Why is a rotary vane pump not suitable for high viscosity and high pressures?

Rotary vane pumps are typically utilized in low to medium-viscosity and low to medium pressure applications because of their efficiency, compactness and versatility. However these pumps face a number of challenges that limit their applicability for high-viscosity and high-pressure conditions.

1. Mechanical Stress: The design of a rotary vane pump usually comprises a rotor with vanes that slide in and out to shift fluid. High-pressure conditions put significant mechanical stress on the pump components particularly the vanes and the housing. This can result in deformations or failures over time which ultimately reduce the reliability and lifespan of the pump.
2. Increased Wear and Tear: Viscous fluids make it harder for the vanes to move as they increase resistance. In high viscosity environments, such materials as metals or some plastics start wearing away at greater rates. With this, the pump decays faster calling for more maintenance activities or replacements.
3. Energy Inefficiency: When moving any highly viscous liquid, rotary vane pumps need more energy to do so hence making them less efficient. The fact that high viscosity fluids resist flow makes it necessary for these blades to use extra force that eventually pushes up energy expenses. This renders it uneconomical in the long-term.
4. Leakage and Sealing: Generally, tolerances and clearances inside a rotary vane pump are not designed to cope with elevated pressures. Consequently, leakages become common which lower its efficiency besides being potential causes of insecurity especially if conveyed media is corrosive or poisonous in nature.
5. Heat Generation: Both conditions; high viscosity as well as high pressure contribute towards increased heat generated during pumping processes. Without good heat management measures, this can lead to overheating problems further impairing functionality of the pump possibly leading to disastrous occurrences.
6. Cavitation Risk: At higher pressure levels there is an increased risk of cavitation whereby bubbles form but suddenly implode thus sending shock waves that destroy various parts within a given system like the pump itself. Cavitation has a huge impact on the operational life of a pump and can lead to sudden breakdowns.
7. Complex Control Systems: When it comes to high-viscosity and high-pressure applications, more complex control systems are needed in order to maintain constant flow rates and pressures. This increases the complexity of operations as well as expenses involved in using a rotary vane pump for such cases.
8. Material Compatibility: High pressure conditions frequently require specialized materials to withstand them. In general, rotary vane pumps are not constructed from materials that can stand up to extremely high pressures hence making them unsuitable for such duties.

In summary, mechanical design, material limitations, energy inefficiency and operational challenges make rotary vane pumps inappropriate for high viscosity or high pressure applications. Different types of pumps like gear or positive displacement pumps are therefore better suited for these difficult circumstances in most cases.