Gravity drain system

The elevation of gravity drain systems must be carefully checked to assure that liquids will flow to the collection point without exiting the piping at an intermediate low point. 

There are three common methods for groundwater collection using pumping systems a well point system, a gravity drain system, and in combination with injection wells. 

The gravity drain system is most effective when circumstances are suitable to gravity flow, the water table is less than 3 m and the contaminant is less than 9 m below the surface. 

A drainage system includes a containment system using solid, impermeable floors with perimeter features (curbing, floor slope, or trenches) to limit and control the spread of liquids and a collection system (floor drains or trenches, catch basins, sumps, piping, and manholes) to direct the liquids into a gravity drain system that routes them to an appropriate location out of the unit. 

Before the gravity drain system is routed, the following basic rules must be applied ... 

Plugs are sometimes used in pipeline repair they create a vapor barrier when a line has been isolated and depressured, but has not been completely cleared of flammable, combustible, or toxic materials. Expandable plugs are also used to isolate sections of gravity drain systems such as sewers. Examples include plumbers plugs— which consist of two parallel disks that compress an elastic material together to form a seal on the inside diameter of the pipe—and inflatable bladders— which are inflated either pneumatically or hydraulically... 

Open, gravity drains should not be combined with pressure vessel drain systems. The gas flashing from vessel liquids may exit an open drain system at any point and create a hazard. 

Subsurface drains include any type of buried conduits that convey and collect aqueous discharges by gravity flow (Figure 16.11). Water collected in a storage tank or a collection sump is then pumped for further treatment. Filters are usually needed in drain systems to prevent fine particles from causing clogging. 

All safety systems are passive and function principally via density gradient-driven flow and/or compressed gas-driven accumulators. To ensure the functioning of densify gradient-driven flow provided by gravity-drain tanks, automatic depressurization systems are also included to depressurize the reactor to operational pressure levels for these systems. 

As with any piping layout, information for an underground gravity flow drain system is often less than what is required at the outset of a project. A list of the most preferred information includes ... 

When gravity flow drain systems are developed, it may be impractical to continue with the required... 

V dump tank for the closed loop (about. 300 fO) is located beneath the panel coils, so that the coils may be gravity drained. Water is returned to the closed loop by means of gas pres.sure. In the event it is necessary to dispose of the water in the clo.scd loop, it may be drained from the dump tank to the I adioactive waste disposal system. 

A drain system that is connected directly to pressure vessels is called a "pressure" or "closed" drain system. A drain system that collects liquids that spill on the ground is an "atmospheric," "gravity," or "open" drain. The liquid in a closed drain system must be assumed to contain dissolved gases that flash in the drain system and can become a hazard if not handled properly. In addition, it must be assumed that a closed drain valve could be left open by accident. Once the liquid has drained out of the vessel, a large amount of gas will flow out of the vessel into the closed drain system (gas blow-by) and will have to be handled safely. Thus, closed drain systems should always be routed to a pressure vessel and should never be connected to an open drain system. 

For low pressure pipelines that have ports open to the atmosphere, eg, sewers or closed effluent culverts, samplers are designed to sample through manholes. In a typical system, the Hquid is lifted through a suction line into the sampling chamber under vacuum. When filled, the vacuum shuts off, and the sample drains into a sample jar. A secondary float prevents any Hquid from reaching the vacuum pump. The suction line then drains by gravity back to the source. 

Subsurface drains are essentially permeable barriers designed to intercept the groundwater flow. The water must be collected at a low point and pumped or drained by gravity to the treatment system (Figure 8). Subsurface drains can also be used to isolate a waste disposal area by intercepting the flow of uncontaminated groundwater before it enters into a contaminated site. 

The capacity of any steam trap will depend on the difference in pressure between its inlet and outlet connections. Under system start-up conditions the steam pressure in the line will at first be only marginally above atmospheric. If the trap discharge line rises to a higher level, or delivers to a pressurized return pipe, no condensate will flow through the trap until the line pressure exceeds the back pressure. It is important that steam traps which can drain by gravity, with zero back pressure, are fitted... 

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