VALVE
These
are devices incorporated in pipelines to control the flow into, through, anf
from them. Valves are also known as faucets, cocks, bibs, stops, and plugs. The
term cock is generally used with an adjective indicating its use. For example,
a sill cock ( also called a hose bib ) is a faucet used on the outside of a
building for connection with a garden hose. A faucet is a valve installed on
the end of a pipe to permit or stop withdrawal of water from the pipe.
Valves
usually are made of cast or malleable iron, brass, or bronze. Faucets in
bathroom or kitchens are usually faced with nickle-plated brass.
The
type of valves generally used in water-supply systems are gate, globe, angle,
ball, and check valves.
Gate valves
control flow by sliding a disk perpendicular to the water flow to fit tightly
against seat rings when a handwheel is turned. The type of valve is usually
used in locations where it can be lrft complectly open or closed for long
periods of time.
Globe valves
control the flow by changing the size of the passage through which water can
flow past the valves. Turning a handwheel moves a disk attached at the and of
the valve stem to vary the passage area. When the valve is open, the water
turns 90% to pass through an orifice endclosed by the seat and then turns 90%
again past the disk, to continue in the original direction. Flow can be
completely stopped by turning the handwheel to compress the disk or a gasket on
it against the seat. This type of valve usually is used in faucets.
Angle valves
are similiar to globe valves but eliminate one 90o turn of the water flow. Water is discharged
from the valves perpendicular to the inflow direction.
Check valves
are used to prevent reversal of flow in a pipe. In the valves. Water must flow
through an opening with which is associated a moveable plug ( or flapper ).
When water flow in the desired direction, the plug automatically moves out of
the way, however, a reverse flow forces the plug into the opening to seal it.
Ball valves
are quick-closing ( ¼ turn to close ) valves, which consist of a drilled ball
that swivels on its vertical axis. This type of valve creates little water
turbulence owning to its straight-through flow design.
