Interpretation ID: nht75-3.46

DATE: 09/03/75

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Peerless Division - Royal Industries

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your July 15, 1975, question whether Standard No. 121, Air Brake Systems, requires "hold back valves" on air brake system reservoirs to guard against loss of air pressure through auxiliary equipment installations.

The answer to your question is no. Standard No. 121 does not contain a prohibition on the use of air pressure from the air brake system for powering auxiliary devices. The vehicle must, of course, conform to Standard No. 121 following installation of any auxiliary devices, if the installation occurs prior to the first purchase in good faith for purposes other than resale. For example, the compressor build-up pressure must still meet S5.1 of the standard whether or not auxiliary equipment is installed.

Although not a requirement of the standard, the NHTSA does consider it appropriate that a pressure protection valve be placed in the line to an auxiliary device so that rupture of an auxiliary line does not cause depletion of air pressure in the brake system.

SINCERELY,

July 15, 1975

Tad Herlihy U.S. Department of Transportation National Highway Traffic Safety Administration

For auxiliary air equipment such as an air ride suspension, we have been utilizing a brake system hold back valve to protect the complete brake system at about 90 p.s.i. We are attempting to get a 100 p.s.i. hold back valve but there does not seem to be one available. We are working with an air valve supplier to develop such a valve. To get a 90 p.s.i. hold back valve, we have to modify an existing valve. Only 60 p.s.i. hold back valve, we have to modify an existing valve. Only 60 p.s.i. hold back valves are available through our normal sources of supply.

It has been brought up by some of our people that they think that we are required to protect only the spring brake release tank and that on some manufacturer's brake system this is provided in their spring brake valve.

I would like to get your legal interpretation on this matter as soon as is reasonable.

PEERLESS DIVISION ROYAL INDUSTRIES

C.J. Baker Director of Engineering