usual unit of pounds per square inch gauge(PSIG). A pressure in PSIG is simply

converted to its equivalent column of liquid. That column of liquid develops the

same pressure in PSIG at the bottom of that liquid column. The length of that

column, in Feet, is referred to as the

velocity is reduced, part of the internal energy of the liquid is released and may be

harnessed as additional head. If the liquid velocity is increased the velocity head

is reduced as part of the internal energy of the liquid is used to accelerate the

liquid.

The formula for calculating velocity head is:

Hv = V^2 / 2g

where Hv = velocity head, in Feet

V = liquid velocity, in Feet per second

g = acceleration due to gravity, in Feet/sec^2

One practical application of this formula is in estimating the head that an impeller

will develop.

Example: How much head will a 15" diameter impeller develop in a pump

operating at 1780 RPM?

Solution: The peripheral velocity of a 15" diameter impeller is:

V = [D x RPM] /229

where v -s the peripheral velocity

The formula for calculating the increase in liquid velocity is:

V = [Q x 0.321] / [A2 - A1]

where Hv = velocity head in Feet

Q = flow rate in gallons per minute

A = the difference in the flow area between the suction nozzle and

discharge nozzle, in square inches.

2.31 is a unit conversion factor

suction pump with a flow rate of 800 GPM?

In the universal pump designation consisting of three groups of figures, the first

figure refers to the discharge nozzle size, the second figure refers to the suction

nozzle size, and the third figure refers to the nominal impeller diameter size.

First, calculate the change in liquid velocity:

V = [800 x 0.321] / [A6 - A4]

V = [800 x0.321] / [28.274 - 12.566] = 4 Feet

Next, calculate the velocity head:

H = V^2 / 2g

H = [4]^2 / [2x32.2] = 0.248 feet

(More on

discussed in a separate article on this web site.)

discharge nozzle over the velocity of the liquid at the suction nozzle. Velocity head

is present only is the discharge nozzle is smaller than the suction nozzle. If the

nozzles are of the same size then the velocity head is zero. The velocity head is

calculated from the equation:

Pump basics

Types of pumps

Horizontal vs. Vertical pump

Axial split vs. Radial split case pump

Parallel-series operation

Self-priming pump

increase in the liquid discharge velocity due to the difference in the pump's

suction and discharge nozzle sizes.

a pump?

(ID) of the discharge nozzle is smaller than the ID of the suction nozzle. (The

velocity head is zero when the ID of nozzles are of the same.) Since the suction

nozzle is never smaller than the discharge nozzle, then the velocity head is never

subtracted in calculating the total head of a pump.

The velocity head (Hv), in FT, is calculated from:

Hv = [V^2] / [ 2g]

where g = 32.2 (gravitational acceleration), and

V = [Q x 0.321] / [A]

where Q is the capacity in GPM, and A is the difference in flow area, in square

inches, between the suction and discharge nozzles.

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