Cheap Thrust Chambers and Their Impact on Reliability

Hampton Creative

In a previous blog post, I wrote about the sad state of the horizontal pump industry and how HOSS is working to change the status quo. I also referenced what I refer to as the “race to the bottom” by our competitors. Many pump providers have focused on reducing cost, which is ultimately reflected in lower reliability. The thrust chamber is the most severely stressed component in any horizontal pumping system. This is the last place a design engineer should try to reduce cost, yet we see many configure their systems to be more competitive on bids with their lowest cost thrust chamber at the bleeding edge of the thrust rating.

To understand why a horizontal thrust chamber (HTC) is so critical to pumping system reliability, you need to understand the HTC’s critical function in pump operation. The HTC is tasked with transferring torque from the motor to the pump barrel, absorbing thrust loads generated by the pump, and securely mounting the mechanical seal that keeps pumped fluid from escaping to the environment. The HTC shaft must be rigid, minimizing deflections that can cause misalignment and seal leakage due to torsional and axial loads. The HTC bearings must be capable of handling the maximum thrust generated across the application range during the life of the pump. While this sounds simple enough, these requirements can be challenging for cheap thrust chambers.

The most common cause of thrust chamber failures, and most frequent source of horizontal pump downtime, is excessive thrust generated by a worn out pump. Horizontal pumps are ideally suited to corrosive and abrasive service, but any pump will eventually fail in severe conditions. Centrifugal pumps usually experience a gradual wearing process. Abrasion or corrosion from aggressive fluids will cause the material surfaces on internal running clearances to wear. This wearing process causes internal hydraulic forces inside the pump impellers and diffusers to change. The hydraulic force balance on the pump impellers will “shift”, as internal recirculation increases and impeller surface area changes. The resulting pump thrust from these increased hydraulic forces can be 200-300% of the original application design condition. Longevity and reliability of the pumping system depends on anticipating pump wear, and mitigating it through sufficient HTC thrust load capacity.

Designing a reliable thrust chamber is actually pretty easy. It’s not cheap, but it is easy. The proven path to reliability requires the use of a high capacity thrust bearing, eliminating the potential for metal-on-metal bearing wear, and keeping the lubricating oil cool.

HOSS has created a patented thrust chamber system that meets each of these objectives. We use a large fluid film bearing that offers three times more thrust capacity than our competitors’ standard thrust ratings. We do not use angular contact ball bearings, as these bearings are designed to fail within 18 months of full load operation (quicker when overloaded). The HOSS thrust chamber is designed for five years of continuous full load operation (longer when lightly loaded). Our fluid film bearing also eliminates the key vulnerability of all ball bearings: metal-on-metal wear. And finally, HOSS installs a lubrication cooler system on every unit. Whether the system is 25HP or 2500HP, it will have a cooler. The reason is simple. If you can maintain a stable oil temperature in all ambient temperatures, and under any load scenario, the thrust bearing is much more likely to survive worn out pumps, hot weather, frequent flow changes, and numerous other operational threats.

At HOSS, we know that downtime is the enemy. Our pumps were purchased by our customers to help them make a profit. And you can’t make a profit when the pump isn’t running. We don’t sell cheap ball bearing thrust chambers, and we haven’t designed our business model around frequent HTC replacements. The HOSS system was designed for uptime by investing in components that ensure reliability. When reliability is critical, I encourage you to choose HOSS.

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