Prepackaged thrust and journal bearings can provide significant advantages for large pump manufacturers and end users.
Combined bearing assemblies are not new to the market; they were introduced in the early 20th century. Certain types and designs, however, are more effective for the pump industry than others.
A good example is a fluid-film bearing package that integrates a self-contained, load-equalizing, double thrust bearing that conforms to American Petroleum Institute (API) Standard 610, along with a built-in oil circulator and self-aligning journal bearing (see Image 1), plus a separate journal bearing mounted on the drive end of the pump (see Image 2).
A unique aspect of this system is that lubrication is autonomous, achieved by the oil circulator and collar, which serve as a viscosity pump driven by shaft rotation. The system eliminates the need for an external lubrication skid to supply a pressurized flow of oil to the bearings. This system also requires no emergency pump, accumulator, rundown tank or other special arrangements for oil lubrication. Additional motor control systems and electric power are also not needed for oil circulation. Because a separate lube system is not necessary, cost savings can be significant.
In contrast to a traditional system with an electrically driven external lubrication skid, if power is interrupted, lubrication continues without causing major problems to the pump bearings. With its autonomous lubrication system, oil flow continues until the pump bearings safely coast to shutdown. Upon startup, oil flow is immediately initiated and continues as long as the shaft is rotating.
Prepackaged fluid film bearing assemblies are designed to spare the pump manufacturer the challenges of designing an appropriately sized system, sourcing the components, machining the housing and assembling the individual parts.
Because these bearings may run heavily loaded, the lube oil must quickly be circulated through the system and cooled to the proper temperature before returning to the bearing cavity. Oil from the reservoir is drawn into a bronze ring called the circulator, which is assembled around the collar. The oil adheres to the collar and moves toward a dam inside the oil circulator, passing through ports leading to spaces between the lowest shoes on both sides. Shaft rotation carries the lightly pressurized oil flow to the other shoes before it escapes above the collar into a passage leading down to the cooler and finally returns to the reservoir.
Besides the ports previously mentioned, another set is arranged to allow the oil to circulate during reverse rotation of the collar. When the direction of rotation changes, the oil's adhesive qualities rotate the circulator until the lug at the top of the circulator meets a stop. In either of the two stop positions, oil enters the groove in the circulator by the proper ports for the prevailing direction of rotation and is discharged through other ports into the spaces between the lower shoes.
The built-in journal bearing is self-aligning and able to take full advantage of the oil film's load-carrying capacity. Testing has shown that shorter journal shells run with unbroken films under severe radial loads imposed by the pump runner.
Standard oil cooling is provided by a plate-style heat exchanger mounted directly on the non-drive end unit and requires freshwater typically provided at a temperature of 30 C (85 F). Standard coolers can meet any speed within the product's published load and speed ranges. Shell-and-tube heat exchangers can be used for applications with special coolants such as seawater, as is the option of forced-air cooling.