2025 Nelsen Corporation Catalog - Catalog - Page 445
Water System Selection 17
285.5
= 123.6 PSI
2.31
TOTAL LIFT, EXCLUSIVE OF TANK PRESSURE
285.5 - 92.4 = 193.1 ft (round off to 200 ft)
To select the proper submersible pump for this installation,
first choose the appropriate table in the catalog, which would
be for a 12 gpm rated pump. Follow the 200 ft Depth-toWater column down until a pump is found that has the entire
desired pressure range covered. The 1 hp model meets the
required performance. Now check the performance at 200
ft. and 60 P.S.I. pressure to make sure that the pump will
generate sufficient pressure to actuate the pressure switch at
the cut-out point with at least 10 psi to spare.
Pressure at pump discharge, in lbs. per square inch
NOTE: In selecting jet pumps, either shallow or deep well
type, the friction loss of the piping in the well is
included in the performance tables. Therefore,
only elevation and friction loss outside the well
need to be calculated. If the offset (horizontal
distance between the pump and the well) is
greater than 35 ft, the offset piping should be
increased one pipe size.
Technical & Engineering
AMOUNT OF PRESSURE REQUIRED: Discharge Pressure
of the pump must be sufficient to balance Pumping Depth
plus Pipe Friction plus Elevation plus tank pressure. Water
system pressure tanks usually operate within the pressure
range of 20 to 40 lbs. per square inch. However, recent high
demands for pressure, caused by automatic washers and
other appliances, have resulted in many systems being set for
30 – 50, or even 40 – 60 ranges. An example for determining
the required discharge pressure for a typical submersible
pump system is shown below. Assume a pumping rate of 12
gallons per minute.
FIGURE 1
1. Convert all measurements to the same units. In this case,
we will change tank pressure from pounds per square inch
to equivalent feet of head by multiplying by 2.31, as shown
in the engineering formulas on Page 416. Using 40 p.s.i. as
the average tank pressure, 40 x 2.31 = 92.4 feet of head.
2. Compute pipe friction by using the tables on
Pages 413 – 415.
(1) 1-1/4" Plastic Tee
TANK SELECTION: Selection of the proper tank completes
the water system. Pressure tanks used with water systems
are of the hydro-pneumatic type. Compressed air in the tank
acts as a giant spring to provide a pressure range, between
pump stops and starts, during which a reasonable amount
of water can be withdrawn. This is necessary to prevent the
pump motor from cycling too often, and to provide s smooth
flow of water to the outlets, without water hammer.
= 1 x 3 = 3 ft Equivalent Pipe Length
(2) 1-1/4" Check Valve = 2 x 7 = 14 ft Equivalent Pipe Length
(1) 1-1/4" Elbow
= 1 x 1.7
= 1.7 ft Equivalent Pipe Length
18.7 ft Total for fittings
PRESSURE DROP FROM PIPE FRICTION
(200* + 130 + 18.7) x 2.33 = 8.1 ft
100
Total Dynamic Pumping Head
8.1 + 160* + 25 + 92.4 = 285.5 ft
FIGURE 2
FIGURE 2. Types of pressure storage tanks. Figure 2A shows
plain steel tanks; Figure 2B, the plain steel tank with floating
wafer; 2C, the diaphragm tank; 2D the bladder tank.
NOTE: While total pipe length must be used to compute
pressure loss due to pipe friction, only the distance
to pumping levels is included with elevation in the
summation for total pumping head.
Call Nelsen Toll-Free from Anywhere in the U.S. - 800.362.9686
All prices and products subject to change without notice. ©Nelsen Corporation
17 - 25
