AUTOMATIC RECIRCULATION VALVES
A special lift check valve design is the Automatic Recirculation Valve. It is usually fitted on the discharge side of boiler feed pumps and designed to maintain a minimum flow during low flow operation. During low flow operation, the pump's efficiency is lower and most of the energy consumed is converted into heat which may result in the partial evaporation of the water volume trapped in the pump.
The low water volume and the resultant insufficient water lubrication can lead to damage due to metal-to-metal contact, e. g. at the balance disc (see Axial thrust). The automatic recirculation or minimum flow valve plug moves downwards when the pump's flow rate decreases, opening a bypass in the process through which a defined minimum flow is bypassed back into the inlet tank. The latter helps to dissipate heat, thus preventing evaporation.
An automatic recirculation valve is also referred to as an ARC. This type of valve has the main function of ensuring that a predetermined volume of a particular liquid passes through a centrifugal pump at any given time. The automatic recirculation control valve helps to prevent centrifugal pumps from over-heating and being damaged permanently; this is what happens when the pumps run dry.
How the Automatic Recirculation Valve Operates
The heart of the automatic recirculation valve is a check valve disk that is used to sense the fluid’s flow rate. The valve disk is not pressure sensitive but rather flow sensitive. It controls the flow to ensure that a specified volume of the fluid passes through. The controlling characteristics result in a stable and consistent flow over a wide range of pressure.
-
When the valve disk is at full capacity, the bypass closes. When the flow decreases, the action is reversed and there is an increase in the flow rate. The fluid then gets into the bypass system which is controlled by the orifices and is found at the bottom of the disk.
-
The increase in the flow of the fluid causes the disk to lift; as a result, the element of the bypass which is important for the functioning of the bypass closes to limit the recirculation. This ensures that the recirculation flow remains higher than the lowest volume of the fluid flowing through the pump.
-
When the disk closes, the bypass opens fully and there is no fluid flow. This helps to protect the pump from damage that would result if the pump continued to operate and there was no fluid.
Design features
-
Reliability, operational safety, and low maintenance
-
By-pass control valve: Saving the pump overheating by managing a passage of fluid via the pump throughout start up, close down and when the pump is run against a closed outlet.
-
Non-return valve: Stopping reverse flow via the centrifugal pumps through the main line and bypass line.
-
Force reduction nozzles: Dissipate the pressure power and permit the line fluid to be delivered to the by-pass systems safety, efficiency, and quietly.
-
Angle patterns valve has the extra spec of not requiring removal from the pipeline during shut downs and maintenance.
Applications
Unique Control Systems Automatic Recirculation Valves general application is to save pumps which manage warm water for boiler cooling or feeding water plants, where partial vanishing of the water content might or else cause the pump to operate dry. Even when the flow rate via the main valve to the boiler is fully shut off, a minimum flow is managed.
Advantages
-
Special design
-
Gather both bypass and check features
-
Lowest flow defense
-
No outside actuation needed