Lesson 8

Lesson 8: Key Considerations for Selecting and Operating a Peristaltic Hose

Objective:

By the end of this lesson, you will have a thorough understanding of the critical factors involved in selecting and operating a peristaltic hose in pump systems. This includes understanding the importance of lubrication, suction lift, temperature limits, pump speed, pulsation management, and material selection.

8.1 Introduction to Peristaltic Hose Pumps

Peristaltic hose pumps are commonly used in applications where the fluids are abrasive, viscous, shear-sensitive, aggressive, or contain solid particles. Despite being on the market for over 60 years, detailed information about their operation is not widely published. This lesson will explore the key considerations for selecting and operating peristaltic hoses effectively.

8.2 Peristaltic Hose Pump Parameters

8.2.1 Lubrication

  • Importance: Lubrication is crucial in peristaltic pumps, whether they use rollers or pressing shoes. The lubricant reduces the friction caused by the pumping action and helps in heat transfer, preventing the hose from overheating.
  • Heat Transfer: The lubricating fluid must have excellent heat transfer properties, especially in high-temperature applications, to remove the heat of compression from the hose and transfer it to the pump housing.
  • Pump Design Differences:
    • Pumps with Rollers: These pumps typically do not operate with a lubricating/cooling bath, making the temperature of the pumped fluid critical for cooling.
    • Pumps with Pressing Shoes: These usually operate with a cooling and lubricating fluid on the outside of the hose, contained within the pump housing, to manage the heat generated by friction.

8.2.2 Suction Lift

  • Maximum Suction Lift: High-pressure peristaltic pump hoses can handle a suction lift of up to 9.5 meters. However, suction lift is often a hose killer as it reduces the volume per rotation, making the hose very oval.
  • Risk Mitigation: To mitigate this risk, it’s recommended to reduce inlet pulsation and pump speed, as high suction lift can drastically reduce the hose’s lifespan.

8.2.3 Temperature Limits

  • Operational Temperature: Peristaltic pumps generate significant heat due to the continuous compression and retraction of the hoses. The maximum fluid temperature is generally limited to 80°C to prevent overheating and damage to the hose.
  • Impact on Hose Life: Operating at or near the temperature limit without proper cooling can lead to premature hose failure.

8.2.4 Pump Speed

  • Speed Zones:
    • Continuous Zone (Green): Represents safe operating conditions where the pump can run continuously without damage.
    • Intermittent Zone (Yellow): Requires a cool-down period after use to prevent hose damage from overheating.
  • Importance of Proper Speed Management: Operating the pump at appropriate speeds within the recommended zones is crucial to avoid excessive wear and overheating.

8.3 Pulsation Management

8.3.1 Inlet Pulsation

  • Cause and Effect: Inlet pulsation occurs when the roller or pressing shoe stops the media flow momentarily, creating a pressure peak followed by a re-acceleration of the fluid. This process creates moments of very low pressure, known as pulsation.
  • Impact on Hose Life: High inlet pulsation can lead to hose delamination and significantly reduce hose life. It is important to manage pulsation levels to prevent damage.

8.3.2 Pulsation Calculation

Pi​=0.16×(Q×La​×N×s.g.​) / D2 = …… kPa

Where:

  • Pi = Inlet Pulsation (kPa)
  • Q = Desired flow rate (Liters/hour)
  • La​ = Actual pipeline length (meters)
  • N = Pump speed (rpm)
  • s.g. = Specific gravity of the product
  • D = Hose diameter (mm)

Guidelines: Depending on the hose diameter, the inlet pulsation should not exceed certain values:

  • ≤ 40 mm = 40 kPa
  • ≤ 65 mm = 30 kPa
  • ≤ 80 mm = 15 kPa
  • ≤ 100 mm = 10 kPa

Consequences: When the pulsation exceeds these limits, the hose life is drastically reduced. This makes it essential to monitor and manage pulsation effectively.

8.3.3 Discharge Pulsation

  • Occurrence: Discharge pulsation happens when the roller or pressing shoe moves away from the hose, causing a brief reverse flow and a pressure drop in the discharge line.
  • Importance of Installation: Proper installation of the hose, ensuring it is fully filled and avoiding high pulsation, is crucial for extending hose life.

8.4 Solutions to Pulsation Reduction

There are several methods to reduce the pulsation caused by both inlet and discharge pulses:

  1. Introduce Air/Gas in the Suction: Adding 3% of gas can reduce pulsation in both inlet and discharge by up to 97%, but with a loss of capacity.
  2. Install a Pulsation Dampener: Placing a pulsation dampener in the suction line close to the pump can reduce pulsation by up to 90%.
  3. Use Flexible Hoses: Installing flexible hoses on the inlet side can reduce pulsation by 10-40%, depending on the hose’s flexibility.

8.5 Peristaltic Hose Type and Material Selection

Selecting the right hose material is essential for ensuring the longevity and performance of a peristaltic pump.

8.5.1 Hose Material Characteristics

  • Resilience: The hose must be able to return to its original shape after being compressed, endure millions of compressions, and withstand vacuum and high pressures.
  • Common Materials:
    • Natural Rubber (NR)
    • Nitrile Butadiene Rubber (NBR)
    • Ethylene Propylene Diene Monomer (EPDM)
    • Chlorosulfonated Polyethylene (CSM)
  • Material Selection: Operators should choose hoses based on chemical compatibility charts specifically designed for peristaltic pumps, not general O-ring or gasket materials.

8.6 Testing and Maintenance

To mitigate the risk of hose failure, it is important to regularly test and maintain the hoses:

  • Immersion Test: An immersion test at 80°C for 7 days can provide valuable insights into the hose’s durability, including measurements of weight, hardness, elongation, and shape changes.
  • Regular Inspections: Regular inspections and maintenance are crucial to detect early signs of wear and prevent unexpected failures.

Open question: These questions aim to explore the key factors in selecting and operating peristaltic hoses, focusing on lubrication, suction lift, temperature limits, pulsation management, material selection, and regular maintenance.

  1. Why is lubrication essential for peristaltic hose pumps, and how does it help in heat transfer and reducing friction?
  2. What is the maximum suction lift that peristaltic hoses can handle, and why is suction lift often referred to as a “hose killer”?
  3. How do operational temperature limits affect the performance and lifespan of a peristaltic hose, and what measures can be taken to prevent overheating?
  4. What is the significance of managing pump speed within the continuous (green) and intermittent (yellow) zones, and how does improper speed management lead to excessive wear?
  5. Explain the causes of inlet pulsation and how it affects the life of the peristaltic hose. What steps can be taken to reduce inlet pulsation?
  6. What is discharge pulsation, and why is proper hose installation critical in minimizing the negative effects of pulsation on hose life?
  7. Describe three methods for reducing pulsation in peristaltic hose pumps, and explain the potential benefits and drawbacks of each method.
  8. How does the material selection of peristaltic hoses, such as natural rubber or nitrile butadiene rubber, impact the pump’s performance and resistance to wear?
  9. Why is it important to conduct regular testing, such as the immersion test, and maintenance for peristaltic hoses, and what insights can these tests provide?
  10. What role do pulsation dampeners and flexible hoses play in improving the efficiency and longevity of peristaltic pumps, and how can they be effectively integrated into the system?

Summary

In this lesson, we covered the key considerations for selecting and operating peristaltic hoses, including the importance of lubrication, managing suction lift, temperature limits, pump speed, and pulsation. We also discussed the significance of choosing the right hose material, managing pulsation using the Breteler Equation, and the need for regular testing and maintenance to ensure the reliability and longevity of the pump system.

Next Lesson 9