|
OCTOBER
APPLICATION
TIPS
Air
cylinders are the largest end-user
of compressed air energy. This is where the work is done. Air cylinders
can provide high force at considerable speed. They are the most economical
way of converting fluid power to mechanical power through expansion of air.
When selecting an air
cylinder design, simplicity, ease of maintenance, optimum rod size, local
availability and reliability, are prime considerations. It is desirable to
have all these features in an off-the-shelf design. Large rod diameters are
available in hydraulic cylinders because of the high operating pressures.
In a pneumatic cylinder, large diameters are usually not required (most rods
break at the piston or clevis ends) and in fact increase gland-bearing loads
and packing wear caused by unavoidable misalignment.
Air cylinder
maintenance is usually limited to piston-cup and gland-packing replacement
and pivot-pin bushings lubrication. Note: - valve exhaust leakage is
usually due to worn cylinder cups.
Consideration should
be given to use of molythane-cups and rod-packing for all temperature
applications. These seals give considerable more life, due to built-in
lubricity.
New and more efficient
compressor and
dryer
designs are coming off the drawing boards now.
FRL's
are plug-in at no additional cost. Synthetic oils are being used safely and
interchangeable solenoid valves (between manufacturers) has been available
for some time.
By investing
additional dollars upgrading your typical compressed-air systems, we can
have efficient, clean and economical fluid power systems. Pneumatic air
power, clean, odorless, non-toxic, fast and invisible. But there is some
cost to keeping it that way; it is this cost we are all striving to
minimize.
Remember, even though
there is no monthly billing, 'the meter is on' while your compressor is
running.
(End of
article)
Courtesy: Tim Skeans, Logging and Sawmill Journal
Top of Page
|
SEPTEMBER
APPLICATION
TIPS
MOISTURE IN THE PIPE
LINE continued from July & August see our archives for back issues....
Air line filters should be
installed as close to the point of use as possible to remove contaminates, some
of which are introduced at the time a system is installed. Of prime
importance for the energy-conscious is the consideration of pressure drop across
the filter. Most catalogue ratings are listed at 5psig. The
unnecessary loss of energy can not be accepted in today's plants. Select
filters (both general purpose and oil removing) with a maximum 2psig pressure
loss (when new), which give the best filtration (small particle size) at
comparative flows and offer ease of maintenance.
Did you know that
literally thousands of dollars can be saved annually through installation of air
line pressure regulators throughout a typical plant? How? By reducing the
pressure from say 100 psig to 40 psig in the rod end of 50 per cent of the air
cylinders in the operation. This simple procedure will reduce compressor
demand; reduce air lost by leakage; and minimize wear on rod end packings.
Pressure reduction may be achieved by: installing a regulator on dual pressure
valves; installing combination pressure/flow control valves;
or installing a regulator and quick dump valve between the
control valve and cylinder actuator.
The third component of the
FRL module is the air line lubricator. Even though modern
manufacturing techniques utilize non-lubricated valves and cylinders, air line
lubrication certainly increased the efficiency of these components.
A light weight, medium
aniline, paraffin base oil is recommended. Check with your lubricant
supplier for his recommendation. Synthetics oils and air line additives
such as de-icers and methyl hydrate tend to attack polycarbonate bowls and
shrink piston seals, adding to the leakage factor.
Airline lubricators should
be of the constant-oil-density and fill-under-pressure type; easily maintainable
and of the correct oil capacity for your application to avoid constant
refilling.
To improve productivity of
new plants and update older ones, air valves are selected on the basis of
reliability, simplicity, fast response and minimal operating cost. Leakage
is not tolerated. Solenoids are more efficient, using less amperage and
downtime is minimal with plug-in designs like the
MAC 92, 93
or even the older 600 series for example.
Today with the emphasis on
cost reduction, manufacturers are offering new designs to provide valves for
specific applications, using the latest in manufacturing technologies. As
many components become interchangeable in over-lapping series, the plant
designer can choose one manufacturer to supply from #10-32 to 2-½"NPT. The
trend is to size a valve for a specific application, but consideration should be
given to simplification.
For example, most four-way
valves used on double acting cylinders can have a cylinder port blocked for
three-way application ie: single acting cylinders, air springs, clutches etc.
Check your flow capacity. All valves manufacturers rate their valves
according to Cv factor. Do not be fooled by port size. One Cv is
equal to approximately 28 standard cubic feet per-minute at normal operating pressures.
Example: ½"NPT,
four-way single solenoid, plug in valve [ Listed Cv = 5.0 ]
Therefore flow capacity =
5.0 x 28 = approx 140SCFM
To simplify installation
and selection of air valves and FRL's, Skeans can
offer all components pre-piped and tested on single formed panels. These
'Air Stations' reduce on-site labour during installation and simplify planned
preventative maintenance programs by numerical identification. Isolation
valves are installed with suitable lock-out facilities. By shutting off
unused areas of the plant, leakage is minimized and dollars are saved.
to be
continued next month...
Courtesy: Tim Skeans, Logging and Sawmill Journal
AUGUST
APPLICATION
TIPS
MOISTURE IN THE PIPE
LINE continued from June....
The purchase of a
properly-sized compressed air dryer is a sound
investment. Plant management should justify their purchase by doing a ROI
(return on investment) analysis. In our typical plant's air system, the 43
gallons per day [see June pneusletter for reference] will cause: premature
failure of air tools and motors; increased wear in cylinder and valve
components; damage to sensitive air devices; and most notably in the winter
season freezing control valves. Elimination of these costly maintenance
problems, the cost of band-aid solutions (airline anti-freeze) and the cost of
lost production due to downtime, can easily show a favorable ROI in a very short
time.
When selecting and
air dryer as part of your air system, energy
efficiencies should be considered. An air dryer, with necessary filtration
and minimal pressure drop, should be suitable sized. Careful consideration
should be given to: method of drying, volume (steady flow or surges); operating
pressure; pressure dew point required; and most importantly, the inlet air
temperature. If we can drop the inlet air temperature from say 95°F to
75°F by efficient after-cooling, we reduce the drying demand on the air dryer by
50%!!
Pressure dew point is the
temperature at which compressed air in the system is saturated with water vapor
(ie 100% relative humidity). Any further drop in temperature will result
in water condensing. In Northern areas of most Canadian provinces, where
compressed air can be exposed to -40°F, a -40°F pressure dew point should be
specified. Or for example in the Lower Mainland of BC or inside heated
plants, a pressure dew point of 39°F is usually adequate to remove most water
that condenses under operating conditions. The cost and type of dryer
required for different applications is considerable and a knowledgeable dryer
supplier should be consulted.
The
piping layout and location of
air-preparation units in the system is of prime importance to an efficient
compressed air system. This ensures; minimum pressure loss; removal of air
line contaminants; proper operating pressure levels; and correct lubrication for
longer component life.
Correct
pipe sizing is important. The investment in
over-size pipe for a new installation is a good one. The small additional
cost provides storage capacity and allows for future expansion and decreased
pressure loss due to aging of pipe walls. Remember, for a given pipe size,
pressure losses increase as flow increases and this loss is on a pre-foot basis.
Today, the popular
TRANSAIR aluminum piping is excellent for low
pressure drop, antirust, and quick connect systems. The old rule of thumb
when installation new piping systems - to slope main lines 1/8 inch to 1/4 inch
per foot down from the receiver or high point - still applies today. This
gradient is to carry condensate to low pointes where it can be automatically
drained in suitably located drop-legs. Obviously auto drains and water
traps are not essential if a compressed air dryer is used, because there should
not be any condensed moisture unless the air temperature goes below the dew
point rating of the dryer.
One should note that the
operation of an air line dryer year round prevents large amounts of water
condensing in summer months and minimizes the chance of pipe scale forming due
to wet/dry exposure. Today's energy manager's are using -40°F PDP Dryers in the
winter and 39°F Refrig Dryers in the summer months.
to be
continued next month...
Courtesy: Tim Skeans, Logging and Sawmill Journal
Top of Page
JULY APPLICATION TIPS
MOISTURE IN THE
PIPE LINE
It is important to
understand the concept of water in a compressed air power distribution
system. It is very simple. Your compressor ingests approximately eight
cubic feet of ambient air for every cubic foot of compressed air discharged
at 100 psig. The compression ratio of approximately 8 times results in a
concentration of water vapor, dirt, hydrocarbons and other contaminants.
Because air increases
its moisture holding capacity as temperatures rises, (capacity doubles for
every 20ºF rise) the effect of the temperature rise resulting from the heat
of compression results in a very high moisture vapor content. As the air
cools, loosing its capacity to hold water vapor, liquid water condenses
out. The more the air cools, the more water condenses.
How much water is in
your typical air system? Ten gallons? Fifteen gallons? Even 50 gallons is a
good guess. Approximately 18 gallons of water a day, in vapor form, are
taken in per 100 cubic feet, under average conditions of a 75ºF day and 75
percent relative humidity. Therefore, in your typical plant with 2 - 150HP
Compressors you could have 18 gal./100cu.ft x 1500 = 270 gallons.
It should now be
apparent that an efficient after-cooling package is necessary. Air-cooled
aftercoolers generally cool compressed air within 20º-30ºF of the ambient
temperature. It is important to keep cooler fins free from dirt and dust.
Water cooled aftercoolers are usually more effective and cool within 10º -
15ºF above the cooling water temperature. Watch for scaling and other tube
fouling factors.
A typical air-cooled
after-cooling system discharging compressed air at 95ºF will condense out,
through an efficient separator, approximately 68 percent of the total air
moisture intake.
Total daily
moisture intake = 270 gallons
Cooling to 95ºF
removes 184 gallons 68%
Remaining moisture @
95ºF 86 gallons
Cooling to 75ºF
removes = 227 gallons 84%
Remaining moisture @
75ºF 43 gallons
It is this 43 gallons
per day that can present maintenance nightmares in a sawmill. In the lower
mainland of BC where are relative humidities approach 100 percent the
problem is even worse. In the Interior or the Northern parts of BC the
relative humidities are lower but the problems are compounded by freezing
temperatures.
This excess moisture
must be considered. Its effect can be minimized by either dropping the
relative humidity of the compressed air using the heat of compression (hot
oil) by the air compressor (re-heating) or by piping through a compressed
Air
Dryer or both (dryer first, then re-heater).
Click here to see a water
calculation chart to see your water intake per day.
to be
continued next month...
Courtesy: Tim Skeans, Logging and Sawmill Journal |
Gardner
Denver 
Large Bore TR Triple Rod
Cylinders
