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Hydrostatic (Bubbler) Level Controls
Slight variations in air pressure in a
pipe probe, inserted vertically to a depth of approximately 3" in the
treatment tank activates this system. The Level Control System
(Bubbler) is
affected very little by wave motion and maintains liquid levels within
one quarter of an inch. Operated by low volume, low pressure air
(approximately 0.5 to 0.8 cu. ft./hr.), the Level Control Sensor is
intrinsically safe. Plant air in the range of 10 to 20 psi is
supplied to the pressure reducing regulator on the system.
 Water
is added by a standard, normally closed solenoid valve (not supplied)
which is
either fully opened or fully closed.
This system eliminates ball floats,
needle valves and hazardous electrodes.
Further, no part of the operating portion of the Level Control is in
contact with the solution except the pipe probe.
A shut-down of the plant air supply,
intentional or otherwise, will cause automatic shutdown of the Level
Control System electrical circuit. Thus, the tanks cannot be overflowed
accidentally. The shutdown of plant air can easily be accompanied by a
warning signal which can be supplied as an option, or by the user.
The Master Level Control System includes
a reducing valve/filter/gauge unit
and a low plant air supply
pressure safety switch. The
latter disconnects the electric feed circuit to the solenoid valves
during periods of low air pressure.
Processes subsequent to the Master Level
Control System can be controlled with a less expensive Auxiliary Level
Control. Both the Master and Auxiliary units monitor the level of
liquid surrounding the level probe. As the pressure in the probe
changes due to the lowering of the liquid level surrounding the probe,
the solenoid valve is actuated automatically to maintain the preset
liquid level.
Single Level Adjustment
Single level controllers (Masters and
Auxiliaries) each have a single low pressure differential switch within.
Each low differential pressure switch is equipped with an adjustment
screw at the center of the diaphragm housing. Each is marked with a
clockwise arrow indicating increase of liquid level.
After each controller is in place and
supplied with air and electric feed, and the air probes are in place
with tubing connected to the controllers, air should bubble from each
probe at the rate of approximately 0.8 CFM. This flow can be regulated
at the Ratemaster Flowmeter Control in each enclosure.
Each tank should then be manually filled
to the operating level desired. On recirculating tanks, this should be
the level obtained when the pump is running high enough to cover heating
equipment and low enough to prevent overflow when the pump is stopped.
Once this level is established, the
adjusting screw is turned until the microswitch just makes and breaks
contact. The red light on the controller will turn off when the proper
level is reached.
Multiple Level Systems
Mid-Western Processes Level Control
Systems can be supplied in multi-point configurations for special
applications such as high and low level alarm or water fill start and
stop. These units are a combination of a Master Level Control System
with additional Auxiliary level Control Systems built into the same
enclosure. These units are available in two, three, and four level
configurations.
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