The question was raised on one of the RV forums I participate on that related to making things easier to deal with filling and checking the pressure in the tires of vehicles equipped with duals. I provided one answer to assist them, but I thought I would also make some notes here on the blog.
The nature of duallys is that one has to be able to check the pressure on both the outside and inside tire, and it is a lot of hassle to have to remove a tire just to check pressure. So, one needs different testers and fillers in order to be able to get the job done. Also, with some of the higher pressure tires, air equipment with higher capacities for air pressure is also needed.
When looking at your duals, first make sure that when you look through the hole in the rim of the outside tire that you can see the hole in the rim of the inside tire. If you can’t then it will be nearly impossible to fill or check the inside tire’s air pressure.
With duals, one needs filler equipment that is called a dual foot fitting. There are two different dual foot heads on the accessories. The first is called the Dual Chuck style and looks like the end on this small tire pressure tester. This one is a Milton S 927 Dual Foot gauge.
The other style is called a straight foot dual head and looks like the end on this fitting for filling dual tires.
With either style of dual foot, they are designed where the end air fitting (the one pointing out) is used to fill the inner tire. The second air fitting is the one pointing backwards and is used for filling the outside tire. That has to be done that way because the valve stem for the outside tire is actually pointing towards the inner tire.
For any tire on a truck, pickup with large dual tires, or motorhomes with duals, one probably wants to have an air tester that has a high capacity. Some of the smaller tire testers are only good up to 120 lbs. psi. While the longer air testers usually have a capacity of 160 lbs. psi. Of course, the longer ones are also easier to use to reach into the inner tire’s valve stem.
The picture of the tester above would have a capacity of 120 psi. The one below is one with a capacity of 160 psi. It is a Milton 982 Dual Head tester.
Now, with either of the above testers, one has to remove the air hose from filling and then place the tester on the valve stems for testing of the air pressure. On occasion, it seems that I can lose a fair amount of air just trying to fill and test the tires. So, to alleviate the issue of constantly inserting and removing air accessories, there is another solution, although it is a bit pricey.
The picture below is of a Milton Window Inflator Gauge model S 506. You will see that there is a handle that when depressed will allow air to flow into the tire from the compressor. It is also equipped with the dual foot fittings, but it has one more feature. The window is actually a magnified reading of the air pressure in the tire. Obviously, this image does not show the chuck fitting that allows one to attach it to one’s air hose.
After putting in air and releasing the handle (but keeping the dual foot fitting engaged to the valve stem), the air pressure will be displayed in that magnified window. This type of air fitting is helpful in ending the need to keep changing tools to fill or test the air pressure. However, there is one drawback with this tool. It only has a pressure capacity of 120 lbs. psi. So, on our Mobile Suite’s 17.5” tires, it won’t be enough capacity as the tires get filled to 125 lbs. psi.
The Milton products are made by a company that has provided air equipment for automotive service stations for years. We used this equipment way back in the ‘60’s. For that reason, I searched out Milton products to get my tire tester.
Since we also have our own air compressor capable of filling the 125 lb. psi tires, I might just purchase one of the window inflator gauges for myself. It won’t be usable on the trailer tires, but the regular tester will function well for that capacity anyway. Since the trailer tire stems all face outward, they are easy to fill and test.