Smart Parts 2nd generation Max-Flow Nitrogen/HPA system
© Ravi Chopra, 1999
Over just the past few years, nitrogen/HPA (high pressure air) has become the propellant of choice in paintball due to the many performance advantages it offers over CO2. Smart Parts, not a company known for walking away from easy money, joined up with Pneu-ventures some years back to design, build, and sell a world-beating nitrogen/HPA system. The system they brought to market was the Max-Flow. It was reputed to be absolutely the best performing regulator on the market, its output so consistent that it did not require secondary regulation to provide exceptionally consistent velocity. Sales of the Max-Flow suffered, though, due to a high price tag and a reputation for developing leaks easily.
Just last year, Smart Parts went back to the drawing board to see if they could address the problems that plagued the original Max-Flow without sacrificing its exceptional performance. The result is the 2nd generation Max-Flow currently available from Smart Parts, also available to owners of the original Max-Flow as an upgrade.
The Max-Flow is a so-called "balanced" regulator design. That is to say, the output pressure from the Max-Flow is compared to the set-point and excess pressure is vented. The advantage of this design is that it provides exceptionally consistent output pressure without a second stage of regulation (as will be seen later). As a nice safety bonus of this design, even if the regulator seat fails completely, the excess pressure is vented off rather than fed into your gun.
The Max-Flow regulator has a relatively complex design when compared to some of the other regulators on the market. To make your life easier, Smart Parts includes an absolutely wonderful owners manual. It includes a list of necessary tools. It has step-by-step instructions on how to set the output pressure, test for problems, troubleshoot, and rebuild the regulator. It has full regulator schematics listing all of the parts and seals. They even include recommended output pressures for various paintguns and filled-bottle weights for CO2 fills! The manual that comes with the Max-Flow is by far the best that comes with any nitro system (some systems dont come with any manual at all). Looking to the entire paintball industry, only the Automags manual is in the same league. Major kudos to Smart Parts for this.
Smart Parts has done a smashing job eliminating sporadic leaks in the 2nd generation Max-Flow. With the original Max-Flow, I was frequently experiencing extremely frustrating leaks. In fact, these leaks were caused by a hard-plastic regulator seat that was easily nicked and did not seal properly. These leaks past the regulator seat would allow excess pressure to slowly build in the output. Doing its job perfectly, the regulator would vent this excess pressure and maintain a perfectly stable output to the paintgun. While this is a nice example of the advantages of the balanced regulator design, the leaks were a constant headache. In the 2nd generation Max-Flow, Smart Parts has replaced this hard plastic reg seat with a differently configured seat and a much softer seal that doesnt nick and fail like the old seal did. In fact, since upgrading my Max-Flow systems I have not suffered a single leak or reliability problem of any kind.
Output pressure is set by twisting a large end-cap that screws down over a large spring that makes up a big part of the regulators volume. It is locked in place by cinching a large nut on the same threads up against the back of the cap. This is one of the systems weak points. This nut does not do much to deter people from adjusting the pressure after its been set. Id really prefer to see a locking screw to fix it in place for tournaments.
All nitrogen-ready Max-Flow systems come with tank and output pressure gauges, a standard fill-nipple, and a nitrogen tank. Tanks can be had in three different sizes: aluminum 53 ci, and fiber-wrapped 68 and 114 ci. The tanks come with their own on/off pin valves that screw into the Max-Flow system. The on/off is controlled with a large, easy to turn knob (no wrenches required). As an added safety measure, the valve has a wide-orifice pin-valve so if the tank does somehow manage to unscrew from the regulator with the on/off open, the pin valve will close and prevent the tank from completely venting. In fact, a channel is cut inside the manifold such that if the tank does start to back out, the pin valve closes, the o-ring blows out, and the pressure inside the gun is vented, all before the tank becomes completely unscrewed from the system. Naturally, the tank valve has its own burst disc to protect from overpressurization. The valve is also reverse-threaded so it cant be accidentally screwed into a standard ASA and 3000 psi pumped straight into your gun. I think it is fair to say that the Max-Flow comes with more safety features than any other system on the market
The Max-Flow can be had as one of two basic setups: gun mounted or remote. The gun-mounted system is a bit more compact and comes with the appropriate parts for bottom-line mounting on most paintguns. The remote system is simpler, looking a bit like Smart Parts expansion chamber remotes and including a steel-braid remote hose and disconnect. The price of the two different systems is the same.
If there is one thing to complain about with the Max-Flow, its that it is big, especially when combined with the bottom-line manifold. Most other nitro systems on the market are much smaller and more stream-lined than this monster. It doesnt impair performance at all, but some people are disconcerted by just how big and goofy it can look.
Design rating [3.5]
The Max-Flow system is virtually all aluminum and is designed for 3000 psi operation only. All of the parts are machined and fit beautifully. All aluminum parts are anodized black. Aluminum makes for a much lighter system than some of the massive stainless steel systems out there.
The 53 ci tank is a thick, heavy aluminum. The 68 ci and 114 ci tanks are the standard fiber-wrapped tanks that have been in use for years. All nitrogen tanks for the Max-Flow are rated to 3000 psi. The tank valves are brass and do not show any signs of significant wear after extended use.
Though there is nothing specifically wrong with the construction of the Max-Flow system, its 3000 psi limit and fiber-wrapped bottles put it a step behind the 4500 psi systems and much lighter carbon-fiber wrapped bottles currently being offered on other nitrogen systems.
Construction rating 
Most regulators will offer very consistent output pressure as long as the load (input pressure the regulator has to control) is constant. This is clearly not the case with nitrogen/HPA systems. With these, you start with a 3000 psi load which drops throughout the game as the tank empties. If you run the tank completely dry, the regulator could be faced with pressures that vary from 3000 psi to 0 psi through the game. Clearly, once your tank pressure drops below the set output pressure, the output pressure will drop with it. What we are really concerned with is how the output pressure changes as the tank pressure drops.
To test the Max-Flow, I filled the tank, set the output pressure, hooked the system up to a paintgun (an Autococker) and fired it 5 times, taking output pressure measurements after each shot. I then bled 500 psi out of the tank and repeated the series of 5 readings. I continued to repeat this procedure until I reached the set output pressure or 500 psi. I ran this experiment at three different output pressures (200 psi, 500 psi, and 900 psi). For comparison purposes, I ran the experiement in parallel at 500 psi and 900 psi with Air Americas venerable Raptor nitrogen system. The three graphs included herein show the results of these tests. The error bars are the standard deviation of five readings taken at any given tank pressure. These curves represent how consistent the system is from shot-to-shot while the curve as a whole represents consistency as the tank runs from full to empty.
As you can see, the Max-Flow is remarkably consistent, both shot-to-shot and over the whole span of tank pressures from completely full all the way down to the set pressure. Furthermore, this consistency comes at high, medium, and very low output pressures. These isnt a paintgun out there that this system will have any difficulty feeding. I am not aware of any other nitro/HPA system that maintains its output pressure as impressively as the Max-Flow
Another issue of course, is flow-rate. I had planned on trying to time the recharge rate, but I found that recharge was represented by little more than a twitching of my 3" reference test gauge needle. In use, I never experienced any velocity drop off with rapid fire. Additionally, Smart Parts includes the Max-Flow as the standard air system for use with their hungy 11-shots-per-second Shocker Turbo. Suffice it to say, the Max-Flows flow-rate will not be an impediment for most players.
Performance rating 
The Max-Flow is really more appropriately considered as just the pressure regulator that comes with regulated Smart Parts gas systems. This is because the Max-Flow regulator is the only part that is really common to all Smart Parts systems. It has a single high-pressure input port and four regulated outputs. These ports are used with a variety of different mounts and fittings to create bottom-line, remote, nitrogen/HPA, and CO2 based systems. As such, the Max-Flow is perhaps the single most versatile system on the market. However you want to run it, Smart Parts can set the Max-Flow up to fit your needs. Even people who sometimes find themselves shooting nitrogen and other times shooting CO2 arent left out in the cold. Smart Parts sells some nitrogen bottles with standard CO2-tank threads so you can buy your system with standard threads and screw in the CO2 or nitrogen bottle of your choice. This also makes it much easier to put CO2 into your Smart Parts nitro bottles (which are rated to more than sufficiently high pressures to be filled with CO2).
If there is any lack for the Max-Flow, its in the simple fact that there arent many aftermerket bottom-line and drop-forward cradles available for bottom-line mounting. Any cradle or mount that a standard bottom-line ASA can be attached to is compatible with the Max-Flow, but you dont see the same impressive array of aftermarket options as you do for Air America systems. This is hardly Smart Parts fault or responsibility, though.
Versatility rating 
The 2nd generation Max-Flow nitrogen/HPA system varies from $250 to $390 depending on the bottle you want with it. While these prices are a good bit higher than those of other 3000 psi nitro systems, you do have to keep a few things in mind. First, the Max-Flow offers more and superior performance, safety, and convenience features. It also offers such exceptionally consistent output that you will never need a second regulator (like a Uni-Reg or Stabilizer) to further control the input pressure to your gun; a potential savings of over $100 there. As such, the Max-Flow is a good value, if not the price leader in this segment.
The warranty that Smart Parts offers with the Max-Flow is 1 year from the date of purchase and covers defects in materials and workmanship. In general, Ive found Smart Parts to offer good, competent customer service.
Price/Warranty rating 
The Max-Flow is a strange mix. It offers perhaps the most impressive combination of performance, convenience, and safety available in a nitrogen system today. Missing, though, are such popular, state-of-the-art features as 4500 psi operation and ultra-light carbon fiber tanks. For the performance junkie who wants the ultimate in output pressure consistency, the Max-Flow is a dream come true. If Smart Parts would offer it in 4500 psi and could pack it into a smaller, more elegant package, the Max-Flow would be perfect.
All material at this site is © Ravi Chopra, 1999