Liquid-Ring Vacuum Pump

Overview

A liquid-ring vacuum pump creates vacuum using a rotating ring of liquid, usually water, as a moving seal between an eccentric impeller and its casing. As the impeller spins, the liquid is flung outward into a ring that follows the casing bore; because the impeller is offset, the gap between the blades and the ring grows on one side and shrinks on the other, so each pocket between blades alternately draws gas in and squeezes it out. It is the workhorse vacuum pump for wet and dirty duties, paper machines, condenser exhausting, food and chemical processing, filtration and distillation, because it tolerates carryover of vapor, droplets and slurry that would damage a dry pump.

The liquid does triple duty: it forms the compression seal, absorbs the heat of compression so the discharge stays near-isothermal, and condenses some of the pumped vapor. The trade-off is that the achievable vacuum is limited by the vapor pressure of the service liquid, so cold water gives deeper vacuum than warm.

How it works

Process gas enters and leaves through ports in the Ported Cone at the center of the Pump Casing. The Rotor Assembly spins eccentrically inside that casing; its forward-curved Liquid-Ring Impeller throws the service liquid into a ring against the bore, and the changing pocket volume between the blades draws gas in over the inlet port and compresses it over the discharge port. Make-up sealing water arrives through the Service Liquid Inlet inlet, where a flow orifice meters it and a check valve guards against suck-back on shutdown.

The rotating shaft is carried on the Bearing Set and sealed where it leaves the casing by the Mechanical Seal, whose lapped faces keep service liquid in and air out. Power comes from the Drive Motor through a flexible Drive Coupling, so the motor and pump can be aligned independently on the Base Frame / Skid.

What the pump discharges is a frothy mix of gas and entrained water. The Discharge Separator knocks that liquid out so clean gas vents and the water can be drained or recirculated. Operators read suction vacuum and liquid temperature from the Gauge Panel, the two numbers that together tell whether the ring is healthy and the pump is reaching its rated vacuum.