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Fast Bag 101
I) FAST BAGGING EXPLAINED
The term fast bag refers to an air suspension
systsem that operates fast, ie - it airs up and
down quickly. To do this, the vehicle must have
some type of on board air compressor and reserve
tank. Typical aftermarket air suspension systems
use 150psi and come with a small tank, usually
between 3-6 gallons. Solenoid operated valves
are typically used to inflate and deflate the
bags. Solenoid valves are great because they
ease the plumbing of the system and allow the
system to be controlled electronically.
So now that you have your air tank, 12V
compressor and solenoid valves, how does
everything work? The way it works is simple. The
compressor has only one responsibility: keep the
tank full. The valves allow air into and out of
the bags by opening and closing the connection
between the air tank and the air bags. Switches
in the cab control the 12v solenoid valves.
That's the grunt of the process, but there's
really a lot more involved than that, here's a
more detailed description of the parts and how
they actually work.
Click parts of the picture to view a detailed
description.
ABOVE:
This is what a typical 8 valve set-up using dual
ports bags looks like. Each bag has two valves,
one for inflate and one for deflate. The tank
has four separate ports that supply each bag.
The pressure switch tells the compressors when
to run and when to shut down. The check valve
allows air to flow in only one direction and is
cheap insurance against leaks at the
compressors. Essentially, the pressure switch is
isolated from the compressors by the check
valve. Flow rate on the compressor side of the
check valve is not important since the
compressors can only put out a small amount of
air per minute. On the other side of the check
valve, everything needs to be maximized for high
flow capability. That means lines, fittings,
tank ports and bag ports must all be considered.
I use an air dryer and a water separator in my
system for additional insurance against water
and particle build up. |
SEE a diagram of an 8 valve set-up using single port
bags.
SEE a diagram of a 6 valve set-up using single port bags.
The following is a list of components that make
up your typical air suspension system. You can
click the topic heading to learn more about the
individual part. This page serves as a quick and
easy way to learn the function of each part.
Compressors: Either belt driven or electric.
Belt driven compressors can put out much more
air volume than your standard 12v electric
compressor. The purpose of the compressor is to
compress air for use in airing up the vehicle.
Pressure Switches: Controls the cycling of
the compressor(s) and the pressure level inside
the tank. Some are adjustable, some are fixed. A
typical pressure switch is rated at 110/145psi.
Air Tanks: Store the needed air reserves for
airing up the vehicle. Come in all different
shapes sizes and colors with different port
variations. Typical tanks have only three ports
while higher end tanks can have 8 ports or more
and be finished in chrome or powder coated to
your liking. A drain valve located on the bottom
of the tank is used to drain the inevitable
water build-up.
Solenoid Valves: Control the inflating and
deflating procedures. There are literally
thousands of valves on the market today. Most
are used in industrial applications to control
gasses and liquids for machine automation. Air
suspension valves for use in a fast bag system
must have a high flow rate (Cv) and operate off
12v solenoids.
Check Valves: Allows air to flow in only one
direction. Useful for isolating the compressors
from the pressure switch.
Air Lines: Come in a variety of sizes and
pressure ratings. Most fast bag systems use at
least 3/8" tubing with faster systems using dual
and quad port bags running 1/2" to 3/4" supply
lines. Measured in Outside Diameter (OD) and
come in Department of Transportation (DOT)
approved and non-DOT flavors.
Fittings: Special Push-To-Connect (PTC)
fittings are used in many air suspension
applications. They come in DOT and non-DOT
varieties. Other types of fitting can be used as
well, such as compression fittings.
Switches: Control power to the solenoids for
airing up and dumping the vehicle. Most are
three-way momentary switches similar to power
window switches.
Wiring: All wiring must be able to handle
the high current demands of the system. Relays
(see next topic) should be used whenever current
becomes excessive.
Relays: Relays allow low current switching
of high current devices. They can also be used
as sensors and wired to create "logical"
systems. Typical areas where a relay would be
used would be to control the compressors and/or
supply voltage to the solenoids.
Dryers and Oil/Water Separators: Dryers and
Oil/Water separators are used to eliminate water
and unwanted particles from clogging the valves
and causing them to stick or leak.
Gauges: Used to indicate system pressure
and/or bag pressure/vehicle height. At least one
gauge should be used to measure system pressure.
There are digital and analog gauges available. A
typical low-tech 160psi gauge runs about $10.
Air Bags: These are the heart of your
system. Care must be taken so the bags have free
unobstructed travel throughout their entire
range of motion. Many fast bag systems use dual
and quad port bags to maximize the amount of air
that can flow into and out of the bag. The
amount of travel varies from bag to bag and some
bags are actually "struts", called air
struts.
Additionally, each bag has a recommended weight
rating for the vehicle, similar to the way a
coil spring is rated. |
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THE COMPRESSOR AND THE PRESSURE SWITCH: |
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As I said earlier, the compressor's sole
purpose in life is to keep the tank full. It
does this via a pressure switch. The switch is
mounted between the compressor and the tank. It
has a pressure 'window' that opens or closes the
contacts of the switch. I use a 110-145psi
switch. That means when pressure is below
145psi, the switch is closed, causing the
compressor to run. When pressure reaches 145psi,
it opens and turns off the compressor. The
110psi is the lower limit where the switch will
close again and activate the compressor. For
example, you wouldn't want the pump(s) to come
on every time the pressure dropped to 139psi.
The 110 limit is there to make it practical. The
compressor pictured to the left is a Thomas 317.
It is rated at 150psi and can draw 20 amps. It
should only run for 5 minutes at a time with a
20 minute rest period between each five minute
interval. |
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This particular switch is a 110-145 unit that
AirLift sells for $20. It has a pipe thread on
it so it can be plumbed into your system via a
T. Be sure to use a relay with this switch. It
will prolong the life of the switch
considerably. |
BELT DRIVEN VS ELECTRIC:
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There's really no comparison between the
two, a belt driven unit is much more capable
of filling high capacity tanks to higher psi
levels than an everyday 12V electric
compressor. The way to go is belt driven,
but for many reasons a belt driven unit is
not always practical. In terms of cost, the
electric units needed to supply the same
amount of air as a large York compressor
makes the belt driven York a better deal,
especially since the added strain of the
pumps would tax the electrical system pretty
hard.
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York Belt Driven Compressor
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As a benefit to the electric compressors,
they are relatively cheap ($100-$200) and
can do the job of airing the vehicle up and
down fairly easily if not abused. The
problem with electric compressors is the
'recovery' time, or the amount of time it
takes to bring the tanks back up to the high
pressure limit after airing up the vehicle
from a deflated state. This will usually
take 1-2 minutes depending on the
application. The amount of air reserves and
pressure level are also weak points for the
electrics. Since it can only fill the tanks
at a certain speed, the capacity of the
tanks and/or pressure level have to be
reduced. A belt driven unit can fill a
bigger tank to higher pressure levels and
therefore give you extra 'play' time.
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100% Duty Cycle, 3/4HP
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Pictured above and to the right is one of the
more capable electric units. It is a 100% duty
cycle, 3/4 horsepower unit that sells for around
$400. A typical electric configuration would be
to run two pumps and five gallons of air off a
110/145psi switch. Belt driven pumps can double
or even triple the capacity and pressure ratings
to give you more freedom when it comes time to
airing the vehicle up and down. For each
electric pump, you should have no more than 5
gallons of air, the more reserves you have, the
longer the pumps have to run to re-pressurize
the tank. |
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BELT DRIVEN PROS AND
CONS AT A GLANCE:
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PROS |
CONS |
1) Higher pressure levels
2) Larger air reserve capacity
3) 100% duty cycle
4) Quick refill time
5) Additional 'clown' time
6) Low current draw
7) Faster Air System
8) Overall higher quality pump
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1) More expensive than a single electric set-up
2) Mounting brackets and hardware are necessary
3) Large size
4) Nowhere to mount unit
5) Decreased engine HP
6) Some require oiling
7) Plumbing can be more difficult
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ELECTRIC PROS AND CONS
AT A GLANCE:
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PROS |
CONS |
1) Inexpensive
2) Easily mounted
3) Simple to install
4) Adequate for function based systems
5) Does not rob HP.
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1) Slow recovery time
2) Noisy
3) Less reserve air
4) Lower pressure levels
5) Increased load on charging system.
6) Lower duty cycle on inexpensive units
7) Overall lower quality pump |
OEM AIR COMPRESSORS (Lincoln and Cadillac Pumps)
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I felt this was at least worth mentioning even
though my experience with anything other than
the Lincoln Mark VIII pump is limited. That
being said, the only pump I can recommend for
use on a fast bag air suspension is the Lincoln
Mark VIII pump. These cars were made from
1993-1998 and are standard equipment on every
Mark VIII sold. The earlier Lincoln pumps will
not work and I have been informed that the
Cadillac pumps do not work very well either. You
can get a remanufactured Mark VIII pump from
Blue Collar Industries for $150. I have been
using one in my system for over a year now and
it has held up to the abuse just fine.
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III) HAZARDS and MAINTENANCE |
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There are many things that can go wrong with an
air suspension. Most are simple and can be fixed
easily or avoided altogether, but others can
leave you stranded with an undriveable vehicle.
Here are some things to look out for when
installing and maintaining your air suspension.
HAZARDS:
1) PRESSURE LOSS: If you your vehicle is capable
of "laying frame", in the event of a bag leak or
blowout, you run the risk of laying that frame
on the ground while driving. This can cause
serious injury to yourself and others if
precautions are not taken to prevent unwanted
"railing".
2) COMPRESSOR FAILURE: In the event of a
compressor failure, you may be left with a
deflated vehicle that is undriveable.
3) SAFETY: While working on the suspension,
realize that as the pressure is bled out of the
system, the vehicle will drop, possibly binding
suspension parts or even human body parts.
NEVER pull an airline off an inflated airbag
with your arm between the tire and fender!!!
4) FITTINGS: Make sure all of your fittings are
AIR TIGHT before putting your project back
together. Leak test the system overnight to
prevent chasing that pesky leak.
5) AIRLINES: Use appropriate airlines for you
application. I recommend DOT approved lines and
fittings. Non-DOT fittings will work on lower
pressure systems (below 150psi), but anything
above that should be running DOT hardware.
6) CHARGING SYSTEM: The high current draw from
electric compressors can tax a stock charging
system. On luxury vehicles and SUVs with high
amp alternators (120amp and up), the stock
alternator should work fine. Try cross
referencing a high output alternator from the
same manufacturer if your vehicle does not come
with one. i.e- If you are bagging a Cavalier,
look for a Cadillac alternator that might work.
7) WIRING: Fuse all 12v leads and make sure
grounds are solid. Use relays to control high
amp loads. Run appropriate gauge wire to the
compressors. I recommend 4 gauge supply with 8
or 10 gauge leads. |
MAINTENANCE
1) Be sure to drain your tank at least once a
month. Water build-up can clog the valves, esp.
in freezing or below freezing conditions.
Disconnect and drain the tank entirely once a
year.
2) Use an air dryer and/or water separator to
keep foreign material out of the system. You
want to keep your valves CLEAN!
3) Pay attention to how long the compressors
run. If they start taking longer to fill the
tank, your compressors are going away.
4) Check your charging system after
installation. Keep an eye on battery voltage and
available 'reserve energy'. If you start
noticing your lights getting dim, think about
upgrading your alternator.
5) Leave the vehicle inflated overnight from
time to time to see if leaks have developed.
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AIR SUSPENSION PROS AND
CONS |
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PROS |
CONS |
1) Minimal equipment needed
2) No leaky fluid
3) Better ride
4) Fast acting if set-up correctly
5) Easily hidden
6) Inexpensive to make a 'functional' system
7) Easily tunable ride quality |
1) Bags may develop leaks
2) Less 'Play Time' w/o running Nitrogen
3) Nitrogen bottles have to be refilled
4) Less suspension travel
5) Harder to make a fast system
6) Harder to hop and 3 wheel
7) Air cannot be recycled and reused |
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HYDRAULICS PROS AND
CONS |
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PROS |
CONS |
1) Very fast system operation
2) No bags to develop leaks
3) More suspension travel
4) More 'Play Time'
5) Easier to make hop and 3 wheel
6) Hydraulic fluid is recycled and reused |
1) Leaks can be VERY messy
2) Harsher ride (w/o accumulators)
3) Many baterries are needed.
4) Weight of the system can be exceptional
5) Lowered overall vehicle performance
6) Relatively high maintenance
7) Batteries need to be charged
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Overall, bags are intended for the crowd that
wants to have good ride quality, low
maintenance, and an overall functional system.
For hopping, 3-wheel motion and more operational
time, hydraulics works better. Since I have a
limited experience with hydraulics, I will allow
others in the know to elaborate on the Pros and
Cons of both systems. Here is a link to "Kenny's
Bags vs Juice" page. The prices for both are
about the same, but can get outrageous depending
on the application. Expect to spend at least
$2000 on either system. |
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