dimension, owing to the smaller flow rate of each channel. Therefore, the energy released is less when the stream bubbles implode. TRI-SHARK valves are able to conduct water jets concentric to the pipeline´s centreline, thereby converting kinetic energy to a smaller level prior to contacting the pipe wall.
Flow laboratory tests verified how individual water jets impinge upon each other at approximately one pipe diameter downstream from the TRI-SHARK control element, thereby converting kinetic energy in the fluid prior to contacting the pipe wall. Thus, less damage at the pipe wall can occur.
As the mass flow is divided into smaller parts through TRI-SHARK’s throttling slots, the sound frequency rises, and as a result the sound can be absorbed more easily through the pipeline, and the frequency is in a region where the human ear notices it less. Optional resistance plates can be added for even more attenuation.
Another important aspect of the throttling trim cartridge is that the dynamic torque is reduced by the changed pressure field. This means that at critical opening angles and flow conditions, with regard to the necessary dynamic torque, 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 control valves, thereby providing exceptional stability throughout its control range. The Triple-Off-Set metal-to-metal 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.
It is the “smart choice” for today’s control systems engineers involved in applications such as chemical and synthetic fuels, oil and gas production, power generation, pulp and paper, water treatment, mining and metals and shipbuilding.