Diatomaceous Earth, a type of filtration media. Can also stand for Dual Element when talking about electrical fusing.
DEAD HEAD
Operating point on the curve where unit is pumping zero GPM - also known as Shut-off Head.
DECKS
Those areas surrounding a pool, spa or hot tub that are specifically constructed or installed for use by bathers.
DEEP AREAS
Portions of a pool, spa or hot tub having water depths in excess of five feet (5’).
DEIONIZATION
Removal of ions from water by exchange with other ions associated with fixed charges on a resin. First, positively charged ions are removed, by a cation exchange resin, in exchange for a chemically equivalent amount of hydrogen ions. Second, negatively charged ions are removed, by an anion exchange resin for a chemically equivalent amount of hydroxide ions. The hydrogen and hydroxide ions introduced in this process unite to form water molecules. This process is also called demineralization by ion exchange.
DEMINERALIZATION
The process of removing minerals from water e.g. deionization, reverse osmosis and distillation.
DESALINATION
The removal of dissolved inorganic solids(salts) from a solution such as water to produce a liquid which is free of dissolved salts. Desalination is typically accomplished by distillation, reverse osmosis or electrodialysis. A common source water may be seawater.
DESIGN RATE OF FLOW (DESIGN FILTER RATE)
The average rate of flow in a system which is used for design calculation (usually the flow in gallons per minute divided by the effective filter area in square feet).
DIALYSIS DEMENTIA
A severe, often fatal encephalopathy which has been attributed to accumulation in the brain of aluminum from dialysate prepared with inadequately purified water. May include consumption of tap water with high levels of alum used in most municipal water treatment processes.
DIATOMACEOUS EARTH (D.E.)
Porous silica from skeletal remains of one-celled plants, which when properly graded, acts as a precoat filter media for water filtration.
DIFFUSER
A piece, adjacent to the impeller exit, which has multiple passages of increasing area for converting velocity to pressure in a pump.
DIRECTIONAL INLET FITTING
An inlet fitting which provides adjustment in direction and flow rate to produce proper distribution of incoming water.
DISCHARGE
Where the water exits the pump
DISCHARGE HEAD
The total head, including static head and friction head, on the discharge side of the pump.
DISINFECTION
A process for the destruction of bacteria. The process may be physical, as with heat or ultraviolet irradiation, or chemical, as with chlorination.
DISSOLVED SOLIDS (ALSO TOTAL DISSOLVED SOLIDS-TDS)
Includes colloidal and suspended particles at sizes far less than one micron in diameter. Associated with evaporation process such as distillation.
DISTILLATION
Steam from boiling water is condensed on a cool surface, collected and stored. Most contaminants do not vaporize and therefore do not pass to the condensate. Removes nearly 100 percent of salts and those organics that do not have a vaporizing temperature near or below that of water. Usually combined with carbon filtration to remove balance of remaining organics with vaporization temperatures below that of water.
DISTILLED WATER
Water which has been purified by passing through an evaporation, condensation cycle; it generally contains less than 5 ppm of dissolved solids.
DISTRIBUTOR (TOP OR BOTTOM)
The device in a filter designed to divert the incoming water to prevent erosion of the filter media.
DIVING AREA
That area of a pool designed for diving. (NOTE: Diving Areas are defined in detail in various standards and regulations such as NSPI, Public and Residential Pool Standards, AAU, FINA, etc.).
DIVING BOARD
A board especially designed to produce diver spring action when properly installed on an anchor (base) and fulcrum. (The term diving board includes non-spring types).
DIVING PLATFORM
Usually used for the standard 5-meter and 10-meter official diving platform.
DIVING TOWER
This term is usually used for the 3-meter (10-ft.) springboard support.
DRAIN
An outlet at the deep point of a vessel or trough through which waste water passes.
DRAWDOWN
The difference between the static water level and the pumping water level in a well. Also can refer to the per cycle capacity rating of a pressure tank at a given pressure range.
DRY NICHE
A normal weatherproof fixture placed in an opening behind the pool wall which illuminates the pool through a watertight window in the pool wall.