[0001] The present invention relates to a pump for liquids having a pumping chamber, a reciprocable
wall in the chamber to periodically alter tha volume thereof, inlet and outlet conduits
communicating with the chamber, and appropriately directed unidirectional valves (such
as check valves, duck-bill valves) controlling the flow direction in the conduits.
Such pumps are known, e.g from EP-A-286 404 and FR-A-2262711. It is sometimes necessary
to make sure that no liquid can pass between the condiuits through the chamber when
the pump is not operative. This is because the pump may have long-term, semi-permanent
connections between a liquid source or reservoir and, either a utilisation device
requiring pumped liquid, or simply an open pipe or tube for attachment to such a device.
Liquid pressure or gravity can then cause prejudicial leaking while the pump is at
rest. It is therefore required to provide a kind of leak-proofing valve, preferably
integrated with the pump and using parts of the pump. Accordingly, the invention provides
that the reciprocable wall is quiescently biased in one direction towards, and in
contact with, another member of the chamber (which is known in itself); and characterised
in that the other member is the mouth of one of the conduits where it joins the chamber,
and the contact is a substantially sealing one. The sealing action is derived from
a spring, so does not absorb power and can be effective during long unenergised periods
of the pump. Also the spring is not an extra, being already a component of the prior
art pumps. Little or no extra space is taken up by the change in geometry of the chamber
and the moving wall, e.g. diaphragm can be virtually unchanged, except that a valve
seat closure or sealing member is now involved. Also the sealed mouth of the conduit
must be provided as, or be made suitable to act as, a valve seat. So leaks are prevented
by an auxiliary mechanical, normally-closed, valve which is provided with minimum
extra parts and changes in flow geometry. An embodiment is described below with reference
to the drawings in which:
Fig. 1 shows a diametrical cross-section on a known pump;
Fig. 2 schematically demonstrates normal use of such a pump;
Fig. 3 likewise shows abnormal use leading to leaks on switch-off; and
Fig. 4 shows the inventive pump.
Referring to Fig. 1, a known pump 1 has a solenoid 2 energised by intermittent pulses,
e.g. by applying rectified ac mains to terminal 3, so that a reciprocating armature
4 rises intermittently against a bias spring 5; then the armature returns each time
towards the rest position shown, whereof a shock-absorbing, resilient extension 6
lies against an abutment 7. However, during reciprocation, the armature never reaches
the rest position on its downward stroke. The resilient extension 6 is part of a flexible
rubber diaphragm 8, which provides one wall of an annular pumping chamber 9, surrounding
the extension 6. The magnetic circuit may be two cylindrical pieces M1, M2, interposed
between the coil former 2A and the armature guide 4A; and a third piece M3 external
to the coil and forming part of the housing. The magnetic circuit and solenoid and
coil former 2A may be retained by a widened eg. snap-fitting portion 17A of the armature
guide 17B, these being integral with an upper pump chamber housing part 17. In the
pump housing there are also formed, or held, an inlet conduit 10 and an outlet conduit
11 leading to respective valve chambers 10A, 11A, in which are located the well-known,
non-return duck-beak (duck-bill) valves 12, 13, and which valve chambers communicate
at 14, 15 with pumping chamber 9. The abutment 7 of this known pump forms part of
a single, moulded body (e.g. of glass loaded nylon), which forms part of the seating
for the diaphragm, holds both valves 12, 13, forms the chamber 10A of the inlet valve
12, and forms the surrounding cylindrical wall 7B of the pumping chamber. The bottom
part 16 of pump housing conforms with the single, moulded body, such that when it
is held by fastener 18 to upper housing part 17 (which is integral with valve guide
4A and a lid part 4B), the valves, the diaphragm and the single body are all clamped
firmly in the position for proper operation. It would be advantageous if these manufacturing
assets, which give repeatability, simplicity and economy in parts, could be retained
in a sealed pump of the invention. Referring to Fig. 2, a normal use of such a pump
1 may be, as indicated by directional arrows, to have inlet conduit 10 connected to
a water source such as reservoir 19 and outlet 11 connected through a long, flexible
pipe 20 to apparatus such as a steam iron 21. For instance, the pump avoids the irritating
task of repeatedly filling a reservoir on the iron itself, typically at the front
below the handle. In the normal use, these items are located on an ironing board 22,
but sometimes (e.g. to avoid dropping the iron, or accidentally coming into contact
with it while distracted, telephoning, etc), a user, houseperson, etc., will place
the instrument on the floor 23, as shown in Fig. 3, below the level of the reservoir
19 and table or ironing board 22. Then, even with the pump de-energised or disconnected
from power, the water will flow by gravity through pipe 20 into the iron 21, or other
instrument, and overflow. If no instrument is connected, water can leak out of the
end of tubing 20. The leaking is caused by gravitational forces being sufficient to
surpass a threshold value, i.e. overcome a threshold resistance, and thus to open
the inlet valve 12, see Fig. 1. Water then passes through the valve cavity mouth 14,
the annular pumping chamber 9, out of the outlet valve 13, to conduit 11, and thence
to the ground 23. Accordingly, only the small threshold resistance to the opening
distortion of the one-way valves opposes, but is soon overcome by, gravitational effects
tending to open them. The threshold resistance can be increased, but this undesirably
increases resulting pumping force and power requirements, i.e. energy costs and heating
may become intolerable, likewise the ratings of components. Accordingly, the invention
is applied to the pump embodiment of Fig. 4, in which the same or nearly analogous
parts are unreferenced, or have the same reference numbers. Down to the arrows 24,
the pump resembles pump 1 of Fig. 1, except for a member 27, which provides abutment
for the resilient extension 6 of the armature 4. As before, extension 6 is part of
a similar rubber diaphragm 8 and may be snap mounted onto a knob-like projection 4B.
The member 27 replaces the composite part 7 of Fig. 1, and likewise provides valve
chambers 10A, 11A, pressure surfaces 28, 29 angled so as to clamp flanges of the valves
12, 13 and hold these in position in their chambers, and the cylindrical wall 27B
of the pumping chamber 9. Also it seats the bottom of the rim 8A of the diaphragm.
The lower housing 26 is shaped to allow inlet valve chamber 10A to be vertical, and
in line with the reciprocating stroke of armature 4, and to allow outlet valve chamber
11A to be about 60 degrees to the vertical, with a bend 30 from a short outlet portion
communicating with the pumping chamber (9) and parallel to the axis. Thus, the valves
and their chambers are no longer symmetrical, and the positioning of the chamber 10A
collinear with the armature stroke achieves the inventive object of sealing, with
the co-operation of spring 5 and armature projection 6. The sealing takes place with
the pump de-energised, because the mouth 27C of member 27 is formed as a valve seat,
without sharp edges or irregularities, to seat the resilient armature extension 6,
preferably provided by the diaphragm. Whenever the pump 25 is operating, armature
4 and projection 6 reciprocate towards seat 27C, but do not reach it to abut and close
it. On switch-off, however, spring 5 urges armature extension 6 into contact with
seat 27C, thus obstructing liquid passage. Therefore gravity, or liquid pressure at
the inlet conduit 10, can only urge liquid as far as the firmly obturated seat 27C,
and it does not enter the pumping chamber 9, far less exit to conduit 11. The obturated
seat could instead be the mouth, if formed suitably, of the outlet valve chamber 11A;
presently preferred is blocking the inlet conduit mouth, however, partly because no
liquid can then enter the chamber when the gravitation, or other pressures, may cause
it to. The invention is not restricted, therefore, to blocking the inlet valve chamber
10A. This conduit is preferably tapering as shown, large enough towards one end so
that the duck-bill valve 12 can be contained, but tapering at the other end so that
the valve seat can be of small diameter. Of course, the invention is not limited to
blocking passage to any specific utilisation device, such as a smoothing iron, nor
to countering only the forces of gravity. The invention is not limited to the seat
being aligned, with the armature stroke and the spring 5, but such alignment is greatly
preferred for a better sealing action. The invention thus provides a pump (25) having
a pumping chamber (9), a moving wall (8, 6) thereof being reciprocable against bias
(5), inlet and outlet valve chambers (10A, 11A) communicable with the pumping chamber
when the pump is operable, one-way valves (12, 13) in the chambers; characterised
in that one of the valve chambers presents a seating (27C) to a part (6) of the moving
wall, moved by the bias towards said seating whereby, only on non-energization of
the pump, the part is moved under the action of the bias, to obturate said valve seating;
or indeed any one of the appended claims. A normally closed valve is thus formed in
the pump housing, which valve uses many pump parts, and plays no role except when
the pump is not operated. The part (6) is preferably in line with the bias and the
armature stroke, and central to the diaphragm.
