106 South Elm Street, Newkirk, Okla. 74647
During the steam engine era you wouldn’t discuss steam
engines very long with a steam engine machinist, especially a
railroad machinist until he would mention, ‘valve blow’ and
‘ring blow.’ In plainer English it would mean leakage
through the valve or the piston.
It is very easy to test a simple traction or stationary engine
for leakage through the valve. Turn the crankshaft until the valve
is at or near the center of its stroke. At this point the admission
and exhaust ports will be closed. Close the steam-chest drain and
open both cylinder drains. Open the throttle. If steam blows at
either cylinder drain or at the exhaust nozzle, it will mean
leakage through the valve. A good slide valve will often show no
leak at all. Piston valves will nearly always show some leakage.
Slight leaks will not amount to much but of course a big leak will
mean poor performance and should be repaired.
It is a little more trouble to test for ‘ring blow.’ One
old engineer who was considered an authority says: ‘Turn the
engine so that the crank is in the first quarter of either stroke,
so that full pressure may be applied, block the cross-head so that
the piston cannot move, disconnect the cylinder drain push-rod so
that the drains can be opened independently of each other, open the
drain on the end that should not be taking steam, then open the
throttle. If steam shows, of course it must be blowing through the
piston rings.’
There is one objection to this method. If the block is not
carefully fitted to the cross-head it can slip and cause damage. In
testing a traction engine an easier procedure can be followed.
Block both drive wheels with a good piece of wood in front and
back. If good pieces of wood are not at hand, dig a couple of holes
about six or eight inches deep and back the engine into them. Do
not dig deep enough to cause difficulty getting out, but enough so
that considerable pressure can be applied. Engage the clutch at a
point where the slack in the gears will be taken up with the crank
position to give full pressure. Open the throttle enough to give
considerable pressure, but not enough to pull over the blocks. In
this way you can find out if steam is leaking through the rings. It
is not often that you will find an engine that will not show a
little leakage through the piston, but a big leak should be
considered a problem and should not be tolerated.
