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Technical Bulletin

Bulletin No.: PRO-03-10 Effective Date: 6/13/77 Page: 1 of 7

Subject: Service Line Protection System (SP-1)

Ref: Attachment (6 pgs.)

Bendix HVSG developed a new tractor-trailer protection system, which not only retains

all of the efficiency of the present system, but also provides the capability of applying the

trailer spring brakes when the trailer service line has failed. This added braking ability is

achieved through the use of a new valve, the SP-1 Service Line Protection Valve, in a

standard tractor-trailer protection system. The driver is not required to reach for any

additional controls to activate this unique automatic braking feature. A self-action

decision to apply the trailer spring brakes is resolved by the pneumatic analysis

performed within this new valve.

With each brake valve application, the service line protection valve makes an

instantaneous pneumatic comparison to determine if the trailer service line has failed. If

a failure is detected, the valve then automatically causes the trailer emergency brakes to

be applied, simultaneously closing off the trailer service air.

This system which utilizes an SP-1, 288428, (see Fig. 1) has been installed on recently

delivered fleets of Mack’s, GMC’s and Peterbilt’s for U.P.S. The valve is usually

mounted at the rear of the cab, adjacent to the TP valve.

A system description and operation is attached with a diagrammatic of the piping

arrangement. Approximately 500 of these units are in the field at the present time.

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Indice de contenidos

Pagina 1 - Technical Bulletin

Technical BulletinBulletin No.: PRO-03-10 Effective Date: 6/13/77 Page: 1 of 7Subject: Service Line Protection System (SP-1)Ref: Attachment (6 pgs.)Be

Pagina 2

288428SP-1Tractor-Trailer Service Line Protection SystemSystem DescriptionThe service line protection valve is used in conjunction with a standard tra

Pagina 3

a metered rate of air to flow to the underside of a piston. With its delayedstart (at 50 psi delivery pressure) and its metered rate of air flow, the

Pagina 4

4. Removal of the trailer supply air from across the tractor protection valve plunger alsocauses the service inlet valve to close. This prevents fur

Pagina 5 - FIGURE 1

FIGURE 1

Pagina 6 - TYPICAL DUAL CIRCUIT

TYPICAL DUAL CIRCUITFIGURE 2

Pagina 7 - FIGURE 3

FIGURE 3