Foundations

Holes for foundation or holding down bolts should preferably be formed in the foundation block, being made with collapsible wooden boxes which can be withdrawn after the block is completed. These holes should be about i-in. larger all round than the foundation bolt plates, or projections on the rag bolts if the latter are used.

Bedplates

Supplied with pumps are machined on the top and bottom, to prevent any difficulty in levelling. They are made as rigid as is reasonably necessary, but even the strongest bedplate can be twisted and warped when the foundation bolts are screwed down on a bedplate inadequately supported. It is essential therefore if the pump is to run satisfactorily to the user that the bedplate be supported all round, and the alignment should be carefully checked before grouting up.

The sizes of suction and discharge branches on the pump do not determine the sizes of pipes required which may in certain cases require to be larger in diameter than the branches.

Discharge Pipes

The diameter of discharge pipe should be fixed in accordance with the length, so as not to increase the total head beyond that which the pump is designed for. It should be remembered that in any length of piping there is a certain " loss of head " due to friction of the water in the pipes. For this reason if the delivery pipe is of considerable length the friction should be kept as low as possible, as this means a saving of power.

Additional head loss allowances for valves, bends, etc., should be made as follows : Equivalent times the friction loss in 1 yard of straight pipe of the same diameter. Foot Valve and Strainer .... 15

Retention Valve .... .... 8

Sluice Valve (full open) .... 5

Sharp Elbow ............ 10

Medium Elbow ........ 3

Entry to Suction Pipe ;.... 10

If it is desired to obtain advantage from the syphonic head in a discharge pipe, the end of the pipe should be sealed below water level and means taken to prevent air accumulating at the highest point of the pipe line.

When there is a considerable length of horizontal discharge pipe it is usually advisable to have a valve near to the pump, so that it will be unnecessary to prime the discharge piping.

Suction Pipes

Sharp bends close to the suction flange of the pump should be avoided where possible. A short straight length of pipe is preferable, but if it is necessary to have a bend directly on the suction flange, this should have a fairly large radius or the efficiency of the pump may be reduced on account of the eddies set up in a sharp bend.

The diameter of suction pipe will depend on the static lift and upon the length of piping, number of bends, valves, strainer, etc., and must be large enough so as not to unduly sacrifice head on the suction side.

It must be remembered that on the suction side the only force available to raise the water to the pump is the pressure of the atmosphere, which at sea level is say 34 ft. of water, and any head lost in the piping due to friction, eddies and bends is subtracted from the available lift.

The joints in the suction pipe should be absolutely air-tight and the pipes themselves free from blow holes or cracks, as any leakage in the suction pipe, which will allow air to pass through, destroys the vacuum and prevents the pump drawing water.

The joints in the pipes may be made by means of India rubber or canvas joint rings.

If the water to be pumped contains large quantities of gas, dissolved or in suspension, it is not possible to obtain so high a suction lift as when the water is free from gases.

If the suction conditions are good and the losses in the suction pipe small, a manometric lift of 30 feet is practicable, but unless the suction arrangements are perfect and free from small air leakages, such high lifts must not be attempted, and it must be remembered that all bends, restrictions, bad joints, swirls at entry, etc., reduce this possible suction lift so that a pump which would be perfectly satisfactory on a 30 feet suction under ideal conditions may not be able to deal with more than say 15 feet suction if the suction conditions are unsatisfactory.

It should be noted that the suction lift or manometric suction of a pump is usually meant to include not only the total vertical lift (in feet) from the water to the centre of the pump, but also the loss (in feet) due to friction in pipes and the losses (in feet) due to all bends, valves, strainers, etc., as shown on the gauge.

Piping

Air locks should always be avoided in suction. The piping should be either dead level or better should have a continuous rise from the pipe inlet to the pump. If it rises and then falls again air is liable to collect in the high portion and eventually break the vacuum and so cause the pump to lose its water. The same effect may be caused by a pipe branching upwards or horizontally from the suction pipe (unless isolated by a valve close to the point of branching) and having a blank end, or any vessel in which air may accumulate.