Ingenious New Automatic Vacuum
Page 17
If you've noticed an error in this article please click here to report it so we can fix it.
Brake for Trailers
SOMETHING new in automatic vacuum brakes for trailers has been introduced by Feeny and Johnson, Ltd., 134-136, Ealing Road, Wembley. The main object of the new system is to provide for efficient and powerful braking of the trailer wheels, in the event of the trailer breaking away from the power vehicle, when, of course, the normal means for control would become inoperative.
So far. as the system on the vehicle is concerned, this is normal with the exception of the driver's control valve, the action of which is reversed. In the case of the trailer, a second vacuum tank is installed, together with a standard F. and J. control valve, which .is ingeniously adapted to come into operation automatically should the vacuum pipe from the vehicle become disconnected or broken.
Attached to the upper end of the valve spindle is a diaphragm arranged to bridge a chamber which screws on to the valve-spindle body of a standard F. and J. control valve. A connection from the engine is taken to the underside of the diaphragm so that, while the engine is running, the control valve is kept shut. When, however, the vacuum operating on the underside of this diaphragm is destroyed, as when the master control in the cab is operated, or the pipe lead from the vehicle to the trailer is broken, the valve opens under the action of a spring. In the latter case, the main vacuum tank not being available, the trailer brakes operate from the auxiliary vacuum tank fitted to the trailer. The vacuum in this tank is preserved through the action of a non-return valve arranged in the pipe lead coming from the engine. By providing an extension to the spindle of the control valve, a hand control is made available, so that the brakes can be applied or released u-hen the trailer is being manoeuvred by manual effort.
The action of this automatic valve depends upon the area of the diaphragm in relation to the area of the valve and the strength of the return spring, and it is possible to arrange these units so as to obtain a high degree of response to variations in the vacuum line.