AN IMPROVEMENT IN VACUUM PUMPS
Year: 1883

page_text: LETTERS PATENT to William Hart Cullen of the Vacuum Pump and Ice
Machine Company Limited of St Petersburg Place Bayswater in the County
of Middlesex, for an Invention of AN IMPROVEMENT IN VACUUM PUMPS
PROVISIONAL SPECIFICATION left by the said William Hart Cullen at the
Office of the Commissioners of Patents on the 17th October 1883.
WILLIAM HART CULLEN of the Vacuum Pump and Ice Machine Company
Limited St Petersburg Place Bayswater in the County of Middlesex "AN
IMPROVEMENT IN VACUUM PUMPS
"
Air Pumps for exhaustion are sometimes made in duplicate, so as to exhaust by
stage pumping, that is to say, while the first pump of considerable dimensions
exhausts the vessel in which a vacuum is required, a second pump of smaller
dimensions receives the discharge from the first pump and compresses it sufficiently
to discharge it into the atmosphere. Such pumps, when once considerable rare-
faction has been effected, have to work against very small pressures, but in first
effecting this rarefaction, they have to act against considerable pressure, and are
therefore subject to be severely strained at first starting. My invention relates to
means of relieving such pumps of the starting strain, and of abridging the time
necessary to effect considerable rarefaction in the first instance. For this purpose,
I apply to the discharge of the second pump a steam ejector, which, being put in
action before the pumps are started, rapidly exhausts to a considerable extent the
spaces of the pumps and passages and also of the vessels in which a vacuum has to
be formed, so that the pumps, when started, have rarefied fluid to deal with. The
working of the ejector may be continued while the pumps are in action, so as to
relieve the second pump of a considerable amount of the strain to which it is
subjected at each discharge. As these discharges are intermittent, whilst the action
of the ejector is continuous, I prefer to introduce between the ejector and the
discharge valve of the pump, an air vessel of considerable capacity, so as to equalise
to some extent the pressure of the fluid acted on by the ejector

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said William Hart Cullen in the Patent Office on the 16th April 1884.
WILLIAM HART CULLEN of the Vacuum Pump and Ice Machine Company
Limited of St Petersburg Place Bayswater in the County of Middlesex
"AN
IMPROVEMENT IN VACUUM PUMPS
"
Air pumps for exhaustion are sometimes made in duplicate, so as to exhaust by
stage pumping, that is to say, while the first pump of considerable dimensions exhausts
the vessel in which a vacuum is required, a second pump of smaller dimensions
receives the discharge from the first pump and compresses it sufficiently to discharge
it into the atmosphere. Such pumps, when once considerable rarefaction has been
effected, have to work against very small pressures, but in first effecting this rare-
faction, they have to act against considerable pressure, and are therefore subject to
be severely strained at first starting. My invention relates to means of relieving
such pumps of the starting strain, and of abridging the time necessary to effect
considerable rarefaction in the first instance. For this purpose I apply to the
discharge of the second pump a steam ejector, which, being put in action before the
pumps are started, rapidly exhausts to a considerable extent the spaces of the pumps
and passages and also of the vessels in which a vacuum has to be formed, so that
the pumps, when started, have rarefied fluid to deal with. The working of the
ejector may be continued while the pumps are in action, so as to relieve the second
pump of a considerable amount of the strain to which it is subjected at each
discharge. As these discharges are intermittent, whilst the action of the ejector is
continuous, I prefer to introduce between the ejector and the discharge valve of the
pump, an air vessel of considerable capacity, so as to equalise to some extent the
pressure of the fluid acted on by the ejector.
DESCRIPTION OF THE DRAWINGS.
Fig. 1 of the accompanying drawings shew an arrangement of compound
exhausting pump with ejector according to my invention. A is the large pump
which discharges by the pipe B into the space C surrounding the second smaller
pump D.
This pump, which is single acting, discharges into the space E above,
from which a steam ejector F of ordinary construction continuously exhausts. The
space E is made of considerable capacity so as to operate as an equalising vessel to
allow for the intermittent discharge from the pump D. This equalising vessel may
be otherwise arranged as shewn in Fig. 2 where it is added as an air vessel G on
the cover of the pump chamber E. Or it may be placed as shewn by H in Fig. 3
as a vessel interposed between the discharge of the pump and the ejector.
Having thus described the nature of my invention and in what manner the same
is to be performed, I claim :-
In combination with a compound vacuum pump, a steam ejector applied to
exhaust from the discharge of the second pump, substantially as and for the
purposes herein set forth.
In Witness whereof I the said William Hart Cullen have hereunto set my hand
and seal this Seventh day of April in the year of our Lord One thousand eight
hundred and eighty-four.
W. H. CULLEN. (L.S.)