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Federal Motor Vehicle Safety Standards; Air Brake Systems Control Line Pressure Balance

American Government Special Collections Reference Desk

American Government Trucking Topics:  Federal Motor Vehicle Safety Standards

Federal Motor Vehicle Safety Standards; Air Brake Systems Control Line Pressure Balance

Patricia P. Breslin
National Highway Traffic Safety Administration
July 13, 1994

[Federal Register: July 13, 1994]


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DEPARTMENT OF TRANSPORTATION
49 CFR Part 571

[Docket No. 85-07; Notice 9]
RIN 2127-AF23

 
Federal Motor Vehicle Safety Standards; Air Brake Systems Control 
Line Pressure Balance

AGENCY: National Highway Traffic Safety Administration (NHTSA), 
Department of Transportation.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: In response to a petition for rulemaking submitted by Sealco 
Air Controls, Inc., this notice proposes to amend the control line 
pressure differential requirements in Standard No. 121, Air Brake 
Systems, for converter dollies and trailers designed to tow another 
vehicle equipped with air brakes. The agency has tentatively concluded 
that the proposed amendments would improve the braking compatibility of 
such vehicles by allowing the use of a relay valve known as a spool-
type low opening valve. The agency does not anticipate any adverse 
safety consequences resulting from amending the pressure differential 
requirements.

DATES: Comments. Comments must be received on or before September 12, 
1994.
    Proposed effective date. The proposed amendments in this notice 
would become effective 30 days after publication of a final rule in the 
Federal Register.

ADDRESSES: Comments should refer to the docket and notice numbers above 
and be submitted to: Docket Section, National Highway Traffic Safety 
Administration, 400 Seventh Street, S.W., Washington, D.C. 20590. 
Docket hours are 9:30 a.m. to 4 p.m., Monday through Friday.

FOR FURTHER INFORMATION CONTACT: Mr. Chris Tinto, Office of Vehicle 
Safety Standards, National Highway Traffic Safety Administration, 400 
Seventh Street, S.W., Washington, D.C. 20590. (202-366-6761).

SUPPLEMENTARY INFORMATION: Standard No. 121, Air Brake Systems, 
establishes performance and equipment requirements for braking systems 
on vehicles equipped with air brakes, including requirements for 
pneumatic timing. For purposes of compliance testing, the pneumatic 
timing tests for trailers, including trailer converter dollies, are 
conducted with the trailer connected to a test rig rather than an 
actual tractor. The test rig delivers air to, and releases air from, 
the trailer during the timing test. The timing tests for vehicles 
designed to tow trailers are conducted with a 50 cubic inch reservoir 
connected to rear control line coupling. This reservoir represents the 
control line volume of the control trailer used in the compliance 
testing.
    On August 21, 1992, NHTSA published a final rule amending the 
pneumatic timing requirements of Standard No. 121 with respect to the 
control signal pressure balance for tractor trailer combinations. (57 
FR 37902). The agency added S5.3.5 which specifies a new test procedure 
for determining the control line pressure differential in converter 
dollies and trailers designed to tow another trailer equipped with air 
brakes. Specifically, the rule requires that the pressure differential 
between the control line input coupling and a 50 cubic inch test 
reservoir shall not exceed 1 psi at all input pressures between 5 psi 
and 20 psi and 2 psi at all input pressures greater than 20 psi. Agency 
research indicates that input pressures below 20 psi represent routine 
braking applications, input pressures between 20 psi and 40 psi 
represent moderate to heavy braking applications, and input pressures 
above 40 psi represent severe braking applications. As explained below, 
NHTSA is proposing to modify the limit above 40 psi to allow a 5 
percent differential (which at higher pressures exceeds the current 
limit of 2 psi) based on the Society of Automotive Engineer's (SAE's) 
Recommended Practice SAE J1505, Brake Force Distribution Test Code 
Commercial Vehicles.
    The agency explained that the amendment is designed to ensure that 
the control signal ``passes'' through a towing trailer or dolly without 
being altered along the way. Since the control signal passes through 
unaltered, each vehicle in a combination unit receives the same brake 
control signal. This serves to increase the braking compatibility of 
combination vehicles since each vehicle in a combination has comparable 
braking performance.

Sealco Petition

    On June 18, 1993, Sealco Air Controls, Inc. (Sealco), a valve 
manufacturer, submitted to NHTSA a rulemaking petition to amend 
Standard No. 121 with respect to the control line pressure differential 
requirements in S5.3.5. Specifically, it requested that NHTSA amend 
these requirements to permit the manufacture of its low opening valves 
that serve to adjust air flow in control lines. These valves are used 
as control line relay valves and service line relay valves in trailers 
and converter dollies. The petitioner stated that unlike other relay 
valves that use a common poppet,1 the low opening valves have a 
balanced spool technology2 that incorporates a low pressure at 
which the valve initially opens (i.e., crack pressure) of 1.5 psi. 
According to Sealco, the spool technology enables the valve to track 
closer between the input control air pressure and the output delivered 
air pressure. As a result, it claimed that hysteresis3 is not so 
prevalent with low operating valves as with the high crack pressure 
poppet design valves.
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    \1\ A rising and falling valve consisting of a disc at the end 
of a vertically set stem.
    \2\ A valve whose primary means of diverting pressure or flow is 
through movement of a cylindrical valve mechanism along its axis.
    \3\ The time lag in a system in reacting to changes in the 
forces affecting it. With respect to braking, the relay valve's 
output (apply pressure) lags more than a few psi behind ascending 
control line (treadle) pressure, and stays more than one or two psi 
above descending control line pressure. Complications may arise when 
a second brake application is made before the first one is fully 
released.
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    Hysteresis in a valve may cause the valve not to track (i.e., 
follow closely) the control line pressure properly, which may cause the 
brakes in the trailer to lag behind the control signal. For example, 
when the driver applies the brakes, the valve's hysteresis may not 
allow the same pressure to be applied to the trailer brakes, which will 
cause less braking in the trailer and cause the trailer to ``push'' the 
tractor. Similarly, when the driver releases the brake, the hysteresis 
in the valve may not allow the brakes in the trailer to be released 
quickly enough and will still have the brakes applied while the driver 
is trying to accelerate, causing the kingpin to jerk on the inside of 
the fifth wheel. On more extreme conditions where the driver goes 
through several fast brake applications and releases in rapid 
succession, the jerking and pushing of the trailer or trailers could be 
difficult to control.
    Sealco stated that the use of low operating valves would further 
NHTSA's goal of ensuring balanced braking in combination vehicles. 
However, the petitioner claimed that while its valve meets the 
amendment's application requirements, it does not meet the provision 
requiring release at high pressure ranges, given the valve's mechanics. 
To comply with the amendment, Sealco has drilled a hole in the valves' 
piston, thereby allowing pressure to bleed to the supply side. This 
action prevents the valves from cracking open when tested according to 
S5.3.5. Sealco believes that this modification to allow compliance with 
the amendment has reduced the valves' effectiveness. Sealco also 
criticized the test procedure which it believed did not simulate actual 
braking conditions. It stated that slow and fast ascending and 
descending control line pressures should be used to check the valves' 
ability to respond appropriately.

Agency's Decision To Issue Proposal

    After reviewing the petition, NHTSA has decided to propose an 
amendment to Standard No. 121 to permit the use of low operating 
valves. Specifically, the agency is proposing to amend S5.3.5 to 
account for input pressures over 40 psi. Under the proposal, the 
pressure differential would not be permitted to exceed 2 psi at any 
input pressure between 20 psi and 40 psi and it would not be permitted 
to exceed 5 percent at any pressure over 40 psi. In other words, the 
pressure differential requirements would remain the same, except for 
applications resulting in pressures over 40 psi. The agency requests 
comments about whether the modification to pressure levels over 40 psi 
is appropriate.
    NHTSA is proposing the value of 40 psi based on SAE J1505, Brake 
Force Distribution Test Code Commercial Vehicles. The agency has 
tentatively determined that the safety problem addressed by the 
requirement in S5.3.5, i.e., slow heat build up and brake fade caused 
by long gradual down hill runs at relatively low air pressure, is not a 
problem for severe brake applications over 40 psi. In formulating this 
proposal, NHTSA contacted all the major valve manufacturers. Other than 
Sealco, no other valve manufacturer stated that they had to drill holes 
in the valve or otherwise modify the valve in a way that might 
adversely affect their real-world dynamic braking performance in order 
to comply with the test in S5.3.5. Aside from Sealco, the valve 
manufacturers believed that the existing test was a realistic, 
reasonable assessment of low pressure differential performance.
    NHTSA has tentatively determined that this amendment would 
facilitate the use of spool valve technology, while not being 
detrimental to safety. The agency's primary concern in these 
rulemakings addressing control line pressure differentials is brake 
performance in the low end of the air pressure range since the vast 
majority of stopping occurs there. Specifically, in the August 1992 
rule, the agency sought to improve low end brake performance with 
respect to slow heat build up and brake fading brought about by 
relatively low brake applications during long gradual downhill 
descents.
    After further review, the agency now believes that the current 
requirement may unnecessarily extend the 2 psi requirement into the 
higher pressure ranges where it is not necessary for safety. As noted 
above, the requirement is designed to prevent brake fade during 
relatively low brake applications below 20 psi and is not applicable to 
hard brake applications, i.e., those exceeding 40 psi. Accordingly, the 
agency has tentatively decided to modify the differential requirements 
at levels over 40 psi. Notwithstanding the agency's tentative 
conclusion, the agency request comments about whether this amendment 
poses any risk of adverse safety consequences.
    However, NHTSA disagrees with Sealco's statements that the test 
procedure in S5.3.5 does not simulate actual braking conditions. The 
agency notes that this test procedure was based on the agency's own 
testing and extensive test data and recommendations by trailer 
manufacturers in response to previous agency proposals. Specifically, 
the agency disagrees with Sealco's statement that ``Slow and fast 
ascending and descending control line pressures should be used to check 
CLV performance.'' As discussed in earlier notices, NHTSA sought 
pressure rises and decays that were neither too fast nor too slow. As 
trailer manufacturers and other commenters to the earlier proposal 
stated, if the pressure rise were too slow, test personnel would waste 
time waiting for the event to occur, and if the pressure rise were too 
rapid, pressure differentials could not be read quickly enough. In 
addition, pressure surges from a fast rate would likely result in a 
loss of normal valve hysteresis and subsequent errors in crack pressure 
readings. Accordingly, the agency believes that the test accurately 
evaluates real-world dynamic braking without creating any significant 
negative safety effects.

Rulemaking Analyses and Notices

1. Executive Order 12866 (Federal Regulatory Planning and Review) and 
DOT Regulatory Policies and Procedures

    This proposal was not reviewed under E.O. 12866. NHTSA has analyzed 
this proposal and determined that it is not ``significant'' within the 
meaning of the Department of Transportation's regulatory policies and 
procedures. A full regulatory evaluation is not required because the 
rule, if adopted, would have no mandatory effects. Instead, the 
proposal would permit spool valve technology. Therefore, this 
rulemaking would not have any cost impacts.

2. Regulatory Flexibility Act

    In accordance with the Regulatory Flexibility Act, NHTSA has 
evaluated the effects of this action on small entities. Based upon this 
evaluation, I certify that the proposed amendment would not have a 
significant economic impact on a substantial number of small entities. 
Vehicle and brake manufacturers typically would not qualify as small 
entities. This amendment would affect small businesses, small 
organizations, and small governmental units to the extent that these 
entities purchase vehicles. However, this amendment would not have any 
cost impact on vehicles. For these reasons, vehicle manufacturers, 
small businesses, small organizations, and small governmental units 
which purchase motor vehicles would not be significantly affected by 
the proposed requirements. Accordingly, no regulatory flexibility 
analysis has been prepared.

3. Executive Order 12612 (Federalism)

    This action has been analyzed in accordance with the principles and 
criteria contained in Executive Order 12612, and it has been determined 
that the proposed rule would not have sufficient Federalism 
implications to warrant preparation of a Federalism Assessment. No 
State laws would be affected.

4. National Environmental Policy Act

    Finally, the agency has considered the environmental implications 
of this proposed rule in accordance with the National Environmental 
Policy Act of 1969 and determined that the proposed rule would not 
significantly affect the human environment.

5. Civil Justice Reform

    This proposed rule would not have any retroactive effect. Under 
section 103(d) of the National Traffic and Motor Vehicle Safety Act (49 
U.S.C. 30111), whenever a Federal motor vehicle safety standard is in 
effect, a state may not adopt or maintain a safety standard applicable 
to the same aspect of performance which is not identical to the Federal 
standard. Section 105 of the Act (49 U.S.C. 30161) sets forth a 
procedure for judicial review of final rules establishing, amending or 
revoking Federal motor vehicle safety standards. That section does not 
require submission of a petition for reconsideration or other 
administrative proceedings before parties may file suit in court.

Public Comments

    Interested persons are invited to submit comments on the proposal. 
It is requested but not required that 10 copies be submitted.
    All comments must not exceed 15 pages in length. (49 CFR 553.21). 
Necessary attachments may be appended to these submissions without 
regard to the 15-page limit. This limitation is intended to encourage 
commenters to detail their primary arguments in a concise fashion.
    If a commenter wishes to submit certain information under a claim 
of confidentiality, three copies of the complete submission, including 
purportedly confidential business information, should be submitted to 
the Chief Counsel, NHTSA, at the street address given above, and seven 
copies from which the purportedly confidential information has been 
deleted should be submitted to the Docket Section. A request for 
confidentiality should be accompanied by a cover letter setting forth 
the information specified in the agency's confidential business 
information regulation. 49 CFR Part 512.
    All comments received before the close of business on the comment 
closing date indicated above for the proposal will be considered, and 
will be available for examination in the docket at the above address 
both before and after that date. To the extent possible, comments filed 
after the closing date will also be considered. Comments received too 
late for consideration in regard to the final rule will be considered 
as suggestions for further rulemaking action. The NHTSA will continue 
to file relevant information as it becomes available in the docket 
after the closing date, and it is recommended that interested persons 
continue to examine the docket for new material.
    Those persons desiring to be notified upon receipt of their 
comments in the rules docket should enclose a self-addressed, stamped 
postcard in the envelope with their comments. Upon receiving the 
comments, the docket supervisor will return the postcard by mail.

List of Subjects in 49 CFR Part 571

    Imports, Motor vehicle safety, Motor vehicles, Rubber and rubber 
products, Tires.

    In consideration of the foregoing, the agency proposes to amend 49 
CFR Part 571 as follows:

PART 571--[AMENDED]

    1. The authority citation for Part 571 would be revised to read as 
follows:

    Authority: 49 U.S.C. 322, 30111, 30115, 30117, and 30166; 
delegation of authority at 49 CFR 1.50.

    2. In Sec. 571.121, S5.3.5 introductory text and S5.3.5(a) would be 
revised to read as follows:


Sec. 571.121  Standard No. 121; Air brake systems.

* * * * *
    S5.3.  Control signal pressure differential--converter dollies and 
trailers designed to tow another vehicle equipped with air brakes.
    (a) For a trailer designed to tow another vehicle equipped with air 
brakes, the pressure differential between the control line input 
coupling and a 50 cubic inch test reservoir attached to the control 
line output coupling shall not exceed the values specified in S5.3.5(a) 
(1) and (2) under the conditions specified in S5.3.5(b) (1) through 
(4)--
    (1) 1 p.s.i. at all input pressures equal to or greater than 20 
p.s.i., but not greater than 20 p.s.i.; and
    (2) 2 p.s.i. at all input pressures from 20 p.s.i. to 40 p.s.i.; 
and
    (3) not more than a 5 percent differential at any input pressures 
above 40 p.s.i.
* * * * *
    Issued on July 6, 1994.
Patricia P. Breslin,
Acting Associate Administrator for Rulemaking.
[FR Doc. 94-16913 Filed 7-12-94; 8:45 am]
BILLING CODE 4910-59-P



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