Decarbonisation Technology November 2025 Issue

Figure 2 Standard bearing design in the industry with graphite protection ring

Figure 4 72in TOV TRI-CON valve

Figure 3 Design of the patented Sealed Bearing

a groove in the ID of the bearing, without a compressive load, will flatten out and become quickly useless after a small number of cycles under pressure. Graphoil has no memory. It might keep some of the heavy debris from entering the bearing cavity, but it will allow the process to enter. Other manufacturers offer a dual packing set with a lantern ring sandwiched between them, in addition to a flush port with a grease fitting located on the bonnet to allow for flushing of the bearings. Certain manufacturers offer O-rings at the bottom of the bearing cavity. This design would be a good solution, but in the petrochemical market Fire-Safe designs are mandatory, and an O-ring in the bearing cavity would not be considered Fire-Safe. An example of efforts being made to address this issue is Zwick’s mechanical design, which ensures that both the inner diameter (ID) and outer diameter (OD) of the bearings are protected in compliance with Fire-Safe design criteria. The design incorporates three rings of die-form graphoil packing rings at the end of the bearing’s ID, along with three rings of the same on the OD. Both are captured by machined edges and are under a packing load, which prevents the graphoil rings from flattening out. This patented design is called the Sealed Bearing feature (see Figure 3 ). In addition to minimising the ingress of media into the bearing cavity, Zwick’s advantageous design reduces

shaft deflection and can be applied to special versions of its standard bearings. Another advantage is that any standard Zwick valve can be upgraded with the Sealed Bearing design. Beyond protecting the bearing, it serves as an additional seal to the packing and minimises fugitive emissions, making it very attractive for applications in ethylene oxide (EO) or propylene oxide (PO). The patented Sealed Bearing has been proven for more than 25 years in various applications, including butadiene, styrene, sulphur, sulphur tail gas, EO, PO, and high-viscosity applications such as thermal oil and acid gas. The Series TRI-CON is available in sizes ranging from 2 to 80in (see Figure 4 ) and pressure classes from PN 10 to PN 250 or ASME Class 150 to 1500. This valve is widely used in the energy, petrochemical, and chemical industries, as well as in specialised industries such as oxygen applications. In addition, Zwick offers its TRI-CHECK check valve for various applications, including pump protection. Where redundant shut-off is required, the company provides its Double Block and Bleed version, TRI-BLOCK, which a single body and can be operated with just one actuator.

Dave Buse and Daniel Zwick Zwick Contact: davebuse@zwick-valves.com, d.zwick@zwick-gmbh.de