Pump designations

These can be controlled by variations in pump design in nonaerosols and by variations in valves, actuators, and concentrate/propeUant ratio in aerosols. 

Fig. 7. (a) Wet-pit pump design. Courtesy of Goulds Pumps, Inc. (b) Submersible pump. Courtesy of Homa Pump Technology, (c) Dry-pit pump. 

Specialty Pumps. There are a multitude of other pump designs in the family of kinetic pumps. Many of these designs have been around for years others continue to emerge. Some of these special-purpose pumps are described herein. 

Disk Pumps. When pumping shear-sensitive or highly viscous fluids, it is desirable to reduce internal turbulence caused by the vanes. The disk pump design rehes on the centrifugal frictional effect of a vaneless disk. Whereas the efficiency of this pump is lower than that of similar centrifugal pumps having vanes, it is often the only solution to certain pumping appHcations. 

Pumps are designed to give trouble-free operation for a long period of time. The ANSI B73.1M pumps are designed for a bearing life of no less than two years (29), and API 610 pumps for a minimum of five years (30). However, in real appHcations, a typical mean time between faUures (MTBF) is often found to be significantly less, and sometimes it is as short as a few weeks. Whereas in some instaUations the seals last from three to four years, in others these are replaced monthly. The reason for such wide variations in pump component life is often not poor pump design but equipment misappHcation. 

Pump designs have largely been standardized. Based on appheation... 

System Curves In addition to the pump design, the operational performance of a pump depends upon factors such as the downstream load characteristics, pipe friction, and valve performance. Typically, head and flow follow the following relationship ... 

Figure 10-48 is a direc t-acting pump, designed for use at pressures up to 0.690 MPa (100 Ibfiin"). In this figure, the piston consists of disks A and B, with packing rings C between them. A bronze liner for the water cyhnder is shown at D. Suction valves are Ei and Eo. Discharge valves are Fi and Fo. 

Certain pump designs use an internal bypass orifice port to alter head-flow curve. High liquid velocities often erode the orifice, causing the pump to go farther out on the pump curve. The system head curve increase corrects the flow back up the curve. 

Since the exacd value of the hydraulic efficiency e, is never known, V/ can be taken as an approximation where e is the gross (hydraulic horsepower/brake horsepower) pump efficiency. Efficiencies of pump designs running as turbines are usually 5 to 10 efficiency points lower than those as pumps at the best efficiency point. 

Low pump head Increase pressure at source pressure., Verify pump design will achieve needed pressure Check for restrictions in suction and discharge lines CCPS G-23... 

Upon developing the. system eurve, the pump eurve will always intersect the. system curve, it doesn t matter about the pump design. We ll. see this later in Chapter 8. 

This type of end suction vertically. split pump is used extensively in the chemical proee,ss industry. It is probably the most popular of all pump designs, see Figure 6-8. 

Most of these pump designs are back-pullout construction. Some meet complete ANSI specs. 

Howe er, most conventional pump impellers receive the fluid into the impeller eye, at the center or inside diameter of the impeller. There are single suction impellers, and dual or double suction impellers with two eyes, one on each side. Dual suction impellers are mostly specified for low NPSH applications because the eye area is doubled (it ean reeeive twice as much fluid at a lower velocity head). Dual suction impellers arc mostly found on split case pumps where the shaft passes completely through the impeller. But they can afso be found mounted onto the end of the shaft in some special pump designs. 

Another distinction in impellers is the way the liquid traverses and leaves the impeller blades. This is called the Specific Speed, Ns. It is another index used by pump designers to describe the geometry of the impeller and to classify impellers according to their clesign type and application. By definition, the Specific Speed, Ns is the revolutions per minute (rpm) at which a geometrically similar impeller would run if it were of such a size as to discharge one gallon per minute at one foot of head. 

The Specific Speed is a dimensionless number using the formula above. Pump design engineers consider the Ns a valuable tool in the development of impellers. It is also a key index in determining if the pump... 

A big part of the overall problem with adequate mechanical. seal life is trying to make a precision mechanical seal run into the same. space that previously was occupied by the packing rings. Pump design evolved over time to accommodate the packing rings. 

Pumps can overheat if they run with the delivery valve almost closed. In one incident a pump designed to deliver 10 tons/hr was required to deliver only 14 ton/hr. The delivery valve was gagged, the pump got too hot, the casing joint sprang, and the contents leaked out and caught fire. 

The report includes pedigree information on each plant. This includes plant name and unit number, type, vendor, number of pumps, pump designer, pump model number, and number of seal stages. 

The report presents the findings from the analysis of the RCP failures. Estimates of the annual frequency for the spectrum of leak rates induced by RCP seal failures and their impact on plant safety (contribution to coremelt frequency) are made. The safety impact of smaller RCP seal leaks was assessed qualitatively, whereas for leaks above the normal makeup capacity, formal PRA methodologies were applied. Also included are the life distribution of RCP seals and the conditional leak rate distributions, given a RCP seal failure the contribution of various root causes and estimates for the dependency factors and the failure intensity for the different combinations of pump designers and plant vendors. 

Certain pump designs have been standardized to aid manufacturer s problems, and to allow the owners to take advantage of standardization of parts and dimensions, and consequently maintain a more useful inventory. The standards are sponsored through the American National Standards Institute however, many manufacturers afso produce to the American Petroleum Institute and their own proprietary standards. These are special pumps that do not conform to all the standards, but are designed to accomplish specific pumping services. 

Hydrocarbons, hot Single suction, often of the special type called refinery pumps, designed particularly for high temperature service. Closed with large inlets. 

Cavitation of a centrifugal pump, or any pump, develops when there is insufficient NPSH for the liquid to flow into the inlet of the pump, allowing flashing or bubble formation in the suction system and entrance to the pump. Each pump design or family of dimensional features related to the inlet and impeller eye area and entrance pattern requires a specific minimum value of NPSH to operate satisfactorily without flashing, cavitating, and loss of suction flowt... 

Figure 3-58. Typical curves showing the effect on a pump designed for water when pumping viscous fluids. (By permission, Pic-a-Pump, 1959, Aliis-Chalmers Mfg. Co.)...

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