Transcript
Q. When selecting a vertical turbine pump design, what factors should be considered when determining the use of open or enclosed lineshaft?
open n lin linesh eshaft aft and an enc enclos losed ed lin linesh eshaft aft-ty -type pe dee deepwe pwell ll pum pump p are A. An ope shown in ANSI/I !"#$ !"!, Rotodynamic (Vertical) Pumps for Nomenclature and Definitions" Definitions" %he open lineshaft pump is often referred to as a product or water-lubricated pump" lubricated or pump" %he lubrication for an enclosed lineshaft pump may be oil, grease, filtered pump discharge water or clean water from an e&ternal source" 'epresentative cutaway sections of open and enclosed line li nesh shaf aftt co const nstru ruct ctio ion n fo forr ve vert rtica icall tu turb rbin ine e pu pump mps s are sh show own n in (i (igu gure res s !")")"*c and !")")"*d"
%he open lineshaft bearing bushings are sub+ect to abrasive wear when the pumped liuid contains sand or other suspended solids" %he open lineshaft type does not have a possible contamination problem, which can e&ist with the enclosed lineshaft type when drip oil or paced grease is used" .ther e&les of product-lubricated pump constructions can be found in ANSI/I !"#$!"!" %he enclosed lineshaft bearing bushings are protected from pumped abrasives and are lubricated by drip feed oil, paced grease or pressuried water in the standard pump configurations" %he shaft-enclosing tube is provided to protect the shaft and bearing bushings from the liuid being pumped and to provide a means for abrasive-free water, grease or oil to lubricate the bearing bushings" A bypass port in the top of the bowl assembly, not necessarily used on lower head or single-stage applications, prevents the buildup of pressure in the shaft-enclosing tubes" 0ineral oil contamination of wells is a possible problem with enclosed lineshaft1 therefore, biodegradable oils are freuently used" Selecting proper
biodegradable oil is important because many of these oils promote molds and bacteria growth" Numerous variations of the open and enclosed lineshaft constructions e&ist, especially in the short-setting pumps and custom engineered-to-order verticals" A variety of bearing constructions and lubrication systems are applied to suit different applications"
Back to Basics: How to Improve Vertical Turbine Pump Reliability through Optimum Bearing Selection By Allan Budris
Vertical turbine pumps (VTPs) ofer many unique advantages or many applications. For instance, the vertical construction taes up little !oor space" priming problems can be avoided due to submersion o the impellers in liquid" the #rst stage impeller can be lo$ered (by increasing the pit depth, i necessary) to provide the desired %P&' margin" multistage construction and midrange speci#c speeds ofer high eciencies" and modular construction allo$s the pumps to be customied or many applications. VTPs are available in deep $ell, $et pit (short setting or close*coupled), canned, and submersible motor con#gurations. +ccordingly, my September 2008 column on the advantages and cautions o using VTPs on $ater and $aste$ater applications concentrated primarily on cavitation, vibration and aial thrust, as $ell as ho$ to avoid the associated #eld problems.
+n additional ey issue that should be considered $hen applying a VTP on liquids that contain solids, abrasives and-or air is the selection o the bearing material and-or construction, given the act that the bearings are immersed in and lubricated by the !uid pumped during most typical applications. +s such, they are also generally the #rst component to deteriorate in a VTP. Conventional Vertical Turbine Pump Bearings
VTP bearings are ound in the bo$l assembly (in each bo$l, suction case-bell and possibly the discharge case) and in the column assembly (unless the pump has a short setting or is driven by a submersible motor located belo$ the bo$l assembly). o$l bearings are normally made o a lo$*lead brone material, set against a /01 stainless steel bo$l shat $ithout any replaceable sleeves (see Fig. 0).
Further, the column assembly connects the bo$l assembly to the aboveground discharge head. Typical column bearings are either constructed o a cutless rubber (see Fig. 2), operating against a stainless steel shat sleeve (lubricated by the !uid pumped) or brone enclosed in a tube (lubricated by either an oil drip or $ater !ush, introduced at the discharge head, and eiting into the $ell or sump at the top o the bo$l assembly" see Fig. 3).
Open Lineshaft
4pen column line shat bearing construction is recommended or ease o maintenance and-or $henever a special bearing material is required" it is not recommended or longer settings greater than about 055 eet. 6ene$able shat sleeves or hard acing on the shat are available or longer lie, and
typical bearing spacing is 05 eet or $ell applications. 'o$ever, or shorter settings, the shat sie and spacing should be selected so that the shating $ill operate belo$ its #rst critical speed (see Fig. /). For eample, at 0,755 6P8, the maimum bearing spacing or a 0 00-01 inch (0.19 inch) shat $ould be #ve eet.
Enclose Column
:n this con#guration, an enclosing tube provides the lineshat $ith protection rom the pumped liquid and ensures clean lubrication to the bearings prior to startup, $hich is especially important or deeper settings (over about 055 eet). The lineshat bearings are typically spaced at #ve*oot intervals to support the lineshat. +n internal spiral groove allo$s the lubricant to !o$ bet$een the shat and the inner ace o the bearing, $hile the outside o the bearing is threaded to connect the enclosing tube sections. This construction minimies maintenance o the column bearings in abrasive services. The oil (or $ater) lubrication or the enclosed construction is introduced at the surace. + tan attached to the discharge head provides oil through a solenoid valve to the tension bearing in the stung bo. :t then !o$s by gravity into the enclosing tube and through the bypass port in the bo$l assembly discharge case. +lternate lubricants such as clean $ater or grease can also be used $ith enclosed lineshat construction. ;ubricating oils are available that are acceptable or discharge into the pumped liquid, even $hen it is intended or drining $ater. Bo!l "ssembl# Bearings
;ine shat bearings can be protected rom abrasive $ear by either constructing them o cutless rubber ($hich can tolerate airly high levels o suspended solids) or by the use o an enclosed tube around the lineshat" bo$l bearings, ho$ever, must operate in the pumped liquid. This means that, in most cases, the choice o bearing material (see Table 0) is normally the only option that $ill allo$ the pump to handle higher levels o solids or air-vapor. +ir can enter a VTP $hen the $ell or sump levels are lo$ (vorteing), can be entrained in the pumpage due to miing, or can be released rom entrainment due cavitation in the #rst and-or second stage o the pump (as discussed in the September 2008 column). 4nce in the bo$l assembly, the air and vapors (being lighter then $ater) can be centriuged into the bearings. &ome VTP manuacturers do, ho$ever, ofer ri!e*drilled bo$l assembly shats $ith an eternal $ater !ush that can greatly improve the bo$l bearing lie $hen handling solids-abrasives and-or air-vapor, as sho$n in Figure 0.
Bearing $aterial Options
Table 0 lists the classes o column and bo$l assembly bearing materials generally available or VTPs, $ith each manuacturer typically ofering their o$n speci#c alloys. The brone alloys typically ofered have very lo$ (i any) lead due to environmental concerns, $hich reduces their dry*running ability.
o you en?oy +llan udris@s monthly Pump Tips columnA 'ere are a e$ o his recent articles= Back to Basics: Pump Factory Performance Tests Selecting the Optimum Pump Control Valve to Save Substantial Waste !nergy "ollars Back to Basics: #o$ to %mprove Vertical Turbine Pump &eliability through Optimum Bearing Selection Pump Protection: The Pros an Cons of Various Centrifugal Pump Casing Types Consierations for "esigning Piping '(acent to a Centrifugal Pump Bearing Burens: &eucing )ubrication Contaminants to %mprove Bearing )ife*
)ifecycle Costs Po$er Precautions: 'naly+ing Pump Startup an Shuto$n Best Practices
