Q.When selecting a vertical turbine pump design, what factors should be considered when determining the use of open or enclosed lineshaft? A. An open lineshaft and an enclosed lineshaft-type deepwell pump are shown in ANSI/HI 2.1– 2.2, Rotodynamic (Vertical) Pumps for Nomenclature and Definitions. The open lineshaft pump is often referred to as a productlubricated or water-lubricated pump. The lubrication for an enclosed lineshaft pump may be oil, grease, filtered pump discharge water or clean water from an external source. Representative cutaway sections of open and enclosed lineshaft construction for vertical turbine pumps are shown in Figures 2.3.3.4c and 2.3.3.4d. not necessarily used on lower head or single-stage applications.2. The open lineshaft type does not have a possible contamination problem. prevents the buildup of pressure in the shaft-enclosing tubes. Other examples of product-lubricated pump constructions can be found in ANSI/HI 2. The enclosed lineshaft bearing bushings are protected from pumped abrasives and are lubricated by drip feed oil. packed grease or pressurized water in the standard pump configurations. grease or oil to lubricate the bearing bushings. A bypass port in the top of the bowl assembly. which can exist with the enclosed lineshaft type when drip oil or packed grease is used.The open lineshaft bearing bushings are subject to abrasive wear when the pumped liquid contains sand or other suspended solids. Selecting proper . biodegradable oils are frequently used. The shaft-enclosing tube is provided to protect the shaft and bearing bushings from the liquid being pumped and to provide a means for abrasive-free water. therefore.1–2. Mineral oil contamination of wells is a possible problem with enclosed lineshaft. especially in the short-setting pumps and custom engineered-to-order verticals. if necessary) to provide the desired NPSH margin. multistage construction and midrange specific speeds offer high efficiencies. the vertical construction takes up little floor space. Back to Basics: How to Improve Vertical Turbine Pump Reliability through Optimum Bearing Selection By Allan Budris Vertical turbine pumps (VTPs) offer many unique advantages for many applications. vibration and axial thrust. the first stage impeller can be lowered (by increasing the pit depth. A variety of bearing constructions and lubrication systems are applied to suit different applications. As such. given the fact that the bearings are immersed in and lubricated by the fluid pumped during most typical applications. abrasives and/or air is the selection of the bearing material and/or construction. Accordingly. canned. and modular construction allows the pumps to be customized for many applications. Numerous variations of the open and enclosed lineshaft constructions exist. VTPs are available in deep well. Conventional Vertical Turbine Pump Bearings . my September 2008 column on the advantages and cautions of using VTPs on water and wastewater applications concentrated primarily on cavitation.biodegradable oil is important because many of these oils promote molds and bacteria growth. as well as how to avoid the associated field problems. For instance. wet pit (short setting or close-coupled). and submersible motor configurations. they are also generally the first component to deteriorate in a VTP. An additional key issue that should be considered when applying a VTP on liquids that contain solids. priming problems can be avoided due to submersion of the impellers in liquid. 3). 2). set against a 416 stainless steel bowl shaft without any replaceable sleeves (see Fig. suction case/bell and possibly the discharge case) and in the column assembly (unless the pump has a short setting or is driven by a submersible motor located below the bowl assembly). operating against a stainless steel shaft sleeve (lubricated by the fluid pumped) or bronze enclosed in a tube (lubricated by either an oil drip or water flush. 1). introduced at the discharge head. and exiting into the well or sump at the top of the bowl assembly. the column assembly connects the bowl assembly to the aboveground discharge head. . Further.VTP bearings are found in the bowl assembly (in each bowl. Bowl bearings are normally made of a low-lead bronze material. Typical column bearings are either constructed of a cutless rubber (see Fig. see Fig. and . it is not recommended for longer settings greater than about 100 feet. Renewable shaft sleeves or hard facing on the shaft are available for longer life.Open Lineshaft Open column line shaft bearing construction is recommended for ease of maintenance and/or whenever a special bearing material is required. the shaft size and spacing should be selected so that the shafting will operate below its first critical speed (see Fig. A tank attached to the discharge head provides oil through a solenoid valve to the tension bearing in the stuffing box. However. the maximum bearing spacing for a 1 11/16 inch (1. This construction minimizes maintenance of the column bearings in abrasive services. for shorter settings. It then flows by gravity into the enclosing tube and through the bypass port in the bowl assembly discharge case.69 inch) shaft would be five feet. The oil (or water) lubrication for the enclosed construction is introduced at the surface. An internal spiral groove allows the lubricant to flow between the shaft and the inner face of the bearing. Bowl Assembly Bearings .800 RPM.typical bearing spacing is 10 feet for well applications. which is especially important for deeper settings (over about 100 feet). For example. 4). even when it is intended for drinking water. an enclosing tube provides the lineshaft with protection from the pumped liquid and ensures clean lubrication to the bearings prior to startup. Alternate lubricants such as clean water or grease can also be used with enclosed lineshaft construction. Lubricating oils are available that are acceptable for discharge into the pumped liquid. The lineshaft bearings are typically spaced at five-foot intervals to support the lineshaft. Enclosed Column In this configuration. while the outside of the bearing is threaded to connect the enclosing tube sections. at 1. Bearing Material Options Table 1 lists the classes of column and bowl assembly bearing materials generally available for VTPs. Some VTP manufacturers do. Air can enter a VTP when the well or sump levels are low (vortexing). . with each manufacturer typically offering their own specific alloys. offer rifle-drilled bowl assembly shafts with an external water flush that can greatly improve the bowl bearing life when handling solids/abrasives and/or air/vapor. in most cases. Once in the bowl assembly. bowl bearings. the choice of bearing material (see Table 1) is normally the only option that will allow the pump to handle higher levels of solids or air/vapor. which reduces their dry-running ability. However. however. Teflon bearings cannot be retained with a press fit due to the potential of cold flow. Carbon graphite bearings probably offer one of the most efficient dry-running capabilities but have very low solids/abrasive tolerance. however. can be entrained in the pumpage due to mixing. plus they are available with a variety of fillers. they are also available with a variety of fillers. Teflon bearings also have excellent dryrunning capability and poor abrasive tolerance. or can be released from entrainment due cavitation in the first and/or second stage of the pump (as discussed in the September 2008 column). as shown in Figure 1. the air and vapors (being lighter then water) can be centrifuged into the bearings. This means that.Line shaft bearings can be protected from abrasive wear by either constructing them of cutless rubber (which can tolerate fairly high levels of suspended solids) or by the use of an enclosed tube around the lineshaft. The bronze alloys typically offered have very low (if any) lead due to environmental concerns. must operate in the pumped liquid. as long as they are not too sharp. they have poor lubricity and should be wetted prior to startup. Rubber bearings are seldom used for bowl bearings due to the larger required running clearance. such as chromium oxide and tungsten carbide. Finally. . However. including Teflon and carbon. hardened surface metal bearings are also available. especially if the pump does not have a foot (check) valve and it takes too long for the pumped liquid to reach the upper bearings.html More Pump Tips Do you enjoy Allan Budris's monthly Pump Tips column? Here are a few of his recent articles: Back to Basics: Pump Factory Performance Tests Selecting the Optimum Pump Control Valve to Save Substantial Wasted Energy Dollars Back to Basics: How to Improve Vertical Turbine Pump Reliability through Optimum Bearing Selection Pump Protection: The Pros and Cons of Various Centrifugal Pump Casing Types Considerations for Designing Piping Adjacent to a Centrifugal Pump Bearing Burdens: Reducing Lubrication Contaminants to Improve Bearing Life. Rubber bearings are primarily used for open lineshaft column applications and are very proficient at handling solids. which could pose a problem with deep settings (over about 100 feet). for abrasive/solid applications.waterworld.com/articles/print/volume-29/issue12/departments/pump-tips-techniques/back-to-basics-how-to-improvevertical-turbine-pump-reliability-through-optimum-bearing-selection. but they are expensive and also have poor lubricity for handling air and/or vapors.Vespel bearings are also much like Teflon bearings but with improved dimensional stability. http://www. and they are also available with a variety of fillers. Lifecycle Costs Power Precautions: Analyzing Pump Startup and Shutdown Best Practices .
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