Hydraulic diaphragm pump with leak compensation device

CA 02571024 2006-12-11 1 The present invention relates to a hydraulically actuated diaphragm pump with protection of the diaphragm in the event of hydraulic leaks in the actuation chamber.

BACKGROUND OF THE INVENTION Suction overtravel is due to a deficit of liquid in the hydraulic chamber for actuating the diaphragm.

In reality, in certain types of pumps, this overtravel does not occur because the diaphragm at the end of the suction is supported on a surface limiting the stroke.

Cavitations can then occur in the hydraulic chamber, and in any event, the displacement of the pump is affected.

In some pumps where there are no mechanical limitations to the diaphragm suction stroke, overtravel, in addition to reduced performance, can cause deformation and excessive fatigue of the diaphragm which is detrimental to its longevity. .

An over-displacement at the delivery is due to an excess of liquid in the hydraulic chamber for actuating the diaphragm.

This situation is encountered, for example, when the pump is shut down for a long time while a vacuum builds up in the working chamber.

The hydraulic control chamber sees its volume gradually increase, filled with the fluid coming from the reservoir through capillary channels resulting from the mechanical operating clearances.

The next time you start up, the membrane may tear.

These phenomena are well known and there are many devices to remedy them.

Mention will be made of pumps which have a plate or a rear support grid for the diaphragm and a calibrated one-way re-supply valve, which opens when a vacuum threshold is reached in the hydraulic chamber.

If this threshold is high, the expansion of the oil in the hydraulic chamber CA 02571024 2006-12-11 2 is too great and the flow stability is affected.

A vacuum peak is also observed at the start of the suction phase due to the inertias of the moving elements and a premature opening of the calibrated valve which leads to overcompensation which is harmful to the discharge.

Document FR 2 557 928 includes means for compensating for leaks which are automatic taking into account the very principle of operation of the pump.

This system is also subject to overcompensation.

Mention will also be made of document EP 547 404.

The device described uses valves whose opening or closing is associated with a position reached by the membrane.

Thus, to eliminate the delivery overtravel, a valve interrupts the communication between two parts of the hydraulic chamber thus isolating the fluid in contact with the membrane from the fluid in contact with the piston when the membrane has reached a setpoint position at the end of delivery. The excess actuating fluid is then diverted to a tank through a relief valve.

Likewise, to eliminate suction overtravel, a valve opens when the membrane reaches an end of suction setpoint position.

This opening places the hydraulic chamber in communication with an oil tank via a resupply duct and a complementary movement of the piston causes the suction of a volume of compensating oil in the hydraulic chamber.

Regarding the compensating valve controlled or driven by the membrane, it is necessary to make it change state, that the membrane develops a force intended to overcome the opposing force of a spring which maintains the valve in its state. for closing the CA 02571024 2006-12-11 3 resupply duct.

This effort to overcome limits the suction height of the pump.

In other words, in the case of operation of the pump with a vacuum at the suction, there may be a non-functioning of the compensation device, a cavitation then originating in the hydraulic actuating chamber without the opening. valve can intervene.

It will be understood that there is great interest in reducing the force of the return spring of the valve on its seat so as not to penalize too much the operation of the pump on suction.

But it is hardly possible to reduce this force below a value corresponding to a pressure of 0.3 bars (3 meters of water column or 300 hectopascals).

Diaphragm pumps equipped with a diaphragm-controlled leak compensation system therefore have poor suction power.

OBJECT OF THE INVENTION The present invention relates to a pump in which the compensation for leaks from the hydraulic chamber is controlled and the suction power markedly improved.

BRIEF DESCRIPTION OF THE INVENTION The subject of the invention is therefore a diaphragm pump comprising, in a body, a hydraulic control chamber arranged between a reciprocating piston and the diaphragm, the pump comprising means for compensating for leaks from the diaphragm. hydraulic chamber with a make-up pipe opening into the hydraulic chamber through a compensation shutter controlled on opening by the diaphragm.

In accordance with a main characteristic of the invention, the aforementioned compensation shutter is operated by pressing the membrane on a free end of a rod of its control while the membrane is under CA 02571024 2006-12-11 4 updated. the force of a suction assistance spring which cooperates with the aforesaid shutter to return it to its closed state by pushing the free end of the rod towards the membrane, this spring forming with the shutter a movable assembly moved without being deformed by the membrane during a suction overtravel.

The suction assistance spring rests, opposite the shutter, on a shoulder located at the end of a rod integral with the membrane and extending from the latter into the hydraulic chamber of the pump.

This particular arrangement has the advantage of freeing the opening of the compensating shutter from any force which is necessary for it to be maintained in its closed state.

The suction height is thus increased, which becomes close to ten meters of water column against seven meters usually. The shutter and the shoulder move along a direction which is that of the movement of the diaphragm.

In operation, the force holding the compensating shutter in its closed state varies according to the greater or lesser compression of the spring since there is a relative movement between the bearing shoulder of the spring and the spring. compensation shutter.

Furthermore, the effect of this spring tending to return the membrane to the rear position, therefore adds a force to be overcome during the delivery stroke.

This addition leads to the fact that there is always a higher pressure in the hydraulic control chamber than that in the working chamber, which has advantages in particular with regard to the degassing of working oil, which is lower.

CA 02571024 2006-12-11 Two embodiments are possible for the compensation shutter, namely, an embodiment in the form of a slide and an embodiment in the form of a valve.

Furthermore, the bearing shoulder of the sol5 lidaire spring of the diaphragm may serve as a diaphragm delivery stroke limiter, either in the form of a stopper, or in the form of an isolation valve. a part of the control chamber close to the membrane of the other part of this chamber close to the piston and provided with a relief valve.

Other characteristics and advantages will emerge from the description given below of exemplary embodiments of the diaphragm pump according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Reference will be made to the accompanying drawings, among which:

- Figure 1 is a sectional view of a pump according to the invention, - Figure 2 illustrates a partial view of an alternative embodiment in which the diaphragm is protected against overflow delivery, - Figure 3 is the illustration of an alternative embodiment of the compensation shutter.

DETAILED DESCRIPTION OF THE INVENTION In a known manner, a hydraulically controlled diaphragm pump is co mposed of a pump body in two parts 1 and 2, between lesque = les is clamped at the periphery a diaphragm 3.

With part 1 of the body, the membrane delimits a pumping chamber 4 which leads to a suction pipe 5, a delivery pipe ~ 6 equipped with unidirectional valves, not shown.

With part 2 of the body, this membrane delimits a chamber 7 filled with a hydraulic fluid which can be moved cyclically forward (to the left CA 02571024 2006-12-11 6 of the figure) or rearward to the means of a piston 8 driven by a reciprocating movement.

A hydraulic control of the variation in the volume of the pumping chamber 4 is thus achieved.

This chamber 7 is also equipped in a known manner with a discharge valve 9 which makes it possible to limit the discharge pressure to a determined safety value and which is often combined with a device for degassing the control fluid.

Note in Figure 1 that the chamber 7 has two parts.

Age nerally cylindrical part 7a on the side of the piston 8, and a part 7b flaring out on the side of the membrane 3.

The parts 7a and 7b are connected, through a partition 2a, by a connecting duct 10.

A resupply duct 14 is provided in the body 2 (the partition 2a) and comes from an oil tank 14a comprising a non-return valve 14b.

This duct 14 opens into the chamber 7 when this outlet is discovered by a closure member 15 which normally isolates the duct 14 from this chamber 7.

The closure member 15 is here a valve equipped with a tubular operating rod 16, mounted to slide tightly in the partition 2a of part 2 of the body and whose end 16a, opposite the valve 15, is adjacent of the membrane 3, when the latter reaches close to a setpoint position which it reaches at the end of the suction stroke.

The valve 15 closes, resting on the wall 2a, the outlet of an annular channel 17 formed at least partially around the rod 16 of the valve and into which the end of the conduit 14 opens.

The rod 16 of the valve 15 forms a sleeve in which slides a rod 12 integral with the membrane 3.

This rod 12 is equipped at its free end with a shoulder 11 (here in the form of a clo CA 02571024 2006-12-11 7 che) to form a support for a spring 13 for assisting the suction of the membrane 3 and the other end of which rests on the valve 15 tending to press it against the wall 2a.

When the membrane 3 reaches its set position, a position which corresponds to the conformation at rest of the membrane, the stiffness of which is such that in the absence of any suction it tends to open the valve 15, it may therefore have already moved this valve 15 and open the communication between duct 14 and chamber 7.

This opening is achieved without effort to overcome because at the moment of contact of the membrane with the control rod 16 of the valve 15, the force of the spring on the valve 15 is neutralized.

Indeed, this force is then exerted between the shoulder 11 and the membrane 3 which form a non-deformable mobile unit carrying the valve 15. The opening of the compensation valve therefore requires no force and the pressure in the chamber 7 is substantially equal, during the suction phase, to the pressure of the pumping chamber 4, which makes it possible to carry out suction under a high vacuum in any case less than 0.3 bars.

At the start of the delivery stroke, the valve 15 closes and it is then necessary to overcome the force of the spring 13 before being able to move the diaphragm 3 forward.

In chamber 7, then, a pressure always greater than that prevailing in pumping chamber 4, which is rather favorable to the correct operation of the pump (less degassing of dissolved gases, for example).

At the end of the delivery stroke, the shoulder 11 can limit the stroke of the membrane 3 by resting on the valve 15 or on the wall 2a.

In the variant shown in Figure 2, the shoulder 11 is bell-shaped 11a which forms a valve capable of closing the outlet of the channel 10 in CA 02571024 2006-12-11 8 part 7a of the hydraulic chamber and which isolates part 7b of this part 7a when the membrane 3 exceeds a setpoint position at the end of delivery.

This part 7a is in permanent communication with the discharge valve 9, so that a continuation of the stroke of the piston 8, when the end of delivery position is reached by the diaphragm 3, leads to the excess fluid being diverted. through the relief valve 9 to an oil tank.

In Figure 3, the closure member 15 is constituted by a slide 18 slidably mounted in a bore of the partition 2a of the body 2 of the pump.

The spool 18 is tubular with a flange 19 at its end opposite the membrane, on which the spring 13 is applied, also resting under the shoulder 11 (valve 11a), thus tending to press the flange 19 against the partition. 2a of the body 2 which is crossed by the connecting duct 10.

The drawer 18 has a stepped outside diameter so that a portion 18a of large diameter covers the outlet of the duct 14 in the bore when the flange 19 is resting on the partition 2a.

When the collar 19 is moved away from the partition 2a, the portion 18b of small diameter of the drawer 18 discovers the outlet of the duct 14 and the chamber 7 can be re-supplied by suction.

The spool 18 forms a sleeve in which the rod 12 of the valve 11a or of the shoulder 11 slides.

Its end 18c opposite to the flange 19 is located near the setpoint position reached by the membrane 3 at the end of the suction stroke.

The outlet of the duct 14 in the bore of the partition 2a is discovered as soon as the membrane 3 has reached its set position at the end of the suction, that is to say as soon as it comes into contact with the end. 18c of drawer 18 with the same effects as those described with regard to CA 02571024 2006-12-11 9 Figures 1 and 2.

Returning to Figure 1, it can be seen that part 2 of the pump body constitutes the enclosure of the hydraulic chamber 7.

This enclosure belongs to a general frame 20 which also forms a support for a drive motor 21 and a housing for a transmission mechanism from the motor 21 to the piston 8, a mechanism which is not shown and which generally consists of a wheel and screw system. endless, the wheel being equipped with an eccentric reciprocating drive of the piston.

This casing also contains an oil bath 22 for lubricating the transmission mechanism.

The casing communicates with the cover 14a of part 2 of the pump body via a filter 23.

Thus, when there is a demand for compensation in the chamber 7, the fluid is withdrawn from the tank 14a which consequently is supplemented by lubricating oil drawn from the filter 23 itself coming from the bath 22 in the tank. housing 20.

It will be noted in this figure that the fluid of the chamber 7 20 diverted by the relief valve 9 returns to the casing 20 in the bath 22.

This arrangement allows a simplified construction of the pump.

In fact, the pumps of the state of the art employing a compensating valve controlled by the membrane all have a separate fluid for the hydraulic control chamber, in order to guarantee its purity while a lubricating fluid is charged. gradually particles coming from lubricated moving parts.

To be able to maintain an acceptable suction height, the calibrated valve must be calibrated to the minimum, hence the use of very low forces to obtain displacements.

These forces may be less than those necessary to overcome untimely friction forces generated by possible particles which would block the valve.

The CA 02571024 2006-12-11 means of the invention have made it possible to dispense with the return spring of the valve and its force for compensation: this made it possible to be able to admit a less purified fluid.