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Do Centrifugal Pumps Require a Bypass Valve?

Centrifugal pumps are used in commercial and industrial applications to pump liquids and slurries. A centrifugal pump consists of an electric motor and a rotary vane pump with either an open or sealed motor shaft. Some liquids may be temperature-sensitive or require a specific flow rate. A bypass valve can provide constant flow rate from a centrifugal pump to reduce temperatures or improve pump efficiency.

  1. Operating Temperature

    • Measure the operating temperature of the liquid leaving the centrifugal pump as you close the discharge valve downstream from the pump. If the operating temperature exceeds permitted levels for the liquid or the pump materials, install a bypass valve to return liquid to the storage tank or receiver feeding the pump. This reduces the operating temperature. A control valve or orifice is needed to reduce the pressure of the recycled product before it reaches the storage tank.

    Operating Viscosity

    • Measure the viscosity of the liquid or slurry leaving the pump as you close the discharge valve. When the viscosity increases the pump, efficiency decreases. Increased viscosity may degrade product quality. Viscosity of liquids normally decreases with increased temperature, but chemical mixtures or thermally sensitive materials may thicken, requiring bypass control. Install a bypass valve to return liquid to the storage tank or receiver to reduce product viscosity.

    Pump Efficiency

    • Centrifugal pumps provide optimum efficiency when flow rates are constant and operating above minimum flow rates. Bypass valve systems provide constant flow by preventing fluctuations in discharge flow due to downstream valves or operating changes. Bypass valve systems should be piped back to a storage tank or receiver that feeds the pump. This prevents product overheating if the pump discharge flow stops.

    Automatic Recirculation Control

    • Centrifugal pumps can be damaged if flow is reversed due to increased downstream pressures. A manual bypass valve is normally installed with an orifice valve or plate to reduce the pressure of the liquid returning to storage. An orifice is a fixed-diameter device that operates best at a single flow condition, so a control valve system may be needed for operations where varying bypass rates are needed. A check valve is also installed on the discharge line from the pump. An automatic recirculation control valve is a cost-effective alternative to manual or control valve systems. An automatic recirculation control valve can provide bypass and check valve control in a single unit. This unit also provides pressure reduction for bypassed liquids to prevent liquid flashing when the product enters the storage tank. Liquid flashing can damage equipment and degrade product quality.

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