Fast Bag 101

I) FAST BAGGING EXPLAINED (back to Table of Contents)

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.
View an Interactive Flash Movie

II) COMPONENT BREAKDOWN

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 powdercoated to your liking. A drain valve located on the bottom of the tank is used to drain the inevitible 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 Transportaion (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 airstruts. Additionally, each bag has a recommended weight rating for the vehicle, similar to the way a coil spring is rated.

THE COMPRESSOR AND THE PRESSURE SWITCH:

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.

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:

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, espcially since the added strain of the pumps would tax the electrical system pretty hard.

York Belt Driven Compressor

As a benefit to the elctric 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 olny 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.

100% Duty Cycle, 3/4HP

Pictured above and to the right is one of the more capable electric units. It isa 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.

BELT DRIVEN PROS AND CONS AT A GLANCE:

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	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

ELECTRIC PROS AND CONS AT A GLANCE:

PROS	CONS
1) Inexpensive 2) Easily mounted 3) Simple to install 4) Adequate for function based systems 5) Does not rob HP.	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)

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.

III) HAZARDS and MAINTENANCE

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.

IV) AIR vs HYDROS

AIR SUSPENSION PROS AND CONS

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

HYDRAULICS PROS AND CONS

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

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.