Tall Pumps Solve Design and Environmental Problems

Ultra-long (more than 50-ft) sump pumps provide a number of benefits to plant designers and operators. Plant engineers can trade the floor space taken up by wide, shallow storage tanks for greater height. They can also reduce the number of instances where plant personnel must descend into pits below the plant floor to service horizontal pumps (or short vertical pumps) at the base of a tank. The main obstacle to ultra-long pumps has been obtaining a sleeve that could protect the shaft along its entire length. This problem has now been addressed by a new shaft-connection arrangement (patent pending) from Vanton Pump and Equipment Co. (Hillside, NJ). Prior to this development, the maximum length of commercially available vertical thermoplastic pumps was 20 ft. Segmented shafts The design breakthrough described in this report uses a complex shaft connection arrangement that assures fluid-tight sealing of the individual shaft joints and segments. This unique construction simplifies assembly and disassembly of the individual segments, while providing for continuous thermoplastic sleeving of the entire shaft, regardless of length. Pump shafts in various corrosion-resistant metals can be produced in short, coupled sections to achieve required lengths. However, if the vertical pump is to be submerged in fluids that attack the metal shaft, isolation of the shaft with a continuous, heavy-duty sleeve of a chemically inert thermoplastic must be provided. This has been accomplished in continuous length shafts, but prior to this new development, no plastic pump designers have been able to achieve this isolation of segmented shaft lengths. The shaft innovation leads to a number of desirable results: System designers can now specify all-plastic vertical centrifugal pumps for corrosive, hazardous, toxic and other aggressive chemicals and waste streams collected or stored in sumps to 50 feet or greater in depth. No metal ever makes contact with the fluid being pumped The segmented shaft design makes it possible to remove individual pump sections, including the pump head, for maintenance purposes, regardless of ceiling height or overall pump length. Ultrapure fluids or reagent-grade chemicals can be safely stored in deep sumps and circulated or transferred, utilizing thermoplastic pumps, without danger of metallic contamination. Appreciable areas of floor space within the plant walls can be allocated to other services because deeper sumps provide extra liquid storage area without sacrificing or interfering with valuable workspace. Modular construction using segmented shafts reduces shipping costs, installation time, labor and maintenance. Overall weight reduction when comparing thermoplastic pumps versus metal ones represents appreciable savings and simplifies handling. Long shaft lengths of 20 feet are considered special orders involving extended delivery schedules and premium pricing. Modular construction, using this segmented design, appreciably shortens pump delivery time, reduces costs of repair and facilitates replacement of damaged steel shaft sections. Maintenance costs related to difficulties in securing or maintaining shaft straightness as lengths increase are reduced through the use of the shorter segments made possible by this new development. Hence, sleeve bearing life is considerably extended. Applications The initial demand for longer thermoplastic pumps for deeper sumps came from those chemical and other process industries handling large volumes of corrosive fluids. Space limitations for storage and treatment became more severe, downtime for maintenance more intolerable, and environmental considerations more complex. Among the companies who are currently using extended length, all-plastic vertical centrifugal pumps are those processing chemicals and pharmaceuticals as well as those involved with effluent streams of varying pH. One 29-ft-high polypropylene unit (Figure 2) was built for a chemical effluent application. There are now 40-foot units under construction for acid waste handling service with flows to 200 gpm, heads to 80 ft and temperatures to 180°F. Fig. 2: A 29-ft polypropylene vertical pump is mounted in a test station at Vanton's New Jersey facility. The segmented shaft design makes possible the installation of the pump in sections, so that limited headroom is not an issue.

Since this segmented shaft design may be used with equal effectiveness for shorter pumps, as well as those over 20 ft in length, potential applications where installation headroom might be a problem are limitless. Shorter length shaft segments are economically feasible and readily available.

Environmental considerations

In recent years, the availability of vertical pumps of all types have taken on new significance. The concurrent development of high-performance thermoplastic materials, with their light weight and broad chemical resistance, has also been a factor.

When chemical storage or waste collection tanks were moved outside plant walls to free up more interior space, vertical pumps were the natural answer. They are installed inside the tank and their design eliminates the need for the troublesome shaft seals or stuffing boxes required in horizontal centrifugal pumps. With the pumphead submerged in fluid, the sump pump would be self-priming and any leakage would be internal, presenting no environmental or safety hazard. Additionally, since aboveground tanks exit from the bottom of a tank, a horizontal centrifugal pump connections could become a source of serious leakage.

The demand for vertical pumps to be used in deeper sumps has become more prevalent as available floor space at the plant site grew more limited and costly. A 10x10x10-ft. tank contains 1,000 ft3 of liquid; an additional 10 ft elevation increases the storage capacity by 100 percent. Increasing the length of thermoplastic vertical pumps involved handling. High axial thrust loadings and radial forces, as well as problems with procurement of long, straight metal shafts beyond 20 ft and the associated difficulties of isolating shaft from the corrosive fluids.

The Vanton solution to these issues involves a steel-shaft, segmented design which permits simple assembly and disassembly of individual shaft segments, and a movable, independent thermoplastic sleeve that slides over the joint and is "O"-ring sealed to prevent the corrosive fluid from coming in contact with the metal surface.

To provide the necessary column strength and stiffness for pumps of such height, the columns are ribbed with thick sections of the same plastic as the other wetted components. The cover plates can be solid thermoplastic or steel with a thick plastic underlay. They can be custom-sized and -shaped to meet tank requirements. A special vapor seal protects exterior bearings and the motor from rising corrosive fumes.

The choice of material for all fluid-contact parts is determined by the characteristics of the fluid-temperature, corrosiveness, and abrasiveness. The casings, casing covers, columns, and impellers, as well as other wetted parts, are furnished in engineered thermoplastics, such as polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polypropylene (PP) and polyvinylidene fluoride (PVDF).

Flowrates for standard thermoplastic vertical centrifugal pumps range to 1,450 gpm for heads to 280 ft and temperatures to 275°F. An interesting design advantage is the fact that these segmented shaft thermoplastic pumps can readily be converted in the field from a standard to a Vortex design for the handling of corrosive fluids containing stringy materials or various sized solids with diameters to 3 in.

Vanton Pump and Equipment Corp., 201 Sweetland Ave., Hillside, NJ 07025. Tel: (908) 688-4216. Fax: (908) 686-9314.

Edited by Nick Basta