Testing and Validation of Hydro Turbine Shaft Seals

Lying in the heart of the UK's Lake District, James Walker's elastomer division is a specialist manufacturer of sealing solutions for static, rotary and reciprocating applications. Offering a bespoke seal design service for a range of industrial applications — including main shaft seals for hydro turbines and valves — the company has invested in the testing and analysis of sealing materials and seal design.

The 130 year-old company prides itself on its abiilty to formulate and compound its own materials, combining high-specification ingredients to create compounds with the ideal properties for specific sealing applications. This capability provides the company with control over both quality and material properties it believes are required when looking to develop high-performance, reliable sealing solutions.

Having produced a potentially suitable raw material, further testing and analysis is conducted in athe on-site, state-of-the-art materials laboratories. The current capability includes spectrometers for detailed chemical analysis, as well as tensometers for exploring a material's mechanical properties, such as torsional and tensile resistance. Tensometer tests can also be carried out within an environmental chamber, allowing the effect of temperature on mechanical properties to be studied. Andrew Douglas, laboratory manager, says that the company has long invested in analysis and testing equipment for its elastomer division, which regularly undertakes design validation and materials analysis for customers and other external third parties.

The materials testing lab is located adjacent to the applications engineering department led by Ray Clifford, applications engineering manager. Clifford explains that the company, among other tools, uses finite element analysis (FEA) to validate new seal designs. In fact, it is the ability to produce new seal designs, develop appropriate materials and then test and validate those materials and designs, all within a single site, that rests at the core of the James Walker approach, the company says. As well as making an effort to understand customer applications to develop targeted solutions, the company believes its bespoke and high-quality strategy allows it to distinguish itself in the market.

Developing new sealing solutions

With a sophisticated laboratory available to assess the mechanical and physical properties of materials and a range of analytical tools to assess design and operational characteristics, it is the application of dedicated test rig analysis and field assessment that forms a crucial third arm of the design and manufacturing process at this facility.

For example, among the company's latest seal designs is its HydroSele family of cartridge main shaft seals for Francis and Kaplan turbines.

Developed over a 15 year design, development and operational period and working under a wide variety of conditions, these cartridge seals have seen about 50 installations to date. HydroSele cartridges are custom-manufactured from modular components to suit each specific application, and the company offers full support, including installation and servicing if required.

Indeed, the company claims a HydroSele installation should have paid for itself in terms of maintenance costs, turbine downtime and improved efficiency often in less than two years. (James Walker actually has evidence of an exceptional cost savings of 800,000 euros in just 15 days at the Iren hydro station in Italy.) With a very low and controlled level of water leakage past sealing faces reducing the risk of flood damage to the plant, at four years, total investment in cash and downtime could be just one-quarter of that for an equivalent mechanical seal, James Walker says. It bases these claims on the fact that some prototype HydroSele installations are still operating 15 years after commissioning.

Given that the HydroSele design can be applied to shafts up to more than 1,000 mm and a maximum surface speed of 33 m/sec at greater than 1,000 Kpa pressure, the importance of a thorough testing program cannot be overstated. Each of the designs is assessed on a test rig at Cockermouth, where the company has explored the performance of more than 25 material combinations. It is these investigations that have enabled the company to improve the performance envelope of its products. Technical advances have resulted from the data derived from field and rig trials.

Testing sealing success

Early work to test the HydroSele design was conducted on small-diameter shafts, typically about 80 mm, and was primarily conducted to verify the sealing principle.

However, this rig did not allow sufficient knowledge to be gained regarding how the relationship between pressure and speed affected the performance of the seal due to low motor loads, meaning the tests were restricted to low pressures and speeds. Consequently, early applications for HydroSele cartridge seals were limited to those with a low pressure-velocity factor, typically turbines with a low system pressure and low to medium speed ranges.

Workers at James Walker's Cockermouth facility can manufacture shaft seals with a diameter of up to 2.3 meters. (Photo courtesy David Appleyard)

Subsequently, the testing progressed on to a dedicated rotary test rig, which confirmed the seal's ability to perform up to the rated pressure of 145 psi (1,000 Kpa) and speed of 3,937 fpm (20 m/sec). In response to a growing requirement for seals in demanding run-of-river and pumped-storage applications with higher speeds and pressures, development work focused on determining the upper performance limits of the seals. In addition, development aimed to deliver a system capable of operating and surviving through periods of spinning in air, overspeed, axial and radial shaft movements and eccentricities, the company says.

In fact, according to James Walker, previous testing produced vital data but provided limited value in terms of pushing the performance envelope. There were also a number of advantages in investing in a purpose-built rig, notably larger shaft diameter capability, higher motor power and increased pump capabilities that are better able to replicate many turbine conditions and configurations.

Seal forms used in the presses are manufacturerd from aluminium at the company's Cockermouth site. (Photo courtesy David Appleyard)

Commissioned in August 2009, the horizontal shaft configuration of the rig acts to replicate a horizontal turbine and was chosen to include the effects of gravity on the seal, as this is a much more arduous test than a vertical configuration, the company says.