17 DEC 2003
5-220.127.116.11 Valves are used to control flow. Valves are selected based on desired ser-
vice. Some function only when fully closed or fully open; by throttling, to reduce the
pressure and flow rate of the water; or to permit flow only in one direction or under cer-
tain conditions of temperature and pressure. Valves basically function by placing an ob-
struction in the path of the water, providing resistance to flow. Some basic valves are
briefly described below.
Gate Valves. Gate valves are used to minimize pressure drop in the open
position and to stop the flow of fluid rather than to regulate it.
Globe Valves. Globe valves are used for controlling flow. The flow passes
through a restricted opening. Associated pressure drop is large.
Butterfly Valves. Butterfly valves operate by rotating a disk from a parallel
position to one perpendicular to the fluid flow.
Ball Valves. Ball valves use a spherical sealing element. The valves may be
used for throttling. Pressure drop is low.
Check Valves. Check valves permit flow in one direction only. When the flow
stops or tends to reverse, the valve automatically closes by gravity or by a spring
pressing against a disk.
More information on these and additional valves is available in Perry's Chemical Engi-
neers' Handbook (McGraw-Hill 1997), EM 1110-1-4008, and vendor literature.
5-18.104.22.168 Piping is specified in terms of its diameter and wall thickness. The optimum
size of pipe for a specific situation depends upon the relative cost of investment, power,
maintenance, and stocking pipe and fittings. Velocities between 0.5 and 2.5 m/s should
ordinarily be favored, especially in gravity flow from overhead tanks. The facilities layout
should minimize pumping and piping requirements.
5-22.214.171.124 Backwash troughs collect the backwash water and transport it to the disposal
facilities. The troughs must be correctly located relative to each other and to the media.
Backwash gutters should be as close to the media as possible to minimize the amount
of dirty water left after backwashing and to minimize the height of the filter box, but
should be high enough to prevent loss of media. The gutter must be large enough to
carry all the water delivered to it. A dimensionless relationship to help determine correct
trough spacing is:
H = 0.34S
where H = height of the top edge of the trough above the fluidized bed, and S = center-
to-center spacing of the troughs.
5-126.96.36.199 Two or more troughs are usually provided. The clear horizontal distance be-
tween troughs should not exceed 1.5 to 2 m (5 to 6 ft), and the top of the troughs should
not be more than 750 mm (30 in.) above the top of the bed (TM 5-813-3).