What values must governor cutout pressure be set within According to Fmvss 121 requirements?

What values MUST governor cutout pressure be set within according to FMVSS-121 requirements? The governor cutout pressure is around 8 psi low on a truck tested during a PMI.

What is the current maximum stopping distance for an Fmvss 121 compliant tractor trailer rig that is unloaded?

Under the unloaded-60-mph Start Printed Page 74271stopping distance requirements of FMVSS No. 121, air-braked buses must comply with a stopping distance of 280 feet, and air-braked single-unit trucks and air-braked truck tractors must comply with a stopping distance requirement of 335 feet.

At what psi does the governor cut out?

When air tank pressure rises to the “cut-out” level (around 125 pounds per-square-inch or “psi”), the governor stops the compressor from pumping air. When the tank pressure falls to the “cut-in” pressure (around 100 psi), the governor allows the compressor to start pumping again.

What are the typical air compressor governor cut in and cut out pressures?

Air compressors typically have a “cut-out” pressure between 110 psi and 130 psi and a “cut-in” pressure about 20 psi lower. Air pressure build-up from 85 psi to 100 psi should take 45 seconds or less.

What does Fmvss 121 mean?

It establishes performance and equipment requirements for braking systems on vehicles equipped with air brake systems, including separately controlled parking brakes of prescribed holding capability, automatic brake adjusters and adjustment indicators, and emergency brakes which activate automatically in the event of …

What is the purpose for the legislation of Fmvss 121?

The safety standard states that “ The purpose of this standard is to ensure safe braking performance under normal and emergency conditions.” Generally speaking, FMVSS 121 is broadly applicable to commercial trucks and buses.

What is the maximum operating air pressure?

Actual cut-out pressure must never be higher than 1000 kPa (145 psi ). Actual cut-in pressure must never be less than 552 kPa (80 psi ). The air brake system is defective when cut-out pressure is above 1000 kPa (145 psi ) or cut-in pressure is below 552 kPa (80 psi ).

What does Fmvss compliant mean?

Federal Motor Vehicle Safety Standard
Overview of Federal Motor Vehicle Safety Standard 126 A part with an “FMVSS 126 compliant” designation indicates that the manufacturer has tested and certified the part to meet the requirements set forth in the safety standard.

What do you need to know about FMVSS No 121?

Most parking brakes on heavy vehicles are of the spring brake design that require adequate brake system air pressure in order to release them so the vehicle can be moved. FMVSS No. 121 has several requirements relating to the reservoirs and air compressor systems on trucks, buses, and trailers.

What are federal motor vehicle safety standards No.121?

This Notice denies a petition by Mr. Wayne Walch of TP Trucking in which the petitioner requested three changes to Federal Motor Vehicle Safety Standard (FMVSS) No. 121, Air brake systems, related to the air compressor operation and low air pressure warning system.

When does the Governor activate the air compressor?

When the reservoir pressure drops to cut-in pressure, the governor activates the air compressor to build the system pressure back up to the cut-out pressure.