Packing.

(III) PACKING AND MARKING

7. Sulphate of iron shall be packed in cloth or duck bags of not more than 100 lb. net weight, or in barrels or containers of not more than 250 lb. net weight as specified in purchase order.

Marking.

8. The name of the manufacturer, net weight and grade of sulphate of iron shall be stencilled on each package, or marked on tag securely attached thereto.

Inspection.

(IV) INSPECTION AND REJECTION

9. (a) All sulphate of iron shall be subjected to inspection.

(b) The sulphate of iron may be inspected at the place of manufacture or point of delivery, or both, as arranged at the time of purchase.

(c) The inspector representing the purchaser shall have free entry at all times, while work on the contract of the purchaser is being performed, to all parts of the manufacturer's works which concern the manufacture of the sulphate of iron ordered. The manufacturer shall afford the inspector all reasonable facilities for inspection and sampling, which shall be so conducted as not to interfere unnecessarily with the operation of the works.

(d) The purchaser may make the tests to govern the acceptance or rejection of the sulphate of iron in his own laboratory or elsewhere. Such tests, however, shall be made at the expense of the purchaser. Rejection.

10. (a) Unless otherwise specified, any rejection based on failure to pass tests prescribed in these specifications shall be reported within 10 working days from the taking or receipt of samples by the purchaser.

(b) Rejected sulphate of iron shall be returned to the shipper or as he may direct. All freight charges in both directions to be paid by the shipper.

Rehearing.

11. Samples which represent rejected sulphate of iron shall be preserved in air tight containers for 10 working days from the date of test report. In case of dissatisfaction with the results of the tests, the manufacturer may make claim for a rehearing within that time.

The first centrifugal pump was invented by Denis Papin of Hesse, Germany, about 1703 or 1704. This was followed by a centrifugal pump described by Ewbanks as "a straight tube attached in an inclined position to a vertical axis and whirled around by the handle." The invention of this pump is credited to M. LeDemour, who sent a description of it to the French Academy in 1732.

While the description of these earlier pumps is rather vague, it is evident that they bore but little resemblance to the modern centrifugal pumps. There is no record of their being used to any great extent, except perhaps as mechanical novelties.

There was but little development of the centrifugal pump for over a hundred years after it was invented or until about 1818 when what. was known as the Massachusetts pump was brought out. This pump while crude as compared to modern pumps showed great improvement over the earlier pumps and it appears to have been used satisfactorily for a number of years.

Further development followed the production of the Massachusetts pump. The principal improvements being those of Andrews in 1839; Bessemer in 1845; Appold in 1848 and those of Gwynne in 1851. There followed considerable interest and some further development for a few years, after which there was but little improvement in design until the beginning of the Twentieth Century when engineers and pump designers began to realize that a pump capable of much higher heads and greater efficiency than those in general use could be developed. The development was then quite rapid as compared with the former history of the pump and within the past few years the centrifugal pump has been recognized as a formidable competitor of the reciprocating pump.

Principles of Operation

A centrifugal pump consists essentially of an outer shell or casing within which revolves an impeller mounted on a shaft. The water enters the impeller at its center and passes out through the vanes into the casing and from the casing to the discharge pipe. The water enters the impeller at a low velocity but passes out from the impeller at an increasing velocity until it reaches its maximum as it passes out of the impeller.

The velocity at which the water leaves the impeller depends upon the speed and diameter of impeller, form of vanes and area of openings. As the water enters the casing and discharge the velocity is decreased ca account of the increased area and is changed into pressure.

The

The velocity of the water upon leaving the impeller determines the theoretical head against which it may be delivered by the pump. efficiency and actual head against which the pump will deliver the water will depend upon the design and construction of the pump, particularly with regard to the impeller and diffusion space.

Impellers

Impellers are of two general forms known as the open and closed type. An open impeller consists of radial vanes attached to a hub and disk; the vanes are open at the sides and revolve between the two fixed sides of the pump. In a closed impeller the vanes are carried between two disks. It is apparent that the friction loss must be greater with the open type of impeller as the water is revolved against the sides of the pump at approximately the same velocity as the impeller. With the closed impeller the frictional loss is confined to the water passing through the vanes and to the impeller revolving in the surrounding water. Therefore, it is possible to obtain much better efficiency with the closed impeller and it is generally used in types of pump adapted to railway water service. The principal friction loss in any type of centrifugal pump is that of the impeller and the friction loss by the open impeller is twice that of the closed impeller. This loss together with the leakage loss causes it to be less efficient than the closed impeller type as far as the handling of clear water is concerned. It is therefore, recommended only for handling large volumes of water at low head and where conditions are such that debris might cause trouble by reason of clogging the smaller passageways of a pump of more efficient design.

The open impeller, volute type was about the first successful design of centrifugal pump and until the year 1900 it was practically the only pump of this kind in use. Since that time theory and practice have developed more efficient types of centrifugal pumps, particularly the enclosed impeller volute and the turbine type.

Turbine and Volute Pumps

For convenience centrifugal pumps may be divided into two general classes or types: Turbine and Volute pumps.

Turbine pumps have circular casings and diffusion vanes surrounding the impeller. The function of the diffusion vanes is to reduce the velocity of the water upon leaving the impeller through gradually enlarging passages, efficiently transforming the velocity head into pressure head.

Volute pumps have no diffusion vanes, but have a casing of spiral form, which gradually reduces the velocity of the water as it leaves the impeller, thus serving the same purpose as diffusion vanes in turbine pumps.

The turbine pump is adapted to and used for heads greater than 150 ft. A head of 100 ft. per stage is figured for most satisfactory results with this type of pump, although it is possible to operate against heads as high as 300 ft. per stage by operating pump at a high rate of speed. This, however, is not recommended as good practice.

The volute pump is a low head pump and is adapted to all classes of pumping service for which centrifugal pumps are used. Where the total head is not in excess of 150 ft. it is quite as efficient as the turbine type for low heads and has the advantage over the turbine type, that there are no diffusion vanes to become clogged up or require renewal.

Single and Double Suction Pumps

A further classification of centrifugal pumps may be made by dividing them into single and double suction pumps, depending on whether the water enters the impeller from one or both sides. Theoretically, the impeller in a double suction pump is balanced by reason of the water entering from both sides of the impeller, but it has been found in practice that this is not always true owing to variation in moving parts, and other conditions, and it is always advisable to have a thrust bearing.

With the single suction pump there is, of course, always an unbalanced condition of the impeller creating an end thrust which should be taken care of by thrust bearings.

Advantages of Centrifugal Pumps

1. Economy as to initial cost.

2. Low cost of maintenance.

3. The centrifugal pump runs with less noise than the average pumping equipment.

4. Centrifugal pumps may be operated successfully with inexperienced labor.

5. Failure to open a valve or the sudden closure of valves on the discharge will not effect the pump.

6. Less floor space is required than for other types of pumps of same capacity.

7. Is particularly adapted for handling muddy or sandy water with the least injury to working parts.

8. Starting valves, relief valves and air chambers on discharge line or vacuum chamber on suction line are unnecessary.

9. Can be used in series more satisfactorily than any other type of pump.

10. Pump is non-pulsating and does not cause water hammer on line.

11. Is particularly adapted where motor is used as power and automatic operation is desired.

Disadvantages of Centrifugal Pumps

1. The necessity for priming.

2.

Will not operate if a slight amount of air leaks into the suction line.

3. Other types of pumps are capable of handling higher suction lifts more successfully.

4. Will not operate efficiently where there is a constant variation in the pumping head.

Proper Size and Stage of Pump to Be Used

In order to determine the above, the following information must be

obtained:

Gallons per minute required.

Static discharge head.

Suction head.

Length and diameter of suction line.

Length and diameter of discharge line.

Number of elbows and bends in both suction, and discharge
lines.

Nature of fluid to be pumped, whether clear or containing

much sediment and grit.

Class of power.

From the above can be determined the total net head under which the pump is to operate and this in turn will determine the size of pump and the number of stages for the unit in question.

The number of stages to be used in a pump size to perform a given amount of work under ordinary circumstances will depend on the total net head under which the pump is to operate, the amount of water to be delivered in gallons per minute, the diameter of the impeller and the speed at which the pump can be operated, based on the power to be used. As a general rule, it is safe to say that with heads ranging from 10 ft. to 100 ft. we can select a single stage pump; for heads ranging from 100 ft. to 200 ft., a 2-stage pump and for heads ranging from 300 ft. to 550 ft., 3 or more stages will be necessary, depending on the size and speed of the pump.

Power to Be Used

The power to be used may be:

1. Electric motor.

2. Internal combustion engine.

3. Steam turbine.

4. Steam engine.

An electric motor may be either direct connected to pump or belt drive used. A centrifugal pump direct connected to an electric motor makes an excellent pumping unit and will meet practically all pumping requirements owing to the fact that motors of practically any speed can be secured. A flexible coupling should be used in direct connecting a centrifugal pump to an electric motor. The belt drive is better suited to small centrifugal pumps than to large units.

Centrifugal pumps may be operated by squirrel cage motors instead of slip ring motors as the starting torque is not great. This shows a saving in the cost of power unit as the squirrel cage motor is not as expensive, nor as heavy as a slip ring motor.

The advantage of direct connected motor driven centrifugal pumps is in the saving in floor space and power transmission losses. High-speed motors are cheaper than low-speed motors and as the centrifugal pump is a relatively high speed machine there is consequent saving in total first cost.