Improvements in Exhausting Pumps.
Year: 1899

page_text: Date of Application, 31st Jan., 1899
Complete Specification Left, 24th Oct., 1899-Accepted, 25th Nov., 1899
Improvements in Exhausting Pumps.
I, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent Agents,
45, Southampton Buildings, in the County of Middlesex, do hereby declare the
nature of this invention to be as follows.:-
The degree of efficiency of an ordinary air-pump primarily depends upon the
volume of its non-effective or useless space. When, in calculating its efficiency
Mariotte's law is taken as a basis of calculation, it is found that, in a pump of
this class, the useful (or effective) piston stroke is less than the entire length
of the piston stroke by the product of multiplication of the clearance into the
ratio of the blow-off (or exhaust) pressure to the suction pressure. Let e.g., the
clearance be ======= 2 per cent. then, with a suction pressure of 1/20 atmosphere the
useful stroke, or in other words, the degree of efficiency of the air-pump, will be
100
_
40:
======
60 per cent.
while, if the suction pressure be = 1/50 atmosphere, or where the absolute pres-
sure of mercury is 15 millimetres the efficiency of the pump will be
=
100 100 = 0.
-
Hence it follows that the highest vacuum that may be attained under these
circumstances is
1/50° atm. 15 millim. mercury pressure.
=
Now in order to enhance the useful effect of air pumps and to attain an
increased vacuum, either of two methods has hitherto been adopted.
One method of accomplishing the purpose stated is as follows: Where one
cylinder only was employed, and where there was a single piston with equally
large operative surfaces, the compressed gases remaining behind in the space
on one side of the piston were conducted to the other side of such piston. By
such means the useful portion of the piston stroke, or in other words the effective
sucking action, certainly is increased, but it is so at the expense of the quantity
of actual work produced, since the necessity of once more compressing the air
transferred to the other side of the piston involves a material reduction of the
amount of work.
The other means which have been employed for raising the degree of efficiency
of air-pumps consists in the arrangement of two cylinders of unequal size which
are traversed in succession by the gases drawn off. To this end the relative
dimensions are so proportioned, that the first cylinder draws off (or exhausts)
the gases; compresses them up to a pre-determined degree; and then forces them

page_text: into the second cylinder, which is of the proper size to receive the reduced
volume of the gases; and in which the said gases are then compressed to atmos-
pheric pressure and finally driven out into the atmosphere. Now, although this
arrangement fulfils its object, it is unduly complicated and expensive because
it makes the provision of two cylinders absolutely necessary. Also, in this last
mentioned case the useful volume (or space) of the two cylinders, which come
into operation successively, must in all cases be unequal, if it be desired to effect
the compression of the air in two successive stages.
Instead of two single acting cylinders, the two ends of a double acting
cylinder-connected so as to act in succession-have been employed; in which
case the areas of the effective piston surfaces are rendered unequal; by an
abnormally thick piston-rod, so that the difference of volume, mentioned above
as being necessary in this instance remains the same.
In the accompanying drawing:
Figure 1 is a longitudinal section of the improved air or gas pump.
Figure 2 is a separate view of the cock shown in Figure 1, and
Figure 3 is a diagram hereinafter referred to.
The present invention is based upon the fact that the useful volume, being the
product of the piston area by the useful stroke, will be unequal also where, instead
of the piston surfaces, the useful strokes are made different. Thus, in accord-
ance with this invention, given a double acting cylinder and a single piston, as
shown in Figure 1 of the accompanying drawing, the proper relative useful
volumes of the two cylinder ends connected so as to operate in succession,-
are obtained by making the useful piston strokes unequal, but leaving the piston
surface the same on each side. At the first glance it may seem that this method
does not lead to a more complete vacuum, since, with two cylinders sides of like
dimensions the gases pass, in the same condition, from one side of the piston to
the other. Such an assumption, however, would be erroneous, as the drawing in
of the gases takes place, not during the whole time taken up by the stroke, but
during part of such stroke only. Now this useful portion of the stroke, which
alone is important, is different for each of the two cylinder ends. And the relative
extent of this useful part of the piston stroke, in this case regulates itself
automatically and has the same effect as that which would otherwise be produced
by piston-surfaces of relatively unequal areas.
The invention will be more fully understood by reference to the diagram
Figure 3, of the accompanying drawing.
Assuming that one side of the piston, during the portion B C of the stroke,
draws in the volume of the gases available, and that in covering the distance
from C to D it will compress such gases to the volume ; then the other side of
the piston, of a like area to the first will draw in the compressed gases only for
the distance from D to A, and will then compress them to the volume That
is to say, with a given clearance, both the volume and the corresponding
pressure P are entirely dependent upon the pressure P₁, to which the quan-
tities and P₂ will consequently proportion themselves of their own accord.
Hence the useful stroke of the second piston side is far less than that of the first.
side, whereby the same effect is produced as that which would result from an
inequality of volume or area existing between the two piston sides.
Given an air-pump in which the clearance amounts (for example) to. 2 per
cent. We will find by calculation that if

page_text: HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.

page_text: Hence it follows that the highest vacuum that may be attained under these
circumstances is
1/50 atm.
15 millim. mercury pressure.
Now in order to enhance the useful effect of air pumps and to attain an
increased vacuum, one of two methods has hitherto been adopted.
One method of accomplishing the purpose stated is as follows: Where one
cylinder only was employed, and where there was a single piston with equally
large operative surfaces, the compressed gases remaining behind in the clearance
space on one side of the piston were conducted to the other side of such piston. By
such means the useful portion of the piston stroke, or in other words the effective
sucking action, certainly is increased, but it is so at the expense of the quantity
of actual work produced, since the necessity of once more compressing the air
transferred to the other side of the piston involves a material reduction of the
amount of work.
The other means which have been employed for raising the degree of efficiency
of air-pumps consists in the arrangement of two cylinders of unequal size which
are traversed in succession by the gases drawn off. To this end the relative
⚫ dimensions are so proportioned, that the first cylinder draws off (or exhausts)
the gases; compresses them up to a pre-determined degree; and then forces themi
into the second cylinder, which is of the proper size to receive the reduced
volume of the gases; and in which the said gases are then compressed to atmos-
pheric pressure and finally driven out into the atmosphere. Now, although this
arrangement fulfils its object, it is unduly complicated and expensive because
it makes the provision of two cylinders absolutely necessary. Also, in this last
mentioned case the useful volume (or space) of the two cylinders, which come
into operation successively, must in all cases be unequal, if it be desired to effect
the compression of the air in two successive stages.
Instead of two single acting cylinders, the two ends of a double acting
cylinder connected so as to act in succession-have been employed; in which

page_text: case the areas of the effective piston surfaces are rendered unequal by means of an
abnormally thick piston-rod, so that the difference of volume, mentioned above
as being necessary in this instance remains the same.
In the drawing left with my Provisional Specification
Figure 1 is a longitudinal section of the improved air or gas pump.
Figure 2 is a separate view of the cock shown in Figure 1, and
Figure 3 is a diagram hereinafter referred to.
The present invention is based upon the fact that the useful volume, being the
product of the piston area by the useful stroke, will be unequal also where, instead
of the piston surfaces, the useful strokes are made different. Thus, in accord-
ance with this invention, given a double acting cylinder and a single piston, as
shown in Figure 1 of the accompanying drawing, the proper relative useful
volumes of the two cylinder-ends, connected so as to operate in succession,-
are obtained by making the useful piston strokes unequal, but leaving the piston
surface the same on each side. At the first glance it may seem that this method
does not lead to a more complete vacuum, since, with two cylinders sides of like
dimensions the gases pass, in the same condition, from one side of the piston to
the other. Such an assumption, however, would be erroneous, as the drawing-in
of the gases takes place, not during part of such stroke only. Now this useful
portion of the stroke, which alone is important, is different for each of the two
cylinder ends. And the relative extent of this useful part of the piston stroke, in
this case regulates itself automatically and has the same effect as that which
would otherwise be produced by piston-surfaces of relatively unequal areas.
The invention will be more fully understood by reference to the diagram
Figure 3, of the accompanying drawing.
Assuming that one side of the piston, during the portion B C of the stroke
draws in the volume, of the gases available, and that in covering the distance
from C to D it will compress such gases to the volume ; then the other side of
the piston, of a like area to the first will draw in the compressed gases only for
the distance from D to A, and will then compress them to the volume . That
is to say, with a given clearance, both the volume and the corresponding
pressure l' are entirely dependent upon the pressure P₁, to which the quan-
tities, and P', 'will consequently proportion themselves of their own accord.
Hence the useful stroke of the second piston side is far less than that of the first
side, whereby the same effect is produced as that which would result from an
inequality of volume or area existing between the two piston sides.
Given an air-pump in which the clearance amounts (for example) to 2 per
We will find by calculation that if
cent.

page_text: at the same time the left-hand side of such piston compresses the air previously
drawn in and forces it through the port H₂ of the cock, and out through the
pipe L into the atmosphere.
If operations simply conducted in the manner just described, the extreme
vacuum attainable, as found by computation, would be
=
1/51 atm. of absolute pressure.
In order to attain a higher degree of vacuum, however it is necessary to turn
the cock H through 90°, or move it into the position indicated in Figure 2.
When this is done, the operation of the pump will be as follows:
As the piston moves from the left to the right, air is drawn in from the vessel
through the pipe L, and valve S₁, while at the same time the right hand side
of the piston drives out air into the atmosphere through the valve D, and pipe L..
As the piston recedes from the right to the left, the pressure valve 1), opens
and allows the partly compressed air to pass to the right hand side of the piston
through the inclined port H, of the cock and through the valve S.
Thus, while the piston performs its stroke from the right to the left, air is
neither sucked out of the vessel nor forced out into the atmosphere. What
happens is a partial compression of air; whereupon such air is driven out, upon
the left-hand side of the piston, and then a suction of the quantity of air thus
driven out takes place upon the right-hand side of the piston. After which the
same cycle of operations is repeated, as the piston moves from the left to the
right; the left-hand side draws in a fresh supply of air from the vessel, through
the pipe L, while the opposite side of the piston compresses the air, which has
previously been admitted through the inclined port H, to atmospheric pressure;
whereupon the air escapes through the valve D, and pipe L.
Thus it will be seen that the pump hereinabove described affords the following
advantages over other arrangements hitherto devised with the same object:
1. From machines comprising means for mutually equalizing (or balancing)
pressures, it differs in the fact that it avoids the extra consumption of power
otherwise involved in such equalization of pressure.
2. Its distinguishing feature, as compared to ordinary two-cylinder machines,
lies in its simplified construction and operation: and
3. In comparison with the known two-phase but single cylinder machines with
unequal piston arcas, it is distinguishable by the fact that, with the two sides
of its piston connected for parallel action, it gives the full effect corresponding
to the diameter of the cylinder, and obviates the necessity of providing an
abnormally thick piston-rod, which cannot without difficulty be properly packed.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed, as communicated to me by my
foreign correspondents, I declare that what I claim is:-
1. An air-pump consisting of the combination of a single cylinder, containing
a valveless reciprocating piston (such as K) with suction and exhaust pipes (such
as L, and L) and with means for guiding the exhaust air through said pipes to
the atmosphere or deflecting said air back to the cylinder, substantially in the
manner and for the purpose described and illustrated."
2. In an air-pump having a single cylinder containing a valveless reciprocating
piston and communicating with suction and exhaust pipes, the combination with
said pipes of an adjustable stop-plug (such as H) having lateral and inclined
perforations (such as H, H, and H.) and being located at any suitable point on
said pipes substantially as and for the purpose described and shown.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.