DUAL DIAPHRAGM PUMP

Abstract: A pneumatically operated reciprocating three-way valve having particular application to a double diaphragm pump is operative without a lubricating oil mist or the inefficiency resulting from air leakage between the valve piston (72) and cylinder (74). Sticking and stalling of the valve piston are prevented by deformation of the cylinder (74) under pressure to provide leakage of selected cavities within the valve. The pump also avoids the use of a deicer mist by an adjustable bleed of high pressure air to provide a two-step exhaust.

Description: Pneumatically driven pumps are well known for their utility and frequently utilize either double acting pistons or diaphragms to alternately compress and expand pump chambers to force the exit of the fluid from one chamber while inducing the entry of additional fluid into the other chamber. Since pneumatically driven pumps do not require an electric or internal combustion engine to drive the pumping chambers, such pumps are particularly useful in locations where combustible or explosive materials are present. One of the problems generally associated with pumps of this type is icing. The actual air flow patterns through the valves are both transient and highly turbulent as a conseuqence of cyclic operation of the air distribution valve to effect repeated openings and closings of valve exhaust ports. The air jets through the air valve passages are at times at very high Reynolds numbers and hence in the turbulent flow range. Associated with such highly turbulent flows are both velocity and pressure fluctuations, the mean-square pressure energy of which can approach the magnitude of the operating pressures. Whenever a gas is expanded from a higher pressure to a lower pressure, a cooling of the gas takes place and internal energy is released, the equation relating pressure (P), velocity (V) and temperature (T) of the gas before (i.e., at time 1) and after expansion (i.e., at time 2) being as follows: P₁V₁ T₁ = P₂V₂ T₂ In the typical three-way air valve used in controlling the operation of such pumps. P₁ and P₂ have time-dependent mean values and P₂ is further subject to severe tubulent fluctuations about the time-mean pressure values. When the valve is operated in environments of low ambient temperatures and high moisture content, icing conditions often develop. Known prior art pumps have attacked the problem of ice formation by incorporating an air dryer to remove moisture from the air supply system. However, air dryers are often extremely expensive and only marginally successful in climatic conditions of low temperature and high humidity. The additional drop in operational pressure through the air dryer may also be undesirable. Others, such as those disclosed in US-A-3,635,125, have provided flexible muffler plates and placed a thermal barrier between the valves and the exhaust ports. Others such as US-A-3,176,719, have sought to physically displace the exhaust ports from the pump. Still others such as US-A-2,944,528, have used oscillating reeds in the exhaust valve or cavity. Still another known approach to this icing problem is the use of chemical deicing agents such as ethyl alcohol and ethylene glycol. However, these chemical deicing agents are often marginally successful and also introduce an undesirable environmental condition in introducing ethyl alcohol and ethylene glycol vapors into the ambient air. In still other known dual diaphragm pumps such as that disclosed in US-A-4,406,596 towards the end of a stroke the two actuating air chambers are connected to reduce the pressure level of the air in the chamber to be exhausted and precharge the chamber to be actuated in the following stroke. Thus air losses can be reduced and efficiency accordingly increased. Reportedly also the danger of icing up is reduced. The problem underlying the invention is to provide a diaphragm pump which prevents icing and stalling. This problem is accomplished by claim 1. A further known diaphragm pump (US-A-3,791,768) comprises a pressure relief valve which is different from the bleeding means of the pump according to the invention as regards its task and working mode. It limits the pressure differential across the diaphragm without any reference to icing problems. In a pump according to the invention icing is reduced by the controlled bleeding of high pressure air from an internal high pressure chamber to an internal low pressure chamber. The high pressure air furnishes internal energy and thus velocity to the exhaust air and thus mechanically displaces ice as it forms. This air bypass provides a stepdown release of the motive gas, i.e., it reduces the pressure drop across the valve by increasing the pressure in the low pressure chamber and increases the pressure drop across the outlet aperture to increase exit velocity as indicated above. Pneumatically operable pumps typically use a source of compressed air which is distributed by a reciprocating three-way valve to drive the pistons or diaphragm in the pumping chambers. Known valves such as described as prior art (US-A-3,071,118) generally require lubrication with an oil mist because the metal piston travels in a metal cylinder. The clearance required between such metal parts prevents a tight seal, allowing a high amount of air leakage, making it inefficient. However, the use of an oil mist is undesirable in many applications because of the contamination of the atmosphere and material such as foodstuffs being pumped. Stalling is prevented in the present invention by the use of a pilot valve cylinder resiliently deformable under pressure so that air can be bled from a selected one of the potentially opposing chambers of the air distribution valve to thereby ensure operation. In addition, the bleeding of air from a selected valve chamber may be used to slow the speed of reciprocating movement of the air distribution valve piston during the terminal part of a movement thereof. This reduces the impact of the piston on the end walls of the cylinder and thus reduces the potential deformation and sticking of the piston to the end wall. These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art from the claims, and from the following detailed description when read in conjunction with the appended drawings. The drawings Figure 1 is a side view in elevation of the pump housing of one embodiment of the pump of the present invention; Figure 2 is a section taken through lines 2-2 of the pump housing of Figure 1; Figure 3 is a section taken through lines 3-3 of the pump housing of Figure 1; Figures 4, 5 and 6 are pictorial views in vertical cross-section illustrating the operation of the pump, and showing the position of the valve piston and the pilot valve piston; Figure 7 is an exploded pictorial view of one embodiment of the air distribution valve assembly of the present invention; Figure 8 is an end view of the assembled valve of Figure 7; and Figures 9(A)-9(C) are pictorial views in cross-section schematically illustrating the operation of the valve assembly of Figures 7 and 8. The detailed description With reference to the pump housing illustrated in Figures 1, 2 and 3, where like numbers have been used for like elements to facilitate an understanding of the present invention, the housing 10 has an air inlet orifice or aperture in which a plug 12 may be threadably inserted. As shown in Figure 2, the inlet passageway for the pump housing leads to the high pressure chamber 14 defined by an internal partition 16 more easily seen in Figure 3. The high pressure chamber 14 communicates via a passageway 18 to the horizontal bore 20 of Figure 1 in which the valve assembly 22 is mounted as shown in Figure 2. As shown more clearly in Figures 1 and 3, the portion of the block 24 external of the partition 16, together with the side plates of the pressure compartments 26 and 28 illustrated in Figures 4-6, but omitted for clarity in Figures 1-3, define a low pressure chamber 29 which communicates with the bore 20 by an aperture 30 as shown in Figure 1. With continued reference to Figures 1 and 3, a passageway 32 is provided from the low pressure chamber 29 to the high pressure chamber 14. A needle valve 36 in a valve seat 34 may be manually adjustable externally of the housing by rotating the end 38 of the needle valve 36 in the threads 40 to regulate the amount of air bled from the high pressure chamber 14 to the low pressure chamber 29. With reference to Figures 4-6, the pump housing 10 may be mounted between left and right lateral chambers divided respectively by a flexible diaphragm 50 into a driving chamber 28 and the pumping chamber 52, and by diaphragm 46 into a chamber 26 and a pumping chamber 48. Entrance of the material being pumped into the pumping chambers 48 and 52 respectively may be provided by suitable conventional one-way valves 54 and 56. Similarly, egress from the pumnping chambers 48 and 52 may be respectively provided by any suitable conventional one-way valves 58 and 60. As shown in Figures 4-6, the diaphragms 46 and 50 may be connected in a suitable conventional manner by the piston 44 slidably mounted within the central bore 42 of the housing shown in Figure 1. In operation and with reference to Figures 1-6, the application of compressed air or other motive fluid from the high pressure chamber 14 through the air distribution valve 62 to the chamber 26 forces the diaphragm 46 to the extreme right as shown in Figure 4 to pump fluid therefrom through the valves 58. At the same time, the motive fluid within the chamber 28 is vented through the orifice 30 of Figure 1 and the air distribution valve 62 to the low pressure chamber 29 and thence to the atmosphere. This venting allows the chamber 28 to collapse as the chamber 26 is filled and to create a suction which draws fluid through the valve 56 into the pumping chamber 52. At the end of the pumping stroke, and as shown in Figure 4, the pilot piston 64 of the valve assembly 62 is mechanically forced to the right by the movement of the diaphragm 50. As will be later explained in greater detail, the movement of the piston 64 to the right effects the operation of the air distribution valve to cause air to be applied from the high pressure chamber 14 of Figure 5 to fill the chamber 28 and to vent the chamber 26. As shown in Figure 5, the piston 64 of the pilot valve remains in this extreme right position as the diaphragm piston 44 completes its movement to the left, at which time the diaphragm 46 mechanically moves the piston 64 to the left as shown in Figure 6. Movement of the piston 64 of the pilot valve to the left as shown in Figure 6 effects movement of the piston 72 of the air distribution valve 62 to the right to effect a further cycle of the pump as will be subsequently explained. Typical operating air pressure is about 70 to 100 psi (4.8-7 Bar) from the compressor and is desirably about 80-85 psi (5.5-5.9 Bar) within the high pressure chamber 14. The high pressure chamber 14 serves to reduce tubulence and may house a filter. The pressure of the motive gas in the low pressure chamber 29 is generally about 20 psi. The adjustment of the needle valve 36 is largely a function of temperature and the quality of the motive gas, and generally comprises less than about eighteen percent of the volume of the low pressure chamber 29. With reference to Figures 7 and 8, the preferred embodiment of the air distribution valve 62 comprises a cylinder 70 and is fitted with end caps 71 and 73. The air distribution valve piston 72 is slidably mounted for reciprocating movement within the cylinder 70 between the end caps 71 and 73, with the projections 75 and 77 providing a seal. In this way, the movement of the piston 72 within the valve cylinder 70 is essentially friction-less and the use of seals avoided. Similarly, the movement of the pilot piston 64 within the sleeve 74 is essentially frictionless and the use of seals likewise avoided. The valve piston 72 internally receives a cylindrical sleeve 74 which together with the end caps 71 and 73 and the cylinder 70 define the housing within which the piston 72 reciprocates. In turn, the sleeve 74 receives the pilot valve piston 64. The cylinder 70 and the pilot piston 64 may be made of a suitable ferrous alloy. The piston 72 and end caps 71 and 73 are desirably made of a relatively light weight plastic material such as polytetrafluorethylene (PTFE) or other low friction coefficient material. The sleeve 74 may also be manufactured of a low friction coefficient material. As shown more clearly in Figure 9, the end caps 71 and 73 serve to maintain the sleeve 74 longitudinally immobile as the pilot piston 64 reciprocates therein. The operation of the air distribution valve 64 of Figures 7 and 8 may be more readily understood by reference to Figure 9. With reference to Figure 9(A), air from the high pressure chamber 14 of the Figures 1, 2 and 4-6 may be applied through the passageway 18 of Figure 2 into a longitudinally centered annular cavity and thence through the aperture 80 of Figures 2 and 7 into the internal annular chamber 82 of Figure 9(A). This high pressure air may then flow out of the one of the apertures 84 through a passageway 85 in Figure 1 into the driving chamber 26 of Figure 4 because of the position of the piston 72 to the left. At the same time, the apertures 86 in the cylinder 70 provide an exit route for the air from the driving chamber 28 of Figure 4 into the annular cavity 88 of Figure 9(A) to the low pressure chamber 29 of Figures 1 and 3, the thence through the passageway 85 of Figure 1 to the atmosphere. With continued reference to Figure 9(A), the piston 72 is maintained in the left hand position by the high pressure air within the cavity 82 applying pressure as shown by the arrows 90. The force represented by the arrows 90 is opposed by the pressure differential between the cavities 82 and 88 as illustrated by the arrows 92. However, the pressure represented by the arrows 90 is controlling because of the difference in surface area. As the chamber 26 fills with high pressure air as shown in Figure 5, the fluid within the pumping chamber 48 is discharged through the valve 58 and additional fluid enters the chamber 52 through the valve 56. As the piston 44 completes its reciprocating movement to the right, the diaphragm 46 pushes the piston 64 of the pilot valve from the position illustrated in Figures 4 and 5 to the position illustrated in Figures 6, 9(B) and 9(C). Movement of the pilot valve into the position shown in Figure 9(B) removes the force represented in Figure 9(A) by the arrows 90, but does not change the force represented by the arrows 92 on the projection 77. Thus, the piston 72 is moved to the right as shown in Figure 9(C). In the piston position illustrated in Figure 9(C), the high pressure air enters through the aperture 80 into the cavity 82 and exits through the apertures 86 to the chamber 28. The pressure of the air within the cavity 82 acts on the projection 77, as shown by the arrows 96, to maintain the piston 72 in the right hand position against the force exerted by the arrows 98 on the projection 75 in response to the pressure differential between the cavities 82 and 100. In the piston position shown in Figure 9(C), the air from the chamber 26 passes through the aperture 84 in the cylinder 70 into the low pressure chamber 29 and thence to the atmosphere. The sleeve 72 is made of a material deformable under a pressure of about sixty percent of the operating pressure of the pump, e.g., about 55 to 60 psi. This pressure deformation serves to effect leakage between the piston 72 and the sleeve 74 when the sleeve 74 is not supported by the pilot piston 64, e.g., as shown by the arrow 102 in Figure 9(B). This leak is effective to prevent stalling by reducing the likelihood of equal and opposite pressures in adjacent cavities within the valve. In addition, the leak decreases the pressure differential tending to move the piston 72 and thus slows the reciprocating movement of the piston slightly, reducing impact with the end caps and the possibility of deformation and/or sticking of the plastic surfaces.

Claims: A gas operated dual diaphragm pump comprising an inlet aperture for fluid communication with a supply of compressed gas, a high pressure chamber (14), a gas distribution valve (22), two diaphragm controlled actuating chambers (26,28), a low pressure chamber (29), an outlet aperture for fluid communication to the atmosphere, means (34,36) for bleeding gas from said high pressure chamber (14) to said low pressure chamber (29) to thereby reduce the pressure differential between said high pressure chamber (14) and said low pressure chamber (29) and increase the pressure differential between said low pressure chamber (29) and said outlet aperture thereby reducing the tendency of the pump to ice, wherein said control valve comprises a stationary housing (70), a reciprocating valve piston (72) and a reciprocating pilot valve piston (64), characterized in that a portion (74) of said housing is elastically deformable under pressure to leak and thereby prevent stalling as a result of equal and opposite pressures and to slow the movement of said valve piston. A gas operated dual diaphragm pump according to claim 1, characterized in that a distribution valve (22;62) in selective fluid communication with said high pressure chamber (14), said low pressure chamber (29) and said actuating chambers (26,28) is provided and that said means (36) for bleeding gas from said high pressure chamber (14) to said low pressure chamber (29) do not pass through said gas distribution valve (22). The pump according to claim 1 or 2, characterized in that said gas bleeding means (36) is manually adjustable. The pump of claim 1 or 2, characterized in that two flexible diaphragm driven pumping chambers (48,52) with valve-controlled fluid inlet and outlet ports (54,56,58,60) are provided and in that said control valve (22;62) admits compressed gas from said high pressure chamber to one of the actuating chambers to alternately drive one of said pumping chambers and to vent the actuating chamber of the other said pumping chambers through said low pressure chamber. The pump of one of the preceding claims, characterized in that said housing includes a metallic outer cylinder (70), a plastic inner cylinder (74) and two plastic end caps (71,73), that said valve piston (72) is plastic and that said pilot piston (64) is metallic. The pump according to one of the preceding claims, characterized in that said deformation occurs at about sixty percent of the operating pressure. The pump of one of the preceding claims, characterized in that said piston is responsive to the position of said pilot piston.

Inventors: BAZAN, ALBERTO, MURPHY, DONALD M.
Applicants: BAZAN, ALBERTO, MURPHY, DONALD M.
Application year: 1985
Main classification: F04B43
IPC codes: F01L25, F04B43