Although you may consider mechanical seals to be relatively small components in slurry-pumping systems, they can be the crucial bridge between failure and success. An incorrect or poor seal selection can cause major damage to the pumping system. The bottom line: If your operation wants to get the most from its slurry pumps, the choice of mechanical seals is crucial. Fluid-handling experts at Crane Engineering (Kimberly, WI, craneengineering.net) offer several tips for extending the life of these components.
— Jane Alexander, Managing Editor
As discussed in a recent blog post on craneengineering.net, increasing slurry-pump reliability starts with an understanding of the challenges involved in moving highly abrasive fluids such as manure, cement, and starch. These pumps clearly have their work cut out for them. Thus, when selecting a mechanical seal for slurry service, pay attention to these details:
Robust design characteristics. Heavy slurry usually involves a high solid content. A seal design that can withstand erosive impacts while protecting the seal faces is a must. Specially designed seals for slurry applications typically feature durable construction materials, hardened faces, and heavy-duty springs to ensure the seal faces have the correct pressure setting to seal the system.
Restriction bushings. When pumping a slurry mixture, process pressure will naturally drive the particle-filled fluid into the sealing interface, causing abrasion and accelerated wear. A restriction bushing isolates the mechanical seal from the harsh process so that the seal is mostly sealing the cleaner, cooler flush fluid.
Proper flushing. A proper flushing plan will keep abrasives away from the seal faces. Seal flushing also keeps things moving in the stuffing box to prevent solids stagnation and build-up. As with any pumping application, you should always avoid dry running conditions.
Choosing the proper seal for a slurry pump is just part of the equation. It’s also imperative to select the right pump for the job and to maintain it properly.
As with other pumping systems, poor equipment conditions caused by bad bearings, cavitation, excessive impeller loads, and misaligned shafts can lead to excessive vibration and shock to the mechanical seal. A slurry pump running under these conditions will generate more heat and more opportunity for abrasives to enter the sealing interface. MT
Lubricating Film Matters
According to Crane Engineering’s fluid-handling experts, regardless of your pumping application, a lubricating film at the sealing interface is always needed.
A film that is too thick will increase leakage and may allow particulate between the mechanical seal faces, increasing wear from abrasion. Conversely, a film that is too thin will generate heat and degrade materials. Keeping the sealing interface cool and clean will promote longer seal life.
Crane Engineering is a distributor of industrial-grade pumps, valves, filters, wastewater-treatment equipment, and other fluid-processing technology. Services include repair, corrosion-resistant coatings, and skid-system design and fabrication. For more information and instructional videos, visit craneengineering.net.