Sensitive Control for Vacuum Trailer Brakes
Page 19
If you've noticed an error in this article please click here to report it so we can fix it.
Simple Addition to Existing Valve Allows the Driver to "Feel" His Brakes in the On or Off Position
WITH the normal type of control valve as used in the W vacuum line of trailer brakes, it is not possible for the driver to use any degree of finesse in his operation of the brake pedal. This is due to the fact that he cannot feel any reaction through the means provided for its operation. The result is that the brake is either fully on or off, a not-altogether ideal arrangement.
We have recently inspected a simple and ingenious addition to the standard F. and J. control valve, a product of the well-known concern of Feeny and Johnson. Ltd., 134-136, Ealing Road, Wembley, which effectively solves the problem. -Operation of the control of the standard valve connects the vacuum line direct to the brake, which is applied to the lull extent of the vacuum obtaining in the pipeline. As
the brake-operating rod is connected, via suitable linkage, direct to the valve proper, it is obvious that no reactioh is transmitted to the controls, and hence the driver cannot " feel " his brakei in the on or off position.
In this new patented device a lead is taken from the vacuum line, on the brake side, to a bell-shaped alloy chamber which is screwed on to the standard valve in the position shown in one of the accompanying illustrations. This chamber, which is an air-tight, fit on the valve body, is provided with a rubber diaphragm, sandwiched between two steel discs, the assembly being locked together .by nuts on the screwed portion of the valve-operating rod. The diaphragm, at its periphery, is secured over the mouth of the chamber, by means of a narrow alloy ring, the securing bolts passing through the ring and diaphragm into the ran of the chamber.
The action is simple. When the valve rod is operated, the vacuum not only takes its normal effect in the cylinder of the brake-operating rod, but on the inside of the diaphragm, and as the brake-control leakage is coupled up to the diaphragm, the responses of the latter are communicated through the controls.
There is, of course, a return spring contained in the body of the valve, but as its value is constant, irrespective of the degree of vacuum, it serves no other purpose than to return the valve to its seating when the brake control is released. It may be of interest to mention that the total movement of the valve is but 1-10th in.
Such a device as this should prove a valuable aid to the effective braking of a trailer, and, incidentally, should have a marked effect in the reduction of tyre wear on any unit to which it is fitted.