Bore 1/2 in
Stroke: 3.4 in
STUART BOILER FEED PUMP.
A most Effective
To achieve this has meant a considerable amount of experimenting but we are now confident that our pump is fully up to the standard of Stuart engines.
It has steam cylinder 1/2-in. bore x 3/4-in. stroke, the pump being 1/4-in bore. The main D pattern slide valve is moved by a shuttle piston. This piston is controlled by a piston valve operated by the arm attached to the piston rod.
The suction pipe is 1/4-in. and the delivery pipe 3/16-in. diameter, the steam pipe being 5/32- in. diam.
We advise that a displacement lubricator be fitted to the steam pipe and the steam cock be fitted close to the pump.
By removing the valve chest cover the whole of the valve gear is exposed.
The pump is constructed entirely of gunmetal and may be set to work at any speed down to 10 strokes a minute.
The finished pump, built and tested in our works.£4 15s. 0d.
Complete set of castings and materials with full working drawings. 17s. 6d..
This is a most interesting model to build, but we must point out that to build a satisfactory pump needs a very high standard of workmanship.
The only machining which a fist-class mechanic may find difficult, with the tools at his disposal, is the machining of the pump bore and cylinder flange ; this we can do for 8/6.
This is an ineresting design with the piston rod doubling up as the pump piston. The valve rod is moved by a bracket bounted to the piston rod so that as the piston moves to one end of its travel the bracket hits a stop on the valve rod switching the valve. This is reversed at the other end of the piston travel. It would not be enough to run a steam valve as in a normal engine where the valve is progressively opened and closed as the engine cycles. With such a short stroke and a pump requiring maximum steam pressure we need the valve to open fully as soon as it is tripped, this a shuttle valve is used. The valve gear being tripped by the piston stroke reaching the end of travel releases a small amount of steam into the shuttle valve which immediatly opens the main steam inlet providing full pressure to the piston. As soon as the valve is tripped at the other end of travel the shuttle valve repeats the process. As can be seen from the picture the valve rod (top rod) has an adjustable limit screw, and the two valve trip adjusters. A long gland nut adjustment thread also allows for careful adjustment of the valve rod resistance. This engine requires a level of accurate adjustment to run smoothly. Mounting the steam valve drectly to the valve chest is also important to minimise condesate build up that can restict the small diameter shuttle valve passageways. Drain cocks and cylinder insulation are also fitted to aid quick cylinder warm up. I have seen a few of these and most dont run well.
With many piston type water pumps an air resevoir is used to even out the compression waves caused by a directly connected pump. The images below show how the pump compression stroke compresses the air and smooths out the action..