ABSTRACT
The net positive suction head (NPSH) is the total suction head in feet of liquid (absolute at the pump centerline or impeller eye) less the absolute vapor pressure (in feet) of the liquid being pumped.It must always have a positive value and can be calculated by the following equations. To help in visualizing the conditions that exist, two expressions are used; the first expression is basis a suction lift-liquid supply level that is below the pump centerline or impeller eye; the second expression is basis a positive suction (flooded), where the liquid supply level is above the pump centerline or impeller eye.For suction lift: NPSH = /la — /lypa /^ st — /ifs For positive (flooded) suction: NPSH — /la — /typa — ^st ~ f^s
where /ia is the absolute pressure (in feet of liquid) on the surface of the liquid supply level (this will be barometric pressure if suction is from an open tank or sump, or the absolute pressure existing in a closed tank); /iypa is the head in feet corresponding to the vapor pressure of the liquid at the temperature being pumped; /ist is the static height in feet that the liquid supply level is above or below the pump centerline or impeller eye; and hfs is all suction line losses (in feet) including entrance losses and friction losses through pipe, valves and fittings, etc.Two values of net positive suction head must be considered: net positive suction head required (NPSHR), and net positive suction head available (NPSH A). 361
R = 0.0821 (atm)(L)/(g-mol)(K) R = 1.987 g-cal/(g-mol)(K) R = 1.987 Btu./(lb.-mol)(R) R = 7.314 J/(g-mol)(K) R = 1.546 (ft.)(lb.-force)/(lb.-mol)(°R) R = 10.73 (lb.-force/sq. in.)(cu. ft.)/(lb.-mol)(° R) R = 18,510 (lb.-force sq. in.)(cu. in.)/(lb.-mol)(°R) R = 0.7302 (atm)(cu. ft.)/(lb.-mol)('>R) R = 8.48 x 105 (kg/m2 )(cm3 )/(lb.-mol)(K)
Acceleration of gravity (standard):
Velocity of sound in dry air at 0°C and 1 atm:
Heat of fusion of water:
Density of dry air at 0°C and 760 mm:
These are given as grains per gallon of sea salt to equivalent parts per million of chloride to parts per million of chlorides in sea water:
The volt (E) is the unit of electric pressure or electromotive force. One volt is the potential that will produce a current of 1 ampere through a resistance of 1 ohm.The ampere (I) is the unit of electrical current (coulombs per sec).The ohm (R) is the unit of electrical resistance-volts/ampere.Watts (W) and kilowatts (kW) are units of electric power. Kilovolt-amperes (kVA) is a measurement of apparent electric power. Kilowatt-hour (kWhr) is a unit of electrical energy or work performed. The joule (J) is a metric unit of energy, watts per second. 1 kWhr = 2,655,000 ft.-lb. = 1.341 hp-hr = 3413 Btu = 3,600,000 J Ohm’s law relationships (direct current):
Dimensions may vary greatly between different manufacturers, and sizes listed here should be used only as a guide.
