[0001] This invention relates to an electrical pump for fluids, eg hot water or for coffee
machines, with economical outlay and power consumption.
[0002] According to a known pump, a generally cylindrical armature/piston combination which
slides axially and has a generally axial internal bore to pass fluid from an inlet
to an outlet, also has one or more radial bores between the axial bore and its exterior
inside a sliding guide for the combination.
[0003] The radial bore serves to prevent fluid build-up between the combination and its
guide. Such a build-up has a braking effect on the armature/piston combination due
to pressure and viscosity, but is relieved by the prior art radial bore. Unfortunately
the bore is expensive to machine and the machining can form a burr (a jagged irregularity
projecting from the hole) which tends to scrape and wear out at least the assembly
and its guide. In spite of consequent expense, burrs of wear, the loss of force and
power due to peripheral fluid build-up can amount to 50%, and so has typically been
dealt with in this way.
[0004] The invention aims also to minimize the peripheral fluid presence and consequent
braking effect, but without causing a burr and/or incurring the expense of radially
machining into the axial bore.
[0005] According to the invention set out in Claim 1 the armature/piston assembly and/or
its guide is shaped to facilitate peripheral fluid mobility. A second aim according
to a preference of the invention is to simplify production of the downstream part
or end of the combination which has in the past been externally tapered or reduced
in diameter by machining, which is quite expensive in time and loss of magnetic material.
The invention preferably provides an armature assembly formed by a reduced diameter
body which may be of a different, non-magnetic material or metal, crimped to the main
body of the assembly. The axial bore must be continuous but can be machined or moulded,
cast etc separately before the two pieces are crimped together. The preferred embodiments
are now detailed with reference to the drawings, in which:
Figures 1 and 2 show in diametrical section a known pump and an inventive pump;
Figures 3 and 4 show likewise an armature/piston piece, and its crimped together combination
with a narrower downstream piece; and
Figures 5, 6 and 7 show guide and armature cross sections.
[0006] Referring to Figure 1, the known pump has an inlet port 1 from which fluid is pumped
by an axially vibrating armature/piston combination 2 to an outlet port 3, through
an axial bore 4 in the entire length of combination 2, an inlet valve 5 and an outlet
valve 6 in an axial passage in the housing 7 leading to the outlet port 3.
[0007] The outlet valve 6 is merely a one-way passive or flow-responsive valve, but the
inlet valve 5 is opened by separation of the piston part, ie by the leftward movements
of armature/piston 2 in its vibrations. The leftward movements cause fluid to be transferred
from inlet port 1 past the inlet valve 5 and thence to the outlet 3. The leftward
armature movements are caused by repeated energizations of a solenoid coil 8 via a
terminal T and act against a return spring 9. The repeated energizations can result
conveniently from half-wave rectified ac, eg at 50 Hz, between the half-waves of which
the spring returns the combination rightward to close inlet valve 5. Both valves 5
and 6 are spring closed by return springs 10 and 11, spring 10 being weaker than spring
9.
[0008] An annular volume 12 is arranged to collect fluid which unavoidably flows between
the outside of the armature/piston and its guide 13, but tends to get full enough
of fluid to impede the amature vibrations. This tendency can be relieved, as known,
by one or more radial bores 14, which provide relief conduits, from volume 12 when
undesirably full of collected fluid, to the central bore 4. Such machining as aforesaid
is costly and can leave burrs or loose metal particles prejudicial to the action or
life of the pump. Another drawback, trapped fluid suffers a time delay before it can
even reach volume 12, so it is impeding the vibrations during this time delay, even
if fluid does not accumulate unduly in volume 12. The invention seeks to avoid all
these possible drawbacks.
[0009] As will also be appreciated, the wider part of the armature 2 comes to rest each
return stroke against a shock absorber ring 15. By the above very desirable avoidance
of the impending of the vibrations, there is an unfortunate tendency to cause greater
shocks. Through ring 15 an elongated narrow part 16 of the armature extends, preferably
via sealing O-rings 17 and 18, to abut and seat inlet valve 5. The state of the art
is to machine the mild steel down from the wider to this narrower diameter which takes
time, wastes material and may cause burrs or leave particles which can separate later
and block flow-ways. Moreover mild steel is heavy, causing greater shocks. More machining
away is involved to provide annular volume 12. The invention appreciates that, although
a relatively long axial bore has to be provided, the narrow end need not be magnetic
or so heavy. The magnetic circuit may comprise outside the coil outer encapsulation
19, a rectangular yoke (not shown) of two L-sectioned pieces crimped together along
their corners, a first cylindrical internal part 20 outside the thin armature guide
13, a ring 21 magnetically connecting the yoke and cylinder 20, a second cylindrical
internal part 22, and a ring 23 communicating cylinder 22 to the yoke. The L-pieces
have respective holes closely surrounding rings 21, 23.
[0010] Many alternative magnetic circuits are possible. The cylindrical magnetic gap 24
between the two cylindrical parts as well known attracts the armature adjacent to
it, ie. leftward in Fig.1 against spring 9, whenever coil 8 is energized. The material
used for the narrow part 16 of the armature therefore need not be magnetic since it
does not interact with gap 24 or other magnetic circuitry.
[0011] Referring to the inventive pump of Fig.2 wherein like numerals reference like components,
there is no external annular volume 12 but the guide 13 has eg. five internal longitudinal
ribs 25 (see also Fig.5) on which the sliding armature bears and between which any
trapped fluid can readily return (as shown by the flow line arrows 25สน) to the pumped
stream travelling rightwards through the bore as before. The ribs can be provided
without machining and at low cost in the mould of plastic guide 13, and free particles
are unlikely and not metallic. Alternatively, the wide part of the armature/piston
can have a non-circular cross-section as shown by the four longitudinal flutes of
Fig.6 or the extended polygon of Fig.7. There should be longitudinal ribs or grooves
or non-circular irregularities providing bearing surfaces, and no trapped space, but
instead, a continuous communication between all peripheral points and the main axial
pumped stream. The longitudinal irregularities can be strictly parallel to the axis,
or can be oblique or helical or otherwise to provide this longitudinal communication,
and hence lack of pressure build-up and viscosity drag, while enabling efficient piston
effect and hence pumping action. The armature/piston can be in two parts as shown
in Figs. 3 and 4, while having the inventive elongated irregularities of Figs.5-7,
although the two-part arrangement could be adopted alone. The pressure reducing irregularities
are best seen in the transverse cross-sectional views of Figs 5-7, but they are longitudinal
in nature, being grooves or ribs or corners either parallel to the axis on having
an axially directed component (eg. helical irregularities).
[0012] Referring to Fig. 3 a wide part 26 of the armature/piston has a central bore 27 and
a holding portion 28, the top of which has an annular groove 29 to surround a lip
30 which can be crimped inwards by a suitable tool (not shown). The section of bore
31 of holding part 28 serves to accommodate a non-magnetic part 32 (eg. of brass or
lighter plastics as suitable) shown in Figs 2 and 4. Part 32 has a waist 33 to accommodate
in fluid-tight manner an annulus of crimped-in material from lip 30 as can be seen
in Fig. 4. The end 34 of part 32 is shaped to serve as a valve seat for inlet valve
5, Fig. 2. The inlet end 35 of wide part 26 may be flared to promote flow and have
a circular projection to seat and hold the return spring 9. Any ribs or grooves in
the wide part of the armature cannot be seen in Fig.4, and indeed may not be present
whenever such flow-conducive shapings are applied to the guide only (as presently
preferred, eg see Fig 5) and not to the armature (embodied as by Fig 6 or Fig 7).).
Not only is the narrow part provided without necessity to machine down the wide part,
but boring only of shorter axial lengths is needed.
1. A fluid pump comprising a reciprocating armature/piston combination, through a
bore in which the pumped fluid passes, characterised by (Fig 6 or 7) a shaping of,
either the exterior of the combination or the interior of a guide for its reciprocation
(Fig 5) , whereby fluid tending to become trapped between the internal walls of the
guide (13) and the external wall of the wide part (26) of the armature/piston combination
(2) is instead returned to the pumped stream, said shaping composing cross-sectional
differential or relative irregularities between said internal and external walls.
2. A fluid pump according to Claim 1 characterised in that shock or noise caused by
lack of braking by trapped fluid is countered by a shock-absorber ring (15) and any
necessary sealing rings (17,18) acting on a transverse face (29,30) of the wide part
(26) of the piston.
3. A fluid pump according to Claim 2 wherein the reciprocating armature/piston combination
has a relatively narrow extension (32) not abutted by said rings but passing therethrough,
which seats and unseats a valve (5), wherein the extension projects axially from said
transverse face (29,30) of the armature, and is a separate bored non-magnetic piece
crimped (30, 33) or otherwise attached to a wide part (26) which is magnetic.
4. A fluid pump according to Claim 3 comprising a waist (33) in the axial extension
(32) receiving a crimped in portion (30) of said transverse face of the wide part
(26) of the combination.
5. A fluid pump according to any of Claims 1-4, wherein the longitudinal irregularities
are guide ribs (25) extending along the inside wall of the armature guide.
6. A fluid pump according to any of Claims 1-4 wherein the longitudinal irregularities
are provided by channelling, or by a hexagonal (Fig 6) or grooved (Fig 5) cross-section
of the wide part (26) of the combination.
7. A fluid pump according to any of Claims 1-6 having series inlet and outlet valves
on the downstream side of the combination, which are passive but biased towards closure
positions.