Achieving Reliable Shear-Off Protection During Railcar Accidents

By OPW | Aug 07, 2020

Midland Manufacturing has developed a Pressure Relief Valve (PRV) that satisfies the requirements of DOT-117/TC-117, a standard adopted by the U.S. Federal Railroad Administration (FRA) and Transport Canada (TC). 

Specifically, the new standard requires that the tank cars on all high-hazard flammable trains (HHFT) and high-hazard flammable unit trains (HHFUT) built after Oct. 15, 2015, have tank shells constructed from 9/16” steel with 11-gauge sheet-metal jackets, 1/2” head shields and – most pertinent for our discussion – improved recloseable valves to mitigate against shear-off incidents and pressure spikes during a rollover incident or accident.

Per its mission to protect people and the environment while also enhancing business performance, Midland Manufacturing developed a Pressure Relief Valve (PRV) pursuant to the DOT-117/TC-117 regulation:

  • Smart-Flow® PRV: Smart-Flow, Midland’s latest PRV innovation, was specifically designed to meet DOT-117/TC-117 regulations. It produces a flow rating of 10,730 scfm at a set-to-discharge pressure of 75 psi. In other words, when the Smart-Flow PRV detects a high-pressure situation, pressure discharge rapidly occurs at a controlled rate of 10,730 scfm, which reduces the likelihood that a high-energy event will result. Additionally, in the event of a fire, the Smart-Flow PRV has demonstrated in testing that it can withstand a 100-minute pool fire and 30-minute jet fire without rupturing. The Smart-Flow’s compact profile (less than 9”) also helps prevent shearing and is retrofittable on existing rail tank cars with standard mounting configurations. The stainless-steel construction of all components also protects against corrosion that can compromise performance.

For more information on Midland’s complete families of industry-leading components for general purpose, pressure and pressure differential railcars, please visit