Pumps general suction system

When a booster fire water pump takes suction from a public main, the design should be such that operation of the pump at 150% of rated capacity will not reduce the public main pressure below 20 psi (137.9 kPa). Provisions against contamination of the municipal system should be made by adding a backflow device is typically required. Local agencies generally have specific requirements. Some locations do not allow direct suction from public water mains. 

The inside of the reservoir generally will have baffles to prevent excessive sloshing of the fluid and to put a partition between the fluid return line and the pump suction or inlet line. The partition forces the returning fluid to travel farther around the tank before being drawn back into the active system through the pump inlet line. This aids in settling the contamination and separating air entrained in the fluid. 

Suction skimmers are similar to weir skimmers in that they sit on the water surface, generally use an external vacuum pump system such as a vacuum truck, and are adjusted to float at the oil-water interface. They also tend to be susceptible to the same problems as weir skimmers. They are prone to clogging with debris that can stop the oil flow and damage the pump. They also experience the problem of rocking in choppy waters that causes massive water intake, followed by air intake. Their use is restricted to light to medium oils. 

In Chapter 14 the use of additives to combat potential fouling was discussed. In the use of chemical treatment for cooling water there has to be an emphasis on effective and rapid dispersion since the concentration of the additives employed must be low, i.e. a few mg/l where possible, to minimise cost and to reduce potential pollution problems. In general the additive formulation will be based on the need to limit corrosion (i.e. the use of corrosion inhibitors), scale formation (i.e. the use of crystal modifiers, dispersants or threshold chemicals or a combination) and biofouling (i.e. the use of biocides and dispersants). In many installations additives are injected on the suction side of the main pump so that turbulence within the pump will provide rapid mixing. In very large cooling systems multiple injection nozzles will be required to enhance distribution. 

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