Centrifugal pumps will be designed hydraulically to the required operating condition - as near as possible to the best point of efficiency. The design is in accordance to the required operating flow rate and the discharge head.
If the operating flow rate falls below the design flow rate, a hydraulically unsteady condition in the pump with two unwanted effects appear. One effect is that the energy of the rotating impellers will heat up the medium with the result of cavitations. The second effect is, because of the instable flow conditions, that recirculation and flow separation in the pump occur. Vibrations, increased noises and bearing load can appear. To avoid pump damages during continuous operation the flow rate should not drop below the specified minimum flow of the pump.
|Automatic Recirculation Check Valves (ARC-Valves) are pump protection devices which prevent that the required minimum flow rate will not be dropped below. They protect automatically centrifugal pumps from damage, which might occur through partial evaporation of the fluid content during low load operation and instable flow conditions.|
For the main flow - to the process - the valves have an inlet flange DN1 and an outlet flange DN2. The minimum flow is going out through an additional branch DN3 back to the reservoir.
As soon as the pump capacity drops below a predetermined flow rate, the ARC-valve opens sufficiently the bypass to maintain the pump minimum flow rate. This rate is maintained even if the flow in main direction to the boiler or process is completely shut off.
The ARC-valve automatically opens and closes the bypass corresponding to the main flow rate. This flow controlled function operates without additional auxiliary energy.
The pressure and flow reduction to the minimum flow requirements in the bypass line takes place through a multistage throttle system (low cavitations and of low noise).
The integrated non-return valve in the main delivery stream avoids of reverse operation of the pump.
- assurance of the required pump minimum continuous safe flow
- no inadmissible temperature increase in the pump
- avoidance of cavitations in the pump
- avoidance of pump and plant damages
- integrated non-return valve in the main delivery stream
- avoidance of reverse operation of the pump
- allows parallel pump operation
- specifically designed throttle system in the bypass (low cavitations and noises)
- reduces pressure and flow rate to minimum flow requirements
- optionally with integrated non-return valve in the bypass
- favorable NPSH-value of the plant (NPSHA) and the pump (NPSHR)
- lower capacity in operating point because of automatic closure of the minimum flow line
- lower prime mover power requirement
- lower facility costs
- automatic degassing of idle and stopped pumps
- avoidance of damages to the pump and plant caused by gas filled and dry pump operation