================+===============+=========+=================+================
| | | | Diameter of
| | | |Plunger required
| | | | in any single
Diameter of | Diameter of |Length of|Gallons delivered|cylinder pump to
Steam Cylinders.|Water Plungers.| Stroke. | per minute at |do the same work
| | | ordinary speed. | at same speed.
----------------+---------------+---------+-----------------+----------------
6 | 7-1/2 | 6 | 285 | 10-1/4
6 | 8-1/2 | 6 | 375 | 12
----------------+---------------+---------+-----------------+----------------
================+===============+=========+=================================
| | |Sizes of Pipes for Short Lengths
| | | To be increased as length
| | | increases.
Diameter of | Diameter of |Length of|------+---------+-------+--------
Steam Cylinders.|Water Plungers.| Stroke. |Steam | Exhaust |Suction|Delivery
| | |Pipe. | Pipe. | Pipe. | Pipe.
----------------+---------------+---------+------+---------+-------+--------
6 | 7-1/2 | 6 | 1 in.|1-1/2 in.| 5 in. | 4 in.
6 | 8-1/2 | 6 | 1 „ |1-1/2 „ | 6 „ | 5 „
----------------+---------------+---------+------+---------+-------+--------
The purposes for which pumps are used on shipboard, aside from the air
and circulating pumps for condensers, are:
(1.) Feeding the boiler.
(2.) Emptying the tanks and pumping out bilge.
(3.) Supplying water for washing down decks, extinguishing fires,
filling evaporators and sanitary service.
A special pump for each separate purpose is not always supplied, but
one pump may have the necessary pipe connections to serve alternately
various duties.
Feeding the boilers is so important an operation that a supplemental
special pump is always required. To make absolutely sure of an ample
supply of feed water one of the other pumps is made strong enough
to serve the same purpose, or sometimes an injector is fitted as an
auxiliary feeding mechanism.
A bilge pump has special fittings, for the reason that it handles very
dirty water, undesirable to be transmitted through any other pipe
system. In small ships, however, one pump, the so-called “donkey,”
often serves for nearly all other purposes, including auxiliary boiler
feeding.
A special form of pump in use on Western river steamers is the
so-called “doctor,” an independent pump with a walking beam, by which
one steam cylinder drives a system of pumps for feed, fire and bilge
pumping purposes (Fig. 450).
The feed pump should be of simple construction, great strength and
ample capacity, to secure great regularity and reliability of service
under the severe conditions of high pressure.
The main parts of auxiliary feed pumps are often duplicated. This is a
desirable point, as one set of spare parts in piston, rings, valves,
etc., is suitable for both pumps.
The main feed pump is, even in the independent type, often placed in
the engine room, while the auxiliary pump, or the injector, is in the
fire room. The feed pumps draw usually from the hot well, feed heater
and feed tanks and discharge through main feed pipe into the boiler.
_This “doctor” pump_ is a substantial piece of mechanism. The bases of
columns and pump chamber flanges are accurately planed, the cylinder
has spring piston packing and the plain slide valve is made of gun
metal.
The hot water pumps, 3-1/2″ diam. × 10″ stroke, have chambers bored and
are fitted with a copper and tin composition for valves and scats; the
latter are driven into their places and riveted over underneath.
[Illustration: FIG. 450.]
NOTE.—Each valve is reached by removing the bonnet covering it. The
joints under caps are made the insertion of sheet lead. The heaters
above the frame, as shown, are 22″ × 5′ 0″ long, of hard rolled
copper, with a copper worm 18′ 0″ long by 2-1/2″ diameter in each.
There is also a baffle plate above the water line in each heater to
prevent the exhaust from throwing the water out at the top.