98 Desert Fox: Main Page Getting Started: Tips for a New Owner    98 Desert Fox Exploded View and Schematic    Classic Fox Exploded View and Schematic Fox Troubleshooting    Troubleshooting: Air Leaks    Troubleshooting: Cycling Problems    Troubleshooting: Ball Breaks Tweaks: Things you can do for your Fox    Regulator Theory and Tuning    Trigger Work and Bolt Polishing    DIY Dial Velocity Adjustor Accessories: Aftermarket Parts for the Desert Fox

Tweaks: Regulator Theory and Tuning

As mentioned in the main Desert Fox page, the recharge rate of the Fox is partly determined by the smallest orifice in the supply system, and this includes passages inside the regulator itself. There are a couple of things which can done to 'open up' the regulator, but first let's look at how it works:

Pretty simple, huh? The Regulator valve is kinda like a teeter-totter. The adjustment knob pre-loads the Valve Spring which tries to open the Valve Poppet via the steel pin in the center of the Plunger. The valve opens until the pressure in the rear chamber equals the spring force, then the valve closes.   For a different look at how Regulators work, see: Rudy Sloup's Regulate This! Ravi Chopra's Regulator Infosheet Doc Nickel's article on Regulator Settings   In the 'Classic' Desert Fox (and in the Automag as well) there is another valve downstream from the main regulator valve, called an On/off valve.   In the 98 Desert Fox it has been eliminated by going to lower pressure operation. (Explaining this is like the chicken and the egg problem, they cannot be separated. Bear with me.) In Physics, the gas laws state that to provide equivalent energy at lower pressure, the volume of gas used has to be increased. In the higher pressure Classic Fox an On/off valve shut off the flow of gas whenever the bolt moved forward to make it easy for the mainspring to cock the bolt back to the rear position. The On/off choked the air flow by turning it on and off constantly, but the higher regulator pressure compensated. Since the On/off lived inside the Air Chamber it also reduced the available volume of pressurized air.   In the new 'Fox the regulator output is open all the time, with the flow shutting off only when the regulator equalizes; so the regulator is much simpler and more efficient. Removing the On/off valve combined with changes to the air chamber milling to increase the internal volume of the makes the volume of stored air quite a bit larger. With a larger volume of air available, the energy transmitted to the paintball is increased. So the regulator can be turned down and yet still give 300 feet per second velocity. With reduced pressure from the regulator the back pressure on the bolt is reduced while the air chamber is filling, and the same bolt mainspring can still push the bolt back to latch on the sear. Reliability is increased since there are now fewer seals, and most of the remaining ones are operating under lower pressure.   It may be possible to upgrade an older 'Fox by ordering the new Regulator Valve, removing the On/off, and installing a lockscrew to hold the valve down, but this would be best done by an advanced machinist.   The Tradeoff: (after all, you can't get something for nothing) There may be a very slight slowing of the bolt return due to the pressure of the valve being open. This should be offset by faster recharge since the airchamber starts to fill as soon as the pressure drops, and then stops filling at a lower pressure. Unscientifically, the firing rate feels the same as the older model, and the changes should reduce pressure dropoffs when strings of shots are fired.   The key openings in the 98 'Fox Regulator are the air passages into the valve, the holes in the forward brass Regulator Valve, and the opening at the top of the rear chamber. Using a needle file, you can open up each of these channels, but be careful not to scratch any of the O-ring sealing surfaces, or you'll be buying a new regulator body.

Tweaks: Regulator Teardown

To disassemble the Regulator, field strip the Reg from the marker and pull off the bolt. Now unscrew the steel Air Chamber from the front of the Regulator Body using padded channellocks. Inside the front chamber is a small socket head cap screw that holds the Regulator Valve in place. Remove this screw with a hex wrench, re-lube the large O-rings around the outside threads, and tighten the air chamber back onto the regulator body.   Slide the Bolt back on, and reassemble the marker. Now attach air to the marker for only a second; you should hear a muffled pop from inside the regulator. De-gas, field strip, and unscrew the air chamber again. The Regulator Valve, Valve Poppet, and a small spring should be loose inside the front chamber now. Remove them to a safe place and remove the rear adjustment screw from the back of the valve body. Use a small blunt tool like and allen wrench to push through the central hole from the front chamber against the plunger pin, it should pop out of the back chamber.

Tweaks: Regulator Openings

The easiest opening to alter is the hole at the top of the rear chamber. This orifice is created when the passageway is drilled from the front of the Regulator Body, and may not be a clean opening anyway. The body is hardened and anodized 6061 T6 aluminum alloy, and can be worked with the sharp tip of a needle file (see the Airsmithing page for tool info). Be very careful not to file too deeply into the side wall where the plunger O-ring seals. Look at the plunger and stop well short of the minimum contact point for the ring. Do not scratch the side walls or the plunger will leak into the rear adjustment chamber. Clean the part thoroughly with alcohol afterwards to remove any metal dust created.   The vertical air passage into the valve is not a problem, since the inner diameter of the sealing O-ring in the trigger frame is smaller anyway. It's best to leave it alone.   The brass Regulator Valve can use some attention. First remove the O-ring. Again using the needle file, enlarge the two side openings to better match the size of the inlet passage. It would be best to line up a hole directly with the inlet, but that's difficult with a blind cylinder, so while you are filing, make an index line on the forward flat face so you can see where the holes are when you are reassembling the regulator. Finally, there is a shallow groove that passes air around the valve cylinder when the holes are not aligned, but it is not very large. Filing it deeper allows air to travel around the cylinder and enter via both holes, which may help recharge speed even after the one hole is aligned.   Advanced Technique: Use a Dremel tool with a small-diameter diamond burr to grind out slots on the interior wall of the brass Regulator Valve running lengthwise from the air inlet holes to the face that rests on the Valve Seal. Be Very Careful to not mar the bottom face or the Valve Seal will not have even pressure. The Poppet inside the valve fills the opening and does not have much clearance for air to pass around it when it cracks off the Valve Seal. These slots channel more air around the head of the Poppet so that the regulator can fill more quickly. Don't try to file these without a Dremel, the part is so small it is very difficult to hold and work on the interior. Be sure to clean everything thoroughly to remove any brass chips and dust before re-assembling.   Obsessive Bonus Activities: Polishing the Valve Tip and outside of the Air Chamber where the bolt slides. Filing the sharp rear edges of the Regulator Body (would be pretty ugly if you have the black model). Using a Scotchbrite pad on the Air Chamber threads at the front of the aluminum Regulator Body. Filing and polishing the ends of the Regulator Spring so the adjustment screw moves more easily.

Tweaks: Regulator Assembly

To assemble the Regulator, start by making sure everything is clean by swabbing down all of the parts with alcohol. Use a dull pick to remove all O-rings, inspect, and replace any worn or damaged ones. Dab your (clean) finger in some silicone grease and rub it all over each O-ring as you put them back on the parts; this gets lube all the way around them and makes it easier to slip them on.   (Tip: the large thick clear washer, unidentified in the exploded view, is the Poppet Seal. It's probably made from silicone, and it will take a 'set' to the cupped face of the Valve Poppet when the marker is gassed up. The poppet probably will not be in exactly the same place when you put everything back together, and you'll want a flat surface when you reassemble to get a good seal. Flip it over to get a clean side, and you'll get double life from these!)   Set the regulator body on the table with the front chamber facing up. Drop the large thick clear washer into the bottom of the front chamber, and push it down into place with a blunt tool. Use a pair of tweezers to place the Valve Poppet (called a Regulator Cup in the Exploded View) centered on top of the clear washer, with the shallow cup down. Again use the tweezers to place the small spring on the stem of the poppet. Now take the Regulator Valve and push it into the hole with the flat side out, using the new index line to make sure one hole is facing down towards the air inlet on the bottom of the regulator body. The blunt face should be flush with the lip of the hole; if it's not, you are hung on the poppet (push out the poppet and valve from the back with a blunt tool and try again). Insert the small socket head cap screw with it's lock washer to hold the Regulator Valve in place.   Turn over the body so the back chamber faces up and insert the Plunger with the steel pin going into the center hole. Lube and insert the heavy steel Valve Spring into the Adjustment Screw, and screw it into the body until you meet resistance, then stop. Screw the Air Chamber back onto the regulator body (Important Tip: spread silicone grease on the aluminum threads of the Regulator Body where the chamber screws on and you can hand tighten this. Much better for maintenance later.) and tighten it down until the gap with the body is tight, use a padded pair of channellocks if needed.   If you've removed the brass Valve Tip, use a fresh piece of PTFE plumbers tape to seal the threads, and make sure the tape doesn't hang over the valve tip O-ring or the the back face where it pushes down on the Piston O-ring. (You'll have to cut down the plumbers tape before wrapping it onto the threads) Lube the outside of the Air Chamber and Valve Tip and push the Bolt back onto the regulator. Give it a turn or two and jiggle it in and out a couple of times to re-distribute the silicone grease on the Piston O-ring. Lube the outside of the Bolt and Mainspring. Now reassemble the marker and test it.

Disclaimer:   The Desert Fox is not a difficult marker to work on, but there is some chance that things could go wrong. If you are uncomfortable about working on the regulator or trigger of your marker, Don't Do It! These tips assume some mechanical aptitude and use of the correct tools. If you mess something up, you'll have to replace it.   Indian Creek Designs has an excellent warranty, and they stand behind their guns. If you have a problem and ship it to them, they promise 24 hour turnaround on repairs. There are many testimonials on the web to back this up. They will also do upgrades based on production improvements.   ICD wants me to make it clear that this is not an official ICD site. Any changes you make to a marker under warranty may void that coverage. Don't blame them, don't blame me. There, that should cover it.   the ICD Official Corporate Website   Finally, Don't use an unsafe marker, and Be Careful with CO2 and Paintballs. Paintball markers are not toys, so be an adult and take responsibility for your own actions...

Links: 'Fox info on this Site

98 Desert Fox: Main Page Getting Started: Tips for a New Owner    98 Desert Fox Exploded View and Schematic    Classic Fox Exploded View and Schematic Fox Troubleshooting    Troubleshooting: Air Leaks    Troubleshooting: Cycling Problems    Troubleshooting: Ball Breaks Tweaks: Things you can do for your Fox    Regulator Theory and Tuning    Trigger Work and Bolt Polishing    DIY Dial Velocity Adjustor Accessories: Aftermarket Parts for the Desert Fox   ICD 'Cats ICD Barrels: Aftermarket Barrel Review Basic Airsmithing Links to ICD Resources on the Web

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