spelling eror: pluming --> plumBing

It seems to be saying that the air rate through a lance is limited by the 'plumbing' - which in this case would be a flexible tube/pipe --> manguera.

Such a limit would arise either because the pipe cannot sustain very high pressure, or because is is of small diameter, for example.

http://www.idealboilers.com/what_is_pluming.html
What is Pluming?
Pluming is the name given by the industry to the visible flue products leaving an appliance terminal. When gas is burnt one of the products of combustion is H2O (water). In a standard-efficiency boiler this leaves the flue terminal sufficiently hot enough to be invisible. However, even the latest standard efficiency boilers plume to a limited degree during winter months. In a high-efficiency condensing boiler the water leaves the terminal at temperatures down to 30°C and the water vapour appears as large droplets. These are now large enough to be visible as a mist leaving the terminal.

The pluming effect happens also in reactors, refineries, etc. Therefore, to avoid accidents, there is a standard lower limit height that the vent extreme must comply with.