Mercer International Inc.

Low-Flow series OWS (5-30 gpm)


Source: Mercer International Inc.

Mercer International

The extraordinary design of this removable plate coalescer allows the highest possible efficiency with the lowest practical maintenance. The 'small flow' series is an industrial-duty separator ideal for smaller vehicle wash stations, sump/pit wastewater, groundwater treatment, and various wastewater treatment applications with solids present. Standard sizes are available in 10, 20 & 30 gpm (2, 4 & 6 m3/h).

Removable Plates

The individual coalescer plates are completely removable and adjustable. This unique feature allows the operator to field adjust the Multi-Pack coalescer to obtain optimal results. If greater oil removal is required, plates can be removed to reduce fouling, thereby reducing ongoing maintenance requirements.

The Multi-Pack module enables you to meet discharge regulations both now and in the future. As discharge limitations become ever more stringent, replacement of standard plates with longer plates will add detention time in the coalescer, thereby increasing oil removal capability. By simply replacing plates, instead of entire units, future capital costs are minimized.


The short plate widths, yield a low Equivalent Diameter (Deq). This is critical in preventing solids from building up and binding the coalescer. A low Equivalent Diameter also reduces turbulence within the separation area.

Cross Flow Design

While most coalescers employ a counter current flow of liquids and solids, MI utilizes a cross-flow design to combat fouling. This feature becomes increasingly important as plate gaps decrease. The Multi-Pack design allows both oil and solids to move in the direction of the flow, minimizing the counter-currents and turbulence that cause solids fouling and oil re-emulsification.

Parallel-Plate Advantage

True flat parallel plates are also used to assure quiet flow through the coalescer . The use of time-honored flat parallel plates, instead of the cheaper corrugated or irregular shaped plates, assures lower turbulence and a lower Reynold's Number (Nre).

Some competitors use 'irregular shaped' coalescers in various configurations, claiming that a higher Reynold's Number 'provides maximal oil droplet collision opportunities. ' This design however , leads to a redispersion of the oil droplets that may have already coalesced.

True parallel plates allow the separator to operate at higher flow rates without deterioration of oil removal capability. Systems that promote turbulence as a means of coalescing oil experience a major decline in efficiency at higher flow rates.

Minimum Rise Rate (MRR)

As important a guideline to oil separation as the Reynold's Number, the Minimum Rise Rate (MMR) is also a critical efficiency indicator.

The MRR describes the lowest vertical velocity that the oil drops can have when rising from the lowest point in the coalescer plate gap to the highest point (the point of impingement) without being carried away by the water flowing out of the coalescer plate section. MI's low Minimum Rise Rate offers a significantly higher oil capture capability.

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