Priming in a steam boiler is the carrying over of large quantities of
water by the steam to the engine, and may occur in a perfectly clean
boiler. It is usually caused by too great a demand on the capacity of
the boiler, too sudden and fierce firing, or after steam pressure is
lowering, an increasing demand is made for it. It is usually a radical
defect in the construction or capacity of the boiler, and is most
frequently the result of insufficient steam space, small evaporating
capacity, and lack of good circulation.
Priming is indicated by the water rising and lowering in the glass
gauge more or less violently, by the clicking sound in the steam
cylinder of engine as the piston forces the water from end to end, and
by the regular shower of water falling from the exhaust.
Q. How do you remedy priming?
A. There are several remedies for priming, none of which will apply
effectually in all cases. Where insufficient capacity is the cause,
the only remedy is a larger boiler. In others, it may be prevented
by carrying the water level lower, if same can be done with safety,
or taking steam from side of dome instead of top, or increasing the
size of steam pipe, or taking out the top row of flues, and in boilers
that have no steam dome, a long dry pipe with perforated top may be of
benefit.
Q. What are other causes and remedies for priming?
A. The piston rings may leak badly. If they do, they should be
replaced, or made to fit cylinder perfectly. The cylinder may be badly
cut by the rings. If it is, it should be re-bored and new piston rings
put in.
The slide valve may be cut, and leak. In this case the valve will need
re-planing and scraping, also the valve seat. If the valve is not
properly set, it may also cause priming. The exhaust nozzle may be
clogged with burnt oil and sediment; if it is, clean it out thoroughly.