The following description of the construction and mode of action is by
Thomas Shaw, M.E., Philadelphia, the inventor.
[Illustration: IMPROVED GUN PRESSURE GAUGE.]
Fig. 1 represents the gauge secured to small ordnance, the gun shown in
cross section. Fig. 2 represents face view of the gauge and indicator,
exposing a vertical section through the hydraulic portion of the gauge,
on line 3 and 4 of Fig. 1. The same principles of reduction of high
pressure are used in this gauge as in Shaw's hydraulic gauge. It will be
observed that a solid steel piston, E, in the cylinder, A, is provided
with a plunger on its under side, which comes in contact with an elastic
packing, D; the plunger may stand as 1 to A 1,000, or as 1 to A 100, in
point of area of exposed surface, as compared with the large piston head,
as desired. Assuming the proportions to be 1 to A 1,000, the 1,000 lb.
pressure on the plunger means only 1 lb. pressure in the fluid chamber,
above piston head, E, and this greatly reduced pressure is now
susceptible of measurement by any of the ordinary light pressure
instruments for measuring pressures. All the passage ways connecting to
dial gauge, R, with the fluid chamber above piston, E, are filled solid
with fluid, permitting no air spaces that can be avoided. The steel plug,
L, that forms a passage way between the fluid chamber and the dial gauge,
is provided on one side with a small screw hydraulic pump, with a
reservoir supply of fluid. This part is shown in longitudinal section;
the steel plunger, I, is firmly secured to wheel, F, the long hub, H, of
which is provided with a screw thread on its inner side, which thread
screws upon the exterior of pump barrel, K. After first filling the
interior of the pump barrel with fluid, the said hub is screwed upon the
pump barrel, causing the plunger, I, to force the fluid into the fluid
chamber and passage way leading to the dial gauge, causing the hand or
pointer to move to any predetermined pressure on dial, in advance of
pressure applied in the high pressure chamber at D. The purpose
accomplished in this act is to give the least possible movement of the
pointer to record any maximum pressure, as, for example, assuming that
20,000 lb. was the expected pressure from any one explosive, then the
pointer, by the means above described, can be set at, say, 18,000 lb., in
which event the pointer is reduced to the minimum movement of only 2,000
lb. to register 20,000 lb.
It will be evident that much greater accuracy of measurement of maximum
pressures can be obtained by the minimum movement of the pointer, as both
the inertia and the momentum are reduced to the minimum quantity. The
subsidence of pressure resulting from explosives being about as sudden as
the creation of pressure, causes the pointer to move too rapidly for
correct ocular observation, on which account a static electric current is
employed, causing a stream of electric sparks to shoot off from the end
of the pointer, B, to the brass outer ring, M. The gauge is insulated for
that purpose by glass plate, S, which is secured concentrically to the
gauge proper and the ring, M. Binding posts for the electric wires are
provided at O and P, which wires are shown in Fig. 2. A spring clamp, N,
Fig. 2, enables the insertion of chemically prepared or other paper,
which lies against the inner side of brass rim, M, and held in place by
the clamp, N. The electric sparks above spoken of pierce the strip of
paper with small holes and colored marks. These holes, etc, show the
exact limits to which the pointer has traveled under pressure, and thus
an indelible record is kept by the electrical indications shown upon the
strip of paper. The paper can have the pressures corresponding to gauge
printed upon the same, when the holes are made prominent by holding the
paper to the light, exposing an exact indication of the pressures or
explosives operated with.
The gases resulting from the explosives are injurious to the gauge
packings, etc., on which account the bore in gun, W, and the connecting
steel plug, B, are filled with fluid. A screw plug, U, enables the
insertion of the fluid, after first pushing an elastic wad of rubber, B,
or cork, in the bore near the inner wall of the gun, which wad will
prevent the escape of the fluid to the interior, and be sufficiently free
to prevent any interference with the pressures. The patentee and
manufacturer of this gauge is prepared to fill orders up to 50,000 lb.
per square inch. This gauge is made of the best steel, and is very
compact, the weight being inside of twenty-five pounds.
The inventor has heretofore made mercury column gauges for gunpowder
pressures, which were too large for direct attachment to guns, but were
connected with special powder chambers to test the pressure, etc., of
confined explosives. The experience thus gained enabled the construction
of the instrument here shown, which is adapted to direct attachment to
the gun, making it as easy now to measure gunpowder pressures as it had
been, heretofore, to measure steam pressures. The effect of this movement
is to reduce the exaggerated statement of high pressures, obtained from
ordinary sporting powders; these have been accredited with pressures up
to 40,000 lb. per square inch, but they only really gave 22,000 lb. by
actual gauge measurement. Artillerists and ordnance officers have, in
this instrument, a true pulse of the internal pressures of the gun, of
inestimable value when determining the quantity of powder and the proper
weight of shot. These are important matters in ordnance practice.
This gauge is a compact machine, designed to measure and indicate the
quick pressures resulting from gunpowder explosives and the slow
pressures of hydraulic force; the same mechanism used in both cases
permits the ready testing and examination of gauge under hydraulic
pressure, to determine its accuracy, for the more sudden pressure
occasioned by the use of gunpowder.
* * * * *