Negative pressure
Less than atmospheric pressure.
N.P.S.H.A.
The net positive suction head available to prevent cavitation
of the pump. It is defined as: Atmospheric pressure + gage pressure
+ static pressure - vapor pressure - friction loss in the suction
piping.
N.P.S.H.R.
Net positive suction head required to stop a pump from cavitating.
This number is given to you by the pump manufacturer. Since the
number was generated by testing with cold fresh water, it can
be lowered in some cases if you are pumping hot water or some
hydrocarbons.
Newton
A metric unit of force. Kilogram x gravity.
Newtonian fluid
A fluid that does not change viscosity as it is agitated.
Non lubricant
The fluid that will not maintain a film thickness of at least
one micron at its operating temperature and load. A concern with
mechanical sealing.