Mechanical systems and pipework

Mechanical systems and pipework

Water path design, pipe and valve selection, flow distribution, network implementation and performance testing

In the previous chapters, the principles of hydraulics, the choice of nozzle and pump, and the design of the pond structure were examined. A mechanical facility transforms these components into an operable assembly.

The quality of plumbing directly affects the height and uniformity of the fountains, energy consumption, the speed of response of the dramatic effects and the ease of repairs. A good pump may also not perform as expected if it is connected to a network with the wrong diameter, trapped air, high drop valves or an unbalanced collector.

The purpose of mechanical design is to deliver the required flow rate and pressure to each consumer in different working conditions; Along with the possibility of measuring, adjusting, emptying and repairing.

The calculations of this chapter are educational. The final specifications of the network must be determined based on the actual map, builders' information, water conditions, and regulations governing the project.

24–1. Knowledge of fountain circuits

Before choosing the tube, the function of each circuit should be clear. In an urban fountain, not all water paths necessarily have the same function.

Demonstration flow is not the same as the flow required for purification. The fountains may be turned off, but water circulation continues to maintain its quality.

In interactive fountains, the way water is returned to the cycle is also of sanitary importance. The CDC distinguishes between single-pass systems and recirculating systems and explains that recirculated water must be routed through proper treatment and disinfection. Interactive fountains and water circulation - CDC ^[149]

Therefore, the independence of the demonstration pump and the purification pump is not enough by itself; The connection between the two circuits and the permitted conditions for the activation of the display must also be specified in the plan.

Figure note from the source manuscript

Figure 24-1 instead

Suggested image: Circuit schematic of a hypothetical fountain with separate colors for display, treatment, gravity return, compensation water and discharge. The border of each circuit, the direction of flow and the location of the tank should be specified. This image should be presented as a conceptual design, not a general implementation plan.

Subtitle: "Separation of circuits' duties is the basis of correct design of fountain mechanical facilities."

24–2. Necessary information before network design

Piping design should start from the table of consumers' needs. For each nozzle or effect group, the following information is required:

• The number of equipment and the flow rate of each;

• Required pressure at the equipment inlet;

• installation level and range of water level change;

• Simultaneous operation situations;

• Time and manner of flow change;

• limitation of water quality and particle size;

• Connection location, installation direction and access space.

Then the actual path of the pipes, lengths, height differences, valves and connections are added to the model.

In a musical fountain, the maximum total discharge is not the only condition to be investigated. Opening a small number of branches, changing pump speed, rapid closing of valves, and sudden stops can also create critical conditions.

The output of this step should include circuit schematic, line list and operation mode table. Each line should have an identifier that remains the same in the map, installation label and operating documents.

24–3. Selection of pipe material and connection

The choice of material should be compatible with pressure, temperature, water quality, installation location, connection method and repair facilities.

This table is not an unreviewed permission to use. For example, the title "steel" is not a sufficient technical specification; Grade, thickness, connection method and compatibility with water should be determined.

Also, the sewer pipe should not be replaced with the pressure pipe just because of the appearance similarity.

The manufacturer of GF in its connection systems guide suggests the simultaneous examination of pressure, temperature, chemical resistance and the type of seals to select the system. Piping systems selection guide - GF ^[150]

Network capacity also depends on the weakest component; High pressure rating pipe does not compensate for weak valves, flanges, fittings or gaskets. Allowable pressure at actual operating temperature, transient pressures and possible vacuum conditions should be checked.

24–4. Internal diameter, nominal size and flow rate

In hydraulic calculations, the actual inside diameter is important.

Nominal size, outer diameter and inner diameter are not the same. Two pipes with the same external diameter and different thickness have different passage surface and pressure drop.

The relationship between the average speed of the flow:

$v=\frac{Q}{A}=\frac{4Q}{\pi D_i^2}$

In this regard:

• $v$ : average speed, meters per second;

• $Q$ : flow rate, cubic meters per second;

• $D_i$ : Inner diameter, meters.

Diameter selection begins with determining an initial velocity and is then evaluated by calculating drop, suction conditions, transient pressures, and cost.

For example, KSB recommends ranges of 0.7 to 1.5 m/s in suction and 1 to 2 m/s in discharge for chilled water. These numbers are a rough guide and are not legal limits or fixed prescriptions for all fountains. Head drop and suggested speeds - KSB ^[151]

In short lines of fast effects, long networks or circuits with limited suction conditions, the final choice may be different.

24–5. Calculation example: the effect of diameter on path loss

Let's consider a hypothetical road segment with a constant flow along its entire length:

• Flow rate: 21.6 cubic meters per hour, equivalent to 0.006 cubic meters per second;

• Straight length: 35 meters;

• Sum of local drop coefficients: $K=8$;

• Hypothetical Darcy friction coefficient: $f=0.024$;

• Gravitational acceleration: $g=9.81m/s^2$.

Friction coefficient is assumed to be constant for educational comparison. In actual design, this coefficient is determined from Reynolds number and relative roughness. Connection coefficients should also be extracted from the valid information of the same components.

Pipe friction loss from the Darcy-Weissbach relationship:

$h_f=f\frac{L}{D_i}\frac{v^2}{2g}$

Local drop:

$h_m=\sum K\frac{v^2}{2g}$

These two groups of losses are caused by friction along the route and local resistance of connections and valves. Basics of head loss calculation - KSB

Calculation results:

The numbers in the first column are approximate inside diameters and should not be used directly as purchase sizes.

In this example, changing the inner diameter from 50 to 75 mm reduces the drop of the same path by nearly 10 m of water column. This difference can have a great effect on pump selection and energy consumption.

However, the total table drop is not the full head of the pump. The required pressure of the nozzle, the difference in level and the loss of other path components should be added according to the energy equation and without recalculation.

Also, in the multidiagonal network, the speed of each part is different; Therefore, all the drop coefficients cannot be calculated without conversion, at the speed of a pipe.

Figure note from the source manuscript

Figure 24-2

Suggested image: column chart of the total drop of the four internal diameters of the example, along with the insertion of flow rate and constant length. Next to the diagram, a cross section of a pipe should be placed showing the outer diameter, thickness and inner diameter.

Caption: "True internal diameter is one of the main determinants of network pressure drop."

24–6. Collectors and uniform flow distribution

The collector divides the main flow among the branches. If the pressure at the junctions is different, the same nozzles may also produce different heights.

The following must be checked in the collector:

• Pressure drop along the main path;

• Reduction of discharge after each branch;

• Length and strength of branches;

• Alignment and pressure requirement of nozzles;

• Changing the current distribution when opening and closing the branches.

The diameter of the collector cannot be determined only by summing the cross-section of the outlets. The calculation must be done piece by piece.

Center feed, side feed, or annular arrangement may help with better distribution, but none of them guarantee equal pressure without calculation.

A branch adjustment valve can correct the remaining differences. Extensive use of current choke to compensate for improper collector causes head loss.

In the collector map, the branch number, flow direction, pressure measurement location, discharge points and opening space of the equipment must be specified.

24–7. Designing the suction path and water harvesting points

The suction path must deliver the water to the pump under suitable conditions. High drop, air entry or asymmetric flow in this section can disrupt the pump's performance.

The important principles are:

• reducing complexity and unnecessary connections;

• preventing the formation of air trapping points;

• Compliance with the inlet conditions and direct length required by the pump manufacturer;

• sealing connections against air entry;

• Access for cleaning and inspection;

• Checking path loss in NPSH calculations.

In a suction line where the pressure is less than atmospheric, a faulty connection may introduce air without an obvious water leak.

KSB advocates using proper routing details and eccentric conversions to prevent air entrapment in horizontal intake lines. The installation direction of the conversion must be coordinated with the actual arrangement of the line. Connections and formation of air bubbles in suction - KSB ^[152]

If the pick-up point is accessible to the public, the design should also cover the risk of entanglement in the body, hair or clothing due to suction. Deceleration in the pipe alone does not prove the safety of the extraction port; Orifice assembly, cover, flow capacity and suction arrangement should be checked. CPSC resources explain the importance of specifically designing suction equipment in accessible water spaces. Suction Equipment Safety - CPSC ^[153]

24–8. Selection of valves based on duty

It is not enough to choose a valve based only on the diameter of the connection.

The check valve should also be checked for behavior when the pump stops. Improper selection of it can be associated with an impact closure.

On the GSO website, the "Switch Valve Fountain" group has been introduced. To use such equipment, selected model information about flow rate, pressure drop, response time and working conditions should be included in the network design. Valve switch fountain - GSO ^[154]

In some steering valves, the operation depends on the minimum pressure difference. Therefore, turning on the electric steering does not necessarily mean achieving the desired hydraulic behavior.

For demonstration circuits, the state of the equipment when the power is cut off and the state of the current in that state should also be known.

24–9. Ram shock and rapid flow changes

In musical fountains, changing flow is part of normal operation. However, a rapid change in speed can create a pressure wave.

KSB introduces the rapid closing of the valve and the stopping of the pumps as factors that cause pressure transients and explains that this phenomenon can cause both a pressure increase and a severe pressure drop. Transient pressures - KSB ^[155]

For a rapid change in velocity, Zhukovsky's simple approximation:

$\Delta p=\rho a\Delta v$

In SI units, the result of the relationship is in pascals. where $a$ is the speed of pressure wave propagation and $\Delta v$ is the change in flow speed.

For a hypothetical example:

$\rho =1000,a=300m/s,\Delta v=1m/s$

$\Delta p=300,000Pa=3bar$

This number is the pressure rise of an idealized state; The wave speed must be determined for the material, thickness, fluid and actual containment conditions. The relationship is not a substitute for the transient analysis of the complex network.

The solutions that can be investigated include changing the operation time of the valve, modifying the program for changing the pump speed, selecting the appropriate one-way valve, modifying the diameter and arrangement of the network, and using transient pressure control equipment.

Remote control alone does not guarantee protection during sudden power outages. Also, the presence of an incidental air volume in the line is no substitute for engineered shock absorption equipment.

24–10. Support, containment and length change

The pipe filled with water, valve and collector have considerable weight. This weight and forces caused by movement and pressure should not be transferred to the pump or nozzle connection without checking.

Three roles should be distinguished in the support plan:

• Weight bearing;

• Longitudinal movement guidance;

• Restraining force at fixed points.

The support distance depends on the material, diameter, thickness, temperature and weight of the fluid. The GF guide also relates the determination of the distance of supports to these variables. Supporting polymer pipes - GF ^[156]

Heavy valves and collectors may require independent support. Sliding points must allow the anticipated movement and fixed points must be designed for applied forces.

Flexible connection also works only within its allowed range; Using it to compensate for irregular installation or lack of proper restraint is not a reliable solution.

When passing through the movement seam of the building or pond, the details of the pipe must be coordinated with the movement of the structure and the sealing of the previous season.

Figure note from the source manuscript

Figure 24-3 instead

Suggested Image: Photograph of a collector before being fitted, showing the independent support, opening fittings, numbered valves and pressure gauge location. Show the difference between fixed point and sliding support in a small box.

Caption: "A maintainable network requires containment and access space in addition to proper routing."

24–11. Gravity return, overflow and discharge

The design of the gravity return line is different from the pump discharge line. In the gravity line, the capacity depends on the slope, the level of the beginning and the end, the amount of filling, the inlets and the condition of the air flow.

The important items in this circuit are:

• Water collection capacity in the highest state of display;

• The possible clogging effect of the garbage collector;

• Preventing backsliding to the surface of the dry fountain;

• Access to remove blockages;

• volume of water returned after shutdown;

• Recipient tank balance.

For the free capacity of the tank, the water in the pipes and the sections that are drained after stopping should be calculated. If the assumed return volumes from the lines and surfaces are 1.2 and 0.8 m3, respectively, the only post-stop return contribution is 2 m3; Other reserves and design margins are considered separately.

Crystal Fountains offers overflow, discharge, suction and inlet equipment in separate groups; This separation corresponds to the difference in the tasks of these points. Crystal Fountains entrances and exits ^[157]

The destination of the draining and washing water of the filter must also be known. The capacity of the destination network and the conditions for accepting water with treatment materials are part of the design.

24–12. Compensatory water and protection of supply source

Compensatory water should be entered based on the actual balance and need. It is better to measure and record its volume; Because an abnormal increase in consumption can be a sign of leakage, continuous overflow or control error.

In the design of this circuit, it must be determined:

• level of start and stop of water intake;

• Feeding milk capacity;

• System behavior in sensor or valve failure;

• warning of abnormal increase in consumption;

• The method of protecting the water source against backflow.

EPA identifies unprotected connections between potable water and non-potable sources as one of the potential routes of network contamination. Protection against cross connection and reverse current - EPA ^[158]

The method of protection, such as appropriate physical separation or approved equipment appropriate to the level of risk, should be selected according to the requirements of the local authority. A normal one-way valve should not be considered equivalent to adequate protection of the drinking water network without investigation.

The dimensions of the air gap, the type of equipment and its test program should be specified in the project documents.

24–13. Placement of engine room and measuring tools

The placement of the equipment should allow the actual work of the repairman: opening the strainer cap, removing the pump, changing the valve and washing the filter.

In the engine room map, in addition to the dimensions of the equipment, the range of opening and the path of transporting the parts should also be shown.

Checkable tools include the following:

• pressure gauge or pressure sensor at the determining points;

• measuring the pressure difference of the equipment that needs to be monitored;

• Measurement of main flow or important circuits;

• Measuring the tank level;

• compensatory water meter;

• Sampling location for water quality monitoring.

The installation location must be in accordance with the instructions of the tool. For example, installing a flowmeter in the vicinity of flow-disrupting connections, without complying with the manufacturer's requirements, can reduce the validity of the measurement.

The path of accidental water exit from the engine room, ventilation and access to electrical equipment must also be coordinated with other fields.

24–14. Performance and connection quality

A properly calculated network requires controlled implementation.

In solvent bonding, surface preparation, compatible materials and necessary time before dewatering are important. In polyethylene welding, preparation, alignment, welding conditions and cooling time should be recorded according to the approved method. In the flange connection, the matching of the surfaces, the type of gasket and the method of tightening the screws are decisive.

During execution:

Cover open pipe openings;

• The entry of materials and shavings into the network should be controlled;

• Repairable valves and fittings remain available;

• Buried tracks are recorded before they are covered;

• The support and harness must be completed before the test;

• The direction of one-way valves and other directional components should be controlled.

The line ID and flow direction must remain legible even after installation.

24–15. Pressure test, washing and start-up

Network pressure test is different from pond sealing test. For each circuit, the boundary, pressure, duration, measuring instrument and acceptance criteria should be specified.

Suggested arrangement of the program:

1. Completion of visual inspection and connection control; 2. Determining the parts that should be separated from the scope of the test; 3. Control of harnesses and test caps; 4. Controlled filling with water and release of trapped air; 5. applying pressure according to the approved method; 6. Record pressure, temperature, time and observations; 7. Fixing the defect and repeating the test of the affected part; 8. Circuit cleaning and protection of sensitive equipment; 9. Setup and performance adjustment.

The pressure and duration of the test should not be determined by a fixed rule for all sexes. Deformation behavior of polymer pipes, test temperature and component limitations should be considered in the chosen method.

For example, GF's SeaDrain White manual specifies hydrostatic testing and evacuation of trapped air and prohibits the use of compressed air to test that system. Detailed instructions should be obtained from the manufacturer of the installed system. SeaDrain White - GF System Test Guide ^[159]

After the leakage test, the performance is checked in different situations: different number of active nozzles, change of speed, change of tank level, stop and return of water. In the performance test, the pressure, flow and height of the effects should be compared with the design values.

Figure note from the source manuscript

Figure 24-4

Suggested image: A set of three archival photos including the pressure test of a section of the network, washing the line before installing sensitive equipment and adjusting the height of the nozzles during startup. Next to each photo, the circuit number and test type should be inserted.

Caption: "Network acceptance includes connection integrity, path cleanliness, and realization of designed performance."

24–16. Delivery documents and necessary information for the user

The mechanical delivery must be accompanied by documents with which the operator can identify, isolate and repair the circuit:

• Construction map with route, alignment and specifications of lines;

• The list of valves and the normal status of each valve;

• Table of balance settings and registered work points;

• The results of the pressure and start-up test;

• Specification of materials, fittings and spare parts;

• Seasonal evacuation and protection guidelines;

• the method of opening the equipment and isolating the circuit;

• Basic values of pressure, flow and compensatory water consumption.

These base values provide the possibility to detect changes. A gradual decrease in flow rate, an increase in the loss of a device or an increase in the consumption of compensating water can be analyzed when the initial performance is recorded.

A proper mechanical grid creates water effects with controllable flow and pressure and provides the access necessary to maintain this function over years of operation.

In Chapter 25: Purification, Disinfection and Fountain Water Quality Management, selection of purification circuit, filtration, sediment and algae control, requirements of interactive fountains, monitoring tools and water quality maintenance program will be reviewed.