MANUALPC-2010 CHAPTER II – INSTALLATION Page 21
FILTER BACKWASH
The Power Board (Error! Reference
source not found.) of the CHEMTROL®
PC7000 includes six (6) double-pole,
double-throw (DPDT) 5A relays for
automated filter backwash. They can be
used to control solenoid valves, motorized
valves, hydraulic valves or pneumatic
valves.
Main Pump Shutoff
To relieve pressure on the backwash
valves, it may be desirable to shut off the
main recirculation pump during opening
and closing of the valves.
Use Filter Submenu 7.8.1 in the
CHEMTROL® PC7000 to specify if the
main recirculation pump is to be shutoff
during cycling of the valves. The standard
shutoff value is 5 seconds but it can be changed through
Submenu 7.8.1.1.
Single Filter Backwash
As shown in Figure 27, backwashing of a single filter is
controlled with four valves that are connected to the Normally
Open (NO) and Normally Closed (NC) poles of Filter Relay 1.
Valves # 1 and #4 are connected to the Normally Open
connectors on Relay #1 (marked NO1 and NO2). These
valves are open for filtration and closed for backwash.
Valves # 2 and #3 are connected to the Normally Closed
connectors on Relay #1 (marked NC1 and NC2). These
valves are closed for filtration and open for backwash.
Multiple Filter Backwash
Figure 28 shows the connections for sequential backwashing
of multiple filters with three-way valves connected to Filter
Relays 1 to 6. If more than six filters are used, several filters
can be banked together.
For filtration, the valves are in the normally open position and
connect the influent and effluent lines through each filter. In
backwash operation (normally closed), the valve is connected
to the waste discharge line.
A partial closure valve (priority valve or flow control valve) can
be connected to the relay marked Deoxidizer. Specify in
Submenu 7.8.1 if it is to be activated during backwash.
Backwash Stager
Multiple filter backwash can also be done with a backwash
stager, a mechanical port selector for multiple filters that can
be used in place of solenoid valves.
The stager is operated through a dry contact
relay connected to Filter Relay #1 on the
Power Board.
Figure 27 - Single Filter Backwash
Electrical Valves
Solenoid or motorized valves can be connected directly to the
NO and NC sides of the filter relays if they draw less than 5 A.
If more than 5 A, an intermediate relay of sufficient amperage
should be installed.
Hydraulic Valves
Water pressure for a hydraulic valve can be controlled with a
three-way piston valve, one port being used to apply water
pressure for backwash and one port open to the atmosphere to
relieve the pressure on termination.
For EPD or STARK filters, use an ASCO 3-way Solenoid Valve
P/N 8221G2, Normally Closed - or equivalent.
Pneumatic Valves
Air pressure to pneumatic valves can be controlled with a
standard two-way solenoid valve installed on the air line.
For MIAMI TANK filters, use an ASCO Solenoid Valve P/N
8210G94, Normally Closed - or equivalent.
Figure 28 - Multiple Filter Backwash
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