A PULSATION DAMPER
The present invention relates to a pulsation damper. In particular, it relates to a pulsation damper for damping a fluid flow from a pulsatile pump. The invention also relates to an assembly of a pulsation damper and a pulsatile pump.
A pulsatile pump is a pump which produces an output flow which periodically varies. In certain applications, such as beverage dispensing, in vitro diagnostics, and water cooling recirculation it is desirable for the flow to be as smooth as possible as this can improve pump efficiency and dose accuracy, as well as reducing noise and vibrations in a system.
Pulsation dampers are known in the art. In general terms, these comprise a biased pressure sensitive element which is positioned in the fluid flow path. High pressure pulses resiliently deflect the pressure sensitive element thereby absorbing some of the energy from the flow during a high pressure pulse which is then returned to the flow as the biased member is returned by the biasing force.
US 2009/0101222 discloses a piston element as the pressure sensitive element which is biased by a deformable bellows. This is a relatively complex arrangement and it is designed for relatively high flow rates of >100Ipm.
The present invention is aimed at providing a simplified damper which is most suitable for use at lower flow rates.
A recent example of such a damper is the KNF FP 70 produced by KNF. This is a two-stage damper which has a first stage upstream of the pump and a second stage downstream of the pump. The second stage is provided with a damping element which appears to be a large sponge like element which provides the biasing force to a diaphragm. The damper is connected to the top of the pump and significantly increases the footprint of the overall assembly.
According to the present invention, there is provided a pulsation damper according to claim 1.
The present invention provides a damper which receives pulsatile liquid flow from the pump and moves the diaphragm by the pressure differential between the liquid flow on one side of the diaphragm and atmospheric pressure on the opposite side of the diaphragm.
This is a very simple structure. In the KNF FP70 damper, the outlet from the pump leads to the part of the damper in which the diaphragm is moved by a large damping element. In the present invention, the diaphragm is movable by the pressure difference between the liquid flow and the atmosphere. This simplifies the design as a necessity for a damping element is removed. The damper is designed so that the diaphragm is movable only by the pressure difference between the liquid flow and the atmosphere. However, it is possible to implement this idea in which some of the movement of the diaphragm is caused by a smaller scale damping element even though this is not necessary for the operation of the diaphragm. Preferably at least 70%, more preferably at least 80% and most preferably at least 90% of the peak return force on the diaphragm in provided by the pressure differential.
The housing is preferably formed of two parts which are fixed together with the diaphragm retained between the two parts to seal the flow chamber. The two parts may be bolted together but are preferably joined using ultrasonic welding.
More than one flow chamber may be provided in the damper in order to provide a smoother damping operation. However, this is not deemed necessary, and it is preferred that the housing defines a single flow chamber.
The fact that the pulsation damper can operate without damping elements means that, when the damper is subjected to abnormally high fluid pressures, all of this pressure acts on the diaphragm itself. This can potentially unduly stretch the diaphragm and cause it to burst. This can be addressed by providing a thicker diaphragm. However, other operational considerations may prefer a relatively thin diaphragm.
To protect and support the diaphragm, the housing preferably covers the opposite side of the diaphragm and has at least one opening so that the opposite side is open to the atmosphere.
Preferably, the maximum gap between the opposite side of the diaphragm in an unstressed state and the facing housing is less than 3mm and preferably less than 2mm. If subjected to abnormally high pressures, the diaphragm will be pushed against the facing housing. As this is relatively close, the diaphragm will quickly reach a position in which pressure is transmitted into the housing thereby limiting the pressure differential on the diaphragm and preventing it from being overstretched.
In order to improve the flexibility of the diaphragm, it is preferably relatively thin. In particular, the thickness of the diaphragm away from its periphery is less than 1mm.
Preferably there is a tubular element connecting the opposite side of the diaphragm to atmosphere. In the event of a leak through the diaphragm, the tubular element provides a port to allow an operator to attach a pipe in order to salvage the leaking liquid, or divert it to a drain.
The diaphragm may be preformed with a non-planar configuration. However, preferably, the diaphragm is a flat disc in its unstressed state. The diaphragm may have any suitable shape, but it is preferably circular.
The present invention extends to an assembly comprising a pulsation damper according to the first aspect of the invention and a pulsatile pump, wherein the outlet of the pulsatile pump is connected to the inlet of the pulsation damper. The pulsation damper therefore operates on the outlet from the pulsatile pump in order to smooth its flow.
The pulsation damper may be from the pump connected by suitable pipework. This allows a conventional pump to be in an unmodified state and allows freedom for the user to conveniently locate the damper at some point downstream of the pump.
Alternatively, the damper may be mounted on the pump housing. In this case, the damper is preferably mounted to a side wall of the housing. This is particularly suited to a rotary diaphragm pump.
These pumps are often used in relatively confined locations. Therefore, preferably, at least 70% of the area of the damper is accommodated within the horizontal projection of the pump housing (excluding the inlet/outlet ducts). This means that there is little or no lateral projection of the damper beyond the pump housing which will allow the pump with the damper attached to be used in many locations where the unmodified pump is currently used without having to move existing components, or at least minimising the reorganisation required.
The maximum thickness of the damper is preferably less than 30% of the maximum thickness of the pump housing. Again, this helps with compactness of the assembly as the thickness of the pump housing with the damper attached is not significantly greater than the pump housing itself.
The outlet of the pump may be connected to the inlet of the pulsation damper via external piping. This allows an existing pump to be used with relatively little modification. However, the outlet of the pulsatile pump is preferably connected to the liquid inlet of the pulsation damper by connecting ducts in the pump and damper housings. This effectively integrates the connection between the two into their respective housings thereby providing a more compact design.
Examples of pulsation dampers and assemblies of a pulsation damper and pump will now be described with reference to the accompanying drawing, in which: Fig. 1 is a cross-sectional view through a first pulsation damper; Fig. 2 is an exploded perspective view of the first pulsation damper; Fig. 3 is a cutaway perspective view of the first pulsation damper Fig. 4 is a perspective view of the first pulsation damper; Fig. 5 is a view similar to Fig. 1 of a second pulsation damper; Fig. 6 is a view similar to Fig 3 showing the second pulsation damper; Fig. 7 is a perspective view of a first assembly of a pulsation damper and pump; Fig. 8 is an exploded perspective view of Fig. 7; Fig. 9 is an exploded perspective view of the first assembly on the opposite side to Fig. 8; Fig. 10 is a plan view of the first assembly with parts of the pulsation damper removed; Fig. 11 is a cutaway perspective view of the assembly shown in Fig. 7; Fig. 12 is a view similar to Fig. 7 of a second example of an assembly; Fig. 13 is an exploded perspective view similar to Fig. 9 of the second example; and Fig 14 is a view similar to Fig 8 of the second example of an assembly including a connection tube Figures 1 to 4 show a first example of a pulsation damper. This is designed to be fitted to a pipe downstream of a pump which produces a pulsatile flow. This has been specifically designed for a rotary diaphragm pump but can be used for any pump which produces a pulsatile flow as it typical of positive displacement pumps.
The pulsatile damper is intended to have a simple structure and to be adapted to low volume/high frequency pump which typically operates at a frequency of 20-70 Hz and produce flow rates of 0.5Ipm to 5.5Ipm. Such pumps are typically used in applications such as beverage dispensing, in vitro diagnostics, and water cooling recirculation.
The pulsatile damper in this example comprises only three components namely a lower housing 1, upper housing 2 and diaphragm 3. The components have a generally circular configuration. The diaphragm 3 has an outer rim 4 which is retained in a groove 5 between the lower 1 and upper 2 housings. The lower 1 and upper 2 housings have a complementary rib/groove configuration 6 allowing the two housing parts to be correctly located. These are then fixed together, for example by ultrasonic welding in order to form the finished assembly shown in Fig. 1, 3 and 4. In the finished configuration, the diaphragm 3 is held and sealed with its rim 4 in the groove 5. Any means of fixing the lower 1 and upper 2 housings together may be employed, such as an adhesive or bolted connection.
The diaphragm 3 divides the housing into lower chamber 7 and upper chamber 8. Lower chamber 7 has a circular dish-like configuration, an inlet 9 to receive liquid from a pump outlet and an outlet 10 on the opposite side of the lower chamber 7 which is connected to downstream equipment. The upper chamber 8 is provided with a number of vent holes 11 such that the upper chamber 8 is open to atmosphere. A vent duct 12 is provided surrounding the vent holes 11 to allow the connection of an auxiliary pipe in the event of the leakage through/around the diaphragm 3. As is apparent from Fig. 1, there is a relatively small clearance between the upper face of the diaphragm 3 and the upper housing 2. This limits the potential upward travel of the diaphragm 3 preventing it from being unduly stretched in the event of abnormally high liquid pressure.
The damper receives pulsatile liquid flow from a pump via the inlet 9 into the lower chamber 7. The high pressure pulses in this flow cause a pressure differential between the pressure in the lower chamber 7 and the atmospheric pressure in the upper chamber 8 which causes upward deflection of the diaphragm 3. As the peak pressure passes, the resilience of the diaphragm in combination with the lower pressure differential caused by the lower pressure in the lower chamber 7 causes the diaphragm 3 to move downwardly adding energy into the liquid flow at a time when the incoming flow is at relatively low pressure. This has the effect of smoothing the pulsatile flow from the pump such that the flow through outlet 10 is a more constant flow than the incoming flow.
As will be appreciated from the description, smoothing of the flow can be achieved with a very simple damper which requires no external power and does not require additional components such as springs, bellows or sponges in order to provide a resilient biasing force.
Figs. 5 and 6 show a second example of a damper. This is constructed and operates in the manner previously described, but the housing 1 is larger and has a larger diameter inlet 9 and outlet 10. This is intended to be connected to a pump with a higher flow rate. The size of the inlet 9 and outlet 10 can be matched to the pump outlet capacity-y. Upper housing 2 can be the same in all cases thereby reducing part inventory. The diaphragm 3 can also be the same in all cases. However, the thickness of the diaphragm material can be adapted so that it is optimized for the required flow rate.
While Figs. 1 to 6 show examples of pulsatile dampers which are intended to be connected to a pipe downstream of a pump, Figs. 7 to 14 depict examples of assemblies in which the pulsatile damper is mounted on the pump housing.
An example of such an assembly will now be described with reference to Figs. 7 to 11.
This example shows a pump housing 20 which is an adapted version of the pump housing that is currently used on our rotary diaphragm pump. Such a pump is known, for example, from EP 0819853 or WO 2019/016518. This has a pump chamber 23 which incorporates a rotary diaphragm (not shown) driven by a motor (not shown), but which is mounted to the back of the pump housing 20 shown in Figs. 7 and 8. The standard pump outlet has been blocked as described below. A damper 24 is fitted to the front face of the pump housing 20 in place of a conventional end plate. This is described in greater detail below.
The pump housing comprises an inlet duct 21 which leads to the pump chamber 23 as in the above pumps. Duct 25 shown in Fig. 8 was conceived for a different purpose and fulfils no function in the present example and does not connect with the inlet duct 21. Cap 22 is placed over what would be the outlet in a conventional pump so that this has effectively been plugged. Instead, internal outlet duct 26 is provided to lead from the pump chamber 23 to the damper 24.
The illustrated pump housing 20 is based on an existing pump housing. The pump could be configured to have a new pump housing in which duct 25 and cap 22 are eliminated and the pump chamber 23 is connected to the damper 24 via the internal outlet ducts 26.
The damper 24 is generally the same in construction as the damper described in relation to Figs.1 to 6. In particular, this comprises a lower housing 31, upper housing 32 and diaphragm 33. The lower 31 and upper 32 housings are ultrasonically welded to sandwich the diaphragm 33 and to retain a diaphragm rim 34 as shown in Fig. 11 and as described previously. The diaphragm 33 forms a lower chamber 37 and upper chamber 38 in the damper 24 which operate as described previously. In particular, the upper chamber 38 has a vent hole 41 to maintain the upper chamber at atmospheric pressure. The lower chamber 37 has an inlet 39 in communication with the internal outlet duct 26 such that the outlet flow from the pump connects to the damper 24 at the inlet 39. The diaphragm 33 operates in the manner described in relation to Figs. 1 and 6 to smooth the flow at outlet 40 in the lower chamber 39.
The lower housing 31 is attached to the pump housing 20 via a bolted connection through bolt holes 42.
As apparent from Figs. 7 to 11, the shape of the damper 24 has been made to fit, as closely as possible, with the side profile of the pump housing 20. This is not an exact match as the top of the damper 24 is wider than the corresponding part of the housing 20 in order to allow space for the internal outlet duct 26 to communicate with the inlet 39. The intention is that the addition of the damper 24 to the pump housing 20 would not unduly increase the dimensions of the pump. As will be appreciated from the drawings, the height and maximum width of the assembly remain unchanged such that there is a high possibility that the pump with the damper 24 attached can be used in situations where a pump is currently used without an additional damper. Although the damper 24 is wider than the pump housing 20 at the top, this is also a region of the pump where the inlet 21 and cap 22 are present so, again, the overall width is not unduly increased in this area.
As set out above, the current design is based on an existing pump housing. If a bespoke pump housing is used, the dimensions of the pump housing and damper could be even more closely matched. The preference is that, excluding ducts 21 and 40, at least 70% of the area of the damper is accommodated within a horizontal projection of the pump housing 20.
In addition, efforts have been made to minimize the thickness of the damper 24 to again maximise the possibility that the pump with the damper attached can be fitted in place of an existing pump without a damper with little or no modification of the surrounding components. To this end, the vent duct 12 of the previous example has been removed and the area of the diaphragm 33 has been maximised in the given area in order to provide optimal damping in the available damper thickness. As a result, the thickness of the damper will add no more than 30% to the thickness of the pump housing 20.
A second example of an example is shown in Figs. 12 to 14. This is similar in most respects to the first assembly and the features will not be described here. Common features are designated with the same reference numerals.
The only difference between the examples is the manner in which the liquid is communicated between the pump housing 20 and the damper 24. The internal outlet duct 26 is no longer present and liquid leaves the pump chamber 23 through a conventional outlet duct 43. A second damper duct 44 is provided in damper 24 leading into the lower chamber 37 in addition to the flow outlet 40 previously described.
An external pipe 45 is connected between the outlet duct 43 and the second damper duct 44 to convey liquid from the pump chamber 23 into the damper 24. The damper operates as previously described and the fluid is emitted at outlet 40. In fact, the damper is capable of operating in the opposite sense in that it is possible to connect the outlet duct 43 to the duct 40 which then becomes the damper inlet and the duct 44 then operates as the outlet. It is possible to set the assembly up in this way if space does not allow a connection between the outlet duct 43 and the duct 44.