Interpretation ID: nht74-2.1

DATE: 01/17/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Aeroquip Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your request of January 8, 1974, made to Mr. Herlihy of this office, for an interpretation of S5.1.2.3 of Standard No. 121, Air brake systems, as it applies to a check valve which is designed to bleed back no more than 5 psi pressure from the service reservoir toward the source of air pressure.

The check valve described in the specification you enclosed would satisfy the requirements of S5.1.2.3 as long as there is no air loss in excess of the designed bleed off, and that total air loss never lowers the pressure at any time below the air compressor "cut in" pressure.

Yours truly,

ATTACH.

AEROQUIP CORPORATION/INDUSTRIAL DIVISION

January 4, 1974

John Womack and Richard Dyson -- Chief Council, National Highway Traffic Safety Administration

Gentlemen:

This letter is a request for approval of our XFF9260-50 check valve for use in truck and bus air brake systems as detailed in the Motor Vehicle Safety Standards #121, Paragraph S5.1.2.3.

The function of the subject check valve is to allow air bleed back of no more than 5 psi pressure from the maximum pressure setting on the primary reservoir. The purpose of the air bleed back is to increase the service life of our Aerofiner Air Purifier (P/N FF9260-01). The air volume used off the #1 air reservoir (pre-dried air) is used to back flush the desiccant bed in the Aerofiner at approximately 3 cfm until the pressure in the reservoir drops to the relief valve setting, (5 psi below maximum reservoir operating pressure) at which time the valve is completely closed. In all other respects, it functions as a typical safety check valve.

Attached is a layout sketch of the subject check valve showing the seal surfaces and flow paths under various conditions.

Also attached, is a copy of Bulletin #5212, describing our Aerofiner brake system air purifier.

Please supply me in writing, the council's approval of our XFF9260-50 check valve in truck and bus air brake systems.

If there are any questions, feel free to contact me.

Sincerely yours

Donald T. Fischer -- Project Engineer, Coupling Section