Carrier 29D User Manual

Carrier

Operating and Maintenance

Instructions

Automatic Water Strainer

29D

Fig. 1 - Typical Automatic Water Strainer Installation

UNIT DESCRIPTION

The 29D Automatic Water Strainer cleans

foreign matter from the return water of a

Rotaspray® system. Figure 1 shows a typical
installation.

OPERATING CYCLE

Water enters the open end of the strainer drum
and passes outward thru the perforated skin. For
eign matter is screened out of the water, and
covers the inside surface of the drum causing the

water level to rise on the dirty side of the tank.
The water level on the clean side rises until it

reaches the height of the high side electrode A
(Fig. 2). This sets the strainer into operation.
The drum begins to rotate and the drum flushing
sprays are turned on. The dirty portion of the
drum passes under the sprays, and foreign matter

is flushed from the drum into the sludge pan. The

pan flushing sprays wash the foreign matter from
the pan into a drain or a perforated collection
basket. (The water drains from this perforated
basket into a sump, and can be returned to the
dirty side of the tank by a small auxiliary pump.)

After the drum is cleaned of foreign matter, the
water levels equalize, and the strainer stops after
the timed operating cycle.

When the water falls below the low side elec
trode B level (Fig. 2) the strainer starts to pro
tect the pump suction when:

1. The "Rotaspray" units evaporate water, caus
ing the water level on the clean side to drop
without a corresponding rise in water level on
the dirty side.

2. Changes in the system water flow requirements
suddenly drop the water level in the clean side
of the tank.

3. The high side electrode fails to operate.

I Carrier Corporation 1967 Printed in U.S.A.

12-67 29D-1SO

f

CONTROL CIRCUIT

Automatic Operation - The water strainer con

trol circuit (Fig. 3) consists of a timer and
level controller. The control circuit is wired thru
an auxiliary contact on the recirculated or chilled
water pump starter. If the fused disconnect switch
is closed, the control circuit is activated when
the pump starts. The strainer is then controlled
automatically by the high or low side electrode.
When either electrode is energized, the control
circuit is completed. This starts the drive motor,
opens the spray water solenoid valve, and trips
the timer.

Normally, as the strainer begins to operate,
the water levels begin to equalize, de-energizing
the electrode. However, the timer contacts remain
closed for the preset timed cycle to maintain
strainer operation. The length of the timed cycle
can be adjusted to suit job requirements. At the
end of the timed cycle, the timer contacts open.
This normally stops the drive motor, and closes
the spray water solenoid valve. However, if the
tank water level is too low, the low side electrode
will maintain the makeup valve open for several
minutes, until the water level rises enough to de
energize the low side electrode.

Manual Operation - A momentary contact switch

is provided to bypass the automatic tank level con

troller and operate the water strainer for one

timed cycle. This switch permits operation of the
strainer when the water pump is shut down.

Cl

^2 - Relay Coi Is

MSI - Strainer Motor Starter

PB — Push Button

SI - Spray Wtr Solenoid Valve

Fig. 3 - Elementary Control Circuit

II0-I-60

S2 - Makeup Wtr Solenoid Valve
TM - Timer Motor
TR — Timer Relay Coil

o - Terminals on Components

0 — Terminals on Terminal Strip