Lesson 16 – RCME SL

Lesson 16: RCME Pump Selection and Troubleshooting Program

Objective:

By the end of this lesson, you will understand why it is crucial to begin with an analysis of fluid properties when selecting a pump or troubleshooting pump issues. This foundational knowledge helps ensure that the pump chosen is well-suited for the fluid it will handle and can prevent common operational problems.

16.1 Introduction to Fluid Properties in Pump Selection

When selecting or troubleshooting a pump, understanding the properties of the fluid being pumped is essential. The fluid’s characteristics directly influence the performance of the pump, its suitability for the application, and its longevity. Ignoring these properties can lead to inefficient operation, frequent maintenance issues, and even pump failure. This lesson will explore why starting with fluid properties is a critical step in both pump selection and troubleshooting.

16.2 Key Fluid Properties to Consider

Let’s break down the key fluid properties that must be considered, as shown in the provided product details table:

16.2.1 Fluid Density (kg/dm³)

Importance: The density of the fluid affects the amount of energy required to move it. Higher density fluids require more power to pump, which can influence the choice of pump type and size.
Impact: If a pump is not adequately sized for the fluid’s density, it may struggle to achieve the desired flow rate, leading to increased wear and potential pump failure.

16.2.2 Product Temperature (°C)

Importance: The temperature of the fluid can affect its viscosity and other physical properties, as well as the materials used in the pump construction. Higher temperatures can cause certain materials to expand or degrade, affecting pump performance.
Pump Speed Relationship: There is a direct relationship between pump speed and the fluid temperature. As the pump speed increases, the friction generated within the pump can raise the fluid temperature, potentially leading to overheating.
Operating Limits: Generally, the fluid temperature should not exceed 80°C during normal operation. However, for special cleaning purposes, a maximum temperature of 115°C is allowed for a limited time of 15 minutes. After such high-temperature cleaning, a cool-down period may be required to prevent damage to the pump components.
Impact: Operating a pump outside of its temperature range can lead to premature wear, leakage, or even catastrophic failure if the materials are not compatible with the fluid’s temperature.

16.2.3 Vapor Pressure (kPa)

Importance: Vapor pressure indicates the tendency of a fluid to vaporize. Fluids with high vapor pressures are prone to cavitation, a condition where vapor bubbles form and collapse within the pump, causing damage.
Impact: Selecting a pump without considering vapor pressure can result in cavitation, which significantly reduces pump efficiency and lifespan. Proper selection can help avoid this damaging phenomenon.

16.2.4 Viscosity (cPs)

Importance: Viscosity is a measure of a fluid’s resistance to flow. Highly viscous fluids require more force to move, which can affect the pump’s power requirements and the type of pump selected.
Self-Priming Capability: The pump is self-priming and can generate nearly a full vacuum (9.5 meters of water column) on the suction side. This capability is particularly beneficial when dealing with viscous fluids that might otherwise be difficult to move.
Velocity Consideration: Be aware that the velocity of viscous fluids is usually slower due to higher friction. This slower velocity can lead to reduced flow rates and may require adjustments in pump speed or hose diameter to maintain the desired output.
Impact: Using a pump that is not designed for the fluid’s viscosity can lead to reduced flow rates, increased energy consumption, and excessive wear on pump components.

16.2.5 Solids Content

Importance: The presence, size, and weight percentage of solids in the fluid significantly impact the pump’s design and material selection. Solids, particularly when measured by weight percentage, can cause abrasion, clogging, and increased wear if the pump is not designed to handle them.
Soft vs. Hard Solids: The selection of whether the solids are soft or hard is crucial to determine if the hose’s inner diameter is correctly sized. Soft solids may deform as they pass through the hose, whereas hard solids require a larger hose diameter to prevent clogging or damage to the hose.
Lesson Reference: Refer to Lesson 3 for a more detailed discussion on the impact of solids in fluids, particularly how the solids’ characteristics influence the choice of pump type and materials.
Impact: Pumps not designed for fluids containing a high solids content by weight can suffer from blockages, increased maintenance, and shorter service life. It is crucial to select a pump that can handle the specific solids content of the fluid, ensuring efficient operation and reduced wear.

16.3 Why Start with Fluid Properties?

16.3.1 Ensuring Proper Pump Selection

Explanation: By understanding the fluid properties first, you can select a pump that is specifically designed to handle those characteristics, leading to better performance, efficiency, and longevity.
Example: For a fluid with high viscosity and large solid particles, a peristaltic pump with reinforced hoses and robust rollers might be the best choice. Without considering these properties, a centrifugal pump might be selected, which would be prone to clogging and rapid wear.

16.3.2 Preventing Common Troubleshooting Issues

Explanation: Many pump issues can be traced back to a mismatch between the pump and the fluid properties. Starting with an understanding of these properties can help diagnose problems more accurately and prevent them from occurring in the first place.
Example: If a pump is cavitating, reviewing the fluid’s vapor pressure and adjusting the pump speed or selecting a different pump might resolve the issue. Without considering these properties, the problem might persist despite other troubleshooting efforts.

16.4 Application of Fluid Properties in Troubleshooting

When troubleshooting a pump, revisiting the fluid properties is often the first step:

16.4.1 Identifying the Root Cause

Process: Compare the operating conditions of the pump with the known fluid properties. Check if the pump is operating within the specified parameters for temperature, pressure, and viscosity.
Result: This comparison can help identify whether the issue lies with the pump itself or if the fluid characteristics are causing operational difficulties.

16.4.2 Adjusting Operating Conditions

Process: If the fluid properties are found to be outside the pump’s design parameters, adjustments can be made. This might include reducing the pump speed, increasing the temperature to lower viscosity, or selecting a different pump material.
Result: These adjustments can often resolve issues without the need for extensive repairs or pump replacement.

16.5 Hose & Insert Details

When it comes to selecting the right materials for the hose and inserts, making the correct choice is critical because these are the only wetted parts in contact with the transferred fluid. Choosing the wrong materials can lead to chemical incompatibility, premature wear, and potential pump failure.

16.5.1 Hose Material Selection

Resource: To ensure the hose material is compatible with the fluid being pumped, refer to the hose compatibility guide available at Hose Compatibility Guide.
Explanation: The hose material, whether it’s Natural Rubber (NR), Nitrile Rubber (NBR), EPDM, or another type, must be selected based on the chemical nature of the fluid, its temperature, and its abrasiveness. For example, NR is excellent for handling abrasive slurries but may not be suitable for oils or fuels, where NBR would be a better choice.

16.5.2 Insert Material Selection

Resource: For selecting the correct insert material, which could be SS316 or another alloy, consult the insert compatibility guide at Insert Compatibility Guide.
Explanation: The inserts, typically made from stainless steel, must be resistant to the chemical properties of the fluid. SS316, for example, offers good corrosion resistance and is suitable for a wide range of chemicals, but other materials might be needed for more aggressive substances.

16.5.3 Importance of Matching Materials

Explanation: Since the inside of the hose and the inserts are the only wetted parts, it is crucial to match these materials perfectly with the fluid’s properties to prevent degradation, ensure a long service life, and maintain efficient pump operation.

16.5.4 Hose Type Selection

Options: When selecting a hose, you can choose between a standard hose (wrapped finish), a rectified hose (ground finish), or a long-life hose.
Long Life Hose Specifics: The long-life hose has less reinforcement, a thicker inner layer, and is only suitable for low-pressure applications (maximum 7 Bar). This type of hose is produced by Bredel and is known as a transfer hose.
RCME Standard: RCME produces rectified hoses as standard, and the quality of these hoses exceeds that of all competitors. The rectified hoses offer superior surface finish and consistency, which contributes to better performance and longer service life.

16.6 Inlet and Discharge Details

Proper analysis of the inlet and discharge details is crucial for calculating pressure losses, understanding the hydraulics, and ensuring the efficient operation of the pump. The parameters for both the inlet and discharge sides of the pump must be accurately measured and considered during the pump selection process.

16.6.1 Pressure Loss Calculations

Importance: The line lengths, diameters, and velocities of the fluid on both the inlet and discharge sides affect the pressure losses in the system. Proper calculation of these losses ensures that the pump can overcome the resistance in the system and maintain the desired flow rate.

16.6.2 Hydraulics of the Inlet and Discharge

Explanation: Understanding the hydraulics of the inlet and discharge involves analyzing the static height, equipment losses, and service pressures. This helps in selecting a pump that can handle the specific conditions of the system, ensuring reliable operation and preventing issues such as excessive pulsation or short hose life.

16.6.3 Static Height and Suction Lift

Importance: The static height on the suction side is crucial when evaluating the suction lift of the pump. While it is commonly advertised that peristaltic pumps can achieve a suction lift of 9.5 meters of water column, it is important to note that this performance is typically achieved at low pump speeds.
Suction Lift Considerations: At higher pump speeds, the fluid may not reach the pump as efficiently, and more time is needed for the hose to recover its shape from flat to circular. Additionally, it is essential to be cautious with the maximum inlet pressure, which is typically around 3 Bars in most pumps. This should be verified with the operating and instruction manual of the specific pump model being used.

16.6.4 Pulsation Considerations

Importance: Pulsation is a critical factor in peristaltic pumps, as the nature of their operation inherently causes pulsating flow. Accurately calculating pulsation and selecting appropriate pulsation dampeners for both the inlet and discharge sides are essential to smooth out the flow and reduce stress on the system.
Dampener Selection: The selection of the inlet and discharge pulsation dampeners is an important part of pump selection and operation. These dampeners help to minimize the pulsation effects, thereby reducing the risk of damage to the system components and ensuring consistent flow.

16.7 Pump Performance Details

The performance of the pump is a key factor in ensuring that the system operates efficiently and meets the desired flow requirements. The following details are crucial for understanding and optimizing pump performance:

Requested Flow Rate: This is the desired flow rate for the installation, typically specified in liters per hour (ltr/hr). It represents the amount of fluid that needs to be moved through the system within a given timeframe.
Volume per Turn: This value is calculated based on the pump size selected. It represents the amount of fluid displaced by the pump with each complete rotation of its mechanism, typically measured in liters.
Calculated Pump Speed at 50 Hz: Based on the manufacturer’s performance curves, the pump speed required to achieve the requested flow rate is calculated. This speed is usually expressed in revolutions per minute (RPM) and is critical for ensuring that the pump operates within its optimal range.

16.7.1 Drive Details

Understanding the drive details is essential for ensuring that the pump motor is correctly sized and capable of handling the operational requirements. The motor’s performance directly affects the pump’s ability to maintain the desired flow rate and pressure.

Motor Size: This is the power rating of the motor, typically expressed in kilowatts (kW). It is an input field and represents the maximum power the motor can deliver.
Motor Efficiency: This is a measure of how efficiently the motor converts electrical energy into mechanical energy, expressed as a percentage. Higher efficiency means more of the input energy is used for pumping rather than being lost as heat.
Motor Output: This is a calculated field that represents the actual power output of the motor, taking into account its efficiency. It is crucial for determining whether the motor can handle the required power for the pump’s operation.
Motor Power Required @ x Hz: This is another calculated field that indicates the power required by the pump at the highest frequency output of the frequency inverter, typically at 60 Hz. It helps ensure that the motor is adequately sized for the pump’s operating conditions.
Motor Service Factor: This is an input field that represents the safety margin for the motor’s operation. A higher service factor allows the motor to handle temporary overloads without damage.
Altitude: This input field is the altitude at which the motor operates, measured in meters. Altitude can affect motor performance due to changes in air density, which impacts cooling and power output.
Minimum Torque Required: This calculated field represents the minimum torque needed by the pump to operate effectively. It ensures that the motor can provide sufficient torque to drive the pump under all operating conditions.
Starting Torque Available: This is the calculated torque available from the motor when starting. It is critical for ensuring that the pump can overcome initial resistance and start operating without stalling.
Torque Considerations: The starting torque available is generally about three times the running torque for a direct-on-line (DOL) connection. This high starting torque ensures that the pump can overcome initial resistance, such as the inertia of the pump components and the load of the fluid in the system. However, when using a frequency inverter, the starting torque is typically reduced to about 1.5 times the running torque. This reduction occurs because frequency inverters limit the current supplied to the motor during startup to avoid excessive inrush currents, which can cause voltage dips in the electrical system and potential damage to the motor. While this controlled start reduces mechanical stress and wear on the pump, it also means that careful consideration must be given to the motor and inverter selection to ensure sufficient starting torque is available for the pump to start reliably.

16.7.2 Drive Adjustments

The functionality of a frequency inverter is crucial in controlling the speed of the pump motor, which directly affects the flow rate and pressure. Here’s why the correct settings and a suitable frequency inverter are essential for peristaltic pumps:

Frequency Inverter Functionality: A frequency inverter, also known as a variable frequency drive (VFD), allows for the precise control of the motor speed by adjusting the frequency of the electrical power supplied to the motor. This flexibility is vital for optimizing the pump’s performance across different operating conditions.
Importance of Suitability for Positive Displacement Pumps: Not all frequency inverters are suitable for positive displacement pumps like peristaltic pumps. It is important to ensure that the frequency inverter is designed to handle the specific torque characteristics of positive displacement pumps.
Constant Torque Output: For peristaltic pumps, it is crucial that the frequency inverter is set to provide a constant torque output, rather than a ramping torque. Constant torque is necessary to maintain a consistent flow rate, especially at varying speeds, and to prevent overloading or damaging the pump components.
Maximum and Minimum Frequencies: The drive adjustments include settings for maximum and minimum frequencies, which correspond to the pump’s operating range. For example, at 50 Hz, the pump may achieve its maximum flow rate and speed, while at 30 Hz, it operates at a reduced flow rate and speed. These settings help in optimizing the pump’s performance and energy efficiency.
Flow Rate and Pump Speed Adjustments: The frequency inverter allows for adjustments in both flow rate and pump speed. For instance, reducing the frequency lowers the pump speed and flow rate, which can be useful in applications requiring precise control over fluid delivery. The settings shown indicate how the pump’s performance is adjusted based on the selected frequency.

16.10 Understanding the Pump Performance Overview

The provided overview is a detailed summary of the pump performance across different models and operating conditions. It is essential to understand this table to make informed decisions regarding pump selection and operation. Let’s break down the key components:

16.10.1 Pump Size and Flow Rate

Explanation: The table lists various pump models (e.g., Bredel 10, APEX 10) along with their corresponding flow rates and operating speeds (RPM). The flow rate is measured in liters per hour (ltr/hr), indicating how much fluid the pump can move within a specific timeframe at the specified speed.
Significance: The flow rate and RPM help determine the suitability of a pump model for a particular application, ensuring it can meet the operational requirements.

16.10.2 Estimated Hose Life

Explanation: This column provides an estimate of the hose life in hours for each pump model at the given operating conditions. Hose life is a critical factor as it directly affects maintenance schedules and overall operating costs.
Significance: Selecting a pump with a longer hose life can reduce downtime and maintenance costs, making it a more cost-effective choice in the long run.

16.10.3 Pulsation and Pressure

Explanation: The table includes details on the inlet and discharge pulsation (kPa.a) and pressure (kPa) for each pump model. Pulsation refers to the fluctuations in pressure during the pump’s operation, while the pressure values indicate the force exerted by the pump at both the inlet and discharge.
Significance: Understanding pulsation and pressure is crucial for ensuring that the pump operates within safe limits and that the connected system components are not subjected to excessive stress, which could lead to failures or reduced lifespan.

16.10.4 Continuous and Intermittent Duty

Explanation: The table categorizes the operating conditions into continuous duty and intermittent duty, with corresponding maximum RPM values. Continuous duty refers to the pump operating under constant conditions without risk of overheating or excessive wear, while intermittent duty allows for short bursts of operation followed by a cooldown period.
Significance: Ensuring that the pump operates within the appropriate duty cycle is essential for maintaining efficiency and avoiding premature wear. Operating a pump beyond its continuous duty range can lead to overheating, reduced hose life, and potential failure

16.10.5 Color Coding and Interpretation

Explanation: The table uses color coding to indicate the suitability of the operating conditions:
- Green: Indicates the selected, optimal operating conditions where the pump performs efficiently and within safe limits.
- Yellow: Represents the intermittent duty zone where the pump can operate, but with caution and limited duration.
- Red: Denotes conditions that are not good for continuous operation, such as the Bredel 25 running at 111.1 RPM, which significantly reduces hose life.
Significance: This color coding helps quickly identify the best operating conditions for each pump model, ensuring that the pump is not pushed beyond its limits.

16.11 Conclusion

Starting with fluid properties is a fundamental step in both pump selection and troubleshooting. By thoroughly understanding the fluid’s characteristics, ensuring the correct selection of hose and insert materials, accurately analyzing inlet and discharge details, and understanding both pump performance and drive details, including the importance of correct drive adjustments, you can ensure that the pump is appropriately matched to the application. This leads to better performance, reduced maintenance, and longer pump life.

Open questions: These questions aim to help learners reflect on the critical considerations involved in pump selection, fluid properties, troubleshooting, and optimizing pump performance.

Why is it important to begin pump selection and troubleshooting with a thorough analysis of fluid properties, and how do fluid characteristics influence pump performance?
How does fluid density affect the amount of energy required to pump a fluid, and what impact does this have on the selection of pump type and size?
Explain the relationship between fluid temperature and pump performance. How can operating a pump outside its temperature range lead to wear or failure?
What is vapor pressure, and why is it critical to consider when selecting a pump to prevent cavitation?
How does the viscosity of a fluid influence a pump’s power requirements, and why is self-priming capability particularly important for pumping viscous fluids?
Describe the impact of solids content in the fluid on pump design and material selection, and why is it necessary to consider whether solids are soft or hard?
How can a mismatch between the pump and fluid properties lead to common operational issues such as cavitation, wear, or reduced flow rate?
What role does the material selection for hoses and inserts play in ensuring compatibility with the fluid being pumped, and how does this prevent premature wear or chemical degradation?
How do pressure losses on the inlet and discharge sides of the pump affect system efficiency, and why is accurate calculation of these losses essential during pump selection?

Why is it crucial to select the appropriate pulsation dampeners for both the inlet and discharge sides of a peristaltic pump, and how does this contribute to smoother flow and reduced system stress?

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