THE PARTS OF A PUMP 91 
sideration. In spite of the care that may be exercised in keeping the 
apparatus in good order and straining all materials used, there will be 
occasions when it becomes essential to inspect the valves or other 
working parts. If, in order to do this, it is necessary to dismount the 
pump, or to take it entirely to pieces, much time will be lost — prob- 
ably on the very day when time is most valuable. Some of the barrel 
pumps first placed on the market were entirely inclosed in a heavy metal 
casting, and required much time and labor for inspecting their working 
parts. Later types have eliminated this, although some of the older 
pumps are still on the market. 
The piston packing should present adequate surface, and the packing 
itself should be easily replaceable. In some makes of pumps _ pro- 
vision has been made for tightening up the packing from the outside. 
Leather is not a good material for packing. The chemicals used in 
spray materials will soon harden it and render it unfit for service. 
In some makes of barrel pumps a stuffing box is employed in place of 
piston packing. The objection to this is twofold: it makes a rather 
more complicated apparatus, and it is difficult or impossible to avoid 
excessive friction. In the horizontal, double-action pump a stuffing 
box is necessary, because of the design of the pump, but in this case, 
there is so much gain in efficiency in other ways that the objection noted 
may be disregarded. 
