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Friday, March 25, 2011

Tire Valves - Not just those little rubber things

I gotta start off by telling you something my wonderful wife Nancy says bout me. If you ask me the time of day, I may end up trying to tell you how to build a watch. I've decided I will try to start some of my posts with a one paragraph summary. If you want to know more then you can read on, but you have been warned.

90+% of RVs should have bolt-in metal valves and it won't hurt if we used them even on a Tear-Drop trailer. Rubber valves on your car should be replaced whenever you get a new set of tires. The rubber gasket part of metal bolt-in valves should be replaced whenever you get new tires. If the valve core is leaking, replace it.

OK now for those that want the details.

Recently a friend, Nick Russell, the editor of Gypsy Journal had a tire failure.


This was an inner dual and you can see right through the tire sidewall where a big chunk is missing. While some would blame the tire and say it was defective and that he had a "Blow-Out". Nick is a bit smarter than that. He knew he had been having problems with air leaking out but there was no puncture. The "Root Cause" of this failure was traced to the use of a rubber valve on his Class-A size tire. The valve stem did not seal properly and he had a slow leak. The end result of someone trying to save a couple of bucks cost Nick over $700 for the service call and new tire.

For those of you wondering, we will cover in future posts a number of specific types of tire failure each of which leave their unique tell-tale signature

Standard rubber valves like the T-414 series are rated for a MAX of 65 psi and for use on the relatively thin passenger rims. There are rubber valves such as the 600HP rated for a MAX of 100 psi but neither of these "snap-in" rubber valves belong on an RV with the possible exception of some very samll trailers and some Class-B units that use standard passenger tires.

Class-A, Class C and most trailers have inflation pressures that exceed 65psi with many above 100psi so a bolt-in metal valve is the only one to use. It is important that the tech doing the installation of these bolt-in valves apply the proper torque. Small bolt in valves such as TR-430 use 25- 45 inch-pounds of torque.



The majority of the TR-500 series use 80-125 inch-pounds.

If you discover the valve core is leaking don't just crank it tighter like you would a leaky water faucet. All the core needs is finger tight. 1.5 to 5.0 inch pounds MAX. If you over-tighten the core, you may split the core gasket (black in the graphic) and it will just leak more. If you look at the graphic from Schrader you will see the part that that lets the air in and out can't be tightened. Your tire dealer should be willing to give you a new valve core for free. You should ALWAYS use some type of cap with metal the best. The primary purpose of the cap is to keep dirt out but a good metal cap with internal gasket can keep most of the air in too.

Watch THIS little graphic on how a valve core works.


A final bit of warning. On your car you may have a Tire Pressure Monitor System. Most of these are Aluminum not Brass so they need special stainless steel valve core and they may be bolt in and have low torque requirements. If you need to service the OE TPMS valve you need to go to a car or tire dealer as they have the correct tools. I will be covering TPMS as a separate topic in the future.

1 comment:

  1. Just placed a metal valve extension on both of my rear inner tires along with a rubber stabilizer placed in the 2 inch diameter hole in the rim Was real happy with the results except on one tire the extension keeps twisting & doesn't get tight like the other tire Can't see whats going on because I now have this rubber stabilizer blocking my view of the valve It would be real difficult to remove the stabilizer I'm concerned the metal valve stem may be twisting???? Please help????

    ReplyDelete

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