Interpretation ID: aiam4090
President
International Transquip Industries
Inc.
P.O. Box 590169
Houston
TX 77259;
Dear Mr. Luce: 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 Safet Administration (NHTSA) does not give approvals of motor vehicles or 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 sectio 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 requirements that onc applied, the parking brakes must be held solely be 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 fals 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 brake system complies with these requirements.; *Question 2: Is an external pressure separation assembly consisting o 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 relevan 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 with th 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 'brak 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 releas 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* tha 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 a 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 warnin 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 enclosin 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