The Crossfire system mounts between dual tires to equalize the pressure, and it also provides a single fill point and a visual monitor to assist owners with maintenance.
By Bill Hendrix, F761S
One of my least favorite duties around the coach is checking the pressure in the dual tires. It concerns me that I invariably let out a quantity of air by not being able to seat the gauge tightly enough. I usually find a slight difference in the pressures between the two tires, which necessitates a decision: do I hook up the compressor and drag out the hose to add a little air, or just let some air out of the tire with the higher pressure? I had considered the idea of some kind of pressure-equalizing device. However, I was hesitant about a direct link that would allow equal inflation of both tires at the same time, because this also would allow equal deflation.
The Crossfire dual tire pressure equalization system, produced by Dual Dynamics, of Lincoln, Nebraska, is such a device. It has been around for a while and has some very desirable features. After discussing its performance with two different owners, I decided that a firsthand look was prudent. The system must be ordered for a specified tire pressure (this is not adjustable), so it is important that you know what pressure you should be running in the duals — based upon the weight on that axle. (See the article titled “Tire Safety” in the April 2000 issue of FMC, page 74.)
The standard system contains two control valves, four hoses, and three different pairs of mounting brackets. Depending on which type of hub you have, one of the three bracket types will mount to a lug, hubcap, or drive axle end, and the valve body mounts to the bracket. One hose has a 180-degree turn connector on the end to accommodate the inward-oriented valve stem of the outside dual. The other hose has a straight end that attaches to the outward-pointing valve stem of the inside dual. If your tire valve stems are not conventionally oriented, as stated above, you will need to specify this when ordering. In addition, to make the connection to the inside dual, you need to be able to reach between the wheels. If you are running very large tires and there isn’t sufficient space between the tires, a valve stem extender might be the only option. We will discuss valve stem extenders later.
If your wheels have wheel covers and the hub or lug bolts are not visible, remove the covers to facilitate installation of the proper mounting bracket. The control valve then bolts securely to the bracket. The hoses are a tight-fit double O-ring held in place by a slotted tab. Once the hoses are attached, the instructions tell you to attach the inside dual first to minimize loss of air pressure. Next, attach the hose for the outside dual. During installation, you are going to lose some air, so have an air hose available to re-inflate the tires to the proper pressure. The installation instructions caution you not to overtighten the hose connection. As you make the connection, the air leak will stop when the gasket bottoms out. From this point, tighten the nut only 1 to 1-1/2 additional turns.
The system is now up and operating, giving a visual display in the control valve window. All red in the display means the pressure is at least 10 pounds per square inch (psi) too high. All black means it is at least 10 psi too low. When the two tick marks in the yellow display are centered, the air pressure is as specified on the valve. If the display is half-yellow and half-black, the pressure is approximately 5 psi low. Half yellow and half red would mean approximately 5 psi high. Crossfire provides a “How to Read” sticker to place at a convenient location.
To adjust the air pressure, you may use the valve stem on the control valve to inflate or deflate both tires equally at the same time. I used a recently calibrated tire gauge to verify the indicators, which proved to be very accurate. The control valve has an air-pressure monitor that will allow up to 10 psi of equalized deflation. However, if either tire deflates more than 10 psi, the valve isolates the two tires so that only the problem tire can deflate further. In the event of a blowout, Crossfire automatically isolates the good tire with only a slight loss of air pressure.
During your walkaround inspection each day before you travel, all you have to do is glance at the Crossfire valve-pressure indicator window to verify that the window is yellow, indicating proper pressure. During the travel day, the tires will run warmer and their air pressure will increase from the heat generated by the tire’s contact with the pavement and its flexing, and the window will be red (showing that the pressure has been exceeded by more than 10 psi), but this is normal and to be expected. If the window is black, a loss of more than 10 psi has occurred, and this must be remedied prior to further travel. On a very cool morning, the air pressure may register a bit low. This also is normal. Since high temperature causes an increase in air pressure, low temperature will, conversely, cause a decrease.
If there isn’t sufficient room between the duals for the inside valve stem connection, a valve stem extender is necessary. Dual Dynamics does not recommend the use of extenders, as this is one more connection that may be subject to leaking. Company officials did, however, note that many customers are using extenders. Two thoughts on extenders. First, buy new ones! They will have a new gasket and should make an airtight installation. Some extenders come with hex shoulders that make positive tightening a great deal easier. Second, purchase extender support grommets. They install around the extender and fill the space between the extender and the hole in the wheel to prevent excessive vibration. If you cannot locate factory-made grommets, make them out of a rubber plug, which usually is available at marine supply stores. Determine the appropriate outside diameter and drill a 1/4-inch hole in the middle. The grommet is not an option — it is necessary! Do not install extenders without the supporting grommets.
After installing the Crossfire and after inflating the duals to the appropriate tire pressure, check the display window after 24 hours or so to see whether any loss of air pressure has occurred. Any leak at the Crossfire system can be detected easily by spraying the device with a mixture of water and liquid soap; if bubbles form, a leak exists. It is imperative that the system be airtight immediately after installation. Even the very slightest leak over a few days can cause significant deflation. Do not assume that the air hoses and control valve are okay; one of my hoses leaked and required replacing.
My Crossfire system has now accrued more than 11,000 miles of service and is performing as expected. It is American-made and comes with a two-year warranty.
For price, local availability, or more information, contact Dual Dynamics, P.O. Box 80436, 3300 N. 35th St., Lincoln, NE 68501; (800) 228-0394; or visit www.dualdynamics.com