TM 5-4240-501-14&PTHEORIES OF OPERATIONIgnitionNow, we haven’t said much about one thing, thecondenser. The condenser is a sort of safety valve onthe primary circuit. It is connected across the breakerpoints to prevent the circuit from jumping the breakerpoint gap, arcing, as it is called.Figure 30A.Let us explain it this way. Suppose we had a large pipethrough which we forced water at a high rate of speed,Figure 30A. This corresponds to our primary circuit.Coming out of the large pipe is a much smaller pipe.This is our secondary circuit. As long as the large pipe isunobstructed, the water is free to flow and very little willflow out through the small pipe.Figure 30B.Now suppose we could suddenly shut off the large pipe,Figure 30B. The water will stop flowing through the largepipe, but the inertia of the water back in the large pipewill force the water out through the small pipe at atremendous velocity until the pressure is dissipated.This corresponds to the high voltage in our secondarycircuit.Figure 30C.However, suppose our valve could not stand thepressure and would break. (Figure 30C.) This wouldcorrespond to arcing across the breaker points. The flowwould continue through the large pipe, and very littlewould flow through the small pipe.Figure 30D.If we put another small pipe near the valve, (Figure 30D)and over the end place a strong rubber bag, we have theequivalent to our condenser. Thus, when we close ourvalve, the pressure on the valve would be partiallyabsorbed by the rubber bag, the valve would not breakand water would stream out the small pipe where wewant it to go.The rubber bag must be of the proper size and strength.If it is too small, it will not take up enough of the pressureand the valve will break anyway. If it is too large, it willhold too much water, and there will not be enoughpressure to force the water out through the small pipe.Figure 31.The ’same thing applies to the condenser. The propercapacity should be about .2 microfarads or 16 to .24.This is just right to prevent arcing at the points and stillcause the primary current to stop flowing.1614
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