Federal Motor Vehicle Safety Standards: Air Brake Systems

DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 571

[Docket No. NHTSA-98-3650]

RIN 2127-AF72

Federal Motor Vehicle Safety Standards: Air Brake Systems

AGENCY: National Highway Traffic Safety Administration (NHTSA),

Department of Transportation (DOT).

ACTION: Termination of proposed rulemaking.

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SUMMARY: This notice terminates a rulemaking action in which NHTSA

proposed amending the Federal motor vehicle safety standard that

establishes requirements for vehicles equipped with air brake systems.

The proposed amendment would have required that trucks, buses, and

truck tractors be equipped with an automatic means of removing moisture

and other contaminants from air brake systems, and would have deleted

the current requirement for a supply reservoir since the reservoir's

function would be performed by the automatic system. Moisture and

contaminants can cause valves to stick, thereby preventing sufficient

air pressure from being delivered to the brake chambers.

NHTSA is terminating this rulemaking action because the agency has

decided that it should address this issue through more broadly worded

performance requirements that would give manufacturers flexibility to

choose the type of air cleaning and drying system appropriate for their

new air-braked vehicles. The agency will continue to study the issue

with a view to initiate a future rulemaking proceeding for regulating

the performance of methods for cleansing and drying the compressed air

that supplies air brake systems.

FOR FURTHER INFORMATION CONTACT:

For technical issues: Joseph P. Scott, Safety Standards Engineer,

Office of Crash Avoidance Standards, National Highway Traffic Safety

Administration, 400 Seventh Street SW, Washington, DC 20590; telephone

(202) 366-2720; FAX (202) 493-2739.

For legal issues: Walter Myers, Office of the Chief Counsel,

National Highway Traffic Safety Administration, 400 Seventh Street SW,

Washington, DC 20590; telephone (202) 366-2992; FAX (202) 366-3820.

SUPPLEMENTARY INFORMATION:

Background

Federal Motor Vehicle Safety Standard (Standard) No. 121, Air Brake

Systems, specifies braking performance requirements for vehicles

equipped with air brake systems. The standard requires such vehicles to

be equipped with, among other things, a ``condensate drain valve that

can be manually operated'' (paragraph S5.1.2.4 for trucks and buses and

paragraph S5.2.1.3 for trailers). Such valve allows contaminants such

as water, oil, and dirt to be drained from the brake system's

reservoirs.

On July 28, 1994, Domenic F. Coletta, M.D., Deputy Medical Examiner

of Salem County, New Jersey, submitted a petition for rulemaking to

amend Standard 121 to require a condensate drain valve that

automatically purges moisture and contaminants from the air supply

reservoir. Dr. Coletta stated in his petition that currently available

automatic drain valves would better ensure safety because reservoirs

equipped with manual drain valves are usually not drained on a regular

basis by vehicle drivers. He argued, therefore, that contaminants are

present in reservoirs, thus creating unsafe conditions for operation of

trucks and buses. He cited conversations with truck drivers and New

Jersey state police to the effect that manual drain valves are normally

not used to remove contaminants from the reservoirs. He supplied no

data, however, on the extent to which requiring automatic drain valves

could be expected to enhance motor vehicle safety.

On February 21, 1995, NHTSA granted Dr. Coletta's petition and, on

July 24, 1995, issued a request for comments seeking data on automatic

drain valves and the effects contaminants in air brake systems before

proceeding to rulemaking (60 FR 37864).

The agency received 34 responses to the request for comments from

vehicle and equipment manufacturers, industry trade associations, a

safety advocacy group, fleet and individual truck operators, a U.S.

senator, and numerous private citizens. In general, the manufacturers

and trade associations stated that a Federal requirement was not

necessary, that the current use of air dryers and the trend toward

their widespread use was sufficient to maintain a safe level of

performance. Several commenters stated that they had no record of any

crashes caused by contaminated air in the brake system. The commenters

were split, however, on whether contaminated air constituted a

significant safety problem in an air brake system.

Based on a thorough review of the comments, NHTSA published a

Notice of Proposed Rulemaking (NPRM) on November 4, 1996 (61 FR 56652),

proposing to amend Standard 121 to require that each truck, bus, and

truck tractor be equipped with an automatic means of removing moisture

and contaminants from its air brake system. The purpose of this

proposal was to improve the safety of air-braked vehicles by improving

the reliability and durability of ABS modulator valves and pneumatic

control valves. The NPRM also proposed the deletion of the requirement

for a supply reservoir since its function, the removal of moisture and

contaminants, would be accomplished by the addition of such automatic

means. Accordingly, NHTSA believed that the deletion of the supply

reservoir would not adversely affect the safety of those vehicles. It

is worth noting that S5.1.2 of Standard No. 121 provides the option of

removing moisture and contaminants by using either a supply reservoir

or a service reservoir(s) with automatic drain valves.

The agency received 26 comments on the NPRM, the majority of which

(17 of 26) supported the proposal to mandate a means of automatically

removing moisture and contaminants from air brake systems. Others

supported the use of such devices, but opposed mandating them.

Agency Decision

The agency estimates that approximately 80 to 90 percent of new

truck tractors and 75 percent of new single-unit trucks are now being

equipped with some type of air moisture/contaminant removal system.

There are 3 basic removal systems which currently can be used on

new trucks, tractors and buses equipped with air brakes: automatic

drain valves, supply reservoirs (wet tank), and air dryers. Each system

has its advantages and disadvantages, as follows:

a. Automatic drain valve. (1) Advantages. This is the simplest

system for ensuring a clean and dry air brake system. It purges most of

the contamination in the supply reservoir, thus preventing

contamination from entering the service reservoirs and pneumatic drain

valves farther downstream. Since drivers and maintenance personnel may

not drain the reservoirs on a daily basis as they should, an automatic

drain valve will systematically drain the reservoirs without the need

for human intervention. Automatic drain valves on each reservoir could

ensure a cleaner air brake system, especially in light of the

requirements for ABS.

[[Page 14675]]

(2) Disadvantages. Automatic drain valves can become clogged and

frozen, resulting in the danger of the valve sticking open or closed.

Particularly in the southwestern United States, an automatic drain

valve would add costs without providing any significant benefits.

Unlike air dryers, such valves do not provide any significant dew point

reduction. Thus, the air in the brake system could still retain

sufficient moisture to degrade the pneumatic valves.

b. Supply reservoir (wet tank). (1) Advantages. The supply

reservoir or wet tank provides a means of collecting moisture and

contaminants before they enter the air brake system, thereby acting as

a buffer between the compressor and the service reservoirs. The supply

reservoir traps most of the condensate and contaminants before they

reach the service reservoirs and provides a backup for desiccant-type

dryers in the event of failure.1

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\1\ In a typical desiccant-style system, the incoming air is

routed into the bottom end of an air dryer where a large portion of

the moisture and contaminants falls to the bottom. The partially

cleaned air then passes through an oil separator. The air, still

moist, then is passed through a drying bed of desiccant material (a

substance, such as calcium oxide, used as a drying agent) that

absorbs the remaining moisture. These dryers are equipped with an

automatic drain valve that periodically purges moisture and

contaminants from the air system.

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(2) Disadvantages. The presence of the wet tank complicates the air

system and reduces the amount of compressed air available for the

emergency brake system.

c. Air Dryer. (1) Advantages. Air dryers with an integrated

condensate drain valve are currently the most effective method of

removing moisture and other contaminants from an air brake system. Air

dryers also provide some filtration of the compressed air by removing

some oils and contaminants from the air. Automatic drain valves do not

provide any dew point reduction, while air dryers can provide a 10 deg.

to 20 deg. Fahrenheit reduction. This is important because moisture can

still be present even with automatic drain valves installed in the

system.

(2) Disadvantages. Air dryers can fail, and can increase the

application times for service and parking brakes. Further, air dryers

could place an unnecessary cost burden on some operators and fleets,

such as those operating in the southwestern United States, where

humidity is low and there is less need for air dryers.

After much consideration and analysis of this issue, NHTSA now

believes that it should address this issue through more broadly worded

performance requirements that would give manufacturers flexibility to

choose the type of air cleaning and drying system appropriate for their

new air-braked vehicles. However, the agency is not yet ready to

propose such requirements. Accordingly, NHTSA is terminating this

rulemaking action.

The agency's goal throughout its consideration of these issues has

been, and remains, ensuring the removal of moisture and contaminants

from air brake systems by improving the reliability and durability of

ABS and associated modular valves and pneumatic control valves. To that

end, the agency is actively working with the Society of Automotive

Engineers (SAE) to establish an SAE Recommended Practice and associated

test procedures for air drying and cleansing equipment used in air

brake systems. These procedures would be valuable for testing the vast

majority of new heavy trucks. NHTSA estimates that, currently, over 80

percent of new air-braked heavy trucks are being built with air dryers

and of those, more than 90 percent are the desiccant type dryers.

Regardless of the results of SAE's efforts, however, NHTSA intends to

propose performance requirements for the removal of moisture and

contaminants from air brake systems, and provide comprehensive test

procedures to measure that performance.

Meanwhile, the agency notes that paragraph S5.1.2 of Standard 121

requires that manufacturers provide ``either an automatic condensate

drain valve for each service reservoir or a supply reservoir between

the service reservoir system and the source of air pressure.'' This

will assure that trucks and buses equipped with air brakes will have a

means of moisture/contaminant removal adequate to maintain the safety

of such systems. Completion of the SAE studies is estimated to be in

the fall of 1998.

For the reasons stated above, NHTSA is terminating this rulemaking

action.

Authority: 49 U.S.C. Secs. 322, 30111, 30115, 30117, and 30166;

delegation of authority at 49 CFR 1.50.

Issued on March 20, 1998.

L. Robert Shelton,

Associate Administrator for Safety Performance Standards.

[FR Doc. 98-7910 Filed 3-25-98; 8:45 am]

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