1019

18 (5.5)

0***

*Can be top or bottom inlet

**Barely acceptable with submergence sufficient to prevent vortexing at inlet ***Very safe

*Can be top or bottom inlet

**Barely acceptable with submergence sufficient to prevent vortexing at inlet ***Very safe

FIGURE 5 An installation of four floats with top inlet cantilevered shaft pumps (Hazleton Pumps, Inc.)

Figure 7 illustrates an interesting installation of a float-mounted pump of unique design. The pump is of cantilevered shaft design (no submerged bearings) with the pump utilizing the motor bearings. Pump construction is shown in Figure 8. This is ideal for barge mounting. It involves a special motor, but the lower center of gravity permits a smaller barge and readily compensates for the extra cost of the motor. No submerged shaft bearing is required, so dirty water can be handled with little maintenance. A double discharge design also provides balanced hydraulic side thrust and eliminates the need for a shaft seal.

If floats are to be used for pump mounting, considerations in addition to hydraulics must be examined. Floats must be designed for safe operation in all circumstances. Floats for individual pumps are simple and readily moved about a mining operation; however, there are other factors beside the weight of the pump and motor. A portion of the discharge line (usually a hose on floats) must be supported by the pump float. Consideration must be given to the possibility that a number of workmen might gather at one side of the float and overturn it. Stability calculations must be made by considering

FIGURE 6 Float-mounted pumps designed to skim the clean liquid in a settling pond (Hazleton Pumps, Inc.)
FIGURE 7 Unique design float-mounted pump (Hazleton Pumps, Inc.)

lateral rotation of the float and the uprighting forces due to the additional buoyancy on one side (or end). The center of gravity must be within the center of buoyancy. If the center of gravity moves beyond the center of buoyancy, the float will overturn. It must also be remembered that, after a pontoon is submerged, that is the limit of buoyancy. In addition to these factors, wind effects must be considered. If the climate is not too severe,

FIGURE 8 Cantilevered shaft design utilizing motor bearings (Hazleton Pumps, Inc.)

pumps on simple floats can be protected from ice damage if the float is surrounded with a simple air bubble system.

As the pump flow rates increase, fixed installations become more manageable. Figure 9 shows four 24 in (610 mm) discharge, 1250 horsepower (750 kW) vertical pumps. The pumps are of stainless steel in a mining operation. This is an ideal installation as a structure is in place for pump maintenance.

The selection of the discharge line will have a significant effect on the total pumping output. If selected for normal pumping conditions, the pipeline may not add significant capacity to the system by the use of an additional pump. As an example, examine an installation utilizing a 14 in (355 mm) Schedule 40 steel pipe discharge line for a normal flow of about 5000 gpm (1135 m3/h). Assume a friction head of 70 ft (21.3 m) and a static head of 180 ft (54.9 m), for a total pumping head of 250 ft (76.2 m). Figure 10 shows that adding a second pump to the system will not double the pumping capacity as the two pump characteristics are added to the system head curve. In this exaggerated example, adding a second pump will increase the total flow by less than 1000 gpm (227 m3/h). Note that each pump now will discharge less than 3000 gpm (680 m3/h). The obvious answer is to either use a larger discharge line and a different pump selection, or the use of a separate discharge line for each pump. In that case, the total capacity would be 10,000 gpm

FIGURE 9 24 in (610 mm) discharge, 1250 HP (750 kW) vertical pumps (Hazleton Pumps, Inc.)

(2270 m3/h). This becomes a study in economics for each installation. In the above example, this installation is obviously poorly designed. As pipeline velocities increase, discharge line transients may present problems on shutdown. The author is aware of one long pipeline that failed in 17 places on the first shutdown. Other factors must also be considered, such as the projected life of the project and the cost if the project is flooded.

Much has been said about pumping from mines. Obviously, the least costly method is to keep the water from entering the mining operation. It is not always applicable, but a ring of "deep-well" turbine pumps, on the periphery of the operation, can lower the water table sufficiently to keep the mining pit relatively dry. A typical large turbine pump with submersible motor is shown in Figure 11.

Pumps for operation in deep mines have different considerations. If a mine is not more than approximately 1200 ft (365 m) deep, Schedule 40 pipe is generally satisfactory for the pressure involved. For example, 12 in (305 mm) seamless Schedule 40 steel pipe is listed as 1200 lb/in2 (82.75 bar) hydrotest pressure. However, if the water is corrosive, wall thickness allowance must be made, or stainless steel pipe used. 1200 lb/in2 converts to approximately 2700 ft of water. Allowance must also be made for water hammer if the line velocity is high. Generally, average line velocities of 10 ft/s (3.1 m/s) will produce high tran-

sient pressures upon pump shutdown, so more conservative velocities should be selected. As these installations are generally long term, considerable savings can be obtained by reduced power requirements if the pipeline velocities are near 5 ft/s (1.5 m/s).

In designing a mine pumping system, an analysis must be made where the water is coming from. It is generally not practical to put the main pump station at the bottom of the mine if the bulk of the water is occurring at an upper level. If this is the case, a decision must be made for the pumping condition of the mine bottom pumps. Should they simply pump to the upper level or directly to the surface? Both financial and safety considerations are essential. Failure of upper level pumps may jeopardize the mine safety. These are decisions that involve much more than basic equipment selection. One solution to the problem of a possible power failure is the use of submersible pumps at the shaft bottom. Singlestage submersible pumps, as shown in Figure 12, are available to 600 HP (448 kW) and can readily pump to upper levels in case of flooding at the bottom level.

If the mine is deeper than 1200 ft (365 m), other approaches must be considered. Consideration of Class 250 or 300 valves and pipefittings may show that the cost warrants pumping only to an upper level to stay within the limits of the Class 150 fittings. This does not necessarily mean a duplicate pumping station as series pumps can safely be installed at an upper level. This is practical only if the bulk of the water occurs at or near the bottom level. Because there are mines deeper than 2000 ft (365 m), the problems become more acute. In any event, the main consideration is to conduct a study to determine at what level the greatest flow of water occurs.

A very old but interesting photo (see Figure 13) shows a sealed pump-room housing three 1000 HP (746 kW) bronze constructed pumps in a coal mine. This pump room had access only from an upper level so water could rise in the mine by approximately 200 ft (36.5 m) before flooding the pump room.

Not all mines suffer from ingress of a great deal of water, but many of those that do have closed because the cost of pumping was too great. An example is shown in Figure 14. There were three 2000 HP (1490 kW) pumps in one pump room in a zinc mine. Note in this

FIGURE 11 A typical large turbine pump with submersible motor (Hazleton Pumps, Inc.)

photograph that these large pumps are in segments so they can be lowered into the mine and reassembled.

Pump discharge line forces must be calculated for all installations. The reactive forces from the piping must be isolated from the pump. Underground pumps generally operate at high pressure and the forces generated are high. Failure to adequately support and restrain the piping can cause pipe failure and result in severe pump misalignment.

Survival Treasure

Survival Treasure

This is a collection of 3 guides all about survival. Within this collection you find the following titles: Outdoor Survival Skills, Survival Basics and The Wilderness Survival Guide.

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