Configuration of Roots Water Ring Vacuum Unit

The core functions of a roots water ring vacuum unit are realized through the coordination of the main pump and the backing pump. The selection and matching of the two pumps form the key to configuration. Meanwhile, basic auxiliary components are required to ensure stable operation. The functions and selection priorities of each component are as follows:

1. Main Pump: Roots Vacuum Pump

As the core vacuum booster of the unit, it further reduces the system pressure pre-pumped by the backing pump to improve the ultimate vacuum level. Key parameters for selection include:

Model and Pumping Speed

The commonly used ZJ series roots vacuum pumps cover a pumping speed range of 30–600 L/s. Selection shall be based on the volume of the system to be pumped and the required pumping rate to avoid insufficient speed or excessive energy consumption.

Stage Configuration

A single roots pump has limited ultimate vacuum; higher vacuum can be achieved through series connection, typically with 1 to 3 stages. More stages result in higher ultimate vacuum (approximately 266 Pa with a single-stage roots pump matched with a two-stage water ring pump, 25 Pa with two-stage series, and as low as 1 Pa with three-stage series).

Structural Features

Clearances of 0.1–0.8 mm are maintained between rotors and between rotors and the housing. No oil lubrication is needed, and the pump is insensitive to dust and water vapor. It is suitable for extracting gases containing moisture and a small amount of dust, adapting to various industrial conditions.

2. Backing Pump: Water Ring Vacuum Pump

As the pre-pumping foundation of the unit, it evacuates the system to a pressure range where the roots pump can start (usually 10–100 Pa). Its performance directly determines the lower limit of the unit’s ultimate vacuum. Key selection points are:

Model and Type

The widely adopted 2BV series water ring vacuum pumps feature high efficiency, compact structure, leak-free mechanical seals, corrosion-resistant aluminum bronze impellers, and high protection ratings, making them the mainstream configuration.

Working Fluid Adaptation

Water is conventionally used as the working fluid for its low cost, availability and pollution-free nature. For higher vacuum requirements, organic solvents with low saturated vapor pressure such as methanol or ethanol can be used. A closed circulation system can be established to reduce environmental pollution and recover organic solvents.

3. Basic Auxiliary Components (Essential)

These components ensure normal operation, reduce failures and extend service life:

Piping System

Use pipe diameters matching the pump inlets and outlets, keep pipelines as straight as possible with minimal bends to reduce pumping resistance. The centerline of the suction pipeline shall not be lower than the pump inlet centerline, and the centerline of the exhaust pipeline shall not be higher than the pump outlet centerline to prevent liquid or gas accumulation.

Seals

Mechanical seals or packing seals are installed at the main pump, backing pump and pipeline flanges. The 2BV series water ring pumps are standardly equipped with mechanical seals, which effectively prevent gas leakage, maintain vacuum stability and avoid vacuum degradation caused by poor sealing.

Connectors

Use properly sized flanges and valves to ensure tight connections. Especially under high vacuum conditions, even minor leakage can significantly impair unit performance. A main valve and vent valve must be installed at the inlet of the secondary roots pump to prevent back-suction of water into the pumped system during shutdown.