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Airgun Designs Flatline
Compressed Air Systems
by Bill Mills
November 2001

Airgun Designs set a new standard in paintball when it produced the 68 Automag, the first paintgun to include a regulator integrated into it's design.  AGD also pioneered the use of compressed air, with Tom Kaye's mantra of "CO2 sucks" being based on how much more reliable the Automag was with compressed air as a power source.  In the early 90s the paintball industry in general said the higher pressures of compressed air were too dangerous for the sport, so Airgun Designs concentrated on their paintguns instead, leaving it to Air America and Paintball Mania to fight the uphill battles that eventually resulted in compressed air becoming the accepted standard for a high end paintball energy source.

Eventually, Airgun Designs threw its hat into the compressed air ring with the 3,000 psi Flatline compressed air system.  At first the name caused some confusion, with both the AGD Flatline, and Tippmann's Flatline barrel being released at the International Amateur Open. 

The Flatline is a full featured, adjustable compressed air system.  Initially released in bundles with the Automag Classic, it provided a "package deal" for players to get into a complete Automag set-up and not have to deal with CO2 related problems.  The 3,000 psi Flatline soon became available as a separate product, with it's adjustability and high flow rate giving it a great deal of versatility.

Soon to be released to the general public is the 4500 psi Flatline air system.  It has the same features as its lower pressured predecessor, but slightly different internals, and the expected increase in the number of shots available per tank fill.

The Flatline regulator body is a cylinder, the same outer diameter as the necks of the fiber wrapped bottles with which it ships.

Nearest to the bottle neck is the burst disk.  Designed to rupture and allow the tank to empty in case of an overfill, the Flatline uses a unified burst disk in which the disk and nut are a single unit.  This avoids problems related to mismatching disks and nuts, or accidentally installing double-disks.

The next item up the neck is the high pressure gauge.  This shows the pressure of the gas stored in the bottle whether the tank is turned on or not.  AGD uses micro gauges on the Flatlines.  They have a definite advantage in their compact size and durability, but sacrifice accuracy in trade.  In practical use however, they do their job well.

Between the tank pressure and output gauges is the shutoff valve.  The Flatlines have one of the nicest shutoff valves seen on any of  today's compressed air systems.  A small winged knob turns as easily as a faucet, regardless of tank pressure.  On other compressed air systems the shutoff valves typically require much more force to operate.  This is an important feature on an adjustable system as it means the output pressure can be set and forgotten.

A 1/8" NPT opening allows elbows, braided hose, microline, or macroline to route the output from the Flatline to the paintgun on which it is installed.  On the front of the regulator is the adjuster.  Much like the rear of an Automag, the adjuster is screwed in with a hex wrench to increase the regulator's output pressure.  A nut on the adjuster is used to lock it in place, both to make it tournament legal and prevent it from creeping under the vibration of firing.

Externally, the 4,500 psi systems are differentiated from the 3K models by both color and shape.  The 4500 psi models are anodized in teal as opposed to black, and they feature cosmetic teardrop milling around the adjuster.

Both models use the same type of cradle to mount on the paintgun.  A band of sheet metal wraps around the regulator body.  This cradle mounts to the sides of AGD's proprietary drop forward.  While this mounting system is perfectly functional, it is definitely utilitarian, and does not allow the end user to take advantage of the wide variety of bottle mounts on the market today.  Custom Products produces an adapter block which mounts on the AGD cradle in place of AGD's drop forward.  The adapter block is slotted for a standard air system dovetail, allowing the Flatline to be mounted with standard drop forwards.  In the photographs for this review, the 4500 psi Flatline is equipped with this adapter and mounted on a Custom Products mini drop forward.

The AGD drop forward provides little room for a hex wrench between the regulator and the screws.  When mounting the Flatline to a paintgun using the stock drop forward, a ball end hex wrench can greatly simplify the task at hand, because it can be inserted into the screws and turned while at an angle.

Once mounted and hosed to the paintgun, adjustment of the Flatline is straightforward.  With a full bottle, the shutoff valve is turned on.  An open end or adjustable wrench is used to loosen the adjuster's lock nut.  A hex wrench is then used to screw the adjuster inward, which increases the regulator's output pressure.  This can be monitored on the low pressure gauge.  Lowering the pressure is achieved by backing the adjuster out of the regulator body, but changes decreasing the pressure will not be reflected on the gauge until after one or two shots are fired through the paintgun.  Once the proper output pressure setting is achieved the adjuster's lock nut is tightened down with a wrench.
 

On the field, both of these systems have proven themselves to be durable and reliable.  Their adjustability makes them ideal for tuning the trigger reactiveness of Automags equipped with the RT or ReTro Valve, while their flow rate has no problem keeping a 'mag supplied with enough air for rapid firing.  Conveniently both gauges are on the same side, the left, making them easy to glance at for right handed shooters during a game.  

CAUTION:  Air system maintenance should be performed only by qualified airsmiths.  The following information is provided to give the reader a better understanding of how the Flatline regulator operates.

For experienced Automag airsmiths the general structure of the Flatline should be familiar.  A spring pack places pressure on the regulator piston.  Output pressure moves the piston against the spring pack.  When the output pressure is low, the piston moves inward, separating the regulator pin from the regulator seat, allowing gas to move past until the pressure is high enough to push the piston back, closing the regulator at the set pressure.  What is different between the Flatline regulator and the Automag's AIR valve is that the regulator pin is connected to the piston, rather than being pushed against the piston by a spring from the opposite side.

The internals of the Flatline are first accessed by removing the Flatline cradle.  This is done with a hex wrench and a box end or socket wrench.  Two hex head socket screws go through the cradle and drop forward into lock nuts on the opposite side.  It is important to keep in mind that the cradle offers outward spring pressure and may "pop" open when the screws are released from the nuts.  

With the screws removed the cradle can be flexed outward and slid off of the regulator body.  This exposes the gap between the upper and lower halves of the regulator, as well as giving more room to work on the shutoff  valve assembly.

With no air pressure in the bottle, the Flatline regulator can be disassembled for maintenance and inspection.  A small hex wrench is used to remove a set screw from the shutoff valve handle.  The handle then lifts off of the valve's cam shaft.
 

With the shaft twisted to the on position, it can be slid out of the regulator body on the side opposite the knob.  This will reveal the two o-rings which seal it from the outside.  If there is an air leak on either end of the shutoff valve shaft, it is one of these o-rings that will need to be replaced.  Much like the camshaft in an automobile engine, the shaft of the Flatline's shutoff valve has an elliptical lobe shaped cam which pushes on a valve when it is rotated.  It is this cam which is the secret to the Flatline's shutoff valve success.  It provides ample leverage to make operation under pressure very easy.

The actual shutoff valve is a pin valve inside the lower half of the regulator body.  It is accessible only by removing the regulator from the bottle.  It can be seen from the side openings when the shutoff valve shaft is removed.  It becomes readily apparent why the shutoff valve must be turned to the on position for removal.  In the on position, the valve's cam presses the pin valve flush with the regulator body wall.

Between the shutoff valve and the regulator itself is a caged ball bearing which can be rocked back and forth by gas flow.
 

Much like the Automag's AIR regulator, the Flatline body is opened by unscrewing the end half to expose the regulator seat and regulator pin.
 

A series of four holes around the regulator body allows the use of a spanner wrench to get a solid grip on the top half of the regulator body in order to unscrew it from the base.  As spanner wrenches aren't sitting around most airsmith's tool chests, it's easy enough to drop a hex wrench in one of the holes and use to to twist off the reg top.  Much like the AIR regulator, a thick o-ring seals the two halves, and is easily inspected for rips or tears.

When the regulators are apart, the differences with the AIR and each other are readily apparent.  

The regulator pin, instead of pushing up against the regulator seat and through it to the piston instead extends out from the piston through the seat, and then flares out on its end to seal against the seat.

In the 3000 psi Flatline, the end of the regulator pin is rounded almost to a ball shape, and the regulator seat is simply a white o-ring.  This makes inspection and reassembly very easy.  The o-ring simply stretches over the end of the regulator pin for replacement.

In contrast, the 4500 psi Flatline reg pin has a more angular nub on its end, and fits through a flat cylindrical seat that is much more reminiscent of the seat in an AIR regulator.  Note that the 4500 psi regulator seat pictured here is slightly different than the final production model, where the regulator seat fits deeper into the surrounding aluminum in order to protect it from deformation.

With both models of the Flatline regulator, the regulator piston and spring pack are accessed by fully unscrewing the adjuster cap.

Relief valves are located inside the regulator pistons.  These protect the paintgun from over pressurizing in case of a leak in the regulator seat.  

A hollow nut in the back of the regulator piston holds in the relief valve assembly.  It can be tempting to grab the piston with a pair of pliers in order to grip it solidly enough to unscrew the relief valve nut.  This is a bad idea though, as it will result in scratches on the piston.  Instead it should be gripped gently in a cloth lined vise.

Beneath the hollow nut is the relief valve spring, a metal backing disk and the seal itself.  The seal will deform to fit the valve face, and any rips, tears or debris could lead to unwanted leaking out the center of the adjuster cap.  

After inspection, cleaning and lubrication, the Flatline regulators are reassembled in the reverse order of disassembly.

Getting the cradle back onto the drop forward can be a bit tricky due to the outward spring pressure involved.  The task is most easily completed by holding the cradle in place with a pair of locking pliers and inserting one screw and nut, then removing the pliers and installing the other.

Both the 3,000 psi and 4,500 psi Flatline compressed air systems are feature rich adjustable air systems with solid performance on the field.  They additionally benefit from Airgun Designs' warranty support which carries a reputation as one of the best in the sport of paintball.  The added shot count offered by the 4500 psi model makes it an ideal companion for the E-Mag or ReTro valve equipped Automag.
 

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