A circulation pump is a class of pump used to move gases, liquids, or semi-liquid material in a closed circuit. A common example of this type of pump is a water-based heating or cooling system. Due to their closed circuit design, this type of pump must overcome the force of friction within the piping system. The amount of effort required to do this is significantly less than in other types of pumping systems, where the pump would need to lift the fluid from the a low potential energy to a high potential energy.
An electrical motor is the standard power source for a circulation pump. The capacity of the motor required is based on the size of the application. Industrial-sized pumps and the related motors are usually quite separate and are connected by mechanical coupling. Home applications are typically sealed units, with the pump and motor positioned very closely together.
Enclosed within the circulation pump are the motor rotor, pump impeller and support bearings. The entire unit is sealed in order to maintain a watertight seal. In a pump, the pressure is greatest at the point where the pump drive shaft entered the pump body. The area of greatest pressure is the area most likely to leak. The best design to overcome this challenge is to seal the entire unit, which redistributes the pressure over a broader area.
Circulation pumps are gaining popularity as a water conservation method when combined with hot water heaters. In the current model, when the hot water tap is turned, the water already sitting in the pipes is sent first, followed by the water directly from the heater. Users will typically allow the cooler water that arrives first to flow down the drain while they wait for the hot water to arrive.
Adding a circulation pump to the hot water heater changes this workflow slightly. When the hot water is not in use, the pump pulls the water in the pipes back to the hot water heater. The boiler functions to maintain the hot water at the required temperature. When the tap is turned, the pump sends the hot water directly from the hot water heater to the user. This change conserves the water that would have run straight into the drain as the user waited for hot water.
The downside to this method is the heat energy lost with the transfer of the water out of the pipes and back into the heater. It is up to the users to evaluate which resource is more valuable, heat or water. A circulation pump used in a closed system can be made of cast iron because the water in the loop can either be de-oxygenated or treated with corrosion inhibiting chemicals. If the pump will have a steady stream of potable water, then a different material is required.