Wondering if you should replace or repair?
Whether you’ve been affected by changing demands or you’ve been battling a bad actor since commissioning, Hydro understand that you can sometimes be stuck with equipment that isn’t meeting your expectations.
With hundreds of combined cycle repairs under they belt, Hydro’s engineered upgrades provide improvements over the original design. Why replace something that still has years of useful life?
Their strict tolerances and assembly procedures are often more stringent than those originally provided by the OEM, resulting in a more rugged piece of equipment.
Why buy new when you can make your existing assets better than new?
KSB Ring Section HGC Series Pump
Hydro has successfully developed several targeted solutions to improve the reliability and efficiency of KSB segmental ring boiler feed pumps. These improvements make the design of these pumps more robust, reducing vibration, increasing efficiency, and significantly extending MTBF.
Rotor Centralization
The relationship and geometry of the impeller to the diffuser are extremely important in high energy multistage pumps. This observation is especially true in ring section pumps, where the design is less rugged than a traditional multistage barrel pump. When properly designed, the geometry at the discharge area of the impeller, commonly referred to as Gap A and Overlap, counteracts the negative
effects of hydraulic instability. When left unchecked, this instability can be very detrimental to pump health.
The geometry at the impeller-to-diffuser interface has both a radial and axial component. Because it has an axial component, it is rendered ineffective when the impeller is offset within the diffuser. In most cases, the OEM or subsequent refurbishers do not perform the due diligence A KSB HGC series pump in Hydro’s shop necessary to center each impeller in its respective diffuser.
This non-centralization results in turbulent flow, which in turn causes high vibration, increased stress on all components, and reduced efficiency.
In Hydro’s drive to increase pump reliability and extend pump life, they have pioneered a process they refer to as Roto Centralization. Hydro performs a detailed dimensional analysis to establish the centerline relationship of the pump’s stationary and rotating components. The rotor is then modified to ensure centerline compatibility at each stage of the pump. While most service centers do not perform the work necessary to achieve axial rotor centralization, Hydro has made this process standard for all multistage diffuser pumps.
Redesign of Balance Disc
The balance device balances the axial thrust of the pump during operation, significantly reducing the load on the thrust bearing. A flanged balance disc, which includes both an axial and a radial clearance, is a self-compensating device capable of balancing this load at any operating point. This design has significant benefits over a straight balance device, but it also has its own risks.
The axial clearance between the balance disc and balance drum is extremely small, generally 0.001 – 0.003”. If these faces touch during startup, the pump will seize and cause a catastrophic failure.
Because the flanged disc will naturally flex outward, the most likely area of contact is at the bottom of the axial clearance.
Providing a negative taper on the balance drum makes the most likely point of contact at the top of the axial clearance. This change allows pressure to build below the contact point, forcing the faces apart to avoid component failure. The negative taper also provides better parallelism of the faces during operation, reducing the likelihood of grooving on the balance disc face due to contact.
An additional safeguard involves providing a Belleville-type spring between the bearing housing and the inboard thrust bearing shoes to open the balance device axial clearance during startup. When the pump comes up to pressure, the spring will compress and the balance device will achieve its normal operating position.
Reassembly: Stay Rod Tensioning Technique
The large number of surfaces that need to be sealed to atmosphere and the significantly lower total mass of segmental ring pumps makes them much more susceptible to leakage and distortion than barrel pumps. External factors can affect the parallelism of the stage pieces and the even compression of the interstage seals, resulting in casing leakage. One of these factors is the tensioning of the tie bolts.
The tie bolts compress the stationary assembly, ensuring each stage piece seals to its neighboring components. Torqueing the tie bolts with the correct process and sequencing is essential to properly compress the stage pieces without distorting the bundle.
In order to ensure that each stage piece is provided with an effective seal and the stationary assembly remains straight, Hydro has developed a tie rod tensioning technique. This tensioning technique ensures zero leakage at startup.
KSB HGC element ready for shipment after Hydro’s repair
Continuously Developing Solutions for the Combined Cycle Market
Hydro’s specialized capabilities for combined cycle plants are the result of 50 years of independent aftermarket pump experience. Rotor centralization, balance device redesign, and tie rod tensioning are just a few of the custom solutions that Hydro’s engineers have developed to improve the reliability of their combined cycle customers’ critical pumps.
