SD-06-1804 Bendix® SL-5™ Stop Light Switch & Bendix® DS-2™ Combined Stop Light Switch & Double Check Valve TERMINAL LEAF SPRING RIVET FULCRUM BENDIX DS-2 VALVE ® PISTON CONTACT STRIP DIAPHRAGM SHUTTLE VALVE (CHECK VALVE) ™ SHORTING BAR BENDIX® SL-5™ STOP LIGHT SWITCH INLET PORT INLET PORT OUTLET PORT FIGURE 1 - BENDIX® DS-2™ COMBINED STOP LIGHT SWITCH & DOUBLE CHECK VALVE SECTIONAL DESCRIPTION The Bendix® SL-5™ stop light switch is an electro-pneumatic, 5 psi, non-grounded switch that operates in conjunction with the brake valve and stop lights. By completing the electrical circuit, the SL-5 switch illuminates the stop lights when a brake application is made. The Bendix ® DS-2 ™ combined stop light switch and double check valve—as the name implies—combines a Bendix SL-5 stop light switch with a Bendix® DC-4® double check valve to perform the function of both. It operates in conjunction with the brake valve and hand control valve by directing the flow of air, from whichever delivers the higher pressure, into a common delivery line and to the stop light switch, closing the electrical circuit to the stop lamps. The stop light switch can be used with either 12 or 24 volt systems. The stoplight switch is not a serviceable item. If found defective in either device, the complete unit must be replaced. The shuttle valve in the DS-2 valve is serviceable and may be replaced. Both the SL-5 switch and the DS-2 valve have been tested and meet the requirements of FMVSS 121. OPERATION The stop switch mechanism is identical in the SL-5 switch and the DS-2 valve. When a brake application is made, air pressure from the brake valve enters the cavity below the diaphragm. The air pressure below the diaphragm moves the piston until it contacts the leaf spring. The leaf spring travels past a fulcrum at which point the leaf spring snaps a shorting bar 1 which mates with the contact strips. The stop light electrical circuit is completed, illuminating the stop lights before the brake application pressures reach 6 psi. Note that the snap action spring design minimizes arcing. The double check valve is activated by air being introduced through either of the two (2) inlet ports. The greater pressure pushes the shuttle along its guides and closes the opposite inlet port. The air is then directed out the common delivery line and to the stop light switch. PREVENTIVE MAINTENANCE Important: Review the Bendix Warranty Policy before performing any intrusive maintenance procedures. A warranty may be voided if intrusive maintenance is performed during the warranty period. No two vehicles operate under identical conditions; as a result, maintenance intervals may vary. Experience is a valuable guide in determining the best maintenance interval for air brake system components. At a minimum, the Bendix® DS-2™/SL-5™ valve should be inspected every six (6) months or 1500 operating hours, whichever comes first, for proper operation and electrical connections. Should the DS-2/ SL-5 valve not meet the elements of the operational tests noted in this document, further investigation and service of the valve may be required. OPERATING AND LEAKAGE TEST 1. Install an accurate air gauge in the service line (or brake chamber). Apply the brake valve gradually. The stop lamps should light at 6 psi or less, and go out after the brake application is released. This checks the electrical function of the stop light switch in either the SL-5 switch or DS-2 valve. 2. DS-2 valve only – Apply the foot valve and coat the exhaust port of the hand valve (or other alternate source). Reverse the above, applying the hand valve or other alternate source, and coat the exhaust port of the foot valve. In either mode, leakage must not exceed 100 sccm or a 1” bubble in not less than five (5) seconds. 3. SL-5 switch or DS-2 valve – When pressurized, leakage must not exceed 20 sccm or a 1” bubble in not less than 10 seconds. If the SL-5 switch or DS-2 valve does not function as described above, or if leakage is excessive, the valve or switch should be replaced with a new unit. In the case of the double check portion of the DS-2 valve, it must be repaired with genuine Bendix® service replacement parts. 2 REMOVING AND INSTALLING REMOVING 1. Block the vehicle wheels or hold by means other than the vehicle service brakes. 2. Disconnect the electrical connections from terminal screws. 3. SL-5 switch – Remove the switch using a wrench on the hex portion of the body. 4. DS-2 valve – Disconnect the air lines and remove the DS-2 valve. INSTALLING 1. Replace the SL-5 switch or DS-2 valve in the port from which it was removed. Do not install with the terminals pointing down. 2. Secure the electrical connections. 3. Reinstall the air line connections to DS-2 valve. DISASSEMBLY (Double Check Valve) 1. Remove three cap screws and cap. 2. Remove the o-ring seal from cap. 3. Remove the shuttle valve. CLEANING AND INSPECTION 1. Blow dust or other foreign material out of the body. Do not immerse in cleaning fluid. 2. Inspect the shuttle valve and o-rings for excessive wear or deterioration. Inspect the valve seats for nicks or burrs. Replace all parts that were discarded, along with any parts not found to be serviceable during inspection, using only genuine Bendix replacement parts. ASSEMBLY Before assembling the DS-2 double check valve, lubricate all o-rings and o-ring grooves with Bendix silicone lubricant (Pc. No. 291126) or the equivalent. NOTE: When using pipe thread sealant during assembly and installation, take particular care to prevent the sealant from entering the valve itself. Apply the sealant beginning with the second thread back from the end. TEST Repeat the “OPERATING AND LEAKAGE TEST” listed in this document. 3 4 SD-06-1804_US_007 © 2013 Bendix Commercial Vehicle Systems LLC, a member of the Knorr-Bremse.Group. All Rights Reserved.