Thermostats Tested to Destruction
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AMONG the machines being used for fatigue testing proprietary components in the research division of Leyland Motors, Ltd., is an unusual device, built by the company;s engineers, for testing the length of life of thermostat units.
Built from such miscellaneous parts as an engine timing gear chain and an electric kettle element, this machine tests the valve gear and bellows of thermostats fitted in the water outlet pipe of the cylinder block to allow hot water to flow to the radiator, or by-pass cool water to the water pump for recirculation.
Like most of the other components bought complete from proprietary manufacturers, the thermostats are tested to destruction. At the present time, three thermostats of different makes have so far completed 1,000 hours on the testing machine and are still going strong. They have been subjected to 50,000 immersions in water at a temperature of 195 degrees F. The speed of the testing is regulated so that each thermostat is dipped into the hot water every 72 seconds. It is then cooled down before its next immersion, thus ensuring full expansion and contraction of the bellows and the operation of the valve gear.
The testing machine has a h.p. electric motor driving through a number of reduction pulleys and a ratchet, a small endless chain which revolves vertically over a water tank. Suspended at equal intervals along the length of the chain are three thermostatic units which are dipped in turn into the water tank as the chain revolves.
In the base of the tank is a 1,000watt electric kettle element that maintains the water just below boiling point. An electric counter records the number of immersions, whilst a separate meter shows the total running hours of the machine. In order to simulate the worst possible conditions under which a thermostat operates, sand is placed into the tank to pollute the water.
It is estimated that the tests up to date are equivalent to about 20. years of operation in a vehicle.