My stainless steel braid valve extensions were leaking air from the rear outside tires. I went to a tire dealer and they installed new steel bolt-in valves, and a European design valve extension that is plastic with a rod down the middle. These extensions do not have air in them except when checking or filling the tires. I checked and found that these are DOT approved and seem to be a better design than the stainless braid.
Since you are a tire professional I would welcome your comments.
I understand the two basic designs of hose extenders.
One is pressurized as it opens the valve core on the stem that is bolted through the wheel. This type can be used with an external TPM sensor at the outer end of the hose or with a "flow-thru" type TPM sensor attached to the bolt in valve and then the hose running out to allow air to be added to the tire.
The second system has a hose with a flexible "rod" on the inside which opens the valve core in the valve bolted to the wheel. This hose is not pressurized except when measuring tire pressure. BUT if you attach an external sensor to the outer end it must depress the "rod" and then pressurize the hose for the sensor to provide a reading. A "flow-thru" sensor could also be used with this system if it is placed on the valve stem with the non-pressurized hose connecting to the outer end of the flow thru sensor. Since this is the hose you have I believe you need to use flow-thru TPM sensors so this might limit your choices.
If properly installed I see no reason for either system to work Now it is of course that either design could have detail features such as better quality hose or "O-Rings" or attaching points of hose to fittings but without doing detailed examination of specific product and possibly conduction some testing so I would not call one any "better" than the other.
RE "DOT Approved" While I have not done research on the specific question of hose extenders, I do understand the "DOT Approval" of tires. This is a very common misunderstanding of how DOT works.
They write rules and regulations and test procedures to be used by a manufacturer when they want to certify a tire or other component as meeting DOT regulations. To my knowledge DOT does not approve specific products. It is the manufacturer who "certifies" that a product would pass all DOT test requirements, if it were tested.
For example, I have seen plastic brake light lenses with "DOT" on them. To me this is nothing more than an indication by the manufacturing company that the lens is "certified" by the manufacture to pass the appropriate DOT standards.
Retired Tire Design and Quality Engineer (40 years experience).
Retired Professional race car driver.
Retired Police Driving Instructor.
Member, FMCA Technical Advisory Committee
Delivered Tire Seminar for RV owners & two seminars on Genealogy at FMCA Bowling Green 2009, Madison 2011 & 2015,
Indy 2012, and Perry & Redmond 2014
I will be presenting two seminars on RV Tires & Three on Genealogy at Perry, GA March 2016 and at GLAMARAMA in June 2016 in Goshen, IN
See my blog www.RVTireSafety.com and subscribe if you want notice of new posts.