From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Article detailing the construction and functioning of the new Schrader valve and a tyre-pressure gauge.
| Identifier | ExFiles\Box 128\2\ scan0111 | |
| Date | 27th January 1931 | |
| The Motor 1210 JANUARY 27, 1931. HOW TYRE PRESSURES ARE MAINTAINED Interesting Details of the Construction and Functioning of the New Schrader Valve Inside and a New Tyre-pressure Gauge THE success of the modern motorcar tyre—whether it be of the low-pressure or high-pressure type—is greatly dependent upon a very small valve—the Schrader, which is used in practically every tyre on the market. Like many other vital features of car design and construction, it is so reliable that hardly any owner-driver ever has cause to dismantle one, and thereby learn the features of its construction. Day in and day out it functions with great reliability, maintaining the pressure of air in the tube, so that even the attention necessary to the tyre from the pumping point of view is reduced to a minimum. General Layout of Valve. The general arrangement of the valve is shown in the accompanying sketch. It comprises a pin of quite fine dimensions, carrying a bridge-type screw plug, below which is a self-aligning swivel plug and then a stabilizing guide and retainer for the main seat washer, which, incidentally, consists of a red rubber ring carried in a metal housing. This is, as a matter of fact, secured tightly to the pin. Below it is a coil spring and an inverted castellated member. This valve inside, as it is termed, is screwed into the valve which is fitted to the tube. When in situ it has actually three points of support, as indicated by the figures in the sketch. The vital part of the valve is the red rubber washer which butts up against the swivel plug, effectively sealing the orifice through which the pin passes with plenty of clearance. There is a black washer around the swivel plug, but this has no control upon the air maintained within the tube. Actually, air never leaks at this point. It is essential that the tyres be checked regularly with an accurate guage and maintained at the proper pressure. When the pump connection is applied to the valve, the ingoing air forces down the pin and the rubber washer against the spring tension. So soon as the air supply ceases the spring drives up the pin assembly and forces the washer hard against its seating, thus effectually preventing any escape. It is really a very simple arrangement and the Schrader valve is not dependent upon any internal air pressure in order to maintain its efficiency, the air passage being sealed regardless of the air pressure within the tyre. Some Causes of Leakage. In the event of air leakage the valve inside should be removed, which can be done simply by inverting the valve cap and inserting it in the valve, whereupon serrations will engage with the valve inside, so that it can be unscrewed. Leakage may be caused by dirt on the seat washer; if this is the case, clean it with a small brush. If leakage still occurs, it is in all probability due to the fact that oil or dirt from a pump may have caused the rubber seat washer to perish, or due to the fact that the valve may have become damaged during inflation by an improperly constructed air-chuck. Any slight leakage past the valve is trapped, however, by the Schrader valve cap, until such time as the inside can be renewed. Within the cap is housed a metal-reinforced rubber washer which makes a perfect seal over the valve mouth when the cap is screwed down tightly by hand. It is not necessary to use pliers for this purpose. It is interesting to notice the care which has been taken to prevent this washer from collapsing; a dome-shaped inner plate is employed in conjunction with a metal pivot-plate at the top of the washer which acts as a guide for centring it over the mouth of the valve. It also prevents distortion and wear when the cap is screwed on or off. The New Pressure Gauge. An important recent Schrader introduction is the Trutest balloon tyre gauge which, before being placed on the market, was subjected to three years' exhaustive and comprehensive tests. This gauge is easy to use, being simply placed over the mouth of the valve when the cap has been removed; air enters the gauge and causes the indicating bar to emerge. When the bar comes to rest the gauge may be removed from the valve, the bar remaining fixed at the pressure indicated until put back by hand after reading. This new gauge sells at 7s. 6d. Incidentally, the set of valve insides can be obtained from practically any garage (as can also the gauge) for 1s. 8d. per box of four. Further information concerning these products can be obtained from A.{Mr Adams} Schrader's Son, Inc., 26-29, New Street, Westminster, London, S.W.1. More damage and wear is caused by incorrect pressures than many owners seem to imagine. Indeed, the life of a tyre can be reduced to a matter of only [illegible] miles by runni[ng] [illegible] pressures [illegible]. (Left) The new Schrader Trutest balloon tyre gauge. (Right) A detailed illustration of the Schrader valve inside. The figures indicate the points of support. [Image Annotations] 3 points of support Bridge type screw plug Self-aligning swivel plug Stabilizing guide and seat washer retainer Heat resisting washer and spring 226 | ||