Fan blower fans with a pressure ratio of up to 1.11 are generally considered. The pressure ratio here is defined as the ratio of the fan discharge pressure to the fan inlet pressure, sometimes called the suction pressure. The pressure ratio of 1.11 and lower in the world of turbo machines is very low. Consider a fan you may have in your living room to help keep summer cool. The purpose of this technique is to create a forced cooling of the skin convection by moving air in the body at a suitable speed. The increase in pressure required to do this is small. The fan should only rely on local fan losses, including losses in the fan blade, loss of resistance of the part Other fans, such as fan cages, and downstream mixing losses prevail. The pressure is only upstream and downstream of the peripheral fan, so the increase in pressure generated by the fan quickly overcomes these local losses. The pressure ratio for the fans can be so low (perhaps 1.01) that the increase in fan pressure is typically given at the head rather than the pressure ratio, for example, 2 inches of water. In general, fans are devices that move more gas with a very low pressure increase.