25 May 2005
Timers. Timers are selected by the specific application for which they will
be used. The duty could be any of the following: signal timer, limit timer, percentage
timer, or calendar program timer. They are often an integral piece of controller
equipment but can also be stand-alone units.
Other Feed Devices
Bypass Feeders. The typical bypass pot feeder is used to feed a solid or
dry product to a water stream. A bypass feeder will operate across an orifice plate, a
partly closed valve, or any other restriction in the line. Bypass feeders are not
recommended for steam boiler systems, cooling tower systems, or systems that require
much makeup water.
Slowly Dissolving Dry Chemical Packages. Nylon mesh bags
containing slowly dissolving dry chemicals can be hung in the cold well of a cooling
tower. This method of chemical addition is useful for small, remote cooling towers that
require little attention.
Eductor Chemical Addition Systems. The regenerant agent used for ion
exchanger softeners is usually fed by an eductor, which is an enclosed unit having a
feed rate set by the manufacturer. The sales representative should be contacted in case
of an equipment malfunction.
Chemical Drip Pots. Chemical drip pots are containers that contain
treatment chemicals; they are mounted or hung in a cooling tower to feed chemical
treatment, which drips into the cooling tower sump. These systems are not
recommended for use, including those with a constant head.
CHEMICAL FEED METHODS. For safety and manpower reasons, water
treatment chemical feed should be accomplished using automated equipment when
possible. In some situations manual feed is the most practical, or only, means available.
Other situations require a combination of manual and automated chemical feed. Finally,
some chemical feed systems are fully automated, thereby minimizing any direct
handling of chemical treatment. The most desirable feed method is to feed product
from pumps directly connected to base tanks. The base tanks are refilled by the water
treatment supplier, thereby eliminating the handling of the products by the user. Pumps
that turn on in response to continuous real-time measurement can provided control to
within 3 ppm of the desired treatment level.
Manual Water Treatment Chemical Feed. Manual water treatment
chemical feed is commonly performed on closed systems, small cooling towers, and
Chemical Pot Feeders. Closed systems, such as chilled water, low-
temperature hot water boilers, and even small steam boilers that return over 99%
condensate, are usually fed manually via a chemical pot feeder (see Figure 7-1).
Chemical pot feeders (also known as shot feeders) are plumbed into a system as a