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Injectors are a misery when they act up, a blessing when they are going well and you are able to switch them on and off at will. To achieve this state, the Injector must have three things, the correct steam pressure, cool clean water, complete freedom from air leaks in the Injector body and water pipe and in the connections leading up to it. Given that these conditions are satisfied, any fault must lie in one of the following – a blocked feed to the boiler (very unlikely), a blockage or partial blockage in the steam nozzle, a leaking non-return valve, or more likely, a build up of scale around the end of the steam nozzle and the entry to the combining cone.
Injectors should be removed and given a good soaking in citric acid or vinegar at the first sign of any deterioration in their performance, but do not steep them in sulphuric acid as this could result in soluble carbonates turning into insoluble sulphates which are much harder to remove. I believe that kettle de-scalers from the DYI stores work quite well. But beware of leaving them in strong acid for too long or your Injector could be damaged. The importance of ridding the Injector of scale is apparent if you consider that the annular gap where the steam cone enters the combining cone is six to eight thous' wide and it has to pass enough water to condense the steam being supplied. So if you have half a thou' of scale, your water supply is reduced by more than 10% and the effect will make starting difficult. The Injector will probably keep operating but will require steam and water to be adjusted, not a good idea when you are driving. The remedy for the purely mechanical faults is obvious. But be very careful if you have to poke a bit of dirt out of any of the cones. Use a piece of sharpened bamboo, not metal. If you are suffering from dirt in the water, a small in-line filter will cure it and in fact it is good to have one in the feed line. If you want to make one, do not use soft solder to fix the copper gauze or you will have bother with electrolysis and the dirt problem will return with a vengeance. Make a filter gauze tube with the seam folded, bend the end over to seal it and bind this on to feed tube with cotton. Then dab a little Loctite on the binding and the bent end to seal them and I guarantee no further problem with dirt in the line. Any Injector has a dry range over which it will work without dribbling. Too much pressure will tend to blow steam and water out of the overflow, but will probably allow some to get into the boiler and too little will just shove water out of the overflow, so it is essential to match the Injector working pressure to the boiler operating pressure. For locomotives, it is better to have two Injectors. One for the low end of the boiler's operating range and one for the upper – the upper one to have an operating range which will allow it to be started when the safety valves are blowing off. The leaky non-return valve tends to heat the Injector body up to a point where the incoming water is unable to condense the steam and therefore unable to create a vacuum without which the Injector cannot work. This can create the condition where steam can be blown back into the water tank, raising the temperature there and causing further havoc with the system. Remember that an Injector is at its best when the water is stone cold. The pipework to and from the Injector does not have to be big and clumsy. If you use thin wall tubing you can drop down a size and still get a good flow through it and those ghastly two inch plus bends that we see on some installations are absolutely unnecessary. As long as the radius of the bends is around five times the nominal bore of the pipe, there should be no problems with the flow. The test being that there is a good flow of water from the overflow with water on and steam off. On the test rig, it is not difficult to get ten pounds above boiler pressure on the delivery side of the Injector and if you think in terms of absolute pressure, with a good vacuum, the water will have a positive pressure of something less than fifteen pounds per sq inch (i.e. Atmospheric Pressure) so where is the need for such clumsy pipework either on the suction or on the delivery? Part of the Demonstration that I arranged with Noel Whiting for our Exhibition is shown below - with the jigs, reamers and the rig for testing them.
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