The purpose of the cooling system is to prevent the overheating of the motor. There are different systems on the market for different types of installations. The cooling media can be air, water, oil, etc.
Since Flygt pumps are submersible even in dry installations, it is not possible to use fan systems that blow air through the rotor. In any case, fan systems have disadvantages such as noise, drawing dust into the motor and heat production that can result in an increase in the cost of air conditioning.
It is preferable to cool with water or a mixture of glycol and water as opposed to oil. Water and glycol provide better heat transfer and require less power for circulation than oil does, due to the viscosity.
In Flygt pumps we use a variety of systems, each designed for optimal performance and efficiency:
- Direct cooling
- Closed loop cooling
- Integrated cooling
- External cooling
Each of these systems has its own set of application areas.
Direct cooling means that the pump is cooled by the surrounding water or air. It is a particularly effective system for column installed pumps. As no cooling jacket or cooling system is required, the system is simple. Cooling by water requires that the pump is submerged while in operation. If cooling is by air, the motor rating or running time must be reduced.
Closed loop cooling – internal cooling
Closed loop cooling means that the cooling liquid is pumped up through the narrow space between the thin inner cooling jacket and the stator housing. The coolant is then circulated downwards between the inner and outer cooling jacket down to the cooling bottom. Finally, the coolant bottom transfers the heat from the coolant to the pumped media.
One of the strengths of closed loop cooling is that it is not sensitive to impurities in the pumped media.
Integrated cooling is a self-supplying system. A portion of the pumped liquid is circulated from the pump housing up between the cooling jacket and the stator housing. The necessary flow is created by back-vanes on the impeller top. The flow is then directed in and out of the cooling jacket by a guide ring. Any air is automatically removed from the system by the air ventilation pipe. Sedimentation in the cooling system is prevented by keeping the water velocity up in the critical areas. Speed limitations must be checked for variable frequency drive (VFD) duty.
When the cooling water is supplied externally from a direct line or by a circulating cooling system, it is called external cooling. Like closed loop cooling, this system is not sensitive to impurities in the pumped media.
As cooling water flow is independent of operational speed, a VFD control will not disturb the cooling function.