This news article was originally written in Spanish. It has been automatically translated for your convenience. Reasonable efforts have been made to provide an accurate translation, however, no automated translation is perfect nor is it intended to replace a human translator. The original article in Spanish can be viewed at Análisis de la rentabilidad económica de un sistema de gestión de presiones

The analyzed system is implemented in a network of supply (water and city)

Analysis of the profitability of a pressure management system

Enrique Martínez Santa María, responsible for the Spanish Association of companies of engineering, consultancy and technological services (ASIC)04/01/2011

on January 4, 2011

It is well known that the overload in a supply network increase both flow escaped as the number of breaks in the network. These overload are due to the need to maintain a minimum pressure at the point more critical of the system throughout the day, appearing when it demand low. Pressure management aims to reduce these excesses of pressure. Its implementation presented costs of engineering, construction, maintenance and exploitation, to the above benefits of reducing the volume of water that enters the system and reduction of breakage of pipes. The comparison of both values through profitability analysis facilitates the decision between the desirability of implementing or not pressure management.

Introduction

All drinking water distribution system aims to provide water to the subscribers with the required quality. The quality of the provision should refer to hydraulic parameters, provided in particular flow required adequate pressure, as a parameters health, for example to ensure a proper concentration of disinfectant or low levels of pollutants.

Following the criterion that the water arrives with a pressure enough throughout the day in the most critical point of the system, there are higher than the necessary pressures during periods in which the demand is not tip, and in those points which have better water conditions. The management of pressure aims reduce this excess pressure, which produces a more homogeneous operation of the network, and a reduction in leakage flow and the appearance of breakage. This article is intended to analyse the feasibility of the introduction of a system of management of pressures, from the point of view of economic profitability, analyzing the costs involving its installation, and the benefits it produces.

Benefits and disadvantages

The decision of the implementation of a system of management of pressure through compare the benefits with the costs that arise. If the initial investment is carried out efficiently and servicing and maintenance costs are minimized, then the benefits will be maximum and the management of pressure would be justified in the majority of cases. It should be noted, as is the case in the majority of economic activities, the marginal returns are decreasing, IE: benefits will decrease as more resources, and therefore lower the grade in terms of saved water.

The main benefits that are available are:

· Caudal leakage reduction: as you know, the flow that escape through a hole is proportional to a true exponent of the pressure. Hence a reduction in pressure, means a decrease in the escapees flows. This affects both the latent leaks and to those produced by the breakage.

· Reducing the frequency of rupture: the pressure not only affects the flow of the leaks, but it may also have a significant effect on the frequency with which appear leakage and breakage, which is often the most interesting economic aspect when it is intended to carry out a programme of management pressure.

· Reduction of some components of the consumer: obviously all those duties that depend on the pressure, such as taps, showers, or irrigation will be reduced by the drop in pressure. It is important to note that generally considered to be the trend of leaving a tap opened more time for more low flow, is more than offset by the reduced flow, so that the total volume consumed is less.

· More uniform supply pressure: without management pressure, pressure supply subscribers is function of the input to the system, less losses of cargo to the distribution network. With this in mind, the pressure can vary considerably between night and day and between the different days of the week.

· Energy cost reduction: reducing the pressure of the system often involves the benefit of lower energy costs, as a result of reducing consumption of the pumping equipment when performing the direct injection of water into the network.

The disadvantages include the following:

· Difficulty in finding the leaks: there was less pressure, leakage make less noise, and cost more to find them.

· Maintenance: the installation of the equipment necessary to perform pressure management involves a maintenance so that it works properly.

· Decline in income: the reduction of consumption, is also a decline in revenues that perceived the supply company.

· Water quality: the closing of the valves of outline of the sectors can produce blind branches causing low water quality problems.

The decision of the implementation of a system of management of pressure is to compare the benefits with the costs that arise

Control systems

Between the various options to implement a system of management of pressures, perhaps one of the most commonly used is through the installation of pressure-reducing valves. The operation of these devices is to produce a loss of cargo in a way that reduces the pressure at the exit of the valve. Currently, there are devices that allow to obtain a variable pressure at the exit of the valve, based on time, the circulating flow, or the pressure at another point in the sector. The most common control systems are as follows:

· Fixed output: this is the traditional method of control, whereby the output of the valve pressure is maintained at a fixed value in such a way that, under the conditions of caudal tip, a minimum pressure at the critical point is obtained. This option is the cheapest to install, and requires minimum maintenance. When the valves are installed with a pressure of exit fixed, the loss produced in the sector means that pressures on the points of consumption will vary according to the demand of users.

Therefore, this type of valve is effective for areas with low-loss of cargo, demands do not vary much seasonally, and characteristics of uniform pressure. In other areas can be inefficient, as pressures of output must be set high enough so that met the minimum pressure at the critical point during demand tip. As the demand of the system decreases, usually at night, load on the system losses are reduced and the pressure of the system tends towards the static pressure, which in many cases it is excessive to meet the night demand and the demand for fire protection.

The disadvantages of this system could be corrected if the sector is alimentase from two or more points, in such a way that is significantly reduced load losses, relative to its value to a single point of power. This solution may not always be the practice due to the possibility of interaction between the valves, as a result of a lack of resistance in the system, that tends to close one of them. In general, a single VRP can be the most appropriate solution where the losses of cargo between the valve and the critical point are under the age of 10 m under any condition of flow. UK Water Industry (1994g).

· Modulation based on time: this is the simplest system to carry out a control of pressure and also the cheapest. Performed using a control device that has an internal clock, in a way that it varies the pressure of the valve depending on the time slot of the day, according to the pattern of demands weighed. It's an effective method for the reduction of pressure in those systems where there is a consistent pattern of daily demand, and may be an optimal solution to reduce the excess pressure at night, I when the majority of users are sleeping (conticinio) and demand is minimal.

This system has the disadvantage that before a sudden variation of flow (e.g., due to a demand for fire protection) during the hours in which the output of the valve pressure is lower, the control system is unable to respond to the new situationwhich can lead to pressures in the area are low, unless the output pressure is fixed with a sufficient safety margin to ensure the minimum level of service in such situations, which will lead to a certain excess of pressures under normal conditions.

· Based on the flow-rate modulation: this system provides greater flexibility than the previous, but on the other hand has a cost which can be approximately twice the. The pressure at the exit of the valve according to the demand of the system, through the connection of the control system for a flow meter that is close to the valve can be controlled through this system. In this way, the loss of cargo occurring in the sector is offset by the variation of the pressure at the exit of the valve, in order to maintain a uniform pressure at the critical point. This solution is best suited for those areas with variable supply conditions requiring an advanced control of the pressure.

The control can be done through a preset pattern, taking into account the relationship between flow and loss of cargo in the district. This relationship is must calculate or obtain through field measurements, and it must be entered in the control system. Alternatively, control system can be improved through your connection via radio or telephone to a meter of pressure at the critical point, in a way that adjusts the pressure at the exit of the valve so that there is not too much pressure at the critical point at any time of the day. This second option involves higher costs due to the necessary communications system, although it allows obtaining a greater water savings, as well as ensure the flow-rates required for fire protection, which makes that sometimes this type of control is more advantageous.

Figure 1: Configuration of a modulation based on flow.

Costs

The main costs, that will analyse later, and that it is necessary to consider when evaluating the profitability of a system of management of pressesures, are the following:

Costs of design

These costs are the necessary to study and define which is the most adapted alternative of management of pressesures in each sector. As it is evident depend a lot of the type of network and of his particular conditions. It can include also, all those proofs or necessary pilot studies to find the most suitable typology. Although cuantitativamente are costs no very high, if that have a main importance. As to find the optimum solution, depends that the profits expected, and therefore the profitability of the installation was maximum. An approximate value of these costs would be between 4000 to 6000 by installation.

Costs of construction

In the present section is to value the costs of construction of a camera type for the accommodation of the elements of manoeuvre and control as well as the assessment of supply and installation of these necessary elements for a regulation of pressesures. They exist multiple disposals to realizar the management of pressesures: of two lines in parallel, of two lines in series-parallel, in three lines, etc. In appears it number 2 can see an example of a typical configuration series-parallel.

Figure 2: Available to mixed series-parallel.

With the following assumptions, the cost of construction of a facility is approximately the one shown in table 1:

· Entrance diameter: 300 mm

· Outlet diameter: 200 mm

· PN = 16 atm

· Civil Engineering:

-Movement of land:

-Red height: 2,50 m

-Slope of excavation: 1 h:5V

-Working at the base of the excavation width: 0.50 m

· Concrete:

-Cleaning concrete thickness: 0.10 m

· Replacements:

-The firm of la calzada thickness: 0,30 m

· Several:

-Safety and health: 4% of the start up.

Table 1: construction costs (budget implementation Material) from a camera to control valve of pressure.

Costs of maintenance and operation

The main activities which includes the maintenance and operation, and therefore must be taken into account in the analysis of the cost-effectiveness of the system, are as follows:

· Periodic review of the facilities.

· Electric power supply.

· Transmission of data via GSM.

· Maintenance and repair of civil works.

· Maintenance and repair of hydraulic works.

· Maintenance and repairs of electronic facilities.

· Maintenance of the remote control.

These costs can be expressed on the basis of the cost of construction, obtained in the previous section, the civil engineering, hydraulic and electronic installations.

Income

All the benefits listed above, the two we are going to be considered to assess the profitability of a pressure management system are as follows: the income derived by saving water and derivatives by reducing failures and repairs. The income derived by saving energy, can have its importance in those systems where the pumping is an essential part. In this case, produced savings would also be linked with the saving of water, and could appreciate knowing this, the heights of pumping and the price of energy.

Extraction of water-saving

The methodology for assessing the efficiency of the sectors from the point of view of the cost used the principles 'BABE' (an acronym for 'burst and background estimate'), originally developed in the United Kingdom UK Water Industry (1994 to 1994g), in order to calculate the components of the actual losses based on the parameters that influence them. The aim of the methodology 'BABE' is to evaluate the individual components of the leaks in a supply area, and then compare the value estimate leakage level obtained from a balance of annual water or night flow analysis, or preferably both.

This methodology is not an exact science, and is based on a number of estimates and assumptions, some of which depend on the availability of good quality by the supplying company data, others are values by default based on averages, and others depend on engineering judgment. However, this does not reduce the validity to this technique, which could be considered similar to the modelling of water networks, which uses a mixture of data measured in field trials and estimated values.

According to the concepts 'BABE', leakage can be divided into several components:

· Latent leaks: this component is composed of numerous leaks that are individually small, with flow rates falling from 10 h until several belts of h, but it may pose a significant proportion of the total leakage, as a result of which are present during large amount of time. In fact, many of the latent leaks are never going to be repaired, what will exist from the time that occurred until the corresponding component of the network is replaced. The appearance on a regular basis of new small leaks, and the cost of its location individually, make that there is always a certain amount of latent leaks, despite peacekeeping operations who repaired some of them. These leaks occur normally in joints and joints of pipes, valves, hydrants, counters, etc., both of the distribution network and the connections of subscribers.

· Breaks reported: are those which are brought to knowledge of the supply company, unless they have had to be sought actively. This can happen because the water reaches the surface and is detected by passers-by, either because the leakage a reduction in the supply of some subscribers, with the result of a claim to the company. These leaks tend to have higher than latent leakage flow, usually between 500 to 50,000 h (although there may be some exceptions), and are communicated to the company shortly after. Takes a value of 500 l since that is usually considered that it is the minimum flow of leaks can be detected by technical acoustic, in the case of metal pipes buried with a normal coating of 1 meter. Repair these leaks usually take place in a relatively short time, in order to restore both the water supply service and some public road that may have been damaged as a result of the break, so that its average duration tends to be a few hours or days. Therefore, while its flow is high, the total volume lost by these breaks is usually small.

· Breaks not reported: these are generally lower than the reported safe, but larger than the latent leaks. They can only be found through the realization of an active control of leakage (with monitoring of sectors one of the methods for carrying out the control). They may be present for only a few days, but they can last several years, depending on the intensity with which carried out the active control of leakage. If the active control, form which the company only intervenes before the reported breakage is not made, said that the company carries out a passive control of leakage, which can only be appropriate when the water is abundant and cheap, and there is a regulation of the Administration with regard to the reduction of leakage. Then will describe the methodology developed (UK Water Industry, 1. 994e and 1. 994f).

Night minimum flow is composed of a series of terms:

· Flow-rate delivered to consumers: is the flow that reaches consumers, regardless of their class (domestic, commercial, industrial, etc.). This in turn can be decomposed into two terms, one which englobe the leaks in the Interior of the Subscriber facilities, and another that would correspond to the intentional use of water. There are significant differences between both terms, given that the first will be formed by consumption of temporary duration high, at an approximately constant flow, while the second will be for consumption of shorter duration with caudal variables, whose temporal modulation can be sliced by the existence of storage tanks.

With regard to leakage in interior facilities, must indicate that they have only taken into account the leak produced between the "point of delivery" of water (the limit of the property) and the "point of consumption" (place where is located the individual counter)Since the leaks occurring ayuso counter, it is considered that part of the consumption of the Subscriber, which are likely to be measured (although in many cases are not, due to the small current flows, and the class metrology and State of conservation of the counter). The latent leaks of internal facilities depend on the status of the installation, and can be estimated using the values indicated in table 2.

Table 2: latent in interior installations leak.

On the other hand, the volume consumed by users can be divided into three categories:

· Exceptional night consumption: any individual consumption, whether domestic or nodoméstico, whose flow exceeds the definition of a breakage (500 h), he is considered as exceptional, and it should be evaluated separately. These users can be identified from the records of the counters. To evaluate their night consumption, normally need to have a continuous record of the reading of the counter during the night, either read the counter at intervals of 1 hour between 1: 00 pm and 5: 00 pm.

Some users will have a constant night consumption, while the others show a significant variation from night to night, or weekend in week. In the latter case, different night consumption records should be considered.

· Domestic night consumption: flow Qd in h due to home users with a "normal" consumption can be assessed through:

Q_d = Q_v · N_v

Being:

Q_v: average value of the domestic night consumption, l/property/h;

N_v: total number of properties in the sector.

According to various studies on the United Kingdom, the value of Qv is 1.7 l/prop./h (or equivalently 0.6 l/capita/h). It notes however, that a small percentage of active units with high consumption can have a major influence on night average flow, which explains that values can be observed higher or lower than the average value, especially in small areas. The average value of the domestic night consumption (1.7 l/prop./h) can be considered from, roughly, from 17 per cent of active housing using 10 l each, which leads to great variability in the night consumption, particularly in small areas.

· No domestic night consumption: due to differences in their uses and features of the Interior of the non-domestic consumers installations, the variability of consumption is still higher than for domestic consumption. Caudal total due to non-household users can obtain is simplified by a similar to equation (1) expression, while taking into account that in this case the average night consumption value is 8 l/no-prop./h. However, this procedure often underestimated the night not household consumption, which makes it more convenient to classify non-household users in different categories of consumption. To do this, simply accounting in the sector study, the number of non-household users in each category, and multiply these values by the average consumption of the category. Adding the results of all groups, you get an estimate of the night consumption of non-domestic users. Table 3 shows the categories proposed in UK Water Industrie (1. 994e).

Table 3: average night consumption for non-domestic users.

Flow lost by leaks in the network: this term include leakage produced in all the elements located before the point of delivery of the water users, which is why include both losses in the distribution network and storage tanks, such as those produced in the rush of users. Annual average losses of reported and not reported in pipelines and undertaken breaks depend on the frequency, volume and duration average. The latent leaks will occur in joints and accessories of pipelines for distribution and the rush, although there are minor points where leakage can produce per meter of pipeline than in a push. Lambert and Hirner (2000) proposed the following general equation for the calculation of latent leaks, which in this document are called unavoidable real average losses (UARL).

where the parameters A, B and C have been statistically obtained after analysis of different systems in 20 different countries:

To = 18 l/km.día.mca

B = 0.80 l/km.día.mca

C = 25 l/km.día.mca

_Network l = total length of pipelines (transport + distribution) (km)

_Acoml = total length of rush (km)

_Acomn = number of rush

P = average of operation (CSF) pressure.

Another similar, but simplified, proposed method in ' Managing leakage' suggests that the night flow is calculated from the following formula, where only is taken into account the number of connections and the length of pipelines.

Q_fl = F ·N_a + G · L

being:

Q_fl: flow produced by leaks latent in the distribution network and connections in l;

Flow F: escaped by onslaught, in l/acom./h;

Caudal G: escaped by length of pipe, in l/km/h.

The values of F and G depend on the State in which they are the rush and the distribution network, respectively, as indicated in table 4:

Table 4: leakage latent in distribution pipes and connections.

The proposed methodology for the assessment of leakage is to calculate each of the components of the night minimum flow, according to the approximate values that have been indicated above. The data that are required to know are the number of users, night mean pressure and consumers exceptional, being able to estimate the number of non-domestic users from the overall percentage of the company. He is therefore to determine the minimum flow which could be reached if only there were latent leaks and consumptions of user, which can be considered unavoidable night drinking water.

Since that night minimum flow depends on several variables, should apply corrective factors when performing a series of measurements, in order to have the results to a common base. Normally considered two factors: the factor corrector of the pressure and the factor corrector of the sampling period, although given that this section is estimating the night minimum flow from the above earlier and not of measured dataonly the first factor be considered.

In order to standardize the values of the night flows, is proposed to refer all the flows to a pressure of 50 m.c.a., resulting in the corrective factors of pressure (PCF) which are indicated in table no. 5. When you perform a measurement of the flow night minimum at a pressure different from 50 m.c.a., can be a standardized flow, by dividing the volume measured by the PCF to night average pressure in the area (AZNP). Conversely, the latent leaks obtained through tables no. 3 and 4 can be also corrected with this factor, if the aim is to perform the calculations to the pressure to which measurements have been (in this case the latent leaks are multiplied by the PCF). However, according to the proposed methodology is considered that intentional water consumption does not depend on the pressure, so it should not affect this factor.

Table 5: correction Factor of pressure.

Apart from the night minimum flows determined earlier, it is necessary to know the following information:

· Evolution throughout the 24 hours of the day:

-Flow injected the sector study.

-Pressure at the point of entry

-Pressure at the median point (also known as AZP or average zone point in English). Usually adopt the point of network which has an average altitude, with the highest population density.

-Pressure at the critical point.

· Levels of the following points:

-Point of entry (ze).

-Point average or AZP (zAZ).

-Critical point (zc).

The methodology of calculation is based on two equations: on the one hand the equation that relates the flow rates of leakage at different pressures; and on the other hand, an equation of loss of load that is used to evaluate it for every hour between the point of entry, and the average and critical points:

H_{L, AZP} (t) = K_AZP (t) * Q (t)²

H_{L, crit} (t) = K_crit (t) * Q (t)²

Being:

H_{L, AZP}(t), (h)_{L, crit}(t): loss of cargo produced between the entry point and the average points and critic, respectively to time t; K_AZP(t), K_crit(t): friction factor set for the section between the entrance and point average, and between the input and the critical point, respectively for the time t. Considered that these factors of friction will remain unchanged when the management of pressure; Q (t): flow injected in time t.

Acquisition of the savings obtained by reducing failures and repairs

One of the most important advantages of the management of pressesures is the reduction in the frequency of break of the pipes. However, the studies and the bibliography related with this appearance is still reduced. It is likely that the break of a pipe occur when the efforts generated by the environingingment and the operation of the system act on the pipes, whose structural integrity has been engaged by, the bite of the corrosion, the degradation, the fracture, the drag, the ablandamiento of the material, the erosion produced by a significant quantity of escapes, an unsuitable installation or by defects of manufacture. The types of break have been classified (by Or'Day and Cabbage., 1986) in three categories: (1) the break circunferencial caused by longitudinal tensions; (2) the longitudinal breaks caused by transversal tensions (encourage to cancel); and (3) the generated in the union type “spike-bell”, caused by transversal tensions in the boards of the pipes.

This classification can complement by additional type, as it is it the one of the orifices been due to the corrosion. The breaks circunferenciales been due to the longitudinal efforts is typically the result of one or but of the following occurrences: (1) the thermal sensors contraction, because of a low temperature of the water in the pipes and of the half that the recubre, acting on a pipe restricted of movement; (2) the effort flector (failure in beam) because of the differential movement of the floor (especially in terrains arcillosos) or to the big empty in the mulch of the pipe like result of the escapes; (3) one resolves and execution of the unsuitable mulch; and (4) the interference by part of third (for example, accidental breaks, etc.). The contribution of the internal pressesure in the pipe to the longitudinal tension, although small, can increase the risk of the breaks circunferenciales when it occurs simultaneously with one or more than the others sources of tension.

The longitudinal breaks because of the transversal tensions is typically the result of one or more than the following factors: (1) the annular tension because of the pressesure in the pipe; (2) the annular tension because of the load of the coverage of earth; (3) the annular tension because of the alive loads caused by the traffic; and (4) the increase of the annular loads, because of the humidity frozen products expanded on the floor, when it produces a penetration of the frosts. As we have mentioned previously, there are not a lot of studies related with this subject. Lambert (2.001) and Trow (2.003) suggest that the change in the frequency of break can be referred to a power of the change of pressesure. That is to say:

B₁/B₀ = (P₁/P₀)^N₂

where

B₁ is the frequency of break after the management of pressesures,
B₀ is the frequency of break before the management of pressesures,
P₁ is the pressesure after the management of pressesures,
P₀ is the pressesure before the management of pressesures,
N₂ is the exponent that it is necessary to adjust.

Recent studies in the United Kingdom (UKWIR, 2.003) conclude that there is not a relation convincente between frequencies of break and pressesures before and after the management of pressesures; but the same study reveals that a relation based in the square of the relation of pressesures in front of the relation of breaks can be used of the side of the hygiene, like the worst of the predictions by effect of the management of the pressesure, taking into account that the results obtained would have to improve, because of the effect stabilizer of the management of pressesures. Thornton And Lambert (2.005) suggest that N₂has to be comprised between 0,5 and 6,5.

It is necessary to consider two appearances in the saving by reduction of failures and repairs. By a part the derivative of the works of location of the escape or failure, that can estimate around some 350 €/Unit On the other hand, the own of the repair of the failure, that as it can comprise, can vary enough in function of the characteristics of the pipe and of the type of repair that have to do.

Profitability

In the previous sections we have analysed possible solutions for the regulation of the pressure, each of which must adapt to the conditions of the sector study, producing a few benefits that must be estimated according to the above-mentioned procedures. Each solution will also have a cost, which should be compared with the benefit to determine the economic viability of the management of pressure in the sector and more effective control system. The cost-benefit analysis also provides a priority of proceedings, to compare all sectors from a same point of view.

The comparison between the cost and benefit can be done by calculating a number of commonly used ratios. These are:

· Net present value (VAN): is called net present value, or value present, a number's 'to perceive after n years, with a rate of interest 'i', to the amount which, if available from her today, generate us all 'n' years the amount 's'.

Than usual in a project of this kind is to have a first disbursement for the total of the investment and, in successive periods have a few (ariables) cash flows that will in general be variable. To accept an investment should be a VAN positive, which means that the assessment of the flows of cash, or cashflows, is higher than the initial disbursement of the same. Between two projects will be more profitable who has a go higher.

· Internal rate of return (IRR): the internal rate of return is the value of the interest rate that makes the net present value zero. This internal rate can be interpreted as the rate of interest that the investment project is able to provide and, therefore, if it is higher than the rate of interest that the company can obtain funds, the investment will be broadly desirableprovided this increase offset the degree of risk that the company assumes to undertake the project. It is always most profitable between two comparable projects, which have a higher IRR.

· Period of return (Pay-Back): defines the period of return as the period of time that has passed so that the investment recovers. More specifically it is the number of necessary periods so that the difference between accumulated cash flow and investment of the project is non-existent. In this regard a project will be much more profitable, the lower your return period.

Practical application

As a practical application of the previously mentioned, is an example. The details are as follows:

· Number of inhabitants of the sector: 23000

· Length of pipes of the sector: 25.0 km.

· Number of connections: 975.

· Elevation at the point of entry (Ze): 310,00.

· Bound on the average point or AZP (ZAZP): 307,80.

· Elevation at the critical point (Zc): 307,50.

· Minimum allowable on the net pressure: 25 m.c.a

· Flow in latent in distribution (Qfld) leaks: 40 l/km/h

· Flow in latent in rush (Qfla) leaks: 2 l/acom./h

Therefore: latent leakage flow is estimated at 2950 h; and the night minimum flow in 13800 h. Figure 3 shows the curves of behaviour of the sector: flow and pressure at the entrance, in the AZP, and at the critical point. It is important to note that the daily delivered volume is 2225700 litres.

Figure 3: Curves of behaviour of the sector.

Calculations

1. The component of the flow independent of pressure at the time of minimum consumption is: 16750,00 h.

2. The component of the flow of the pressure at the time of minimum consumption is: 37214,00 h.

3. The values of the flow of the pressure in the rest of the day are those shown in table 6.

Table 6: pressure-dependent flow.

4. The flows independent of pressure during the rest of the day are those shown in table 7:

Table 7: flow rates independent of pressure.

Paper presented during the National Congress of environment CONAMA 2010.

Solutions

A) reducing valve with luggage set output to 36 m.c.a. The results are shown in table 8.

Table 8: solution with VRP with fixed slogan.

In Figure 4, you can see the behavior of the sector once the pressure management.

Figure 4: Curves of behaviour of the sector. (Solution A).

(B) reducing pressure valve with the following slogan based on flow:

· Older than 20 l/s, pressure flows are reduced to 36 m.c.a.

· Less than 20 l/s flow rates, pressures are reduced according to the formula: p = 0.13 q + 34.6

The results are shown in table 9.

Table 9: solution with VRP with slogan based on flow.

In Figure 5, you can see the behavior of the sector once the pressure management.

Figure 5: Curves of behaviour of the sector. (Solution B).

Profitability

The comparison of the main values economic and profitable for each of the solutions is shown in table 10. You can see the huge returns that presents, in this example, the introduction of a system of management of pressures. Therein, the optimal solution would be the placement of a pressure reducing valve to fixed slogan of 36 m.c.a. at the entrance to the sector.