Pumps and selection principles

Pumps and selection principles

Reading the performance curve, determining the arrangement of the pumps and controlling the energy consumption

The pump must supply the water needed by the nozzles with sufficient energy and under controllable conditions. Its selection is correct when it is compatible with the piping network, nozzle type, display program and installation conditions.

A pump that creates the desired height of the fountain in just one moment is not necessarily the right choice for years of operation. Performance in different modes, efficiency, suction conditions, repairability and control quality should also be checked.

In chapter 20, the hydraulic requirement of the system was calculated and in chapter 21, nozzle selection was examined. This chapter shows how this information translates into pump selection and proper alignment.

22–1. Necessary information before choosing a pump

Selection should begin with a requirement sheet. Its minimum information is:

• required flow rate and head in the main operating modes;

• Type and number of nozzles for each circuit;

• Minimum and maximum water level;

• Temperature and characteristics of water;

• installation and access conditions;

• Working hours and number of launches;

• the need to change the height and speed of the response;

• Specifications of electricity and control system;

• Required level of work continuity and reserve equipment.

For a dramatic fountain, one design point is not enough. The pump may feed all nozzles in one part of the display and only one group in another part. Each mode creates different hydraulic conditions.

Also, the flow rate of display pump, purification pump and discharge pump is obtained from different needs. Their selection is not done by a common criterion.

22–2. Classification of pumps

When choosing a pump, several independent features must be specified:

In the introduction of urban fountain pumps, GSO presents submerged and dry installation as well as fixed and variable cycle operation in separate categories. This breakdown is useful for initial selection; The final specifications must be derived from the detailed model. GSO urban fountain pumps ^[133]

The brand name or general use of the pump alone is not decisive. Performance curve, permissible installation conditions and compatibility with fountain application should be checked.

22–3. Submerged pump or pump with dry installation?

The submersible pump is installed in water and in some arrangements it can shorten the transmission path. On the other hand, access for service, minimum working depth, cables and the possibility to remove the pump become more important.

A dry mounted pump is usually placed outside the pond or tank. This arrangement can provide convenient maintenance access, but requires design of suction path, service space, ventilation and leakage control.

Dry installation is different from dry working. A pump that is allowed to be installed out of water should normally still have water in its hydraulic path and be run according to the manufacturer's instructions.

Some models accept both installation methods, but their temperature limits and conditions are different. For example, OASE states separate submerged and dry installation requirements for the Varionaut 150. Specifications of Varionaut 150 ^[134]

Figure note from the source manuscript

Figure 1–22: Two schematic cross-sections of a similar circuit with a submersible pump and an out-of-tank pump. Determine the water level, suction path, service access and equipment location. Suggested caption: "Pump installation method should be coordinated with hydraulics, architecture and maintenance."

22–4. Read the pump performance curve

The main curve shows the relationship between flow rate $Q$ and head $H$ in certain conditions. The actual working point is obtained from the intersection of this curve with the grid curve.

For a thorough review, the following information is usually required:

This set of information is also described in the pump curve guide of the Hydraulic Institute. Manual of Pump Curves, Hydraulic Institute ^[135]

Before reading the diagram, the circumference, impeller diameter, power frequency and fluid conditions must be known. The curve of one pitch or propeller diameter cannot be extrapolated to another arrangement without checking.

Also, the maximum head and maximum flow do not usually belong to the same point. The inclusion of these two numbers in the catalog does not indicate their simultaneous supply.

22–5. The point of best efficiency and working range

The point of best efficiency or BEP is the point of maximum efficiency of the pump at a given impeller diameter. For selection, two other ranges are also important:

• POR: preferred range of work;

• AOR: allowable operating range, the limits of which are determined by the design and conditions of the pump.

The proximity of normal operation to the desired range is important in terms of efficiency and reliability. However, it is not possible to declare a fixed percentage of BEP flow rate for all pumps as the permissible range. Fundamentals of pump operating ranges, Hydraulic Institute ^[136]

In the musical fountain, the duration of the presence of the pump in each situation should also be checked. A short pass from a point is not the same as a long run at the same point.

Operation with a very low flow rate or close to the closed output state is acceptable only within the limits and duration allowed by the manufacturer. The presence of remote control alone does not remove these limitations.

Figure note from the source manuscript

Figure 2–22: Training graph of head and efficiency showing BEP, preferred range, and allowable range. Suggested caption: "Pump selection should cover design point and actual operating range." The boundaries should be schematic and not presented as a general percentage.

22–6. Example of choosing between three hypothetical pumps

In the example of Chapter 20, the network requirement was obtained as follows:

$Q=21.6m^3/h$

$H\approx 11.56m$

We assume that the three pumps in the investigated circuit, at the same flow rate, have the following characteristics:

This data is educational and does not belong to the actual product. For example, it is assumed that the curves are downward and stable in the investigation range.

Option A: There is not enough head at the target discharge. Therefore, it cannot provide the required flow rate and head in the examined cycle.

Option B: It matches the needs of the network at the checked point and is more suitable for further evaluation.

Option C: Produces more head at the target flow rate. Connecting it directly to the grid does not necessarily keep the flow at the design value; The work point is moved to the new intersection of the curves.

If we want to keep the flow of option C at the target value with the valve, the additional head is approximately equal to:

$\Delta H=17.33-11.56\approx 5.77m$

This head is lost in added resistance. Adjusting the lap or selecting the appropriate blade, if allowed for the product, are other options to consider.

Choice B is still not final. Full curve, suction condition, permissible range, engine power and performance of other scenes should be confirmed.

22–7. Comparison of power and operating cost

For two options B and C, in the same debit:

$P_h=\rho gQH$

Assuming 88% motor efficiency and no drive in this comparison:

$P_{electrical}=\frac{\rho gQH}{{\eta }_p{\eta }_m}$

For option B:

$P_B=\frac{1000\times 9.81\times 0.006\times 11.564}{0.65\times 0.88}\approx 1.19kW$

For option C with the valve set to the same flow rate:

$P_C=\frac{1000\times 9.81\times 0.006\times 17.334}{0.60\times 0.88}\approx 1.93kW$

The consumption difference in this condition is about 0.74 kW. Assuming annual operation of 1800 hours in the same situation:

$\Delta E\approx 1336kWh/year$

This result is only valid for the assumptions of the example. In the actual project, the consumption should be calculated with the duration of work in different scenes, the actual efficiency of the motor and drive, and the power of the peripheral equipment.

Also, the rated power of the motor is not the same as the instantaneous power consumption. It should be clear that the power entered in the document is the axis power, the engine input power or the power of the whole assembly.

22–8. Check suction and minimum water level

Suction conditions should be evaluated in the most unfavorable operating mode; including the lowest water level, the highest expected temperature and the increase in suction smoothness.

The presence of water above the pump alone does not complete the investigation. Eddy currents, air entrainment, and poor flow near the inlet can also cause problems.

The value of $NPS{H}_A$ should be compared with $NPS{H}_R$ and the appropriate margin. If the constitutive curve is based on $NPS{H}_3$, reaching that value does not mean the absence of cavitation; This index is related to the specific drop in performance in the test. Basics of NPSH and suction margin ^[137]

The minimum immersion, the distance from the floor and the wall and the inlet geometry should also be determined according to the product and installation arrangement.

In spaces accessible to the public, the design of the suction inlet should be checked for entrapment and access by individual persons. The normal smoothness of the pump alone does not confirm the safety of such an inlet.

22–9. Remote control and display response

The remote control can be used to adjust the height, reduce consumption in some modes and coordinate with the display. But the type of control must be compatible with the pump's motor and electronics.

Two common arrangements are:

Motor compatible with external drive: the drive changes the engine speed within the permitted range.

The pump has a dedicated electronic control: the command is given to the set through a defined input or protocol.

Any single-phase pump or pump with built-in electronics should not be connected to the general drive. Compatibility must be documented.

GSO introduces DMX 24V control pumps for fountain control. Crystal also mentions a brushless motor and DMX/RDM control in the 70 Basin model. GSO control pumps ^[138], Crystal control pump ^[139]

The response speed depends on the pump, pipe and nozzle assembly. For example, OASE gives a time to reach full altitude for a Varionaut 150 with a Comet spec nozzle of 10–12. This data should not be generalized to any network. Varionaut 150 dynamic response information

Minimum revs, cooling, number of starts and behavior when the steering is disconnected must also be specified.

22–10. Common pump or dedicated pump of each group?

A common pump can feed several nozzles or groups. This arrangement reduces the number of pumps, but changing the status of one branch may change the pressure of other branches.

A dedicated pump for each group allows for more independent adjustment, but the number of equipment, cables and maintenance points increases.

The selection should start from the display scenario. If several groups must have different heights at the same time, a common pump without proper adjustment equipment will not provide this independence.

22–11. Parallel arrangement, series and reserve

In parallel arrangement, the flow of the pumps in the same head is collected together. The actual discharge of the set is obtained from the intersection of the combined curve with the network curve; So turning on the second pump does not necessarily double the actual flow rate.

In this arrangement, the compatibility of the curves, prevention of reverse flow and single pump operation should also be checked. Parallel operation of pumps, KSB ^[140]

In a series arrangement, the heads are assembled in a common discharge. Allowable shell and joint pressure, subsequent pump inlet conditions, and start-up coordination become important.

The reserve pump has a different role. If two pumps are required to provide full capacity, neither is considered a full reserve of the other.

The level of support should be clear: the continuation of the entire show, the continuation of part of it, or simply maintaining the necessary circulation of water. This decision determines the number and capacity of reserve pumps.

Figure note from the source manuscript

Figure 3–22: Three simple schematics of a shared pump, independent group pumps, and main–reserve arrangement. Suggested subtitle: "The number of pumps should be coordinated with the display independence and level of work continuity required."

22–12. Materials, sealing and protection

The material of the body and propeller must be compatible with water, materials used in operation and environmental conditions. Titles such as "steel" or "waterproof" do not take the place of detailed specifications.

Seals, cables, fittings and internal parts are also part of the selection. IP rating alone does not guarantee compatibility with water quality, desired depth or waterproof operation.

Protections are determined by product and circuit and can include:

• stop the water level drop;

• Overload protection and unauthorized temperature;

• detection of inappropriate flow or pressure conditions;

• electrical protection according to the system;

• Error logging and preventing unsafe startup.

Level sensor, thermal protection and flow control have different functions. The presence of one of them does not necessarily replace the others. The details of electrical protection will be discussed in the chapter on electricity and safety.

22–13. Maintainable placement and installation

For the pump, the removal path, working space and the possibility of separation should be provided. The dimensions of the valve should be proportional to the size and weight of the replaceable equipment.

In dry installation, the suction path should be checked according to the conditions of the pump and the points prone to air accumulation. The support of the pipes should also prevent improper load transfer to the pump.

In submerged installation, stable placement, access to the entrance and cable route are important. The power cable should not be used as a means of lifting the pump.

In both arrangements, suitable locations for pressure and flow measurement should be anticipated from the design stage. The absence of these points makes it difficult to determine the cause of the lack of height of the fountain at the time of installation.

22–14. Purchase documents and delivery test

In addition to name and capacity, purchase documents must have evaluable specifications:

Delivery test should be done in defined modes. Measurement of flow, pressure, speed or control command and power input allows comparison with the design.

To calculate the actual head of the pump from pressure gauges, the difference in height and head speed at the measurement points should also be taken into account. The pressure alone is not always equal to the pump head.

The test of different groups of display, stop and start and operation of protections should also be done according to the approved method. To test the protection, the pump should not be intentionally placed in an injurious condition without the manufacturer's permission.

Figure note from the source manuscript

Figure 4–22: Actual photo of installed pump assembly with equipment label and specified measurement points. Suggested caption: "Pump delivery is completed by recording actual performance in the project circuit." Data should be inserted only from the valid report of the same project.

22–15. Maintaining and recording reference status

After starting up, the reference status of each pump should be recorded: flow, head, power, steering or working speed, water level and filter conditions. This information is valuable for detecting future changes.

If the height of the fountain decreases, the cause should be investigated before increasing the distance. Strainer clogging, water level change, air ingress, valve condition change or wear and tear can produce a similar result.

The maintenance schedule should be in accordance with the manufacturer's instructions, water quality and working hours. Necessary spare parts, replacement method and configuration backup should also be provided to the user.

In chapter 23, the structure, pond and sealing of the fountain are examined; From water loads and equipment to the details of seams, pipe passage, coordination of structure and facilities and sealing test before final installation of equipment.