TM 10-4610-310-14
0003 00
ULTRAFILTRATION PROCESS
In each UF membrane cartridge, there are hundreds of hollow fibers inside which the raw water is fed. The water
is then forced through to the outside of the hollow fibers and filtered in the process. The particles left inside are
then disposed by traveling through the hollow fibers and discharged with the reject stream.
The UF membranes are occasionally backwashed to clean out the deposits inside the membranes. This is done
by using a backwash pump to draw the filtrate from the filtrate tank and forcing the clean water from outside of the
membrane to the inside of the hollow fiber and to the reject.
During backwash, the reject valves are automatically timed to close for 3 seconds while the flow is continuing,
allowing the pressure to build up, and then opened up for 7 seconds. This is called pulsing: by pulsing, greater
flow energy is achieved which aids in dislodging the sediments in the membrane.
Each individual cartridge is backwashed for 30 seconds each for a total of 3 pulses.
After backwashing the membranes are fast flushed to remove any remaining sediments. During fast flush
backwash pump is turned off and booster pump is turned on to draw the raw water from the settling tank and
100% of the flow is pushed out the reject line, carrying the dislodged sediments from the membranes. Pulsing
occurs in fast flushing also they are fast flushed for 30 seconds each for a total of 3 pulses each. All backwash
and fast flushes are all done automatically. They can also be done manually.
There are two different types of backwashes. In backwash up, the filtrate is drawn from the filtrate tank, fed from
the bottom of the cartridge and rejected from the top. In backwash down, the process is reversed. The cartridges
are backwashed up for three cycles and then followed by one cycle of backwash down. This, also, is done
automatically.
A normal cycle consists of 15 minutes of filtration operation, followed by 1-1/2 minutes of backwashing and 1-1/2
minutes of fast flushing.
Electrically actuated pilot solenoid valves are used to automate all the operations in the UF module. There are a
total of seven of these valves; three as top reject valves (V3- A, B, C), three as bottom reject valves (V2- A, B, C),
and one as permeate valve (V7). The top reject valves have orifices in them to allow 10% of the feed water to be
rejected.
A low level switch monitors the level inside the filtrate tank. The purpose of the switch is to protect the high-
pressure pump in case of water loss from the filtrate tank. The high-pressure pump cannot be ran dry.
SAFETY DEVICES
Pressure switches
There are two pressure switches located on the HP module. The high-pressure switch is set at 1250 psi and is
used to shut down the diesel engine in case of excessive pressure in the high-pressure piping. Low-pressure
switch is set at 160 psi and is used to shut down the chemical injection pumps in case of pressure increase in the
low-pressure piping.
The pressure switches are factory set. If they needed to be calibrated in the field, refer to WP 0096 00.
Rupture discs
There are two rupture discs: high-pressure and low-pressure. High-pressure rupture disc is rated at 1480 psi and
is located on the HP module. Low-pressure rupture disc is rated at 160 psi and located on the RO module.
0003 00-6
