Interpretation ID: 1982-2.13

DATE: 05/19/82

FROM: AUTHOR UNAVAILABLE; Frank Berndt; NHTSA

TO: Transequip Industries Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your recent letter asking whether Federal regulations allow a brake hose to be used as a dual purpose hose for both the service brakes and the emergency brake.

Standard No. 121, Air Brake Systems, does not preclude the use of common components in parking, emergency, and service air brake systems. Accordingly, nothing would prevent you from using a common hose in those systems. However, the common component would have to comply with the requirements for each system. This means that a failure of the hose would always be treated as a failure in the parking, emergency and service brake systems. Applying this to the standard in section S5.2.1.1, it would be necessary for the parking brakes to be capable of being released with a failure of the common hose at any time. If your system cannot perform in this manner, which it appears it cannot, it could not comply with the safety standard.

Our engineering staff has reviewed your brake system very carefully over the past years. It appears that your system can be properly plumbed in a manner that it would seem to comply with the requirements. You have continued to seek slightly less expensive methods to plumb your system. In our opinion, these methods would not be capable of complying with the standard. We cannot see how your system can comply with the standard without traditional plumbing that is being used by many brake manufacturers today. Accordingly, we suggest that you concentrate your efforts on constructing your system in that manner.

SINCERELY,

transquip industries, inc.

March 22, 1982

Chief Counsel, NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION

Sir:

In an air actuated, mechanically held system for trailers, such as described in the enclosed drawing, a single diaphragm brake chamber is provided using one delivery hose per chamber.

The brake hose (#25 on the drawing) is used as a dual purpose hose; It is used as a service brake hose when the service brakes are applied, and it becomes an emergency brake hose when the emergency brakes are applied. The destinction is in the application.

Should the hose break or puncture while applying the service brakes, three of the brakes would apply while air from the broken hose would go to atomosphere.

With the use of two 1400 cu in air tanks and the supply line continuously refilling the tanks, it is virtually impossible to cause a mechanical lock-up while using service brakes.

Should the trailer be parked with the emergency brakes applied and then cut the brake hose the air tanks would drain to zero. When the driver pushed in the tractor protection valve the broken hose would be sealed off, the tanks would refill and the parking brakes would then release when air pressure reached about sixty PSI. The failure which caused the lock-up could only occur when the trailer is in emergency.

My question is as follows: "Can a hose be used as a dual purpose hose and be considered a service brake hose while applying the service brakes and as an emergency brake hose while applying the emergency brakes"? Please advise.

Edward H. Clapp, President

(Graphics omitted)

NOTES:

1. DASHED ITEMS (Illegible) ARE NOT INCLUDED IN KIT.

2. FOR USE WITH DISC BRAKES, CONTACT FACTORY.

3. LENGTH TO BE DETERMINED BY CUSTOMER.

(Graphics omitted)

TRANSQUIP INDUSTRIES, INC.

614 West Main Street

Memphis, Texas 79245

TITLE TWO TANK - SINGLE VALVE SYSTEM TANDEM AXLE (2800 C.I.)