Interpretation ID: nht74-4.33
DATE: 07/08/74
FROM: AUTHOR UNAVAILABLE; R. L. Carter; NHTSA
TO: Bendix Corporation
TITLE: FMVSS INTERPRETATION
TEXT: This responds to your May 28, 1974, question whether a short neoprene connector of two steel vacuum brake lines in the Bendix Hydrovac unit is subject to Standard No. 106, Brake hoses.
The neoprene connector functions as a brake hose under the definition set out in the standard:
"Brake hose" means a flexible conduit that transmits or contains the fluid pressure or vacuum used to apply force to a vehicle's brakes.
The determination of the "flexibility" of a particular brake line material is a difficult but important decision. Flexibility is required in brake lines for at least two reasons. First and most important is the flexibility required to accommodate large amounts of relative motion in service, in frame-to-axle applications for example. Less obvious but important is the flexibility required in the event a brake line is displaced during repair or alteration of the brake system or other nearby vehicle components. A mechanic's decision to bend a brake line during repairs may depend on whether it "looks" flexible, and therefore appearance becomes an important element of the determination. On this basis the NHTSA has concluded that copper and steel chassis plumbing, for example, do not invite bending during repairs because their appearance makes their relative inflexibility obvious.
In contrast, plastic air brake chassis plumbing and small sections of hose used to connect steel or copper tubing, are examples of "flexible conduits" that invite bending in order to make repairs. To ensure that these "flexible conduits" are not damaged when they are displaced, they are considered brake hose subject to the bend and deformation requirements of the standard. In the case of the Hydrovac, the presence of the neoprene connector would appear to permit flexibility to compensate for component misalignment and to permit removal and repair of the steel tubing. It therefore is considered a brake hose under this standard.
Sincerely Yours,
The Bendix Corporation
Docket Section
National Highway Traffic Safety Administration
May 28, 1974
Gentlemen: Subject: Request for Clarification of Certain Portions of the Federal Motor Vehicle Safety Standard (FMVSS) No. 106
Clarification is requested concerning the requirements of FMVSS 106 (published in Notices 8 and 10 of Docket No. 1-5) as applied to the Vacuum Tube - Fig. 1 (Enclosure 1) used in our Hydrovac in-line vacuum/hydraulic brake booster. For convenience, a detail drawing of the Vacuum Tube is shown in Fig. 2 (Enclosure 2
On October 17, 1973, Bendix stated its opinion to the Bureau of Motor Carrier Safety (BMCS) regarding applicability of its regulations to the above-mentioned Vacuum Tube (Enclosure 3) and requested comments from BMCS. In reply, BMCS (Enclosure 4) concurred with Bendix' interpretation stating that "the use of 'tubing' rather than 'hose' is appropriate."
The request to BMCS was concerned primarily with BMCS' requirements for cord or duck ply in hose construction. We do not believe there is a question of construction of the tube as related to FMVSS 106; however, Enclosres 3 and 4 are included herewith only to help clarify the nature of the present request.
Reviewing the text of the Standard and the introductory comments to Notices 8 and 10, we are led to the conclusion that the definition of "Brake Hose" (S4, Paragraph 2) does not apply to the Bendix Vacuum Tube because of the lack of any requirement for flexibility. This conclusion seems to be supported by the lack of any bend requirement in Table V for hoses shorter than fourteen (14) inches in the diameter in question. On the other hand, the Bendix Vacuum Tube does "transmit or contains the fluid pressure or vacuum used to apply force to a vehicle's brakes". Hence, NHTSA is requested to verify Bendix' interpretation that FMVSS 106 is not applicable to the Bendix Vacuum Tube.
Your consideration of this request will be greatly appreciated in order to clarify the status of this part of the Hydrovac, which is a high volume component.
Respectfully submitted,
J. R. Farron
Group Director of Engineering
Enclosures (4)
FIG 1. SINGLE DIAPHRAGM HYDROVAC
(Graphics omitted)
(Graphics omitted)
The Bendix Corporation
October 17, 1973
U.S. Department of Transportation
Federal Highway Administration
Attention: Docket Clerk
Bureau of Motor Carrier Safety
Subject: Request for Clarification of Subchapter B - Motor Carrier
Safety Regulation, Part 393 - Parts and Accessories
Necessary for Safe Operation
Our review of Docket No. MC-41; Notice 73-9 has brought to our attention a need for clarification of the Part 393 of the Motor Carrier Safety Regulations.
The vacuum tubes for Bendix' Hydrovacs, an in-line vacuum/hydraulic brake booster, may fall within the provisions of Parts (b)(1)(iii) and (b)(2)(ii) of Section 393.45 of the above reference. The item under discussion is noted as "Vacuum Tube" in Fig. 1. The cited Parts of the Regulation call for conformance of vacuum brake hose to SAE Standards which requires cord or duck ply reinforcement, whereas Bendix' tube is solid neoprene rubber. The detail drawing of the Vacuum Tube is given in Fig. 2.
One logical interpretation of the Regulation could conclude that it is intended to specify vacuum hose only between brake system components, and not specify hose where it is an integral part of a component such as the tube used in our Hydrovacs. It appears the Regulation's thrust is to avoid arbitrary selection from many types of hose which are available in bulk form, particularly in the field, and to assure sound installation of a flexible member that is formed as it is installed. This reasoning is exemplified by Part (a) of the Regulation which covers "General Requirements".
Our vacuum tube, on the other hand, is fully specified as to type, and is formed before installation, just as is any other part of the Hydrovac.
Bendix' historical experience indicates that the tube has been used in 8,000,000 Hydrovacs produced since 1947, and to our knowledge there have been no tube failures. It is not of SAE grade hose because it is used as a connector, as opposed to flexible plumbing in the vehicle vacuum system.
For purposes of clarification due to ambiguity in the language of the cited Parts, it is requested that you confirm our interpretation that the cited Sections of the Regulation do not apply to the vacuum tube used as an integral part of the Hydrovac.
If this request cannot be granted, we hereby enter a petition to change the cited sections as follows (added words underlined):
(b) (1) Change to read: "except as provided in Paragraph (c), brake hose installed on a motor vehicle for connection between brake system components on or after October 1, 1973, must conform to one of the following specifications"
(b) (2) Change to read: "except as provided in Paragraph (c), brake hose installed on a motor vehicle for connection between brake system components before October 1, 1973, must conform to either"
Your consideration and response to this request will be appreciated.
J. R. Farron
Group Director of Engineering