Lesson 14: Why Shimming?
Objective:
By the end of this lesson, you will understand the critical role of shimming in the operation and maintenance of peristaltic hose pumps. This lesson will cover the importance of shimming for precise pressure control, its impact on hose compression, and how to properly implement shimming during pump setup and maintenance.
14.1 Introduction to Shimming in Peristaltic Hose Pumps
Peristaltic pumps operate by using rollers or shoes to compress and release a hose in a controlled manner, creating a vacuum that draws fluid through the hose. Shimming, the process of adding or adjusting thin strips of material (shims) to control the pressure exerted by these rollers or shoes, is essential to ensure uniform and effective compression of the hose. This lesson will delve into why shimming is necessary, how it affects pump performance, and the steps to properly shim your peristaltic pump.
14.2 The Importance of Shimming
14.2.1 Ensuring Uniform Compression
Challenge: Without proper shimming, uniform compression might not be achieved in peristaltic pumps. Even with high manufacturing standards, slight variations in the dimensions and geometry of pump components, such as the rollers, shoes, and pump housing, can occur. These variations can lead to uneven compression of the hose, reducing pump efficiency and increasing wear.
Solution: Shimming allows for fine-tuning the pressure exerted by the rollers or shoes, compensating for these minor variations. By ensuring uniform compression across the hose, shimming helps maintain consistent flow rates and extends the hose’s lifespan.
14.2.2 Compensating for Hose Variations
Challenge: Rubber hoses, even from the same manufacturer, can exhibit variations in thickness, flexibility, and resilience. These differences can affect how the hose compresses under the rollers or shoes, leading to inconsistent performance if not addressed.
Solution: Shimming helps adjust for these hose variations, ensuring that the hose is uniformly compressed throughout its length. This consistency is crucial for maintaining the desired flow rate and preventing backflow or slippage, which can occur if the hose is not fully compressed.
14.2.3 Accounting for Thermal Expansion
Challenge: The components of the pump, including the housing, rollers, shoes, and the hose, can expand or contract due to temperature changes during operation. This thermal expansion can affect the gap between the hose and the rollers or shoes, potentially leading to uneven compression.
Solution: Shimming allows for adjustments that account for these thermal expansions, maintaining the correct compression of the hose even as temperatures fluctuate. This ensures that the pump operates efficiently across its entire performance curve, regardless of temperature changes.
14.3 Shimming for Optimal Pump Performance
14.3.1 Shimming During Setup and Maintenance
Shimming adjustments are typically made during the initial pump setup or during routine maintenance. Proper shimming ensures that the pump operates efficiently and that the hose is fully compressed throughout each revolution. This full compression is vital for creating the peristaltic action needed to move the fluid without backflow or slippage, which would negatively impact both pump performance and hose life.
Key Considerations:
- Correct Compression: Shimming ensures that the shoes or rollers compress the hose properly at all points, maintaining the integrity of the peristaltic action.
- Performance Across RPM Range: Shims must be selected and adjusted to ensure proper hose compression across the entire RPM range, even as discharge pressures change.
14.4 Steps for Correct Shimming Installation
Proper shimming is crucial for the correct installation and operation of a peristaltic hose pump. Follow these steps for effective shimming:
14.4.1 Tolerances
Action: Measure the “A Dimension” (the distance between the pump housing and the hose) in three locations and use the largest measurement to ensure proper fit and uniform compression.
Importance: This step accounts for any manufacturing tolerances in the hose, pump house, rotor, and pressing shoe or roller, ensuring that the hose is evenly compressed.
14.4.2 Hose Finish: Wrapped vs. Rectified Hose
Action: Determine whether the hose is wrapped or rectified, as this affects the number of shims needed.
Importance: Wrapped hoses typically have a more consistent thickness, while rectified hoses may require additional shimming to achieve uniform compression.
14.4.3 Hose Tolerances
Action: Always check the internal diameter (ID) of the replacement hose to ensure it meets the pump’s specifications.
Importance: Variations in the hose ID can affect how the hose fits within the pump, potentially requiring adjustments to the shimming.
14.4.4 Hose Material Expansion with Warm Product Transfer
Action: Reduce the number of shims if the hose material expands significantly when transferring warm products.
Importance: Warm fluids can cause the hose to expand, which may require reducing the shimming to maintain proper compression without overstressing the hose.
14.4.5 Adjusting for Speed and Pressure Changes
Action: Check and adjust the shimming at different speeds and pressures to ensure consistent compression and performance across the pump’s operating range.
Importance: The speed of the pump changes the pressure exerted on the hose, so shimming must be adjusted accordingly to maintain efficiency and prevent hose damage.
14.4.6 Accounting for ΔP (Discharge Pressure − Suction Pressure)
Action: Ensure that shimming accounts for both inlet and discharge pressures, especially at peak pulsation pressures.
Importance: The differential pressure across the pump can impact hose compression, requiring precise shimming to maintain performance under varying conditions.
14.4.7 Handling High Viscosity Fluids
Action: Reduce the number of shims when handling high-viscosity fluids, as these fluids create more resistance in small cavities and make backflow more difficult.
Importance: Proper shimming helps to maintain flow rates and prevent hose damage when pumping high-viscosity fluids.
14.4.8 Calculating Shims for Each Shoe or Roller
Action: Calculate the required number of shims for each shoe or roller individually, then multiply by the total number of shoes or rollers in the pump.
Importance: This ensures that each compression point on the hose is properly shimmed for uniform performance.
Conclusion:
In this lesson, we explored the vital role of shimming in the operation of peristaltic hose pumps. Proper shimming is essential for achieving uniform hose compression, accounting for variations in components, and ensuring optimal pump performance. By following the steps outlined in this lesson, you can effectively manage shimming during both setup and maintenance, leading to improved pump efficiency and longevity.
Open questions: These questions will help learners reflect on the critical importance of shimming in ensuring the efficient operation and longevity of peristaltic hose pumps.
- What is the role of shimming in the operation of peristaltic hose pumps, and why is it critical for ensuring proper hose compression?
- How does shimming help compensate for slight variations in the dimensions of pump components like rollers, shoes, and the pump housing?
- Explain how shimming helps maintain uniform compression in hoses that may have variations in thickness, flexibility, or resilience.
- Why is it important to account for thermal expansion in pump components when setting up or adjusting shimming for peristaltic pumps?
- How can improper shimming affect the performance of a peristaltic hose pump, particularly in terms of backflow, slippage, and flow rate consistency?
- Describe the steps for correctly installing shimming in a peristaltic pump, and explain how tolerances in the “A Dimension” should be measured.
- How does the type of hose (wrapped vs. rectified) affect the number of shims required for proper compression, and why is this distinction important?
- In what ways does the temperature of the fluid being pumped impact the need for adjustments in shimming, particularly when handling warm products?
- Why is it necessary to adjust shimming for varying pump speeds and pressures, and how does this ensure optimal hose compression and performance?
How should shimming be calculated for each shoe or roller in a peristaltic pump, and why is it important to account for the total number of shoes or rollers in the system?