Abstract:
A hydraulically-controlled diaphragm pump having a pump head in which a first deformable diaphragm defines a pump chamber, a pump body that co-operates with the first diaphragm to define a hydraulic working chamber, and a piston mounted to move back and forth in the pump body so as to form a controlled movable wall of the working chamber. The movable wall also includes at least one second diaphragm secured to the piston head and to the body of the pump, and providing sealing for the working chamber.

Description:
[0001]    The present invention relates to a hydraulically-controlled diaphragm pump, and more particularly to a diaphragm pump having high suction capacity. 
       BACKGROUND OF THE INVENTION 
       [0002]    Presently-known diaphragm pumps that are mass-produced generally have a suction capacity of the order of a water column of 4 meters (m) (and up to a water column of 7 m in special designs). This capacity can be increased by careful manufacture beyond the standards of mass production, resulting in special devices that differ from conventional pumps, in particular in terms of price. Such “special” pumps are of conventional architecture, with a compensation valve for compensating leaks of hydraulic oil (transmission oil leaks between the diaphragm and a piston that is mechanically driven back and forth), a rated safety valve for allowing hydraulic oil to escape in the event of excess pressure, and a device for de-gassing and purging air in order to evacuate, usually continuously, the air or gas that is present in the circuit firstly when the pump is put into operation and that comes secondly from gas that is dissolved in the oil itself and that returns to the gaseous state as a result of variations in the pressure of the medium that contains the gas in solution. The increase in the suction capacity of such “special” pumps results from the care applied to the fabrication and to the assembly of each of the parts making up the moving equipment of the pump for the purpose of optimizing clearances and fitting between the various components. 
         [0003]    There exists a need for pumps having high suction capacity (of the order of 9 m of water column) that are capable of being mass-produced, and thus with fabrication and assembly constraints that come within the ranges of tolerance that are normal for mass production in this field, in order to remain within market prices. 
       OBJECT OF THE INVENTION 
       [0004]    The invention constitutes a response to this need in that it provides a diaphragm pump of architecture that is modified in order to limit or even eliminate certain elements for which fabrication tolerances need to be very tight in order to achieve the required suction performance. 
         [0005]    The invention thus provides a hydraulically-controlled diaphragm pump comprising: 
         [0006]    a pump head in which a first deformable diaphragm defines a pump chamber; 
         [0007]    a pump body that co-operates with the first diaphragm to define a hydraulic working chamber; and 
         [0008]    a piston mounted to move back and forth in the pump body so as to form a controlled movable wall of the working chamber. 
         [0009]    The controlled movable wall also includes at least one second diaphragm secured to the piston head and to the body of the pump, and providing sealing for the working chamber. 
         [0010]    This second sealing diaphragm of the movable wall serves to eliminate leaks of oil from the working chamber along the piston where it co-operates in sliding with the body, and to do so regardless of the sealing gaskets that are implemented. In preferred manner, the second diaphragm that is used is of the same type as the mechanically actuated diaphragm described in document FR 2 697 589. Eliminating these leaks thus reduces the topping-up requirements of the working chamber, and thus the volume of compensation fluid that is needed for such topping up. 
         [0011]    In order to improve this sealing, a third diaphragm is arranged between the piston and the pump body in order to co-operate with the second diaphragm secured to the piston head so as to form within the pump body a closed chamber that is filled with oil and in which the piston and the body co-operate in sliding. Thus, the second diaphragm at the front is suitable for accommodating the delivery pressure of the pump, while the third diaphragm at the rear is capable of accommodating a high suction value corresponding to a high suction capacity. 
         [0012]    The safety valve, for protecting the pump from excess pressure on delivery, is a member that also puts a limit on the suction capacity of a pump. When triggered, it purges the working chamber of a certain amount of oil, which requires an oil top-up valve to be put into place. The safety valve and the top-up valve of the pump are particularly important when the cylinder capacity of the pump is large, as are the potential leaks and the uncontrolled ingress of fluid into the working chamber when it is under negative pressure. In the pump of the invention, the piston comprises two telescopic portions that are maintained in an extended position by a spring that is rated at a value corresponding to a safety setting. The safety valve is then omitted, thereby avoiding the drawback that stems from its existence, given the suction capacity. 
         [0013]    Furthermore, in the pump of the invention, the working chamber is connected to a sealed reserve capacity for topping up and de-gassing the working chamber by means of pipework comprising two mutually parallel channels, a de-gassing, first channel being fitted with a check valve in series with a constriction of section, with a flow direction that is towards the reserve capacity, and a topping up, second channel being fitted with a rated check valve through which the flow direction is towards the working chamber. This reserve capacity may be very small in size, since the topping-up requirements have been reduced. This small size makes it possible without drawback for this capacity to contain a high pressure, namely the delivery pressure of the pump, which pressure is easily isolated from the working chamber by a check valve when the working chamber is under negative suction pressure. This capacity may receive the gas contained in the circuit and the oil of the working chamber, which gas then accumulates above the reserve oil. In order to do this, the reserve capacity is situated above the working chamber when the pump is in operation and the de-gassing check valve is a heavy body. 
         [0014]    Finally, and advantageously, the topping-up channel is provided in the body of the de-gassing check valve, while the reserve capacity is made in the form of an assembly that is fitted on the pump body, said assembly including a transparent plug for monitoring the level of oil in the capacity. 
         [0015]    Other characteristics and advantages of the invention appear from the description below of an embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Reference is made to the accompanying drawings, in which: 
           [0017]      FIG. 1  is a fragmentary section view of a pump in accordance with the invention; 
           [0018]      FIG. 2  is an axial section view showing a detail of the pump of the invention; 
           [0019]      FIG. 3  is a functional diagram of the components of  FIG. 2 ; and 
           [0020]      FIG. 4  is a like axial section view showing a variant embodiment of the topping-up/de-gassing valve. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    In  FIG. 1 , there can be seen a pump head  1  that forms a stationary wall in a pump chamber  2  into which there open out suction ducts  3  and delivery ducts  4 . In conventional manner, the ducts are fitted with valve boxes (not shown) through which the fluid is sucked in order to enter into the pump chamber and is delivered under pressure on going away from the chamber. 
         [0022]    The other wall of the pump chamber is formed by a first deformable diaphragm  5 , itself known, clamped in leaktight manner at its periphery between the head  1  and the body  6  of the pump. The face  5   a  of the first diaphragm  5  faces towards the pump chamber  2 , while the opposite or rear face  5   b  is exposed to the pressure of the fluid that exists in a hydraulic working chamber  7 . The hydraulic chamber  7  is arranged in the pump body with fluid-passing channels  7   a  that enable fluid to reach the rear face  5   b  of the first diaphragm  5 . The hydraulic chamber receives the head of a piston  8  that is driven with reciprocating rectilinear motion by means of a conventional mechanical transmission that acts on the piston remote from its head. 
         [0023]    The head of the piston is constituted in this example by a front plate  8   a  assembled to a rear plate  8   b  by screw-fastening, with an intermediate spacer  8   c  clamped between them. The piston head is guided in sliding by a ring  6   a  secured to the body  6 , surrounding the spacer  8   c . A second diaphragm  9  of annular shape, and more precisely of a shape similar to that described in document FR 2 697 589 (which relates to a mechanically-actuated diaphragm pump), has an inner peripheral portion  60  that is substantially plane and that is clamped in leaktight manner between the front plate  8   a  and the spacer  8   c  of the piston head, and an outer peripheral portion  61  is that is substantially plane and that is clamped in leaktight manner between the ring  6   a  and the body  6 . The second diaphragm  9  includes an intermediate portion  62  between its outer peripheral portion  61  and its inner peripheral portion  60 , the intermediate portion  62  being concave with its concave side facing towards the hydraulic working chamber  7 . 
         [0024]    In the same manner, a third diaphragm  10 , similar to the second diaphragm  9 , has an inner peripheral portion  63  that is substantially plane and that is clamped in leaktight manner between the spacer  8   c  and the rear plate  8   b  of the piston head  8 , and an outer peripheral portion  64  that is substantially plane and that is clamped in leaktight manner between the ring  6   a  and the body  6 . The third diaphragm  10  includes an intermediate portion  65  between its outer peripheral portion  64  and its inner peripheral portion  63 , the intermediate portion  65  being concave, with its concave side facing towards the rear plate  8   b.    
         [0025]    As a result, the intermediate portion of the second diaphragm  9  and the intermediate portion of the third diaphragm  10  have their concave sides facing in opposite directions, the concave sides of the concave portions facing towards the outside of the closed chamber  11 . 
         [0026]    Thus, between the second and third diaphragms  9  and  10 , the spacer  8 , and the ring  6   a , there exists a sealed chamber  11  that is filled with oil by means of a duct  12  that is closed by a plug  13 . The fluid in this chamber provides hydraulic coupling between the second diaphragm  9  and the third diaphragm  10 , thereby enabling the third diaphragm  10  to transmit its own ability to draw a vacuum to the second diaphragm  9 , with the second diaphragm  9  having a design that enables it to accommodate the delivery pressure. The two diaphragms as coupled together in this way constitute the moving wall of the chamber  7 . Since sealing of the working chamber  7  in register with the piston  8  is completely leaktight as a result of the second and third diaphragms  9  and  10 , there is no need to provide close tolerances between the two parts that move relative to each other. The volume of the chamber  11  is very small, in particular because of the shapes of the second and third diaphragms  9  and  10 , thereby making it possible to avoid any air being trapped in the chamber  11  during filling. 
         [0027]    Opposite from its head, the piston  8  includes a rod  8   d  that is slidably mounted in the rear plate  8   b  of the head, having a shouldered end  14  capable of bearing against a shoulder  15  of the inner bore in the plate  8   b  that receives the rod  8   d . The other end of the rod  8   d  carries a nut  16  that serves to adjust the compression of a spring  17  having the effect of pressing the shouldered end  14  of the rod  8   d  against the shoulder  15  of the plate  8   b . It can thus be understood that the piston  8  behaves like an undeformable piece of moving equipment so long as the delivery pressure does not exceed the rating of the spring  17 . Otherwise, the piston head  8  is blocked by the pressure that exists in the working chamber  7 , and thus also in the pump chamber  2 , and continuing the delivery cycle gives rise to the rod  8   d  being pushed into the piston head. The rating of the spring  17  is thus set at a value that corresponds to a safety setting representative of the maximum delivery pressure that the pump or the pump installation can withstand without damage. Safety is thus ensured without making use of a discharge valve for the working chamber, and thus without any need to top it up with oil, thereby eliminating any sealing imperfections that such a valve would necessarily present, and eliminating the associated topping up system. 
         [0028]    A final provision of the invention is shown in the detail view of  FIG. 2 . The members shown in this figure are installed at the outer opening of a channel  20  that comes from the working chamber  7  (see  FIG. 1 ) and that passes through the pump body  6 . A tubular endpiece  21  is fitted by screw-fastening in leaktight manner to the end of the channel  20 . The tubular jacket formed by this endpiece is subdivided into two sections. A first section  22  carries a bottom seat  23  through which the fluid from the channel  20  flows, and it defines a cylindrical bore  24  in which a valve member  26  is mounted with calibrated clearance  25 . A second section  27  above the valve member  26  defines a reserve capacity  28  for fluid and for accumulating gas. This capacity is closed in leaktight manner by a plug  29  that is transparent in this example. 
         [0029]    The valve member  26  is a heavy body that under the effect of gravity tends to rest on the seat  23 . In operation, the pump is in a position such that the channel  20  stems from the top portion of the working chamber  7  and is vertical. The valve member  26  is itself fitted with a through channel  30  going from the channel  20  to the capacity  28 , which channel passes through a seat  31  and includes a valve member  32  that is normally urged against the seat  31  by a return spring  33  of adjustable force. The valve member  32  leaves its seat  31  only when the difference between the pressures that exist respectively in the capacity  28  and in the channel  20  is greater than the rating of the spring  33 . 
         [0030]      FIG. 3  is the functional diagram of the elements shown in  FIG. 2 , and it uses the same references. Thus, when the pump is in operation, the pressure in the channel  20  varies between the pump delivery pressure and the pump suction pressure. 
         [0031]    During the initial strokes of the piston  8 , when the pump is put into operation, after the circuit of the working chamber  7  has been filled, a fraction of the working fluid that is to be found in the capacity  28  becomes trapped in said capacity, and the pressure that exists therein becomes established at the value of the delivery pressure. Thus, during suction strokes of the piston  8 , during which de-gassing occurs as a result of the pressure drop to which it is subjected during suction, in particular of any gas dissolved in the oil, the capacity  28  is isolated from the working chamber  7  by the valve member  26 . When the pump is put into operation, this gas together with the gas contained in the working fluid circuit accumulates in the top of the channel  20 . Given the inertia in the movement of the valve member  26 , the pressure that exists in the capacity  28  is in fact always a little less than the delivery pressure, and on each stroke of the pump the valve member  26  rises to allow at least some of the gas that has accumulated under its bottom face to pass into the clearance  25 . This gas forms a pocket  34  ( FIG. 3 ) that is situated above the bath of oil in the capacity. 
         [0032]    When there is a lack of oil in the hydraulic chamber  7 , the pressure that exists in said chamber is such that the force holding the valve member  32  against its seat  31  (typically equal to a value suitable for withstanding the value of the delivery pressure plus the value of the suction) is exceeded and the valve opens, thereby enabling the working chamber  7  to be topped up with additional fluid contained in the capacity  28  under the pocket of gas  34 . This ensures continuous compensation for leaks that, even though small as a result of the way the pump is constructed, necessarily exist as in any moving mechanical system. The initial filling of the working fluid circuit enables this excess fluid needed for compensation to be built up. The consumption of working oil as a result of leaks can be seen through the transparent plug  29 . The level of the bath in the capacity  28  can be monitored therethrough (e.g. the end of the rod of the valve member  32  can be seen to emerge in the surface of said bath). 
         [0033]      FIG. 4  shows a variant of the embodiment described with reference to  FIGS. 2 and 3 . This variant embodiment enables the rating of the de-gassing and topping up valve to be preadjusted independently of the operating conditions of the pump, and in particular it enables the maximum delivery pressure to be preadjusted to a value that is directly associated with the desired degree of suction. 
         [0034]    A tubular endpiece  40  is fitted in leaktight manner by being screwed into the pump body  6 , at the outlet of the channel  20 . This endpiece defines an internal chamber  40   a  that communicates with the channel  20  via a seat  41  formed at its base and facing towards the channel  20 . A valve member  42  is urged against the seat by a spring  43 . The valve member  42  is guided in sealing sliding in a tubular jacket  44  that is fitted in sealed manner by screw-fastening onto the top of the endpiece  40 . The valve member  42  has an internal channel  45  that also communicates with the channel  20  via a seat  46  against which a valve ball  47  is urged under the effect of its own weight or with the help of a very weak return spring. The ball co-operates with the channel  45  to define a de-gassing passage  48 . The channel  45  opens out into the chamber  40   a  of the endpiece. In its upper portion, the valve member  42  possesses a sealed capacity  49  that communicates with the chamber  40   a . This sealed capacity is closed by a transparent top plug  50 . It should be observed that the spring  43  is mounted in an inside space  44   a  of the jacket  44  for guiding the valve member  42 , said space being closed by a plug  51  that is likewise transparent, for protecting this space that remains at atmospheric pressure. 
         [0035]    During the initial strokes of the piston  8 , after the circuit of the working chamber  7  has been boosted, when the pump is put into operation, a fraction of the working fluid that is to be found in the chamber  40   a  and in the capacity  49  becomes trapped therein, and the pressure which exists in that fluid becomes established at the value of the delivery pressure. Thus, during the suction strokes of the piston  8 , during which de-gassing takes place in particular of any gas that is dissolved in the oil as a result of the pressure drop to which it is subjected during suction, the chamber  40   a  and the capacity  49  are isolated from the working chamber  7  by the valve member  42 . While the pump is being set into operation, this gas plus any gas that is contained in the working fluid circuit accumulates in the top of the channel  20 . Given the inertia in the movement of the valve member  26 , the pressure that actually exists in the chamber  40   a  and in the capacity  49  is always a little less than the delivery pressure, and on each stroke of the pump the valve member  42  rises and allows at least some of the gas that has accumulated under the bottom face of said valve member to pass into the passage  48 . This gas forms a pocket  42  that is situated above the bath of oil in the capacity  49 . 
         [0036]    If there is a shortage of oil in the hydraulic chamber  7 , the pressure that exists in this chamber is such that the force from the spring  43  keeping the valve member  42  on its seat  41  (which force is typically equal to a value that is suitable for withstanding the pressure reduction due to suction plus the sliding resistance due to the sealing ring between the jacket  44  and the valve member  42 ) is exceed and the valve opens, thereby enabling the working chamber  7  to be refilled with additional fluid that was contained in the chamber  40   a  and the capacity  49 , under the pocket of gas  52 . As in the above-described configuration, leak compensation is thus ensured on a continuous basis. The initial filling of the working fluid circuit serves to set up this excess fluid that is needed for compensation purposes. The consumption of working oil by leaks can be seen through the transparent plugs  50  and  51 . The level of the bath in the capacity  49  can be monitored therethrough. 
         [0037]    Naturally, the invention is not limited to the embodiment described but covers any variant coming within the ambit of the invention as defined by the claims. 
         [0038]    In particular, although the presence of capacities  28  and  49  is extremely advantageous in combination with the diaphragm secured to the piston head, they could be omitted and replaced by some other system for compensating oil leaks.