Valve Repair Takes Center Stage in Houston

Seals

Nathan Sowder, business development engineer at Parker’s O-ring division, enumerated that engineers need critical design information to make the right recommendations for seal materials, including operating temperatures and pressures, what fluids or gases are being processed, environmental conditions and whether the valve is operating in a horizontal or vertical motion.

Sowder outlined some of the options in the field of elastomers and explained the various polymers used. He compared the pros and cons of various reinforcing fillers, plasticizers, process aids and cure systems.

Typical tests run on the compounds for this field include rebound resilience, ultimate elongation (the strain at which a specimen would rupture), tensile strength (the stress required to rupture the specimen) and hardness (the resistance to penetration of an indenter.) He also offered several solutions to damage incurred during installation of o-rings.

Welding

James Vela, welding engineer at United Valve, compared traditional manual welding processes such as shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW) to semi-automatic, automatic and machine welding processes of the 21st century. He explained the variables that would determine the selection of which method is used for what process.

One of the most important factors in selecting the best welding process is heat input, Vela pointed out. This is because excessive heat input can have an adverse effect on the microstructure of a welded joint and subsequently affect the mechanical properties of the finished piece. Other important considerations when choosing which process to use in weld repair are size, diameter, material thickness, which type of weld was originally used and position. Small-diameter valves and butt joints in pipes are generally welded with manual processes, he explained. SAW and GMAW-spray transfer are limited to flat and horizontal positions.

Belleville Springs

Adding Belleville springs to gland follower studs maintains the packing load of a valve, according to George Davet, vice president/chief engineer, Solon Manufacturing Co. The best candidates for this process are valves that are: frequently cycled, air- or motor-operated, intended for use in critical applications, intended for use in difficult or potentially unsafe locations or those that have a history of packing leaks or are monitored valves.

The reason Belleville springs are useful is that a loss of packing load is one of the reasons valves leak. He demonstrated several examples of the way live-loading can be achieved.

He also compared compression between valves that do and those that do not have live loading (Figure 1).

Davet said that when choosing which springs to use, considerations include: bolt material, temperature, the environment in which the valve operates, the intended application, and cost and availability of the springs.

Horizontal Orientation

Greg Johnson, president of United Valve, explained the many challenges of properly installing, aligning and actuating valves in the horizontal position.

These include misalignment between body guides and disc guides, discs that hang up when closing, discs with “cocking and locking” problems, stems that break, seating surfaces that are damaged and stems that get scratched when actuated. Part of the problem can be sloppy guides from casting issues, poor machining, misalignment during manual fitting or limited or inept quality control.

However, Johnson pointed out that some gate valves have excellent guiding for horizontal orientation. These include nuclear valves, which have precision-machined body guides; forged pressure-seal valves, which have welded-in, precision-machined body guides; and many of the large American Water Works Association valves, which have rollers and guides for smooth horizontal operation.

It’s important for repair shops to check the guides very carefully for proper engagement and minimum slop, Johnson said. He stressed that newer and non-U.S.-manufactured valves need more scrutiny. He also said it’s important to determine from the valve owner if horizontal orientation is a possibility.

“If in doubt, hard-face the disc guides and take extra care when actuating,” Johnson said.

Stay tuned to VALVEMagazine.com in the next few weeks for more additional coverage of this Valve Repair Council event.

Kate Kunkel is senior editor of VALVE Magazine.