The Several Shaft Seal Methods for Liquid Ring Vacuum Pumps

The shaft seal is one of the core components of a liquid ring vacuum pump. It is responsible for creating an effective seal between the high-speed rotating pump shaft and the stationary pump housing. Its primary tasks are preventing the working liquid (usually water) from leaking out of the pump into the environment, and stopping external air from being drawn into the pump (which is crucial for maintaining vacuum levels). The choice of shaft seal directly affects the pump's operational reliability, maintenance costs, and suitability for specific processes.

The following are the main types of shaft seals used in liquid ring vacuum pumps and their detailed characteristics:

1. Packing Seal (Gland Packing)

This is a traditional and mechanically simple sealing method.

Working Principle: Soft rope-like or ring-shaped sealing material (called "packing," such as graphite, PTFE, or aramid fiber) is packed into the area where the pump shaft exits the housing. An adjustable "gland follower" applies radial pressure from the outside, forcing the packing to tightly grip the surface of the shaft or a sleeve, creating a seal through contact friction.

Key Characteristics:

Allows Controlled Minor Leakage: Packing seals are not designed for zero leakage. A small amount of working liquid must be allowed to drip out (typically a few drops per minute) to lubricate and cool the friction interface between the packing and the shaft. This is both a feature and a drawback.

Requires Ongoing Maintenance: The packing wears down over time, increasing leakage. Operators must periodically and skillfully tighten the gland follower. Once significantly worn, all the packing must be replaced during a shutdown.

Causes Sleeve Wear: The direct solid friction between the packing and the shaft sleeve leads to wear, necessitating periodic sleeve replacement.

Applicable Scenarios:

Applications where the working environment is not critical, and minor visible liquid leakage is acceptable.

Pumping non-toxic, non-hazardous, and non-flammable gases.

Users with limited initial investment budgets and the capability for regular maintenance.

2. Mechanical Seal

This is currently the most mainstream and high-performance sealing method for liquid ring pumps, representing a leap from "contact" to "face-type" sealing.

Working Principle: The core of a mechanical seal is one or more pairs of precision-lapped rings (called the "rotary face" and the "stationary face"). The rotary face spins with the pump shaft, while the stationary face is fixed to the pump housing. Under the combined action of fluid pressure and spring force, the faces remain in close contact with a minimal gap, creating a seal while rotating relative to each other. An extremely thin fluid film between these faces is essential for lubrication, cooling, and sealing.

Key Characteristics:

Excellent Sealing Performance: Achieves virtually no visible leakage (on a micro-leakage scale), meeting modern industrial requirements for environmental protection and safety.

Long Service Life: Because the wear is across flat faces, it is even and slow. Under normal operating conditions, lifespan can reach thousands or even tens of thousands of hours, far exceeding that of packing seals.

Low Operating Power Consumption: Frictional resistance is much lower than with packing seals, resulting in more energy-efficient operation.

No Shaft/Sleeve Wear: Wear is confined to the seal faces themselves, protecting the pump shaft or sleeve.

Higher Demands on Operating Conditions: The fluid film between the faces is critical. Therefore, mechanical seals are very sensitive to solid particles in the medium, which can scratch the polished sealing surfaces and cause rapid failure. They often require a clean flush fluid system.

Types and Advanced Options:

Primary Advantage: Provides dual safety and absolute containment. If the inner seal fails, the barrier fluid leaks into the pump, not the process gas into the atmosphere. Conversely, if the outer seal fails, air leaks into the barrier fluid, not the process gas out.

Applicable Scenarios: Extremely demanding conditions involving toxic, hazardous, flammable, explosive, highly corrosive, expensive, or oxygen-sensitive media.