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Interpretation ID: 86-2.15

TYPE: INTERPRETATION-NHTSA

DATE: 04/09/86

FROM: AUTHOR UNAVAILABLE; Erika Z. Jones; NHTSA

TO: Ron Luce, International Transquip Industries, Inc.

TITLE: FMVSS INTERPRETATION

ATTACHMT: 3/14/77 letter from F. Berndt to Sergio Campanini, The Berg Manufacturing Co.; 8/27/79 letter from F. Berndt to the Berg Manufacturing Co.; 9/30/77 letter from R. L. Carter to R. W. Hildebrandt, The Bendix Corp.

TEXT:

Mr. Ron Luce President International Transquip Industries, Inc. P.O. Box 590169 Houston, Texas 77259

This responds to your request for an interpretation of FMVSS No. 121, Air Brake Systems. You asked several questions relating to whether vehicles equipped with "Mini-Max" brakes, a type of brake produced by your company, comply with the standard. Your questions are responded to below. We note that while Question 4 was not asked directly by your letter, the question is implicit with respect to one of the questions you did ask.

By way of background information, the National Highway Traffic Safety Administration (NHTSA) does not provide approvals of motor vehicle or motor vehicle equipment. Under the National Traffic and Motor Vehicle Safety Act, it is the responsibility of the manufacturer to ensure that its vehicles or equipment comply with applicable safety standards. The following represents our opinion based on the facts provided in your letter.

Question 1: Is delayed mechanical parking permissible under section S5.6.3 as long as the requirements of S5.6.1 or S5.6.2 are satisfied?

The second sentence of section S5.6.3 provides that "(o)nce applied, the parking brakes shall be held in the applied position solely by mechanical means." As discussed by a recent notice granting a petition for rulemaking submitted by the California Highway Patrol (copy enclosed), there are at least two issues relating to whether a braking system such as Mini-Max complies with these requirements.

The first issue is whether the system meets the requirement that once applied, the parking brakes must be held solely by mechanical means. As currently designed, the Mini-Max parking brake can be held by air and not by mechanical means, solely or otherwise, for many hours. Indeed, since a driver will often park the vehicle for a period of time shorter than that required to obtain mechanical holding, there will be many instances when the vehicle is parked and the parking brake never is held by mechanical means. The second issue is whether the parking brakes are held in the applied position. With the current design of the Mini-Max braking system, the air pressure leaks down over time until the mechanical lock is activated. Since the position of the brake components necessarily changes during this time, resulting in reduced parking brake force, there is an issue whether the parking brake is being held in the applied position.

While NHTSA has never concluded that a brake system resulting in false parking is safe or provided an interpretation that the current Mini-Max system complies with section S5.6.3, we recognize that some past interpretations, as well as one issued by the Bureau of Motor Carrier Safety, could contribute to ambiguity concerning whether some of the features incorporated in the Mini-Max design are permitted by the standard. In light of that ambiguity and for the other reasons discussed in the grant notice, NHTSA decided to grant the CHP petition to initiate rulemaking on the delayed mechanical park issue rather than issuing an interpretation whether or not such a braking system complies with these requirements.

Question 2: Is an external pressure separation assembly consisting of a two-way check valve and accompanying steel hex nipple considered to be a component of a brake chamber housing under section S5.6.3 if the assembly is "permanently bonded" to the housing?

The answer to this question is no. Section S5.6.3 provides in relevant part that "(t)he parking brake system shall be capable of achieving the minimum performance specified either in S5.6.1 or S5.6.2 with any single leakage-type failure, in any other brake system, of a part designed to contain compressed air or brake fluid (except failure of a component of a brake chamber housing)." (Emphasis added.) The dictionary defines "housing" as "a fully enclosed case and support for a mechanism." See Random House Dictionary of the English Language (unabridged edition). Thus, the term "brake chamber housing" refers to the case enclosing a brake chamber. An external pressure separation assembly does not become part of the brake chamber housing merely because it is attached to the housing, whether by "permanent bonding" or some other means. However, a brake chamber housing could be cast or molded to include a fitting, serving the same purpose as the external pressure assembly, as an integral part of the brake chamber housing.

Question 3: Is an internal assembly consisting of a diaphragm within the brake chamber housing considered to be a component of the brake chamber housing under section S5.6.3?

The answer to this question is no. As discussed above, the term "brake chamber housing" refers to the case enclosing a brake chamber. A diaphragm within the brake chamber is not a component of the case enclosing the brake chamber.

Question 4: Does section S5.2.1.1 require that capability of release must be unaffected or that air pressure in the tank must be unaffected?

Section S5.2.1.1 provides that "(a) reservoir shall be provided that is capable, when pressurized to 90 p.s.i., of releasing the vehicle's parking brakes at least once and that is unaffected by a loss of air pressure in the service brake system." (Emphasis added.) The word "unaffected" refers back to "reservoir". Thus, the required reservoir is not permitted to be "affected" by a loss of air pressure in the service brake system, i.e., it must be protected. A reservoir would not meet this requirement if a loss of air pressure in the service brake system resulted in a loss of air pressure in the reservoir, even if the reservoir was still capable of releasing the parking brakes.

Question 5: If the emergency brakes on trailers can be modulated so as to provide a driver with several applications and releases to move the disabled vehicle off the road after the signal from the low air warning system that the vehicle has lost its service brake system, is it unnecessary for an S5.2.1.1 reservoir to be capable of releasing the brakes?

The capability of modulation after activation of the low air warning system does not satisfy the requirements of section S5.2.1.1 (quoted above). That section requires that the reservoir not be affected by loss of service air, i.e., that it be protected, and that, when pressurized to 90 p.s.i. (a pressure that corresponds to the lower end of the range of pressures maintained by compressors), it be capable of releasing the parking brakes at least once. A vehicle's emergency brakes could be capable of modulation after activation of the low air warning system and not meet either of these requirements.

In addition to the notice granting the CHP petition, we are enclosing copies of interpretation letters concerning the Mini-Max system addressed to Navistar, P.T. Brake Lining Company, and the New Jersey Division of Motor Vehicles.

Sincerely,

Erika Z. Jones Chief Counsel Enclosures August 20, 1985 U.S. Dept. of Transportation National Highway Traffic Safety Adm. 400 Seventh Street S.W. Washington, DC 20590 ATTN: Duane Perrin

Subject: Our letter of August 6, 1985 and Docket No. 75-16: Notice 27. Request for immediate interpretation - Federal Motor Vehicle Safety Standard 121.

Dear Mr. Perrin:

After our July 31, 1985 meeting in Washington, DC and subsequent to my letter of August 6, 1985 I have requested, received and reviewed copies of all information contained in all volumes of the "Red Book" of 121 interpretations maintained in the document section of the D.O.T. After review of this information it is very evident that the NHTSA has offered several interpretations with respect to delayed mechanical parking that clearly allows this means of parking to satisfy the requirements of S5.6.3 as long as either S5.6.1 or S5.6.2 can be achieved. The references are as follows.

1. Berg Mfg. Co. letter dated February 9, 1977 that describes a system that is air applied on initial emergency or parking application and is held by spring application only in the event of service application pressure loss. The NHTSA response N40-30 (TWH) dated March 14, 1977 does not allow all design features of the Berg system but does clearly allow delayed mechanical parking as stated in the last sentence of the reference letter.

"In other respects the system you described does not appear to violate the requirements of Standard No. 121. The use of service air pressure to actuate the parking brakes has been used in certain bus applications and is permissible as long as a source of energy to apply the parking brakes is usable at all times and is unaffected by any single failure in the service brake system."

Supporting copies are marked "Exhibit A".

2. Berg. Mfg. Co. letter dated June 28, 1979 that describes a parking brake system that employs delayed mechanical parking. This system, I believe, was later denied because of non compliance to section S5.2.1.1 because emergency springs were released by supply air rather than from a protected reservoir. However, the NHTSA interpretation is clear with respect to application by service air and subsequent spring application as the air supply is depleted. The NHTSA response NOA-30 dated August 27, 1979 covers this point in the second paragraph.

"You first ask whether section S5.6.3 allows the use of service air to apply the parking brakes as long as a source of energy to supply the parking brakes is available at all times and is unaffected by a single failure in the service brake system. The answer to this question is yes. On August 9, 1979, the agency published in the federal register a notice amending section S5.6.3 of the standard to permit the type of parking brake system that you outlined in your letter."

Supporting copies are marked "Exhibit B".

3. Bendix letter dated September 14, 1977 that explains the many benefits of delayed mechanical parking by use of service air for initial application and spring application only after service pressure has depleted. This system also was later determined to not be in compliance to S5.2.1.1 because no reservoir was provided for release of brakes. However it clearly describes the delayed mechanical parking mode. The NHTSA response dated September 30, 1977 states in the last paragraph:

"You also requested written confirmation that the interpretation of S5.6.3 of FMVSS No. 121 given by NHTSA to Motor Coach Industries Inc., on April 14, 1976, would pertain to the air/spring parking brake system described in your letter. Your assumption is correct, and this letter constitutes such written confirmation."

Supporting copies are marked "Exhibit C".

Upon review of the information presented we respectfully request written confirmation that our assumption is correct that our delayed mechanical system as outlined in the information provided with our August 6, 1985 letter does comply with S5.6.3 of the 121 Standard.

We also request an interpretation with respect to the use of an external pressure separation assembly detailed in the information provided with our August 6, 1985 letter. Is our assumption correct that both the external and internal assemblies are a component of the brake chamber housing in this unique brake chamber design.

We further request an interpretation with respect to S5.2.1.1. Is our assumption correct that as discussed in our August 6, 1985 letter and detailed in the enclosures with the same letter that our "system" complies to section S5.2.1.1 of the 121 Standard. Without considering the above, in our letter of August 6, 1985 page 6, we also disclosed the fact that our trailer system allows modulation of emergency brakes. Are we correct in assuming that if we are able to modulate emergency brakes on trailers, this improvement in safety would also dictate that no release is necessary because a modulated emergency system provides a driver with several applications and releases of the emergency brake system to move the disabled vehicle off the road after the signal from the low air warning system that the vehicle has lost its service brake system. We understand that this would not exempt us from the requirement that "a reservoir shall be provided..." however it should remove the release requirement in emergency situations and would result in improved vehicle safety.

Please respond as quickly as possible to these requests for interpretations. We again point out that the absence of compliance checks at the OE level have placed us at an extreme disadvantage when compared to systems that were being marketed prior to discontinuation of compliance inspections. Thanks again for your assistance and early reply.

Regards, Ron Luce enc.:

See 3/14/77 letter from F. Berndt to Sergio Campanini, The Berg Manufacturing Company. See also 8/27/79 letter from F. Berndt to The Berg Manufacturing Company. See also 9/30/77 letter from R.L. Carter to R.W. Hildebrandt, The Bendix Corporation.