PRESSURE IN AIR TYRES.
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Retaining and Gauging It.
0 NE IS very apt to look upon a tyre valve much as one does a-n electriclight switch—a playing an essential, but quite unimportant, past in the system which, in the one ease, gives us travel comfort and in the other brightens our dark hours. Each of these components, however, may and should be regarded from quite a different angle. When a lighting system is installed, the item which, thereafter, has to he operated by the user is the switch, and it needs to be effective, reliable and long lasting, or the whole system breaks down. In the same way, the valve of a pneumatic tyre is the means by which the pressure of the tyre can be maintained, regulated or released. It also must be effective, reliable and long lasting, for it is the detail of a tyre that the motor driver has most to do with.
It seems only a few years ago—of course, it was over 30, although we are loth to admit it 1s—when we had to be content with extremely elementary devices for keeping the air in inflated articles. The " rubber trade valve," as it was called, served for air cushions (and the present writer, who invented an inflated saddle cover for bicycles, devised a new valve for it and also a means of preventing the air from rolling from sits to side), whilst the football bladder valve was fis crude as ever such a thing could be. These valves were useless for the pressures required for pneumatic tyres, and special valves were gradually developed for the purpose. No valve has undergone the universality of adoption accorded to the Schrader, devised -by A. Schrader's Sons and manufactured in London for the European market. At least 30,000,000 are in use in the States and Canada alone, and it is employed on three-fourths of the tyres in the world.
Recently we had the privilege of witnessing the whole of the processes (except one,-and of that, being a carefully preserved secret, we could only form surmises concerning it!) of the manufacture and preparation for marketing of the Schrader valve, and we certainly , learned to admire the extraordinary accuracy of the workmanship and the skill and ingenuity that had been displayed in designing the machine tools that pro duced such good work, that maintained the production at a predeter mined level and that, provided safe guards against faults as no human eye or mind could do. We were sur prised to find that there are 18 dis tinct parts to the valve, the body with its washers and nuts accounting for six, the cap for four, and the " inside " or valve mechanism for the remaining eight.
There are a number of operations on the body of the valve, and it was extremely interesting to watch the automatic machines receiving the raw material, passing it from tool to tool and ejecting the finished article (requiring only to he proved, cleansed and plated), which has three different threads cut upon it and is drilled to different bores at different distances from the mouth. The making of the caps from sheet steel was a very pretty operation, but extremely interesting and informative is the manufacture and assembly of the
"inside or working portion of the valve. One learns what an immense amount of thought has been given to this part and to the whole question of valve function4ing when examining the " inside " and its method of manufacture. One learns that the valve is not closed by the internal air pressure, but by e small spring, so that pressures so low as 4 lb. per sq. in. are retained. (High pressures are easily held, as they drive a valve on to its seating, but a low. pressure requires mechanical safeguarding.)
The rubber-faced seating cone of the " inside " has to cork the valve barrel, and the locking plug above it serves, when screwed down by the slotted valve cap, to hold the cone on its seat, and
when it is screwed up, to lift the cone off its seat. So these tWa actions are positive. The spring, through the little cup (F) at the bottom of the central pie (upon which the whole of the operating mechanism is mounted) abuts upon a restriction in the air passage of the valve and presses the cup (D), which is faced with soft, red rubber, upwards on to the bottom of the seating cone, and this forms the valve proper, for, when it is pushed away from the bottom of the seating cone by depressing the central pin, the air follows the pin through the centre of the seating cone and thus escapes. With such an arrangement the relatively low' initial pressure of 15 lb. to the square inch will lift the valve off its seat when inflating, after which the least pressure above the pressure in the tyre will pass by Whilst prior to inflation there is no operation to perform beyond
unscrewing the valve cap and screwing or pressing on the inflator connection. It is not even necessary to depress the pin in order to "free" the valve. This is why a Schrader facilitates tyre inflation and holds the air once it is in.
Another device which has been popularized by Schraders is the tyre-pressure gauge, the construction of which was shown us, accompanied by an explanation of the principle underlying its design. What is important to the user, however, is the knovviedge that each gauge is individually tested, altered, or rectified until it is found to be %site accurate. Hence, it is absolutely reliable, although its apparent simplicity of operation is apt to leave one sceptical of its accuracy. It is hard to believe that it can do what it professes, but, from all we have seen, we realize more than ever (and we have used one for ten years) that we may rely upon the information it gives us when testing air pressures. The importance of being able to keep pneumatic tyres at their right pressure and to be able easily to ascertain the pressure cannot be over estimated. Virtually, the life of the tyre depends upon such facilities as are provided by these two Schrader productions.