_Answer._ Their operation is indicated by the force of the stream which escapes from the pet-cock when it is open. When the pump is in good condition the water begins to escape promptly in a strong stream as soon as the pump-plunger begins its inward stroke, and continues to escape until the plunger completes its stroke. If the pump is not in good condition, this escaping stream is weak and is apt to continue during the outward stroke of the pump-plunger. It is difficult to tell, however, when the engine is running slowly, whether the pump will work well at higher speeds, and therefore a locomotive runner should always test the condition of the pumps during the previous run. QUESTION 459. _What should be noticed in connection with the throttle-valve?_ _Answer._ As a failure of the throttle-valve to work may be the cause of a most serious accident, it should be certain that it is in good working condition, that all the bolts, pins and screws and other accessories are in good working order. It should also be known whether the throttle-valve is steam-tight. This can be learned by observing whether steam escapes from the exhaust-pipes or cylinder-cocks when the latter are open, the reverse lever in full gear, and the throttle-valve closed. If the throttle-valve leaks, enough steam may accumulate in the cylinder, when there is no one on the engine, to start it, and in this way cause a serious accident. The throttle-lever should always he fastened with a set-screw or latch of some kind when the engine is standing still. QUESTION 460. _In inspecting the cylinders, pistons, guides and connecting-rods, to what points should the attention be directed?_ _Answer._ It should be known whether the piston packing is properly set out, that is, whether it is so tight that it will not “_blow through_,” or leak steam from one end of the cylinder to the other, which of course will waste a great deal of steam. Of the two evils, it is, however, better to have piston-packing too loose than too tight, because if it is too tight, it is liable to cut or scratch the cylinders so as to make it necessary to rebore them, and at the same time if the packing-rings are lined with Babbitt metal, the heat created by the intense pressure and friction will melt the metal. In some cases the cylinders become heated to so high a temperature from this cause that the wood-lagging with which they are covered on the outside is burned. The packing of the piston-rods should be steam-tight, and it should be observed whether the rod and the pump-plunger are securely attached to the cross-head.