Liquid cooling systems and apparatus and data processing systems and communication systems with liquid cooling systems are presented. A number of embodiments are presented. In each embodiment a plurality of heat transfer systems capable of engaging a plurality heat generating components and each such heat transfer system adapted to transfer heat from the heat generating components is implemented. Each of the heat transfer systems is in liquid communication with a heat exchange system that receives heated liquid from the heat transfer systems and returns cooled liquid to the heat transfer systems. The liquid communication from/to the heat exchange system and the heat transfer systems is in parallel, in series or a combination of parallel and series. Another embodiment disclosed is for data processing systems and communication systems having rack mounted sub-assemblies which can be inserted into or retracted from a rack or other holding device (and even while the data processing system or the communication system is operating) wherein the liquid communication to the heat transfer systems on a sub-assembly may be switched on or off. Another embodiment is disclosed for the cost effective and noise-muffling deployment of fans in a liquid cooling system having more than one heat exchange system therein.