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Westinghouse Shows Systems and Parts to Meet New Code

4th December 1964
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Page 71, 4th December 1964 — Westinghouse Shows Systems and Parts to Meet New Code
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Which of the following most accurately describes the problem?

By The Technical Editor ALTHOUGH operators are clamouring for artics able to run at 26, 28 or 30 tons gross as allowed in the new regulations, there seems little likelihood that they will be able to get them within the next three or four months. This is a conservative estimate, as there are still a lot of different views amongst manufacturers on what braking system layouts are to be used. And it iS important with artics that there should be standardization to allow matching of tractive units with the variety of semi-trailers they will meet in their life. It need not be necessary to have just one standard layout, but if there are to be two or more it must be possible to mate the tractive unit portion having one layout with a semi-trailer having another. This is why S.M.M.T. committees have been meeting frequently in the past three months or so. and to speed things up the small sub-committee referred to in last week's issue was formed—obviously to reduce the number of people putting views forward. The end product of all these discussions will be a "Code of Practice" which will be issued by the Ministry of Transport. The future code was referred to by the Westinghouse Brake and Signal Co. Ltd. last week when the concern invited trailer manufacturers to Bristol to hear its views on the probable requirements, to inspect systems designed to meet them and to comment on them. One of the results of the meetings arranged by Westinghouse will be to help the company in formulating its plans for the future and help expedite the process of getting the necessary components to the production stage. One certainty is that brake operating systems to meet the new requirements will be very complex. They cannot be designed (and certainly not developed) overnight, and to a large degree the Ministry of Transport is responsible for operators' inability to get hold of higher-weight vehicles and for rushing manufacturers into designing systems which may not be the best possible. This is because the required braking performances were not known until the amendments were announced, And even now the Ministry of Transport is said to be not sure itself what the final requirements will be. At present 50 per cent efficiency is required for the service brake, 25 per cent for secondary brakes and there is a requirement for mechanical parking brakes of 16 per cent. There is no certainty that the same 50 per cent efficiency will not be required for the secondary brake also (some factions are pressing for this) and there is a suggestion that the parking brake on new vehicles will have to provide 20 per cent efficiency. There is also another point on which details are eagerly awaited. This is the number of service-brake applications that the brake system will allow without loss of efficiency and with the engine of the vehicle not running. At present designs of layout cater for between five and seven applications, and it is thought that the Ministry will raise this to 12 to 15. This requirement will be fairly difficult to meet and in many cases would mean that bigger compressors and reservoirs would be needed. Some vehicles have compressor capacity in hand, but on others it would necessitate an increase from 9 ft/min to 13.5 fr6/rnin units.

Until a decision is reached on the final code there is an impossible situation for equipment makers such as Westinghouse, Twelve layouts have been designed to meet the range of requirements that can be specified, but the work of making dies and setting up tooling cannot go ahead to make the components until the possible demand is known.

One of the most important things that Westinghouse set out to do in last week's exercise was to show that doublediaphragm brake, actuators were as safe as triple-diaphragm types. It will be realized from various reports appearing in The Commercial Motor that there is a basic difference of opinion between Westinghouse and Clayton Dewandre on this subject, Westinghouse going for doubles and Clayton for triples. It is as well to look at the history behind the developments in multi-diaphragm actuators. Doubles have been used in America, triples on the Continent—by the Westinghouse associate company, incidentally— hut in the latter case Westinghouse says these are made for only one customer and with a particular layout specified by the French Westinghouse company. It is known and agreed by Clayton Dewandre that trouble has been experienced on the Continent with triples, there being some early diaphragm failures because of the chafing of one diaphragm against another. Westinghouse says that it could not get a sufficient improvement in life in spite of a large increase in the spacing of the diaphragms, but on the other hand Clayton says the problem has been overcome as far as the units it is offering are concerned,

The advantage of the triple-diaphragm actuators is that the central diaphragm provides a safety factor in the event of secondary-brake diaphragm failure. This is the one farthest from the operating rod and if there is no diaphragm between it and the forward (service) diaphragm, puncture will allow the escape of air ts) atmosphere on application of the service brake, and equally make the secondary circuit inoperative. This possibility in the case of double diaphragm actuators has been overcome by Westinghouse by adding a lip seal to the operating face of the diaphragm for secondary braking which locates around the air-input aperture in the casing; a central aperture is essential. The diaphragm return spring keeps the seal against the casing to prevent the escape of air pressure in the

ev.at of diaphragm failure and the seal is strengthened as the pressure is applied. If there is failure of the service diaphragm, the emergency circuit will he intact to allow the vehicle to be braked.

A new unit shown by Westinghouse was particularly interesting and of considerable importance in relation to devising a parking system capable of giving 16 per cent efficiency—or holding the vehicle on a 16 per cent gradient—and particularly so with the prospect of 20 per cent being specified for new vehicles. This amount of braking effort may be difficult to obtain from the tractive unit axle (or axles) alone, and additional parking effort may be required tO be provided. by the semi-trailer. .Although the semi-trailer will probably have an individual parking brake this would require the driver, to leave the cab to apply it, or necessitate him carrying a mate. The future requirements will be clarified by the Code of Practice, but. as it seems obvious that there will have to be a .mechanical brake -on the .semi-trailer which can be applied from the cab, Westinghouse is contemplating offering a recently developed locktype actuator which can perform. this function. The unit is called the D.D.3 Safety 'Actuator and was introduced by Bendix-Westinghouse of America about

c32 a year ago. It does the same job as spring-brake actuators which have been used in the U.K. recently, although application is by the normal brake system, the brake being held on by a ball-type locking mechanism.

The accompanying drawing is of the American product and if the units are to be sold in the U.K.—the Ministry of Transport appears to accept the use of spring brakes for parking—the two diaphragms will be the same size so that the same service and secondary brake efficiency can be' obtained. To use the D.D.3 actuator, additional components have to be included in the brake systems of both the tractive unit and semi-trailer: a drawing of the complete layout shows the details. As the handbrake is applied the secondary brakes come on, and as the .handbrake is set, the secondary line is exhausted through atmosphere, but the service line is pressurized by the parking valve. This brings about semi-trailer service application of the lock actuators, the service line operating through the relay emergency valve to allow, pressure from the semi-trailer reservoir to the service diaphragms.

The lock port of the D.D.3 actuator is piped to the emergency line, and for normal brake applications the balls in the lock mechanism are held away from the operating shaft. As the emergency line is exhausted when the handbrake is set, they are forced into contact with the shaft by a coil spring moving them inside a tapered ring. This has the action of holding the operating rod in the applied position when the service diaphragm is pressurized. The timing reservoir is incorporated in the system to release the service pressure and so demonstrate to the driver that the parking system is operative.

To release the locks, the handbrake is released so that the emergency line builds up and pressurizes the lock piston. The tractive unit service brake is applied and the locks will release. This explains the presence-of the limiting valve in the feed line to the semi-trailer reservoir as it must be ensured that, when fully charged, this is at a lower pressure than the tractive unit reservoir to be certain that the locks can be released.

AIR CLEANER HOSE

IN "Road and Workshop" on 1 November 20 a prizewinning reader

reported a cure for collapsing.air-cleaner hoses on B.M.C. FH series lorries.

It is now understood that this problem has already been dealt with by B.M.C. at the production end, and a new air cleaner hose of improved specification (part no. 80K 2249) is now available through Austin and Morris distributors and dealers.

Tags

Organisations: Ministry of Transport
Locations: Bristol

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