Twin pumps

Pump Structure and Operating Principle

T and AT series twin pumps are vertical in-line centrifugal pumps with a two-part pressure chamber cast as a single piece.

Alternation of the pump units can be easily automated, as valves do not need to be opened or closed during switching. The pump is equipped with an automatic check valve to prevent internal circulation if only one pump is operating or if the other is removed for maintenance. When one pump unit is replaced with a blind cover, the other unit can be operated independently. Note that the check valve does not function as a system-required non-return valve. Twin pumps are available with constant speed operation or with an integrated frequency converter. Pumps with a frequency converter can be equipped with pressure or temperature transmitters and controlled by external automation systems.

Applications, Size Range and Technical Data

T and AT series pumps can be used for circulation, pressure boosting, and transfer of clean liquids in closed and open systems in applications requiring high dependability, reliability, and a wide range of pumping capacity on demand.

The range covers flanged pump sizes DN32–DN125 (ISO 7005) and power ratings from 0.05 kW to 22 kW (per unit). The bearings of the electric motors are permanently lubricated and maintenance-free. The modular structure of the pump allows for easy maintenance and replacement of components.

A wide range of accessories and optional features is available for the pumps.

Operating principles of a twin pump:

a) Standby pump and alternating operation:
When one pump unit is operating, the other acts as an automatic standby pump, which is started by the automation system if the running pump stops, for example due to a thermal relay trip. Alternating operation is recommended to ensure even operating hours for both units, keeping them in similar condition. A suitable alternation interval can be achieved, for example, with a weekly timer.

b) The twin pump can also be operated so that high flow rates are pumped with both units simultaneously, while only one unit operates under low demand. In this mode, the operating points must be carefully determined using the pump QH curves and the system characteristic curves. Particularly in circulation systems, parallel operation of even identical pumps often does not result in increase in pumping capacity. This operating mode may be suitable for applications with static head, such as transferring liquid from a lower level tank to a higher level. Alternating operation is also recommended in this operation mode to maintain good condition of the units.

Pumped fluid temperature:

• Constant speed operation and NC frequency converter:
  -10 … 120 °C (depending on sealing solution).
• MD frequency converter: -10 … 90 °C