Tire Pressure

Can you take a wider picture? That looks (to me at least) like the bendix system that inflates your trailer tires for you. Do you have a small plastic box in front of your front trailer axle (mounted underneath about center of the trailer width wise)?

 

That system is meant to keep your tires at 100 psi. Hook up your red glad hand to the trailer, then release your trailer brakes. That supplies air to the system. If you're not losing air pressure, and tires are low then the system isn't working correctly.

 

If you are getting a reading of 70 psi on that tire and it has a self inflating system installed then there is either something wrong with the system not pumping enough air into that tire air line or you have ran over something on the road that could have perhaps punctured the tire. I had that happen to me on my rear inside trailer tire and a lovely piece of steel was removed from it at Loves. Get yourself over to a WE terminal and call them. Not safe to be driving on a 70 psi tire. If you can't make it to a terminal then find a truck repair shop (Loves, TA, Pilot). Probably need to get authorization to open up a company card to pay for the repair. Not sure if your company provides you with a company card.

DO NOT touch that self inflating system or remove any of those lines to try and inflate it yourself. This one is beyond our expertise. Take it to a shop.

*Edit* I just read you said that one of your tires blew on you yesterday so during that blowout something could have happened to the air lines. Definitely need to get it checked out by a mechanic.

 

Get with your WE shop, find out where you can go on the road to have the system checked like Arctic said. Justify it as you believe a tire is low, and 1 blew out yesterday so you think the system might be malfunctioning.