In order to explain stimulation of water selection, in other words, prove a provision of continuous technological process under different terms of operation of water inlet silts, it is necessary to study processes that take place in the mouth of a water inlet slit under different schemes of water flow, define the worst one of them; develop a mathematic model and provide an analysis of the process of protecting slits from sanding, show that the suggested scheme meets the listed requirements.
While analyzing schemes of water flow towards a slit under same initial data of water-bearing horizon (coefficient of filtering (Cf) and filtration of rock (μс), power of water-bearing layer (ml), etc.) it is necessary to underline that the most unfavourable scheme of water flow is that of water inlet to a slit in a pressure water-bearing horizon. It proves the fact that while comparing all variants of water flow towards to a slit, under a same output, the greatest decrease in dynamic level is observed on the scheme of water flow towards slit in a pressure water-bearing horizon [3].
To prove a continuous operation of slits under any scheme of water inlet, we will study the worst of them – the scheme of water inlet in pressure water-bearing horizon.
While analyzing dynamics of soil water motion to a slit, we need to make a number of assumptions, introduced by Dupuit, that can simplify all reasonings:
– mirror of soil waters is horizontal and parallel to the surface of underlying waterproof layer;
– the soil is homogenous, and, therefore, coefficient of filtration is the same, and motion of the inflowing underground waters has a laminar nature.
According to these assumptions, mirror of soil waters was horizontal before pumping out water-bearing layer, in other words, the slit was placed down into a soil pool, not gravel flow. A funnel of depression is formed around the slit when the water is pumped out. Sections of this funnel by vertical flatnesses that cross the slit’s axis, give us symmetrical curves of dispersion in all cases [7].
Under the given assumptions geometric place of the points of the dispersion curves touching the lowered surface of soil waters present a round that is described from the slit center by radius R (in other words, radius of Dupuit).
In order to define the amount of water that inflows to a slit, it is necessary to define an area of some surface Ss that is equal to pressure and speed of filtration.
When coefficient of filtration Cf is known, amount of water that goes through this slit wil equal:
(1)
where dy is a difference between curves of dispersion on equipotential surface ас and the nearest equipotential surface а1 с1 that is locater on distance dS from the first line of flow.
A decrease in water level in a slit under pumping out of duration tday in no-pressure water-bearing layer is defined with formula:
(2)
In formula (2) value 
characterizes hydraulic resistance from hydrogeological conditions that can be generally expressed as:
R = RО + β ξ, (3)
where 
is a deviation of output of one slit to an output of another slit (dimensionless coefficient);
ξ is an additional resistance (defined according to tables) [3], dimensionless coefficient.
A slit’s efficiency for pressure water-bearing layers:
Qw = πCf Δhadd(2H – Δhadd)/(RО + β ξ), (4)
where Δhadd is an optimal decrease of water level in a slit, m; Нw is a domestic power of water-bearing layer, m.
An impact of water level over the slit’s output hO = H – Δh has a great practical significance. Pumping off water can alter a position of water level in a slit, and, therefore, regulate the slit’s efficiency.
A mark water level outside a slit is always higher than that inside it. This difference of marks increases as a deepness of water drop increases. An emergence of water level leap by the slit walls is explained by the fact that the surface of equal pressure near the slit, where curve of dispersion comes with greater angles to the slit wall, obtains a curved form and, if we draw a surface of equal pressure from the point of crossing slit walls by the curve of dispersion, its probable form in a cut will be presented as a curved line А В that deviants from the higher limit of the slit with an angle that equals an angle of fall of dispersion curve, and from the lower limit it comes to a vertical line. On this line piezometric pressure will be same in all cases and equal to the height of soil waters at a final point A of dispersion curve. If water level in a slit was also at the same height, then water, placed in the area between surface A – B and slit surface, would not be able to move, as this motions requires a certain decrease in pressure h0, that can develop only via water levels in a slit and across walls in its water-bearing soil.
S.K. Abramov has suggested the following empiric formula that considers an impact of basic factors over h0 [5]
(5)
where а is a coefficient that depends on a construction of filter, m2; h0 is a leap in levels, m; Q is an output of slits, m3/day; Δh is a decrease in water level inside the slit while pumping off, m; Cf is coefficient of water layer filtration, m/day; So is an operative area of the filter, m2, So = πdl, d is an outer diameter of the filter, m; l is the filterlength, m.
Analysis of processes that take place in slit mouth under the starting regime of submersible pump shows us that operative pressure increases 1,5 times at this moment, and, therefore, consumption increases as well. An increase in consumption leads to a sharp alteration in difference of water level marks in a silt and at the filter border. The less permeability of the soil, the higher a value of level leap Δh.
A sharp change in level leap value Δh, and, therefore, alteration in water flow to silt causes destruction of natural filter and carrying out soil.
While using the suggested construction of reverse valve, an even change in consumption under any pressure takes place. Therefore, we can conclude that under transitive processes in submersible pumps the reverse valve with an adjustable period of opening excludes the possibility of a sharp change in water level difference in a slit and at the border of the filter with a sufficient level of reliability (process of diffusion is not present).
Our theoretic premises will be confirmed by test results.
The work is submitted to the International Scientific Conference «Actual problems of science and education», Cuba, March, 20-31, 2013, came to the editorial office 28.01.2013.