Aquaculture Engineering

Pumps - Points to be considered for design of pumping station

Unit 12 - Management of ponds

Pumps

Points to be considered for design of pumping station
The following points to be considered while designing the pumping station

• Pumps should be placed as low as practicable near the source of supply and it may be in pits to minimize the length of suction pipe. Motors can be fixed high up connected by vertical shafts to reduce the danger of flooding. Suction lift should as far as possible be avoided. Where suction lift is must provision has to be made for priming the pumps or vacuum pumps installed to exhaust air from the suction line.

• No point of suction line should be at a higher level than the suction eye of the impeller as this will form air pockets. This may however be permitted where a vacuum pump is used. Horizontal suction line is practical up to 300 m length and the suction pipe should be given a gradual rise of at least 1 in 180 (towards the pump) to prevent air pockets forming which seriously interfere with the flow of water. The suction line should be made perfectly air tight and it should be so arranged that any air in it can be easily let off through suitably placed valves. The end of the suction pipe should be submerged in water at least three times its diameter to prevent admission of air. Suction pipes are usually larger than delivery pipe. Usual practice is to have the suction pipe at least one commercial size larger than suction connection size of the pump. The diameter of suction pipe is about 10 mm bigger for 32 mm to 80 mm pipe than the delivery pipe and for 100 mm and above the size of suction and delivery pipe is generally the same on long suction lines the pumps should be driven at slower speed and should have a vacuum chamber to assist the suction and prevent pounding. Both suction and delivery pipes should be free from bends as practicable.