In industrial settings, as pumping systems evolve towards higher heads, greater pressures, and longer continuous operating cycles, multistage and high-pressure pumps are increasingly becoming core equipment in the chemical, power, petroleum, and environmental protection industries. In these operating conditions, mechanical seals play a crucial role not only in preventing leaks but also in maintaining equipment operational stability, ensuring media safety, and reducing enterprise maintenance costs. Compared to ordinary centrifugal pumps, multistage and high-pressure pumps face more stringent sealing conditions: greater axial force, higher cavity pressure, faster temperature rise, higher speed, and longer shafts. Any slight mismatch can lead to dry friction of the sealing end face, escalating leakage, or even complete machine failure.
Analysis of Seal Arrangement Features
Higher Pressure: Sealing Cavity Pressure is the Core Risk Point
The most significant characteristic of multistage and high-pressure pumps is their high pressure. However, the sealing cavity pressure is often not the inlet pressure but rather the final stage pressure after impeller stacking. Therefore: Single-end-face seals have limited pressure resistance, easily leading to end-face cracking and leakage.
Higher pressures necessitate pressure-equalizing structures or double-end-face seals to balance the forces.
High circumferential speeds and compressed liquid films make end-face temperature control more difficult.
In this type of pump, ‘suitability for pressure bearing’ is often more important than ‘corrosion resistance.’
Double-end faces are more common: not only preventing leakage but also providing pressure-sharing and cooling
At higher pressures, double-end face seals have become mainstream, with advantages including:
Both end faces share the pressure, reducing the load on a single end face.
Stable lubrication can be achieved using shielded fluid/pressurization systems (such as Plan 52/53).
Compensation for external pressure fluctuations, resulting in smoother end-face operation.
Especially at pressures exceeding 2–3 MPa, internal double-end faces are almost a necessity.
Cooling is paramount: end-face temperature determines lifespan. Multistage pumps have long shafts and limited cavity space, making it difficult to dissipate heat from the seals. Therefore:
Plan 11 uses internal circulation for basic cavity cooling.
Plan 23 is used for high-temperature conditions, enhancing localized end-face cooling.
Plan 32 is used in environments containing solids/high impurities, with external cleaning fluid protecting the end faces.
High-pressure pumps are often paired with Plan 53A/B, relying on external pressurized fluid for thermal control.
For every 10°C increase in end face temperature, lifespan can decrease by 30–40%, highlighting the importance of cooling strategies.
Higher requirements for axial stability: Shaft runout directly kills the seal
Multistage pumps have long shafts, high speeds, and greater end offsets. If axial force is unbalanced or shaft runout is excessive:
The seal end faces will partially contact → localized dry friction → temperature rise → instantaneous burnout
The spring cannot stably compensate → the end face fit is not secure → leakage escalates
The circulating liquid film is unstable → the liquid film ruptures → the failure expands.
Therefore, such pumps often require:
Stronger bearing support
Balance discs/balance drums to reduce axial force
Seals using spring structures with larger compensation and higher rigidity.
The seal itself cannot compensate for shaft system problems; therefore, shaft stability is a fundamental condition for seal lifespan.
Stricter Material Requirements: Pressure Resistance + Wear Resistance + Stability are Indispensable
Common material configurations tend towards high hardness and high pressure resistance, for example: Hard-on-hard end faces (silicon carbide vs. silicon carbide) prevent abrasive damage to the end face; Tungsten carbide end faces are used in impact scenarios involving solids or high pressure; Bellows structures are commonly used in high temperature and high pressure environments to avoid spring fatigue; O-rings tend to use fluororubber/perfluororubber to avoid softening at high temperatures or permanent deformation under compression. In multi-stage high-pressure environments, only a material system that combines pressure resistance, temperature resistance, and wear resistance can be selected.
Limited Space: Sealing Chamber Size Determines Available Structure
Multi-stage pumps have a compact structure, and the final stage sealing chamber often has limited space. Therefore:
Most models must use internal seals; Metal bellows seals often require custom customization due to volume limitations; Some pump bodies cannot even use large double-end face seals, requiring modification of the chamber or the addition of extensions.
Therefore, the seal is not simply about ‘choosing the most expensive,’ but rather about matching the chamber space.
The sealing arrangement of multistage and high-pressure pumps is one of the most demanding areas of expertise in the field of mechanical seals. Compared to ordinary centrifugal pumps, they face higher chamber pressures, greater axial forces, faster end-face temperature rises, and more complex flow conditions, placing higher demands on structure, materials, flushing methods, and installation precision. Not all high-quality seals are suitable for high-pressure pumps, and more expensive seals do not necessarily guarantee a longer lifespan. The key factor is the compatibility between the seal structure and the pump design, operating conditions, and media characteristics. In high-pressure systems, the mechanical seal is not just an accessory, but a core safety component. Understanding its placement logic will significantly improve operational reliability, reduce maintenance costs, and enable equipment to maintain stable operation for extended periods in the most demanding environments.
