U.S. patent application number 10/518785 was filed with the patent office on 2005-10-20 for high-pressure small volume pump.
Invention is credited to Gyger, Fritz.
Application Number | 20050232792 10/518785 |
Document ID | / |
Family ID | 35149174 |
Filed Date | 2005-10-20 |
United States Patent
Application |
20050232792 |
Kind Code |
A1 |
Gyger, Fritz |
October 20, 2005 |
High-pressure small volume pump
Abstract
An improved high-pressure pump (1) for an accurate, largely
pulsation-free flow of the working medium, more particularly an
HPLC pump, includes one or a plurality of the following measures:
reduced dead space due to adapted seals (48, 70); reduced dead
space thanks to a device (15, 16; 32; 36, 38) for adjusting the
length of the displacement piston; adjustable dead space and
therefore adjusting capability of the pulsation freedom through a
displacement chamber provided with an adjustable opposed piston
(58); and seals compensating construction tolerances by a
combination of a cambered sealing surface and a conical sealing
surface.
Inventors: |
Gyger, Fritz; (Thun-Gwatt,
CH) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
|
Family ID: |
35149174 |
Appl. No.: |
10/518785 |
Filed: |
December 20, 2004 |
PCT Filed: |
June 18, 2003 |
PCT NO: |
PCT/CH03/00394 |
Current U.S.
Class: |
417/415 ;
417/571 |
Current CPC
Class: |
F04B 53/164 20130101;
F04B 53/16 20130101; F05C 2203/08 20130101; F04B 53/147 20130101;
F04B 2201/0201 20130101; F05C 2225/12 20130101; F04B 53/162
20130101; G01N 2030/326 20130101; F05C 2225/04 20130101; F04B
11/0075 20130101 |
Class at
Publication: |
417/415 ;
417/571 |
International
Class: |
F04B 017/00; F04B
035/04 |
Claims
1-23. (canceled)
24. A pump for delivering precisely determined, small liquid flows
comprising: at least one pump device including a displacement
chamber, a piston that is movable in the displacement chamber, the
piston having at least a first, foremost seal for sealing the
piston against the displacement chamber, the first seal comprising
a sealing element with a sealing lip surrounding the piston, the
sealing lip having a first surface and a second surface; a
spring-elastic element resting on the opposed second surface of the
sealing lip for prestressing the first surface of the sealing lip
against the piston, the second surface being in contact with the
displacement chamber, the sealing element and the spring-elastic
element are essentially C-shaped in cross-section; and a filling
body that is essentially incompressible under operating conditions
of the pump disposed in the chamber in order to reduce dead space
of the pump device resulting from the seal.
25. The pump according to claim 24, wherein the C-shaped profile of
the spring element includes a slot having a width essentially equal
to a height of the interior of the C, such that the filling body is
axially insertable into the spring element and is shaped to
substantially fill out the interior of the C at least
preponderantly.
26. A pump comprising at least a first and a second pump device
each according to the pump of claim 24 and each comprised of a
displacement chamber and a piston, the second pump device being
downstream of the first pump device and being operatable as a
storage device of pulsation of the first pump device.
27. A pump for delivering precisely determined, small liquid flows
comprising: at least one pump device including a displacement
chamber, a piston that is movable in the displacement chamber, the
piston having at least a foremost seal for sealing the piston
against the displacement chamber, the seal comprising a sealing lip
surrounding the piston, the sealing lip having a first surface and
a second surface; a spring-elastic element resting on the opposed
second surface of the sealing lip for prestressing the first
surface of the sealing lip, the second surface being in contact
with the displacement chamber; the spring element is essentially a
closed, spring-elastic band having an inner side in contact with
the second surface of the sealing lip, and the displacement chamber
has an internal wall located at a small distance from an external
surface of the spring element in order to reduce the dead space of
the pump device resulting from the seal.
28. The pump according to claim 27, wherein the band comprises a
coil of a spring-elastic material wherein turns of the coil are
wound around the sealing lip.
29. A pump comprising at least a first and a second pump device
each according to claim 27 and each comprised of a displacement
chamber and a piston, the second pump device being downstream of
the first pump device and being operatable as a storage device of
pulsation of the first pump device.
30. A pump for delivering precisely determined, small liquid flows
comprising: at least one pump device including a displacement
chamber, a piston that is movable in the displacement chamber, the
pump has a driving unit, a piston rod operatively connecting the
piston to the driving unit of the pump; a piston adjusting device
connecting the piston to the piston rod, the piston adjusting
device between the piston and the piston rod is adjustable in
length in order to be able to adjust the total length of the piston
and piston rod assembly to the distance between the driving unit
and the bottom of the displacement chamber, and thus to be able to
adjust dead space in the chamber.
31. The pump according to claim 30, wherein the piston is mounted
on the piston rod in a longitudinally displaceable manner.
32. The pump according to claim 30, wherein the piston adjusting
device includes a clamping device allowing to lock the piston in a
determined position with respect to the piston rod.
33. The pump according to claim 30, wherein in the piston adjusting
device, a spring is disposed between the piston and the piston rod
such that a reduction of the total length of an assembly of the
piston and the piston rod is effected against the restoring force
of the spring element.
34. The pump according to claim 30, wherein the displacement
chamber has a bottom in the form of a body of a material that is at
the most negligibly compressible under the operating pressure of
the pump but sufficiently more elastic than the piston, and that
fills out the cross-section of the displacement chamber completely,
for allowing the piston to be adjusted to an indefinitely small
distance from the bottom of the displacement chamber in the upper
dead center without risk of damage of the piston through contact
with the bottom of the displacement chamber during the adjusting
procedure or in operation.
35. The pump according to claim 30, wherein the piston comprises a
bar-shaped piston portion of a mechanically resistant material, and
having a rear end mounted in a seat of a sleeve such that the
clamping device can be applied against the sleeve substantially
punctually, thereby locking the sleeve in the piston rod without a
risk of damaging the bar-shaped piston portion by the clamp.
36. A pump comprising at least a first and a second pump device
each according to the pump of claim 30 and each comprised of a
displacement chamber and a piston, the second pump device being
downstream of the first pump device and being operatable as a
storage device of pulsation of the first pump device.
37. A method for adjusting the dead space in a pump for delivering
precisely determined, small liquid flows wherein the pump
comprises: at least one pump device including a displacement
chamber, a piston that is movable in the displacement chamber, the
pump has a driving unit, a piston rod operatively connecting the
piston to the driving unit of the pump, a piston adjusting device
connecting the piston to the piston rod, the piston adjusting
device between the piston and the piston rod is adjustable in
length in order to be able to adjust the total length of the piston
and piston rod assembly to the distance between the driving unit
and the bottom of the displacement chamber, and thus to be able to
adjust dead space in the chamber; the method comprising moving the
piston rod to the upper dead center, advancing the piston into the
displacement chamber until the desired dead space results, and
locking the piston in the piston rod by actuating a locking device
of the piston adjusting device.
38. A pump for delivering precisely determined, small liquid flows
comprising: at least one pump device including a displacement
chamber, a piston that is movable in the displacement chamber, the
displacement chamber has a bottom which essentially comprises a
front end of an opposed piston that is displaceable in the
displacement chamber such that a dead space of the pump device is
adjustable.
39. The pump according to claim 38, wherein the opposed piston
includes an adjusting device comprising a position indicator, for
making the adjustment of the dead space in the displacement chamber
detectable from the outside.
40. A pump comprising at least a first and a second pump device
each according to the pump of claim 38 and each comprised of a
displacement chamber and a piston, the second pump device being
downstream of the first pump device being and operatable as a
storage device of pulsation of the first pump device.
41. Application of the pump according claim 38, wherein the opposed
piston is adjustable according to an intended operating pressure in
order to achieve a reduced pulsation.
42. A pump for delivering precisely determined, small liquid flows
under high pressures comprising: at least one pump device including
a displacement chamber, a piston that is movable in the
displacement chamber; at least one working medium access bore of
the pump device having a detachable connecting assembly including
at least one pair of sealing surfaces forming a junction that is
tight to a working medium, one sealing surface is essentially
dome-shaped and convex and the other sealing surface is essentially
concave and conical, and the sealing surfaces have a center with a
respective opening of a channel for the working medium defining an
annular contact line between the two sealing surfaces even if the
channel openings are not precisely aligned to each other.
43. The pump according to claim 42, wherein a seal is interposed
between the sealing surfaces of at least one pair of the sealing
surfaces.
44. The pump according to claim 42, further comprising at least a
first and a second pair of the sealing surfaces, a sealing body is
disposed between the first and second pairs of the sealing
surfaces, the first and second sealing surfaces including inner
surfaces; the sealing body having the respective inner sealing
surfaces of the two pairs of sealing surfaces formed thereon and
the inner sealing body is comprised of a dimensionally stable,
highly pressure-resistant synthetic material.
45. The pump according to claim 42, further comprising at least a
first and a third pair of sealing surfaces each including an inner
and an external sealing surface, and the two inner sealing surfaces
each face the other pair of sealing surfaces, a connecting body
disposed between the external sealing surfaces of the two pairs of
sealing surfaces, so that the two pairs of sealing surfaces each
form a tight junction with the connecting body.
46. The pump according to claim 42, further comprising a pair of a
first and a second contact surface contacting each other, a second
connecting body in the connecting assembly on which the first
contact surface and the sealing surface are formed, the second
connecting body being held between the second contact surface and
the other one of the sealing surfaces; a duct for the working
medium fixedly connected to the second connecting body wherein the
duct communicates with the channel having the opening located in
the sealing surface of the second connecting body.
47. The pump according to claim 46, wherein the contact surfaces
are cambered and complementary to each other to center the second
connecting body in the second contact surface.
48. The pump according to claim 46, wherein in at least one of the
first sealing surface pairs at least one of the sealing surfaces is
provided with a concentrically stepped surface in order to provide
a plurality of sealing lines.
49. A pump comprising at least a first and a second pump device
each according to the pump of claim 46 and each comprised of a
displacement chamber and a piston, the second pump device being
downstream of the first pump device and being operatable as a
storage device of pulsation of the first pump device.
Description
[0001] The present invention refers to pumps according to the
preamble of claim 1. Furthermore, the invention refers to adjusting
methods and to applications of such pumps.
[0002] Pumps capable of delivering smallest volumes of liquids
under high pressures with minimum losses, minimum pulsation and a
correspondingly accurate, determined flow rate are required
particularly for HPLC (High Performance Liquid Chromatography).
Current flow rates today range up to approx. 5 ml/min (milliliters
per minute) at an operating pressure of the chromatography column
of e.g. 100 bar, while the gradient capability extends down to 100
.mu.l/min (microliters per minute). However, pressures up to 700
bar are already being applied, and there is also a tendency to use
volumes as small as 1 .mu.l/min and thus smaller flow rates.
Therefore, in such applications, losses below one microliter are at
least noticeable or even unacceptable.
[0003] A current construction comprises two positive displacement
pump units arranged in series. The fist unit is the feed pump,
which aspirates the liquid at low pressure, e.g. at ambient
pressure, and delivers it to the second unit, the storage pump, at
operating pressure. The storage pump essentially operates in a
push-pull relationship with the first unit. It delivers a liquid
flow while the first unit aspirates the liquid and stores the
surplus while the first unit is expelling the working medium at the
operating pressure. This allows achieving a regular flow with low
pulsation.
[0004] Especially in high-grade pumps for this application, the
pistons are made of mechanically resistant materials, more
particularly ceramic (preferred), crystalline and/or mineral
materials, which are guided in stone bearings, i.e. ruby, sapphire,
synthetic corundum, or ceramic bearings. Tightness is ensured by
piston seals that are open towards the working volume. Thus, since
the working medium under pressure accesses the outside of the
sealing lip, the latter is pressed against the piston surface by
the working pressure, thereby providing the corresponding sealing
effect by itself. In order to ensure the required pressure
resistance and chemical inertness, the parts in contact with the
working medium are made of high-grade materials, metals, and
precious stones. Thus, the use of titanium is current practice, for
example. The pistons are driven by camshafts acting on the rear end
of the pistons in combination with resilient restoring
elements.
[0005] However, on account of the high pressures and of the
required accuracy, the compressibility of the liquids becomes
noticeable, so that a pump of this kind can be adjusted for minimum
compressibility only at a given pressure by mutually adjusting the
sequences of movements of the two pump units. An additional
difficulty is that the dead space of such pumps is relatively large
compared to the dispensing volume of approx. 10 to 50 microliters
per stroke in gradient applications, so that the dead space may
even be greater than the dispensing volume. The large dead space is
mainly a result of the minimal distance of the piston from the
bottom of the displacement chamber and of the piston seal. The
minimal distance is necessary to prevent the piston from hitting
the bottom in spite of manufacturing and mounting tolerances: such
a collision may damage the piston, the bottom, or other parts of
the pump. Regarding the piston seal, it appears that in the
mounting position where the seal is open towards the working
medium, the seal is filled with the working medium, which requires
relatively large volumes in the order of the dispensing volume.
Thus, the dead space as well as minimal leaks, which are not even
detectable visually on account of the small volumes, will impair
the dispensing quality of the pump, particularly the uniformity of
the adjusted flow rate and the absence of pulsation.
[0006] In particular, the dead space affects the gradient
capability, i.e. it determines the minimal dispensing rate at which
a working medium of changing composition can still be delivered by
the pump without being substantially mixed. A large dead space
contains correspondingly large quantities of the working medium
that also have to be exchanged to avoid mixing in gradient
operation.
[0007] Furthermore, the pumps are subject to aging, thereby
requiring maintenance. Due to the stringent requirements especially
in the assembly, this must be done by a specialist.
[0008] Suitable pumps are e.g. known from DE-A-43 08 467. The
particularity of these pumps is that they are composed of
disk-shaped functional blocks that are clamped together in a
clamping device. The fact that the junctions extend between the
blocks eliminates the need for external connecting ducts.
[0009] However, an inconvenient in this arrangement is that the
pump must be assembled extremely carefully in order to achieve the
required tightness since the tolerances add up. Therefore, inter
alia, two ruby guides must be provided in the pump blocks to
achieve a precise guidance of the pistons in the displacement
chamber: a direct contact of the piston with the wall of the
chamber must be avoided because of the resulting abrasion that may
e.g. distort the result of the HPLC and destroy the piston
seal.
[0010] In addition, it is generally necessary to dismount the
entire assembly for maintenance operations. Finally, this pump has
a considerable dead space.
[0011] It is therefore an object of the present invention to
provide a pump of this kind that reduces the influence of
construction tolerances on the dispensing quality.
[0012] Another object consists in controlling and/or reducing the
influence of the dead space.
[0013] Pumps of this kind allowing to attain at least one of the
above-mentioned objects are indicated in the device claims. Methods
for the operation of the pumps and applications thereof are the
object of additional claims.
[0014] Thus, a main aspect of the invention is to provide the
possibility of adjusting the dead space and furthermore a general
reduction thereof. One measure to this effect is a construction of
the displacement chamber and/or of the piston that allows the
adjustment of a minimum dead space or of a dead space resulting in
an optimum behavior of the pump at the desired operating pressure.
It is therefore suggested, on one hand, to make the total length of
the piston adjustable by dividing it into the proper piston and a
piston rod. The connection between the piston and the piston rod is
adjustable in length, thereby allowing an adjustment providing a
minimum distance of the piston from the bottom of the displacement
chamber. The distance may even be set to zero if in order to avoid
damages, the bottom of the chamber is formed of an insert that is
sufficiently incompressible under operating pressure but
nevertheless capable of yielding enough to prevent damages when hit
by the piston. Another approach consists in providing an opposed
piston whose front end essentially forms the chamber bottom,
thereby making the chamber bottom adjustable.
[0015] Furthermore, novel constructions of the seals between the
piston and the displacement chamber also provide a reduction of the
dead space. The classic piston seal comprises a spiral spring
enclosed in the piston seal and surrounding the sealing lip.
Particularly the interior of the spiral spring causes a large dead
space.
[0016] In a first variant, a laterally open spring element is
suggested. The aperture allows a filling body to be inserted in the
spring element such that the major part of the cavity within the
spring element is filled. In the second variant, the spring element
is essentially in the form of a band-shaped element surrounding the
sealing lip. Preferably, the latter is a spiral of a spring-elastic
material, particularly metal. The flat shape of the spring element
allows a small cross-section of the internal wall of the
displacement chamber also in the area of the seal, thereby keeping
the dead space small.
[0017] Furthermore, the reduction resp. adjusting capacity of the
dead space also counteracts the effect of manufacturing
tolerances.
[0018] Another problematic zone with regard to tolerances in
assembly consists in small misalignments or angular deviations of
the connecting elements required at the inlets and outlets of the
pump units, i.e. at the access points of the working medium. To
this effect, in the known embodiment, a connecting piece in the
form of a so-called cartridge is inserted between the connecting
element and the access. Such a cartridge may essentially have the
form of a pipe section (coupling sleeve) or e.g. comprise a check
valve ("valve cartridge"). According to another aspect of the
invention, it is suggested that the involved pairs of surfaces are
designed as a combination of a cambered (convex, spherical) and a
concave conical surface. A misalignment between the medium inlet
and the connecting element results in a slightly canted fit of the
cartridge. The mentioned design nevertheless provides a circular
contact line and a regular contact pressure. Besides, the involved
pairs of surfaces may be formed not only on the mentioned parts but
also on the corresponding part and on a sealing body (a capsule).
In this case, the cambered surface will preferably be provided on
the capsule.
[0019] The invention will be further explained by means of an
exemplary embodiment and with reference to figures, where:
[0020] FIG. 1 shows a longitudinal section through a pumping head
of the invention according to I-I in FIG. 2;
[0021] FIG. 2 shows a sectional view according to II-II in FIG.
1;
[0022] FIG. 3 shows detail III in FIG. 1: first embodiment of a
piston seal (enlarged);
[0023] FIG. 4 shows detail IV in FIG. 1: second embodiment of a
piston seal (enlarged, sectional view);
[0024] FIG. 5 shows the spring in the seal of FIG. 4 (sectional
view);
[0025] FIG. 6 shows an enlarged detail of FIG. 7: schematic
illustration of a misalignment;
[0026] FIG. 7 shows an enlarged detail of a junction between the
displacement chamber and a connection;
[0027] FIG. 8 shows a variant of a seal on a connection in a
strongly enlarged sectional view;
[0028] FIG. 9 shows the design of the sealing surface in an
enlarged partial view IX of FIG. 7;
[0029] FIG. 10 shows a variant of the sealing surface of FIG.
9;
[0030] FIG. 11 shows a sectional view of a seal for an opposed
piston;
[0031] FIG. 12 shows a partial section of a variant of the
connections;
[0032] FIG. 13 shows a longitudinal section of a connecting
assembly in the straight state.
[0033] FIGS. 1 and 2 show sectional views of head 1 of a HPLC pump
designed according to the invention. The elements that are not
represented (driving units with cam disks etc.) are realized
according to the prior art. The piston assemblies for feed pump
device 3 (feed pump) and storage pump device 4 (storage pump),
replacing the undivided pistons of the prior art, are formed of
respective pistons 7, 8 and piston rods 11, 12. The piston rods are
guided in high-grade linear guides in the enclosure of the driving
unit, more particularly in linear ball bearings (not shown).
Bearings of this kind are known per se in the art.
[0034] At the rear ends of pistons 7, 8, respective sleeves 15, 16
are fixedly fitted on hard material bars 19, 20, i.e. bars of a
mechanically resistant material (e.g. ceramic). Sleeves 15, 16 are
closed at their rear ends. In order to precisely determine the
total length of pistons 7, 8 (distance between the front ends of
hard material bars 19, 20 and rear ends 22, 23 of sleeves 15, 16)
in assembly, respective steel balls 25 (e.g. of hardened steel) are
first inserted in bores 26 and the corresponding hard material bar
19, 20 is pressed into the collar. Balls 25 provide a defined
contact in the center of the hard material bars, on one hand, and
on the other hand, an annular contact on the bottom of bores 26
whose shape is conical due to the shape of the tips of usual
drills.
[0035] Sleeves 15, 16 are seated in location holes 28 in the ends
of piston rods 11, 12. In the case of the piston 8 of storage pump
4, a spring 32 is inserted in a smaller location hole 30 in the
bottom of location hole 28, the free end of the spring resting on
the bottom 23 of sleeve 16. Each one of piston rods 11, 12 is
surrounded by a set collar 36. Each set collar 36 comprises a set
screw 38 in a thread 39, the end of the screw contacting sleeve 15,
16 through a bore 40 in piston rod 11, 12. The pistons 7, 8 are
thus capable of being locked in the respective piston rod by
fastening screw 38. Screw 38 of storage pump 4 is accessible from
the outside through an aperture 42 in the enclosure of pump head
1.
[0036] In contrast, in the feed pump, bore 31 in piston rod 11 is
internally threaded to receive a threaded stem 33 attached to
sleeve 15. A precise adjustment of the piston length is thus
possible through a rotation of threaded stem 33. Generally,
however, to prevent an undesired change in length, a locking device
is required here too, e.g. a set collar 36 with a set screw 38. In
this embodiment, the adjustment of the dead space in the assembled
state is obtained by varying the displacement chamber, for which
purpose a solution will be indicated below.
[0037] Both hard material bars 19, 20 extend into the proper
displacement chamber 47 through a conventional piston seal 44, a
stone bearing 46 (e.g. of synthetic precious stone such as ruby)
and finally through a piston seal according to the invention that
provides a reduced dead space. Chamber 47 is formed of a highly
resistant and chemically inert material, e.g. of titanium.
[0038] Outlet 112 of feed pump 3 is connected to inlet 115 of
storage pump 4 by a known flexible conduit 114 having a small
internal volume. Conduit 114 is tightly fastened to the connections
by screwed joints known per se.
[0039] The dispensing piston is shown with a first embodiment 48 of
a piston seal of the invention that is illustrated on an enlarged
scale in FIG. 3. It is essentially formed of a sealing body 50 of
essentially L-shaped cross-section, one leg, 52 of which forms a
sleeve-shaped sealing lip in which hard material bar 19 resp. 20 of
a piston 7 resp. 8 is insertable. The sealing lip is surrounded by
a spring 54 in such a manner that the spiral turns themselves wind
around the sealing lip. As appears in FIG. 1, this allows a
relatively narrow design of internal wall 56 around seal 48 as
compared to the environment of the conventional piston seal 44,
thereby providing a considerable reduction of the dead space. This
is illustrated by the following data of an embodiment of a pump
having a dispensing volume of 23 microliters: dead space of a
conventional piston seal itself: 18 microliters; dead space of the
additional space in front of the piston seal inside the
displacement chamber: 11 microliters; total dead space of a piston
seal of the conventional type: 29 microliters. The described seal
of the invention thus allows a reduction to approx. 20%, i.e.
approx. 6 microliters. The dead space is therefore reduced to a
fraction of the dispensing volume.
[0040] Displacement chamber 47 of feed pump 3 is open at the bottom
and closed by means of an opposed piston 58 whose front end forms
the (movable) bottom of the displacement chamber. Opposed piston 58
is also made of titanium. Opposed piston 58 extends through a
sealing bushing 60 retained by a clamping sleeve 62 in an enlarged
portion 64 of displacement chamber bore 57. It is also possible to
provide a screwed attachment both of sleeve 62 in enlarged portion
64 and of opposed piston 58 in sleeve 62 to allow a displacement of
the opposed piston by rotation thereof and thus a variation of the
displacement chamber volume.
[0041] FIG. 11 shows a seal 64 of the prior art that may be
inserted instead of sealing bushing 60 and results in a reduced
dead space. Since opposed piston 58 is not moved in operation and
only rarely otherwise, the requirements with regard to this seal
are substantially less stringent. Seal 64 comprises a seal body 65
with a sealing lip 66 that is pressed against opposed piston 58
(not shown). The contact pressure is initially provided by embedded
O-ring 67 and in operation by the internal pressure of the pump
acting upon O-ring 67 and on the sealing lip. Possible materials
for the seal body are pressure-resistant materials that are
chemically inert under the operating conditions, such as PTFE, in
particular. A corresponding elastomer will be selected for the
O-ring, e.g. KALREZ (DuPont). Seals of this kind are known per
se.
[0042] In the storage pump, another embodiment 70 of a piston seal
according to the invention is illustrated. An enlarged view of the
applied piston seal 70 is shown in FIG. 4 and the special spring
element in FIG. 5. Sealing element 72 of the piston seal is
C-shaped in cross-section, and so is spring element 74. A thickened
or cambered portion 75 is formed at the end of internal sealing lip
73. The internal surface 76 of spring element 74 and its curved
portion 77 are divided by multiple slots 79. Depending on the
desired rigidity, the slots also divide external surface 81, the
rigidity decreasing with the width of remaining lands 82. Curved
portion 77 describes an angle that is a little smaller than
180.degree., so that the internal surface is slightly biased
inwards. Thus, when spring element 74 is inserted in sealing
element 72, a prestress of sealing lip 73 is achieved.
[0043] According to FIG. 4, spring element 74 is arranged in
sealing element 72 with the cross-sections extending in parallel,
and an annular filling body 83 is inserted in the resulting annular
gap. The filling body consists of a material that is chemically
inert to the working medium and substantially incompressible under
working pressure. The filling body is so dimensioned that it
largely fills out the interior of the spring element, i.e. at least
half of it, preferably at least 90% and more preferably at least
99%. Basically, is should be as voluminous as possible, however
without reducing the spring action of the spring element below the
required level.
[0044] By filling out the empty volume, the dead space caused by
the seal is substantially reduced while maintaining the same
mounting dimensions as in the case of a conventional piston
seal.
[0045] The storage pump also comprises an arrangement for adjusting
the dead space that includes the adjusting device between piston 8
and piston rod 16 as well as an insert 87 in displacement chamber
89. The material of insert 87 is chosen such that a contact between
hard material bar 20 and insert 87 is possible without causing
damages. In particular, a material will be chosen that is inert to
the working medium and substantially incompressible under operating
pressure while still being slightly deformable by the mechanically
resistant material. It will be noted in this context that the
circumference of the front ends of hard material bars 19, 20 is
rounded to avoid damages of the seals and guides when they are
inserted in the displacement chambers. The material of insert 87 is
capable of a certain adaptation to this rounded edge, thereby
additionally reducing the dead space.
[0046] Displacement chambers 47, 89 are located in bores of a pump
block 91. For a correct alignment to laterally arranged access
bores 92, displacement chambers 47, 89 comprise a groove 93 in
which a pin 94 engages.
[0047] Displacement chambers 47, 89 are followed by an extension
ring 95 which is fixed in block extension 96 by a threaded ring 97.
Block extension 96 is screwed to block 91.
[0048] All parts that are exposed to the working medium are made of
materials which are inert to the working medium. In addition, if
they are also exposed to the operating pressure, they must resist
the pressure without noticeable compression or deformation. For
parts of the enclosure such as displacement chambers, cartridges,
connections, but also for metallic sealing membranes, titanium has
been found to be a particularly suitable metal. Generally, the
pressure resistance of the mechanically resistant material of the
pistons is unproblematic. As the case may be, care must be taken of
the chemical inertness, although it is generally ensured as well.
For those parts which must have a certain elasticity (insert 87,
body of the piston seals, seals, etc.), an elastomer, preferably
the synthetic material PTFE (polytetrafluorethylene) may be used,
particularly PTFE reinforced with graphite fibers, which offers an
increased wear, pressure, and temperature resistance. Particularly
for seals, PEEK (polyetherether ketone) is possible, too.
[0049] Finally it will be mentioned that the feed pump and the
storage pump may also be identical in design. Thus, in particular,
both pumps may be provided with the same inventive piston seals of
either type.
[0050] In a further preferred embodiment, instead of an opposed
piston, the feed pump may comprise a closed displacement chamber
with an insert 87, i.e. it may be designed like the described
storage pump and conversely, the storage pump may be designed like
the described feed pump. It is thereby possible to adjust the dead
space of the feed pump to nearly zero, which is optimal in almost
all operating conditions. A subsequent adjustment of the opposed
piston in the storage pump allows to minimize the pulsation, i.e.
to adjust the pump to the working pressure and to the
compressibility of the working medium.
[0051] As the storage pump operates under constant pressure and is
therefore subject to less stringent requirements, measures for
reducing resp. adjusting the dead space in its displacement chamber
may alternatively be omitted. In applications with particularly low
quality requirements, on one hand, it is even possible to use a
conventional piston seal in the storage chamber, and on the other
hand, some measures for reducing the dead space may also be omitted
in the feed pump.
[0052] The adjustment of a determined dead space at the bottom of
the displacement chamber, or in the extreme case of a dead space
reduced to nearly zero, is always effected by first moving the
respective piston to the upper dead center, i.e. by moving the
drive to the position of maximum penetration of the piston into the
displacement chamber, while the corresponding set screw is
loosened. In the embodiment provided with an insert 87, the hard
material bar of the piston now contacts insert 87. Set screw 38 is
tightened, whereby the dead space is adjusted to minimum.
[0053] If an opposed piston is provided, the dead space may
subsequently be enlarged to a desired amount by retracting the
opposed piston.
[0054] A further basic aspect with regard to the quality of a pump
of this kind is tightness. It will be noted that minimal leakage,
which is not detectable externally due to the small volumes of e.g.
substantially less than 1 microliter, may already influence the
result. In this respect, the sealing of the various connections
against the displacement chambers constitutes a problem of utmost
importance.
[0055] To this effect, it is known practice to connect the
connecting elements directly to the sealing surfaces of the
displacement chambers by means of cartridges 101, 102. As usual,
the cartridges may simply represent passages (see FIG. 7, cartridge
101), or e.g. check valves 102 as provided according to FIGS. 1 and
2 at the inlet 111 and outlet 112 of the feed pump.
[0056] However, the risk of a lateral misalignment 113 (FIG. 6) of
the displacement chamber access bores 103 with respect to the
connections fastened to the outside of block 91, resp. the access
bores thereof, is inevitable. Such a misalignment leads to a slight
canting of cartridge 101 (see FIG. 6). In the embodiments of the
prior art provided with plane or alternatively with conical sealing
surfaces of the access bores, this leads to a slightly irregular
contact pressure along the sealing line since the sealing surfaces
of the cartridge and of the access bore form a small angle between
each other. Under the existing high pressures, this results in
leaks or may even cause the seal to be pressed out in the direction
of the opening of the angle.
[0057] As shown in FIGS. 6 to 8, in order to solve this problem,
one of the sealing surfaces of a junction is cambered, more
particularly in a convex spherical shape, and the respective
corresponding surface has a concave conical shape. In such a
combination of the sealing surfaces, even if one of the sealing
surfaces is inclined, i.e. if the longitudinal axis of the channel
for the working medium extending therein is inclined with respect
to that of the mating part, a circular contact line is still
obtained, and thus also a substantially constant contact pressure.
If the two contact surfaces are made of metal, a metallic sealing
membrane is preferably interposed, preferably one of titanium
because of its contact with the working medium, or of a synthetic
material, particularly of PEEK.
[0058] In the example, the rounded sealing surfaces are provided on
the connecting elements and on the displacement chambers and the
conical ones on cartridges 102. However, the inverse arrangement is
also possible. Furthermore, it is possible to use a sealing capsule
119, e.g. of PEEK, having rounded sealing surfaces on both sides
(see FIG. 8: junction between a connection 100 and a simple
cartridge 101).
[0059] In the same manner, the described construction also avoids
leaks due to angular deviations between the parts to be joined.
[0060] According to a further preferred embodiment, in each
junction, one 120 of the two sealing surfaces, or possibly both
sealing surfaces in the case of two sealing surfaces with an
interposed membrane, particularly metallic ones, may have steps 121
formed thereon (see FIG. 9). The result is a stepped sealing action
or a plurality of line contacts, thereby further improving the
sealing effect.
[0061] Another useful solution consists in providing concentric
grooves 123 (FIG. 10).
[0062] A further preferred embodiment of the junctions for the
connection of a capillary conduit without additional functions is
shown in FIGS. 12 and 13. Conduit 114 is made of titanium and is
welded to an end piece 130. Connecting piece 100 is in the form of
a threaded collar that is displaceable on the capillary conduit.
The passage for conduit 114 through connecting piece 100 is
enlarged at its inner end 132 to leave room for the weld seam 134.
Sealing surface 136 of end piece 130 is designed as described above
so as to ensure a perfect seal also in the case of a misalignment.
In particular, the embodiment using a sealing capsule or the
embodiment using a sealing membrane (see above) may be chosen. For
the attachment of the conduit, the threaded collar is screwed into
the pump enclosure in a known manner.
[0063] The contact surfaces 138 between end piece 130 and
connecting piece 100 have complementary cambered, conical, or
similar shapes to provide a self-centering action when the
connecting piece is screwed into the pump enclosure.
[0064] However, contact surfaces 138 do not have a sealing
function. Connecting piece 100 is made of PEEK or of steel.
[0065] Compared to the first described embodiment, this solution
eliminates two sealing surfaces as well as the dead space caused by
the channel in the empty cartridge, whose diameter is relatively
large, and around the additional threaded collars screwed into
connecting pieces 100.
[0066] FIG. 13 shows a connecting conduit 114 whose ends are
provided with the above-mentioned connecting devices. Prior to the
welding of the second one of end pieces 130, the two threaded
collars 100 have to be slipped on conduit 114. The operation of
bending conduit 114 to the required shape, e.g. the shape of a U,
may take place afterwards.
[0067] While each one of the measures leads to in increased quality
of the pump, they may also serve to simplify maintenance, i.e.
particularly to reduce the skills required of the technician. Thus,
in particular, maintenance can be carried out on site by the user
without accepting losses in quality.
[0068] Further possible advantages follow from the description of
the preferred embodiment:
[0069] Gradient capability down to 30 .mu.l/min or less,
particularly due to the reduced dead space (in the practical
example: 9.45 .mu.l vs. 36 .mu.l in the prior art);
[0070] Increase of the operating pressure up to 1000 bar;
[0071] Possibility of providing cartridges 101, 102 with other or
additional functions, e.g. for monitoring the flow rate or the
operating conditions;
[0072] Safe and simplified assembly, resulting in easier
maintenance; and/or
[0073] Possible application in high-pressure gradient systems where
the mixing of the different components is effected in the
high-pressure section.
[0074] The described exemplary embodiment enables those skilled in
the art to find apparent modifications and complements without
leaving the protective scope of the invention as defined by the
claims. A number of such modifications have already been mentioned
above. In addition, it is conceivable in the case of lower
requirements to omit the adjusting capacity of the piston length or
ball 25 for the accurate positioning of the hard material bars in
sleeves 15, 16. However, such simplifications are more likely to be
applied in the storage pump because of their smaller influence on
the properties of the pump. It is also possible to use the
inventive design of the sealing surfaces only in locations under
operating pressure. Also conceivable is a pump having only one pump
unit, i.e. only a feed pump, e.g. in applications where an accurate
metering of small amounts of a flowable medium, more particularly a
liquid is the only requirement (syringe or metering pumps).
[0075] Instead of being screwed in, the connecting elements may
also be flanged to the pump body or fastened in another manner.
However, they are preferably removable for uncomplicated
maintenance and repair.
* * * * *