Note: Descriptions are shown in the official language in which they were submitted.
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DIAPHI.tAGM PUMP SYSTEM
Technical F`ield
This invention relates to a pumping system incorporating a diaphragm pump,
particularly but not exclusively for supplying liquid paint to a paint
spraying
system.
Background Art
Diaphragm pumps are well known and generally comprise a pumping
chamber bounded in part by a moveable diaphragm, the diaphragm being
moveable by the application of fluid under pressure to reduce the volume of
the pumping chamber and so expel fluid, usually liquid, from the pumping
chamber. Generally diaphragm pumps are constructed as double-acting
pumps in that there are two pumping chambers each having an associated
diaphragm, the two diaphragms being physically interconnected so that when
one is moving to reduce the size of its pumping chamber to expel fluid from
the pumping chamber the opposite diaphragm is moving in a direction to
increase the volume of the pumping chamber and so draw fluid from a fluid
supply into the pumping chamber. It is to be understood however that in its
simplest aspect the present invention could be applied to a single acting
(single diaphragm) pump although in practice it is much more likely to be
applied with double-acting diaphragm pumps and so throughout the
remainder of this application reference will be made to double-acting pumps
rather than single acting pumps.
Conventionally the fluid being pumped by a diaphragm pump is a liquid, and
also, conventionally, the pressurised fluid applied to the diaphragms to cause
them to perform their pumping strokes is compressed air. Usually diaphragm
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pumps exhibit a 1:1 pressure ratio in that air at 1 bar pressure is applied to
the pump to drive the pump, producing a liquid pressure in the output line of
the pump which is also 1 bar. It is known to provide diaphragm pumps with
an increased pressure ratio in that, for example, a 1 bar air pressure driving
the pump produces a 3 bar output pressure in the liquid output line of the
pump. However, although such diaphragm pumps are significantly larger
and more expensive to produce than are pumps which have a 1:1 ratio, their
use in systems in accordance with the present invention is not excluded. For
convenience hereinafter in this specification it is assumed that the pump has
a
1:1 ratio.
In the paint spraying industry it is conventional to provide a paint spray
shop
with an air pressure supply rated nominally at 5 bar. In practice the air
pressure is unlikely to be less than 5 bar, but may be as high as 6 bar.
Additionally, it is recognised that in many applications it would be desirable
to supply liquid, for example paint from the diaphragm pump to a paint
spraying system at a nominal minimum pressure of 10 bar, and the
present invention seeks to provide a pumping system incorporating a
diaphragm pump in which the delivery pressue can be increased in a
simple and convenient manner, it being understood that the invention
has a broader application than simply to achieve a nominal 10 bar
paint pressure in a paint spraying system supplied with air at
nominally 5 bar.
Disclosure of the Invention
In accordance with the present invention there is provided a pumping system
comprising a
diaphragm pump and in association therewith a pressure intensifier receiving
pressurized
drive fluid from a supply, characterised in that the intensifier is driven
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by said drive fluid to boost the pressure of the drive fluid beyond its
supply pressure and suppling the drive fluid, at said increased
pressure, to said diaphragm pump, to generate pumping strokes of the
pump producing a pump output pressure in excess of the drive fluid
supply pressure.
Conveniently said pressure intensifier is at least a two times intensifier
(preferably a 2.5 times intensifier) and conveniently the pump has a 1:1 input
to output pressure ratio whereby the pressure in the output line of the pump
is
two times (preferably 2.5 times) the supply pressure of the drive fluid to the
pressure intensifier.
Desirably the pressure intensifier is incorporated into the diaphragm pump.
Conveniently the diaphragm pump is a double-acting diaphragm pump and
the pressure intensifier is incorporated in a spool valve controlling the
supply
of drive fluid to the diaphragms of the double-acting diaphragm pump.
Preferably the diaphragm pump has a 1:1 input to output pressure ratio.
Brief Description of the Drawings
One example of the invention will now be described with reference to the
accompanying drawings wherein:
Figure 1 is a diagrammatic cross-sectional view of a double-acting diaphragm
pump;
Figures 2 and 3 are diagrammatic representations of part of the pump of
Figure 1 showing how the pump operates; and
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Figures 4 and 5 are diagrammatic cross-sectional views of altemative
constructions of pressure intensifier for use in combination with the
diaphragm pump of Figures 1, 2 and 3.
Preferred Mode of Carrying Out the Invention
Referring to the drawings, Figures 1, 2 and 3 illustrate a known form of
diaphragm pump in which a generally cylindrical central metal body 11 has
an axial through bore 12 and is fitted, at its opposite ends respectively,
with
first and second end plates 13, 14. The face of the body 11 presented to the
end plate 13 is concave, and the face of the end plate 13 presented towards
the body 11 is also concave. The concavities of the end plate 13 and body 11
define an internal chamber which is divided into a drive chamber 15 and a
pumping chamber 16 by a flexible metal diaphragm 17 having its periphery
trapped between peripheral regions of the end plate 13 and the body 11. The
arrangement at the opposite axial end of the body 11 is similar in that an
internal chamber is divided into a drive chamber 15a and a pumping chamber
16a by means of a diaphragm 17a. A link rod 18 is slidably received in the
bore 12 of the body and is connected at its opposite axial ends respectively
to
the diaphragms 17, 17a. At each end the rod 18 passes through the
respective diaphragm and diaphragm control washers 19, 21 of different
diameter are clamped against opposite faces of the diaphragm by a nut 22
engaged on a screw threaded end region of the rod 18. The diaphragm pump
illustrated in Figure 1 is designed to be driven by compressed air, and to
pump a liquid paint. The references to drive air, and pumped liquid will be
retained throughout the remainder of this application, but it is to be
understood that there may be applications in which fluids other than liquid
paint are pumped, and fluids other than compressed air are used to power the
pump.
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Each end plate 13, 14 includes a liquid inlet passage 23 which communicates
with its respective pumping chamber 16, 16a through a non-return valve 24
conveniently in the form of a ball check valve. ' Similarly, each end plate
13,
14 includes a liquid outlet passage 25 communicating with the respective
chamber 16, 16a through a non-return valve 26 also conveniently in the form
of a ball check valve. The liquid inlet passage of the end plate 14 has an
open union 27 whereby the inlet passage can be connected to a supply of
liquid to be pumped in use. The inlet passage of the end plate 14, upstream
of the respective non-return valve, is coupled to the inlet passage 23 of the
end plate 13 upstream of the non-return valve 24 by a transverse passage 28
extending axially within the body 11.
The liquid outlet passage 25 of the end plate 23 has an open union 29 for
connection to the arrangement to be supplied with pumped liquid, for
example a paint spraying system. The union 29 is downstream of the non-
return valve 26 of the end plate 13 and a transverse passage 31 parallel to
the
passage 28, extends within the body 11 axially to interconnect the liquid
outlet passage of the end plate 14, downstream of its non-return valve, with
the passage 25 of the end plate 13 downstream of the non-return valve 26.
Thus liquid enters the double-acting diaphragm pump through the union 27 to
be pumped either from the chamber 16, or the chamber 16a, and irrespective
of which chamber is performing a pumping stroke, the pumped liquid issues
from the pump by way of the union 29.
Intermediate its ends the rod 18 forms part of a spool valve 32 controlling
the
admission of compressed air to the drive chambers 15, 15a of the pump.
The spool valve 32 forms part of a change-over valve arrangement of the
pump and operates in combination with a change-over valve 33 the housing
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of which forms part of, or is secured to, the body 11. The change-over valve
33 has a first operative position (as shown in Figure 2) to which it is urged
by the application of compressed air to one end of the valve, and a second
operative position (as shown in Figure 3) to which it is urged by a return
spring 34 of the valve. A compressed air inlet port 35 of the spool valve 32
is supplied with compressed air from a standardised mains supply (indicated
at "B" in Figures 2 and 3) associated with the liquid pumping system. For
the purposes of this example it can be assumed that the pressure at the
standardised supply line B is 5 bar. An air pressure inlet port 36 of the
valve
33 is supplied with compressed air from the standard mains supply through
the intermediary of a pressure intensifier 37 (Figure 4). The pressure
intensifier 37 is a 2.5 times intensifier, and so the pressure in a supply
line
"A" from the intensifier 37 to the inlet port 36 is 12.5 bar.
Figure 2 illustrates the double-acting diaphragm pump at the right-hand end
of its travel, in which the diaphragm 17a has moved towards the end plate 14
so that the chamber 16a has undergone a pumping stroke. As this point in
the travel of the rod 18 relative to the body 11 is reached the spool valve 32
places the port 35 in communication with an outlet port 38 coupled to the
pressure sensing port of the valve 33. Mains supply air pressure applied to
the valve 33 from the port 38 of the body 11 drives the valve 33 against the
spring 34 to a position in which the intensified supply "A" is connected
through a line 39 to the chamber 15 of the pump and at the same time the
chamber 15a is connected through a line 41 and the valve 33 to atmosphere
so that pressure in the chamber 15a can be exhausted. Thus compressed air
at 12.5 bar is supplied through the valve 33 to the chamber 15 driving the
piston 17 to the left carrying with it the rod 18 and the piston 17a. Liquid
within the chamber 16 is expelled by this movement of the diaphragm 17 and
flows from the chamber 16 through the non-return valve 26 and the pressure
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supply port 29 of the pump. The non-return valve 24 on the inlet side of the
chamber 16 remains firmly closed and thus the left-hand end of the pump (as
drawn in Figure 1) performs a pumping stroke. Simultaneously the chamber
16a at the right hand end of the pump is undergoing reduced pressure as the
volume of the chamber 16a is increased and so the non-return valve at the
outlet side of the chamber 16a remains firmly closed, but the non-return
valve at the inlet side of the chamber 16a opens to permit fresh liquid to be
drawn into the chamber 16a from the liquid supply port 27.
As the diaphragm 17 achieves its maximum displacement to the left, that is to
say at the end of the pumping stroke of the chamber 16, the spool valve 32,
moving with the rod 18, achieves a position in which the pressure sensing
port of the valve 33 is connected to an exhaust port 44 of the body 11 and the
position of the change-over valve 33 switches, under the influence of the
spring 34, to place the line 39 in communication with atmosphere through the
valve 33 and to place the line 41 in communication with the intensified air
pressure at "A". Thus the chamber 15a is now supplied with pressure and so
the diaphragm 17a performs a pumping stroke while the diaphragm 17 is
retracted, increasing the volume of the chamber 16, and allowing liquid to be
drawn from the inlet union 27 through the passage 28 and the valve 24 into
the chamber 16. The liquid pumped from the chamber 16a by movement of
the diaphragm 17a flows through the non-return valve at the outlet of the
chamber 16a and through the passage 31 to the outlet union 29 of the pump.
The pump continues to reciprocate in the above manner under the control of
the spool valve 32 and change-over valve 33 as long as there is compressed
air at "A" and "B". As the pump is a 1:1 pump and the air pressure applied
to the diaphragms 17, 17a is 12.5 bar, then liquid is pumped from the union
29 nominally (ignoring usual operating losses) at 12.5 bar.
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The 2.5 times pressure intensifier 37 illustrated in Figure 4 is of known,
commercially available form, and will be connected between the standard
mains air pressure supply of the system and the port 36 of the change-over
valve 33. It is anticipated however that a pressure intensifier fulfilling the
same function as the intensifier 37 can be mechanically incorporated into the
change-over system consisting of the spool valve 32 and the change-over
valve 33 thereby minimising the component count of the system, and
ensuring that the pump incorporates the pressure intensifier, and so can
simply be coupled to an existing compressed air and liquid supply
arrangement.
The intensifier shown in Figure 4 utilizes pistons of different diameter
appropriately dimensioned to effect pressure intensification at 2.5:1. It is
to
be understood that while pressure intensification of about 2:1 is desired for
the above described paint spraying system, other applications may require
other pressure intensification ratios. The skilled man will recognise that
other ratios can be achieved using intensifiers based upon the Figure 4 design
with their relative dimensions adjusted according to the required ratio.
Figure 5 shows an alternative intensifier design arranged using pistons of
equal diameter to achieve a 2:1 pressure intensification ratio, which could be
substituted for the Figure 4 design in an appropriate application. The
construction and operation of the intensifi,ers of Figures 4 and 5 will be
well
understood by the skilled man.
Although the pump described above has a 1:1 pressure ratio between the
input air and the output liquid it is to be understood that the invention can
utilize pumps having other input to output ratios if desired .
