Mr. Porter warrants the following action in this governor, operating any regulating valve or cut-off which is in reasonably good order.  The engine should be run with the stop-valve wide open, and, except the usual oiling, will require no attention from the engineer, under any circumstances, after it is started, until it is to be stopped.  No increase in the pressure of steam will affect its motion perceptibly.  The extreme possible variation in the speed, between that at which the regulating valve will be held wide open, and that at which it will be closed, is from 3 to 5 per cent., being least in the largest governors.  This is less than 1/6 of the variation required by the average of ordinary governors, and is with difficulty detected by the senses.  The entire load which the engine is capable of driving may be thrown on or off at once, and one watching the revolutions cannot tell when it is done.  The governor will be sensibly affected by a variation in the motion of the engine of 1 revolution in 800.  Notwithstanding this extreme sensitiveness, or rather by reason of it, it will not oscillate, but when the load is uniform will stand quite, or nearly, motionless.

For the supply of the water to the boiler, in many positions, it is very convenient to have a pump unconnected with the engine.  On this account it is very usual in this country to have what are called donkey pumps or engines independent of the main engines, which can be used to feed the boilers, or for supplying water for many other purposes.

Fig. 62 is a longitudinal section of the Worthington Steam Pump, the first of its kind, and for many years in successful operation.

The general arrangement is that of a Steam Cylinder, the piston rod of which, carried through into the water cylinder and attached directly to the water plunger, works back and forth without rotary motion, and of course without using either crank or fly wheel.

[Illustration:  Fig. 62.]

In the figures, a is the Steam Cylinder—­b, the Steam Chest—­d, a handle for regulating the steam valve—­f, the starting bar g, g, tappets attached to the valve rod, which is moved by the contact of the arm e, on the piston rod with said tappets—­h, the double-acting water plunger working through a packing ring—­o, o, force valves—­o’, o’, suction valves.  The pump piston is represented as moving from right to left, the arrows indicating the course of the water through the passages.  The suction valves o’, on the right side, and the force valves o, on the left side, are show open; x, is an air chamber made of copper; s, the suction pipe terminating in a vacuum chamber; made by prolonging the suction pipe, and closing it perfectly tight at the top, the connection being made to the pump by a branch as shown; m, m, are hand-hole plates, affording easy access to the water valves; n, n, small holes through the plunger, which relieve the pressure near the end of the stroke, to give momentum to throw the valves when working at slow speed.