Norgren Filter Contents - Manual (Page 4)

Filters
Littleton, CO USA Phone 303-794-2611 www.norgren.com ALE-Filter
1.4 DRAINS
1.4.1 Semi Automatic:
A semi-auto drain is one which operates when the
air-line is depressurized eg at the end of a shift. It is
a normally open two-way valve which is held closed
by 7-10 psig (0.7-0.8 bar). When the filter is
pressurized, the drain may be operated manually by
pushing the tube, which protrudes outside the bowl,
upwards.
1.4.2 Automatic:
An automatic drain is a two-way valve, which will
close when the system is pressurized. The drain
opens when the float rises due to accumulated liquid
and on depressurization.
1.4.3 Where should an Automatic Drain be Used?
Automatic Drains should be used where the filter
location may make servicing difficult, where filters
may be hidden from view and consequently be
overlooked or where equipment is in continual use.
Areas where large quantities of liquid may
accumulate over a short period of time should also
be equipped with auto-drain filters. High labor costs
for draining a large number of filters manually will
generally justify the use of auto-drains.
Machines which have been shut down for a
long period of time, such as over a weekend, can
draw slugs of water during start-up which can
overload a filter unless drained immediately. (This
situation can normally be handled by a drip leg
drain, see.)
Norgren float type automatic drains are
‘normally open’ type drains. During periods when
the air line pressure is shut off, the automatic drain
will open allowing liquids to drain rather than flood
the air line piping system. When re-pressurizing the
air line, the automatic drain valve will close when
pressure reaches approximately 10 psig (0.7bar).
This results in a flow through the drain to
atmosphere of about 1.77 scfm (0.84dm3/s) until
the valve automatically closes. (See 1.4.4 below.)
1.4.4 Where should a Low Flow Automatic Drain
be used?
In systems where the compressor capacity is
insufficient to close a number of standard auto
drains a ‘low flow’ drain is available which requires
only 0.5 scfm flow before closing. An ultra low flow
auto drain is also available. ‘Low flow’ drains have
less clearance around the valve for expelling
contaminants, so should only be used where the
standard unit cannot be used. ‘Low flow’ drains can
be identified by red plastic parts.
1.4.5
07 Automatic (spitter) Drain:
When a rapid increase in flow occurs through the
filter it results in the pressure above the drain’s
diaphragm being less than that below it. This
differential pressure causes the drain to
momentarily lift and ‘spit’ out the condensate
collected underneath the drain.
1.4.6 Where should a Drip Leg Drain be Used?
The drip leg drain is a system protection device.
Most compressed air distribution systems have
varying flows and/or are shut down at the end of a
working day. As the system cools, water in the
compressed air condenses and collects in the
distribution pipe work. This water will run along the
pipe work and settle at the low point(s). On start up
of the plant this water can be pushed under
pressure into the nearest device or process and
cause malfunction or damage.
By running a vertical pipe down from
these low points water will flow into the drip leg
drain where the automatic drain will expel it.
A filter screen within the drip leg drain
prevents particles interfering with the auto-drain
operation. A ball valve should be included above
the drip leg drain to allow for maintenance when
the system is running.
1.5 PERFORMANCE
1.5.1 Performance of General Purpose Filters
Filters have their flow measured in terms of the
pressure drop across them. As the flow increases
then the pressure drop also increases. These
pressure drops are energy losses in the system.
A well designed filter not only removes
water and particles efficiently, but also has a low
pressure drop at a given flow. The flow figures
quoted in Norgren catalogues for general purpose
filters are at a pressure drop of 5 psig (0.3 bar),
from a 100 psig (7 bar) inlet pressure.
Beware! not all competitors quote their
flows under the same conditions. If a higher inlet
pressure is used or a higher pressure drop is quoted
then the apparent flow will be higher. This does not
mean it is a better unit , simply that a different point
on the curve has been selected. Often the only way
to compare units is to test them under the same
laboratory conditions.
1.5.2 Performance of Coalescing Filters:
The maximum flow of an oil removal filter is usually
determined by the oil removal efficiency under
saturated conditions. In the catalog there are
maximum flows quoted ‘to maintain stated oil
removal characteristics.’ These are the steady state
flows which should not be exceeded to guarantee
that the oil in the outlet air remains below the
0.01ppm (parts per million) quoted. Cyclic or
pulsating flows will result in oil carry over, as will
elevated temperatures.
If a higher oil carry over is acceptable (or
there is no oil in the air-line) then higher flows are
achievable, and will be determined by the
‘acceptable’ pressure drop. For a new (dry) element
a flow which gives a pressure drop of less than 5
psid (0.3 bar) is recommended.