GB2233716A - Diaphragm pump - Google Patents

Abstract

A diaphragm pump for pumping liquids has inlet and outlet valves (12, 14), a diaphragm (20) controlled by a reciprocatable plunger (26) and a chamber (24) filled with actuating liquid for transmitting movements of the plunger to the diaphragm. A valve (32) controls a connection between the chamber (24) and a reservoir (34). A valve opening mechanism comprising a cam (54) is timed to open the valve (32) during the return stroke of the plunger (26) whereby release of gas from the actuating liquid is inhibited and any gas which is released can escape during the period when the valve is open. <IMAGE>

Description

PUMP AND METHOD OF OPERATING SAME This invention relates to pumps and methods of operating same. More specifically, the invention relates to diaphragm pumps for pumping liquids.

Previously proposed diaphragm pumps in which the diaphragm is actuated by a reciprocatable plunger through a pumping liquid have been provided with valve means communicating with the control side of the diaphragm to permit fluid flow at certain times, thereby to regulate the action of the pump. The arrangement of the valve means in these prior proposals has been found to be subject to significant shortcomings. These shortcomings include the following.

Firstly, there is the factor relating to the operating characteristics of diaphragm pumps concerning their use in pumping metered quantities of liquids during use. For example, a typical use of such a pump might well be to dispense liquids such as corrosion inhibitors or pesticides or plating solutions in accordance with predetermined quantitative requirements of manufacturing processes, or user processes. This requirement for volumetric accuracy has led designers of previous proposals to include relatively complex and costly valve arrangements in an attempt to maintain and improve accuracy. For example, one prior proposal includes a compensation valve intended to maintain the correct volume of pumping liquid behind the diaphragm. In addition, this prior proposal includes a relief valve incorporating an integral air bleed permitting manual release of air from the system.

The complexity and cost of these prior proposals is one significant shortcoming, an aspect of this being the need to provide means for timing the operation of these valves. A further factor concerns the effect on accuracy of such a pump of the presence of any gas at all on the control side of the diaphragm. Obviously, the compressibility of such gas will seriously affect the volumetric accuracy of the pump.

An object of the present invention is to provide a diaphragm pump offering improvements in relation to one or more of the matters discussed herein, or generally.

According to the invention there is provided a diaphragm pump as defined in the accompanying claims.

In a preferred embodiment a diaphragm pump for pumping liquids comprises inlet and outlet valves to provide directional control over a liquid to be pumped. A duct interconnects the inlet and outlet valves. A pumping chamber is connected to or forms part of the duct interconnecting the valves. A diaphragm in the pumping chamber divides same into a pumping side chamber portion and a control side chamber portion. A plunger is reciprocatable within a plunger chamber to control the diaphragm. The plunger causes by its forward and return movements, the diaphragm to reciprocate. The diaphragm thereby effects a pumping action through the inlet and outlet valves. The diaphragm has a forward pressure movement and a return suction movement corresponding respectively, with the forward and return movements of the plunger.The plunger chamber communicates at its head side with the control side chamber portion of the pumping chamber, and a pumping liquid is provided therebetween to transmit a pumping action to the diaphragm from the plunger. Valve means communicates with the control side chamber portion to permit fluid flow through the valve means at certain times, thereby to regulate the action of the pump.

In the preferred embodiment, the valve means communicates with a reservoir of the pumping liquid and has valve opening means operative to open the valve means at least partially during at least a portion of at least some of the return strokes of the plunger. In this way, the control side chamber portion is at least partially opened to the reservoir at such times. Preferably the valve means is open throughout the entire return stroke of the plunger on every stroke thereof. The valve means is closed on the forward strokes of the plunger. In short, the valve means is operative to connect the control side of the diaphragm to tank during the return stroke of the diaphragm.

Further features of the preferred embodiment include the provision of a driven valve opening mechanism for the valve means, operating in timed relationship with the plunger. The valve means comprises a spring-closed ball valve and the drive means therefor comprises a rotary cam.

The valve means is located above the diaphragm in the normal operating attitude of the pump, whereby any gas separating from the pumping liquid tends to rise to the valve means. Multiple passages from the upper portion of the control side chamber portion and extending towards said valve means permit such gas to rise to the valve means.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which Figs 1 and 2 show front and side elevation views, both partially sectioned, through a diaphragm pump forming an embodiment of the invention; Fig 3 shows a section through a second embodiment having a modified valve and camshaft assembly to replace that shown in Fig 1; Figs 4 and 5 show front and side elevation views of the pump of Fig 3, corresponding to Figs 1 and 2 of the first embodiment; and Figs 6 and 7 show elevation and sectional views (not on the same scale) of a third embodiment of valve and associated valve seat for the diaphragm pump.

As shown in the drawings a diaphragm pump 10 for pumping liquids comprises inlet and outlet valves 12, 14, respectively, to provide directional control over liquid to be pumped. A duct 16 interconnects valves 12 and 14. As can be seen duct 16 comprises drillings at right angles connecting the valves to a pumping chamber 18, which itself forms part of the duct interconnecting the valves.

A diaphragm 20 in the pumping chamber 18 divides that chamber into a pumping side chamber portion 22 and a control side chamber portion 24.

A plunger 26 is reciprocatable within a plunger chamber 28 to control the diaphragm 20 by its forward and return movements. The plunger causes the diaphragm to reciprocate and thereby effect a pumping action.

The plunger chamber 28 communicates at its head side 30 with the control side chamber portion 24 of chamber 18.

A pumping liquid, for example any suitable known pumping oil, is provided to fill the control side chamber portion 24 and the head side 30 of the plunger chamber 28, together with the associated passages (to be described below) communicating therewith. The pumping liquid transmits a pumping action to the diaphragm from the plunger.

Valve means 32 communicates with the control side chamber portion 24 to permit fluid flow through the valve means at certain times during each stroke of the plunger 26, thereby to regulate the action of pump 10. The other side of valve means 32 communicates with a reservoir 34 of the pumping liquid and has valve opening means 36 which is operative to open the valve means at least partially during at least a portion of the return stroke of plunger 26. In this way, the control side of diaphragm 20 is connected to tank (ie to reservoir 34) during the return stroke of plunger 26, and thus during the return stroke of the diaphragm also, and in this way significant advantages accrue, as more fully described below.

Having now described the principal features of pump 10, we now consider its construction in a little more detail.

Inlet and outlet valves 12 and 14 may be of conventional construction, typically comprising spring loaded ball valves (not shown).

Duct 16 is formed by drillings in the end cover 38 of the pump. The end cover defines chamber 18 together with the pump housing or main body portion 40. The cover and housing are assembled by bolts 42 on a common pitch circle and serve to clamp diaphragm 20 in its working position.

The diaphragm may be of conventional construction, for example comprising ptfe (polytetrafluoroethylene). The diaphragm is of a resilient construction and, in its forward pressure stroke, flexes from its Fig 2 position towards the end of chamber 18 as defined by cover 38. In its return stroke, it returns under its own resilience to the equilibrium position as shown in Fig 2.

Plunger 26 is driven by a conventional reciprocating drive mechanism of any suitable kind.

Valve means 32 communicates with the control side chamber portion 24 through a generally vertical drilling 44 (the pump being shown in Figs 1 and 2 in its normal upright operating attitude) , from which a series of downwardly inclined drillings 46, likewise formed in housing 40 communicate with chamber portion 24. These drillings permit any gas released from the pumping liquid to pass upwards and accumulate around valve means 32.

Looking now at the structure of valve means 32 in more detail, as shown in Fig 1, it will be seen that it comprises a valve ball 48 loaded by a spring 50 against a seat 52 and actuated by a cam 54 rotated by a cam shaft 56 driven in timed relationship to plunger 26 by a drive 58 and journalled on a support 60.

Cam 54 opens ball valve 32 during the return stroke of plunger 26.

Oil reservoir 34 communicates with the other side of the ball valve through a short chamber 62 in which cam 54 is sealed by O-rings 64. The reservoir contains a suitable volume of oil to maintain a full complement of liquid in the system at all times.

Reservoir 34 is in the form of a generally cylindrical casting 66 having a cap 68 and secured by bolts 70 acting through a clamping plate 72 to mount the assembly on housing 40.

In use, valve 32 opens during each return stroke of the plunger 26 and of diaphragm 20. As a result, the return movement of the diaphragm is purely under its own resilience. Accordingly, the pressure in the control side chamber portion 24 is not significantly, if at all, reduced below atmospheric pressure during the return stroke of the plunger, and accordingly the tendency for disolved gas to form bubbles is greatly reduced. Any gas which does form can freely escape to the region of valve means 32 and be discharged to the reservoir when the valve opens.

Interestingly, the above embodiment provides in a simple and effective way a means for inhibiting the formation of gas bubbles in the control side chamber portion of a diaphragm pump, thereby increasing the volumetric accuracy of the pump. The same valve means which effects this action also serves to bleed off any gas which does collect. The arrangement for opening the valve is simple and relatively inexpensive.

In the embodiment of Figs 3 to 5, the general construction and arrangement and operation is as described above, and therefore parts corresponding to those of the preceding embodiment are given the same reference numerals.

In this embodiment, modifications have been made to the replenishing valve assembly to make it easier to manufacture and operate. Broadly speaking, the ball valve has been replaced by a plunger valve assembly, and the method of sealing the camshaft has been improved.

Turning now to the detailed structure shown in Fig 3, it will be seen that cam 54 acts on the head 74 of a valve member or plunger 76 having a generally mushroom-shaped valve member 77 which sits on a rubber valve seat 78. The stem 80 of plunger 76 is adjustable relative to the head 74 by means of screw threaded engagement of a shank 82 projecting from stem 80 into a corresponding threaded recess in head 74. This arrangemenbt enables adjustment of the timing of the valve opening with respect to the cam itself, thereby enabling fine adjustment of valve performance to achieve maximum efficiency.

In this embodiment, the fluid reservoir 34 is constituted by a generally horizontally extending chamber 84 in which camshaft 56 rotates.

It will be seen that valve head 74 has a radial drilling 86 providing for through-flow of fluid from the reservoir past the valve 76 when the latter opens. It will also be noted that a spring 88 normally holds the valve in its closed condition.

Turning now to the embodiment of Figs 6 and 7, it will be seen that these drawings show a modified valve and seat arrangement. Fig 7 is drawn on a larger scale than Fig 6.

In Fig 6, valve member 90 is direct replacement for the plunger 76 of Fig 3 and is provided with its own seat 92 mounted on the lower portion of chamber 84. Valve member 90 has a stem 92 from which a threaded shank 94 projects for screw threaded engagement with a head corresponding to head 74.

The head 96 of valve member 90 has a generally diamond-shaped profile having a frusto-conical surface 98 for seating engagement with the complementary surface 100 on valve seat 92.

In operation, the modified profile of valve head 96, and its reduced volume provide improved operating characteristics, while the screw threaded adjustment facility still enables valve timing to be optimised.

Claims (13)

1 A diaphragm pump for pumping liquids comprising : a) inlet and outlet valves to provide directional control over liquid to be pumped; b) a duct interconnecting said inlet and outlet valves; c) a pumping chamber connected to or forming part of said duct; d) a diaphragm in said pumping chamber and dividing the chamber into a pumping side chamber portion and a control side chamber portion; e) a plunger reciprocatable within a plunger chamber to control said diaphragm and cause by the foward and return movements of said plunger, said diaphragm to reciprocate and thereby effect a pumping action through said inlet and outlet valves by forward pressure and return suction movements of the diaphragm in said pumping chamber;; f) said plunger chamber communicating at its head side with said control side chamber portion, and pumping liquid being provided therebetween to transmit a pumping action to said diaphragm from said plunger; and g) valve means communicating with said control side chamber portion to permit fluid flow therethrough at certain times thereby to regulate the action of said pump; characterised in that h) said valve means also communicates with a reservoir of said pumping liquid and has valve opening means operative to open said valve means during the return strokes of said plunger, thereby at least partially to open said control side chamber portion to said reservoir at such times, said valve means being closed on the forward stroke of said plunger.

2 A diaphragm pump characterised by valve means operative to connect the control side of the diaphragm to tank during the return stroke of the diaphragm.

3 A pump according to claim 1 or claim 2 characterised by a driven valve opening mechanism for said valve means operating in timed relationship with said plunger.

4 A pump according to claim 3 characterised in that said valve means comprises a spring-closed valve member and the drive means therefor comprises a rotary cam.

5 A pump according to claim 4 characterised in that means is provided for adjusting the timing of opening of the valve member with respect to the cam.

6 A pump according to claim 5 characterised in that said means for adjusting the timing comprises screw-threaded adjustment means enabling position-adjustment of said valve member with respect to the portion thereof which contacts said cam.

7 A pump according to any one of the preceding claims characterised in that said valve means is located above said diaphragm in the normal operating attitude of the pump, whereby any gas separating from said pumping liquid tends to rise to said valve means.

8 A pump according to claim 7 characterised by multiple passages from the upper portion of said control side chamber portion to said valve means to permit said gas to rise to said valve means.

9 A diaphragm pump substantially as described herein with reference to the accompanying drawings.

10 A method of operating a diaphragm pump according to claim 2 characterised by the step of connecting the control side of the diaphragm to tank during the return stroke of the diaphragm.

11 A method according to claim 10 characterised by the step of allowing gas separating from the pumping liquid to collect around said valve means and to allow same to escape to tank during opening of said valve means.

12 A method according to claim 10 or claim 11 characterised by the step of adjusting the timing of opening of said valve means, with respect to the operation of the pump.

13 A method of operating a diaphragm pump substantially as described herein with reference to the accompanying drawings.