2025 Nelsen Corporation Catalog - Catalog - Page 443
Water System Definitions 17
TOTAL
DISCHARGE HEAD
(TDH)
SERVICE PRESSURE
ELEVATION
HORIZONTAL RUN
WELL SIZE
DRAWDOWN – The distance that the water level in
the well is lowered by pumping. It is the difference between
the STATIC WATER LEVEL and the
PUMPING LEVEL.
ELEVATION – The vertical distance between the level where
fluid enters a pipe and the level where it leaves. It must be
added to the TOTAL DISCHARGE HEAD if the inlet is lower
than the outlet and subtracted if the inlet is higher. As a rule
of good installation practice, however, pipes should slope
continuously upward from the inlet to the outlet to prevent
entrapment of air.
FRICTION LOSS – The loss of pressure or head due to the
resistance to flow in the pipe and fittings. Friction loss is
influenced by pipe size and fluid velocity, and is usually
expressed in feet of head.
HORIZONTAL RUN – The horizontal distance between
the point where fluid enters a pipe and the point at
which it leaves.
PUMPING LEVEL – The lowest water level reached during
pumping operation.
SERVICE PRESSURE – The range of pressure in the pressure
tank during the pumping cycle, usually expressed on pounds
per square inch gauge (P.S.I.G.)
Technical & Engineering
FRICTION LOSS
STATIC DEPTH
SETTING
STATIC
WATER
LEVEL
DRAW DOWN
PUMPING
LEVEL
SUBMERGENCE
10’ OR MORE TO KEEP OUT OF SEDIMENT
STATIC OR STANDING WATER LEVEL – The undisturbed
level of water in the well before pumping.
SUBMERGENCE – The vertical distance between PUMPING
LEVEL and the bottom of the pump or jet assembly.
Submergence must be sufficient to insure that the suction
opening of the pump or jet assembly is always covered
with water, while maintaining enough clearance from the
bottom of the well to keep it out of sediment (at least 10 feet
clearance is recommended).
TOTAL DISCHARGE HEAD – The total pressure or head the
pump must develop. It is the sum of the depth to pumping
level, THE ELEVATION, THE SERVICE PRESSURE, and THE
FRICTION LOSS. Of course, all of these measurements must
be expressed in the same units, usually feet of head, before
adding them together.
SETTING – The vertical distance from the level at which the
discharge pipe leaves the well to the bottom of the pump of
jet assembly in the well.
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