EP1319475A2 - Method of operating a hydraulic pressing tool and hydraulic pressing tool - Google Patents

Abstract

The process applies to a machine with a no-return valve (1), a return spring (3), a moving part (4) and a fixed part (25). A closing force is exerted on the no-return valve when a pre-selected return position is reached by the moving part on its return stroke, this being before the moving part reaches its end position.

Description

The invention initially relates to a method for operating a hydraulic Pressing device, in particular hand-pressing device, wherein the pressing device a hydraulic pump, a moving part, a fixed part and a Return valve, wherein further the moving part through the structure a hydraulic pressure is moved into an injection position and the Return valve automatically only at a predetermined, an injection pressure corresponding hydraulic pressure moves into an open position, wherein further the moving part is designed to be self-acting under the action of a return spring to move back from the injection position into an end position and the return valve is adapted to close only after the moving part has reached the end position.

The prior art is to refer to the WO 99/19947 of the applicant.

In the known device is already with great benefit such a method has been realized and has found a wide application. As a general rule the design is also advantageous and satisfactory. There are, however Cases in which premature stopping of the moving part is desired, without that in other cases the movement of the moving part in the final position would be hindered. The task is therefore to see a hydraulic Specify hand-pressing device, which is an optional stopping of the moving part in a position enabled.

The invention proposes that on the return valve before reaching the End position of the moving part with a corresponding locking force acted becomes.

This can optionally in any position of the moving part by immediate Act on the return valve. If necessary, also by hand. For this purpose, initially, optionally, if necessary, also be done by hand. For this purpose, the fact can advantageously be exploited that the return valve a continuing to outside the device operating portion having. On the user in the simplest case, for example, from Hand with the required force. Such is an interruption of the Rewind in any position of the moving part readily possible. Possibly Over a leverage this impact possibility for the Users can also be conveniently moved to the area of the device handle. Approximately there, if necessary via another button, where also the trigger button of the device is arranged.

In further detail, it can also be provided that the return valve until reaching a preselected or predetermined return position of Movement part is locked. This makes it possible, the said closure force for example by means of a force acting on the return valve return spring higher Provide force. In the course of reaching the Verpressdruckes this is Return spring high force automatically by the also on the moving part acting hydraulic pressure in a bias position and there arrested immediately. The return valve is thus basically at the return of the Movement suspended part of this force, but the catch catches this Force up until it is activated by the user, or by the device even when reaching a predetermined return position of the moving part, is released. The action on the return valve takes place accordingly by releasing a previously stored shutter force.

In an embodiment of the above-mentioned known device, it is also possible Magnetically form the return valve and the said force characterized to generate an electromagnet switched on at a given time becomes. The solenoid can then either the return valve pull in its closed position or, in opposite Gleichpoliger Arrangement that push return valve in its closed position. It is next also possible to make an electromechanical lock. in this connection is by an electric actuator, for example. Again, an electromagnet, a mechanical locking part in the travel of the return valve, whose Open position, pushed. In the same way can by electrical actuation then this lock can be pulled out again.

However, the magnetic or electromagnetic action is evident not or at least not necessary by releasing a previously stored shutter force. It is rather by voltage application a corresponding electromagnetic or electromechanical Arrangement.

It is recommended that the operation for locking or lifting the Locking the return valve or the operation for the action of the required Closing force, regardless of the position of the return part, in to integrate the already given operating handle of the device. In simpler For example, as already mentioned in principle, via a mechanical Lever device which acts on the end of the return valve.

In an advanced embodiment can be provided that the actuation button for starting the electric motor or the associated hydraulic pump at the same time with an action button on the locking part the return valve is provided.

In further concretization, the release button can be suspended like a lever and provided with a resettable locking spring mandrel be, in turn, an adjustable against spring force locking part, the acts on the return valve, engages under this and overflowed again can.

In concrete terms, the invention proposes a hydraulic pressing device with a in a cylinder running hydraulic piston, wherein the hydraulic piston can be moved back against the force of a return spring.

To solve the problem, a more advantageous pressing device, in particular Hand-grouting device to provide, the invention proposes that the return of the hydraulic piston before reaching the starting position by a triggering device, acting on the return valve, is sustainable.

In a first embodiment, this can be achieved by the fact that the Tripping device from a connected to the return valve train or Pressure part exists. The tensile or pressure part not only passes through the valve cylinder but also a usually outside of the valve, the device still surrounding Housing. This can be acted about by hand. When the return valve in an embodiment according to WO 99/19947, the The disclosure of this document is hereby incorporated in full in the disclosure of the present application, also for the purpose of the features of To include the application in claims of the present application, included during the return of the moving part in the closed position is pulled or pressed, the hydraulic volume further outflow prevented. The movement part comes to a standstill. On a renewed release operation of the electric motor out, the moving part then from the point where it was stopped, again in the closed position be driven.

With regard to a tensile part, for example, the tip of the closure valve as Rod may be formed passing through the housing. Of course, under appropriate Seal. In the known device is an opening direction pointing, the housing wall passing through extension of the return valve designed as a tensile part. About a here associated rocker, which ultimately only the outer housing cover interspersed, it can be used to open the Return valve can be used. This extension is now designed as a pressure part. He has a freely accessible end area on which to close the Return valve can be acted upon.

In a further embodiment can also be provided that on the return valve an electromagnet acts. Such a hand-pressing device is in some embodiments operated with an accumulator. Or with direct connection to an electrical network, for example in an assembly hall. This can be used to associate with the return valve an electromagnet provided. The electromagnet can, depending on the polarity with the Return valve, either push or pull it to the closed position.

In a further embodiment, it can be provided that the return valve with a to move to the closed position at each time of return of the moving part sufficient biasing force is applied. This can first, regardless of a possible procedure in the closed position at any time of the return of the moving part, already from the Point of view and advantageous that the automatic return of the moving part in the least possible dependence on the by the on the return valve acting pressure spring is generated pressure. This also at Independence of the return valve of the generated by the return spring Print.

In this aspect, the invention first proposes that the open position the return valve until reaching a predetermined return position the movement part is locked. According to the invention, it is provided that the opening position of the return valve is mechanically locked. And until the moving part in its initial position, or a desired return position of the moving part, has gone.

In an embodiment, it can be provided that the return valve is a latching receptacle has, which engages in locking a locking projection. The latching receptacle is suitably rearward to the effective piston surface provided the return valve.

The locking projection entering into the locking receptacle is suitable under spring preload.

With regard to the locking projection, a separate release part is provided, which moves out the locking projection from the locking receptacle. This in Dependence of given mechanical conditions or pressure conditions, as further explained below.

The release part can cooperate with a ramp of the locking projection. Suitably, on the locking projection for this purpose, a conical surface or another ramp-like surface formed. The release part has a corresponding surface. It thus results in a Keilschieberwirkung.

The release part is according to a first embodiment of the moving part mechanically acted upon. The moving part is usually a piston of the Pressing device. The release part is for mechanical loading in the direction of travel of the piston, so that the traversing piston or the traversing Moving part of this in a certain path section of the travel path, preferably at the end of the travel, mechanically operated.

According to a second embodiment, the release part under spring tension stand. The spring bias drives the release part in the release position. The Spring preload is due to the compression and return of the moving part surpassing prevailing hydraulic pressure. Only after standstill of the moving part, the hydraulic pressure drops so far that the release part by the spring preload impressed on it from a movement path of the The locking projection, which then, because he in turn under spring preload stands, moves out of the locking receptacle of the return valve and this releases it to the closure.

The release part can also be used to allow the hand-operated To lift out the locking projection from the locking position. For this can in a simple version of the locking projection from the housing be led out one-stop and there by hand about against its biasing force be pulled into the locking position. The release part is then the rearwardly protruding portion of the locking projection.

But it can also be provided insofar as a separate release part, which, anyway over a certain range of motion, positively with the locking projection interacts. For example in the form of a seesaw. When moving the release part is then inevitably the Arretierungsvorsprung also from his Pulled out locking position. In further detail, the Löseteil For this purpose also be coupled with an operating switch of the device. Approximately with the trigger or start switch of the device. About in the way that one pressing the start switch again to pull out the locking projection from the Arretierungsstellung and thus to a stop of the moving part leads. A subsequent operation of the start switch then leads again to a start of the electric motor or a work the pump, so that a new grouting process begins.

Fig. 1

eine Querschnittsansicht eines hydraulischen Verpressgerätes mit einer Einrichtung zum wahlweisen Schließen des Rücklaufventils;

Fig. 2

eine ausschnittsweise Querschnittsdarstellung des Verpressgerätes mit einer tasterbetätigten Auslösung zum Verfahren des Rücklaufventils in die Verschlussstellung, in einer ersten Stellung;

Fig. 3

eine Darstellung gemäß Fig. 2, beim Start des Gerätes;

Fig. 4

eine Darstellung folgend der Fig. 3, nach weiterem Durchdrücken der Starttaste und angelaufener Pumpe:

Fig. 5

folgend der Fig. 4 nach Erreichen des Auslösedrucks des Rücklaufventils und Abschalten der Pumpe; Freigabe der Rückbewegung der Starttaste und Verriegelung des Rücklaufventils in der Offenstellung;

Fig. 6

folgend der Fig. 5 Wieder-Unterfahren des Löseteils bei freigegebener Starttaste und in der Öffnungsstellung verriegeltem Rücklaufventil;

Fig. 7

eine Grundstellung eines zweiten Ausführungsbeispiels, das Bewegungsteil ist in seiner Anfangsstellung und das Rücklaufventil geschlossen;

Fig. 8

das zweite Ausführungsbeispiel, nachdem Verpressdruck aufgebracht worden ist und das Bewegungsteil in seine Verpressstellung verfährt; das Rücklaufventil ist geschlossen;

Fig. 9

einen Zustand des zweiten Ausführungsbeispiels in welchem das Rücklaufventil geöffnet hat und das Bewegungsteil zurückverfährt;

Fig. 10

die Ausgangsstellung bei einem dritten Ausführungsbeispiel, das Rücklaufventil ist geschlossen;

Fig. 11

einen Zustand des dritten Ausführungsbeispiels, bei welchem Verpressdruck aufgebaut wird, das Rücklaufventil ist geschlossen;

Fig. 12

einen weiteren Zustand des dritten Ausführungsbeispiels, das Rücklaufventil ist geöffnet und das Bewegungsteil fährt in Richtung seiner Ausgangsstellung zurück.

In the following, the invention will be explained further with reference to the attached drawing, which, however, merely shows exemplary embodiments. Hereby shows:

Fig. 1

a cross-sectional view of a hydraulic Verpressgerätes with means for selectively closing the return valve;

Fig. 2

a partial cross-sectional view of the pressing device with a button-actuated release for moving the return valve in the closed position, in a first position;

Fig. 3

a representation of Figure 2, at the start of the device.

Fig. 4

a representation following the Fig. 3, after further pressing the start button and started pump:

Fig. 5

following the Fig. 4 after reaching the release pressure of the return valve and switching off the pump; Releasing the return movement of the start button and locking the return valve in the open position;

Fig. 6

5 again re-driving under the releasing part with the start button released and in the open position locked return valve;

Fig. 7

a basic position of a second embodiment, the moving part is closed in its initial position and the return valve;

Fig. 8

the second embodiment, after Verpressdruck has been applied and moves the moving part in its Verpressstellung; the return valve is closed;

Fig. 9

a state of the second embodiment in which the return valve has opened and the moving part zurückverfährt;

Fig. 10

the starting position in a third embodiment, the return valve is closed;

Fig. 11

a state of the third embodiment in which pressure is built up, the return valve is closed;

Fig. 12

another state of the third embodiment, the return valve is open and the moving part moves back in the direction of its initial position.

First shown and described in Fig. 1 is a detail of a hydraulic pressing device, as it except for the features described here and in further detail, for example, in WO 99/19947 is. To explain the construction and operation of the return valve and the groover in general, also for the others described here Embodiments, is also fully to the said Reference, also for the purpose features of this document in claims to receive the present application, incorporated herein by reference.

There are two embodiments that are also separate from each other taken in the Fig. 1.

First, it is important that the return valve 1 is an outward over the device has continuing printing paragraph 2. With this, the return valve 1 from its open position optionally, at each position of the spring 3 moved back movement part 4, here a hydraulic piston, in its closed position can be brought. The movement part 4 and the hydraulic piston is then stopped at the point where he joins this Time is.

Additionally or alternatively, an electromagnet 5 may be provided, which also acts on the return valve 1. In the embodiment are Coil windings 6 are provided which are magnetic when electrically charged with an associated section, for example the section 7 of the return valve interact. In that case a pulling effect is given. It can just as well to be formed a pressure effect. Also, the prevailing Section of the return valve used as moved by the magnet anchor be.

The embodiment of FIGS. 2 to 6 basically also relates to a hydraulic grouting device as known from WO 99/19947 is. Here, however, the return valve 1 is constantly, in the case of the embodiment by a compression spring 20 with such a force in the closed position biased that regardless of the movement by the part 4 when running back exerted pressure the return valve at any time in the closed position would proceed. This is prevented by a locking projection 8, which, as further below in further detail with respect to the embodiments Fig. 9 to 12 explained in a corresponding recess retracts the return valve.

Of importance now is that the locking projection 8 rearward from the Device body 9 is led out and forms a Beaufschlagungsabsatz 10. This is under attack by a release part 11, which in turn rocker around a pivot point 12 is attached to the device body 9. At the same time is the release part 11 or the holder 13 of the release part 11 rigidly connected to a release button 14 of the device. The trigger button 14 acts on actuation of an electric switch 15th

In detail, this will be explained below with reference to FIGS. 3 to 6.

Fig. 2 shows the state of the switched-off electric motor. The hydraulic groover is at rest. The return valve 1 is in an open position and is locked therein by the locking projection 8. The movement part 4 is in a fully backward position.

In Fig. 3, the state is shown that the user perform a compression want. He begins to act on the trigger button 14. This one has, against the action of a compression spring 16, the other end to a fixed Housing part 17 is applied, moved in the direction of the electric switch 15. Of the Lösevorsprung 11 moves in this case on a circular path around the joint 12. He has the Arretierungsvorsprung 8 already partially from its Arretierungsstellung pulled out.

Furthermore, cf. Fig. 4, the user has by further pressing of the Tripping button 14 on the one hand the electric switch 15 is actuated, so that the electric pump starts and the hydraulic chamber 18 filled with hydraulic fluid becomes. At the same time, however, the release projection 8 has been excavated so far that the return valve 1 under the action of the compression spring 7 in the closed position procedure is. The hydraulic piston or the movement part 4 has already moved away from its end position, it is not visible in Fig. 4. Because in further detail the release member 11 against the action of a compression spring 19th can be moved back from its foremost position, can when releasing the shutter button 14, as shown in FIGS. 5 and 6, the release part 11 again under the Snap projection 10, without thereby locking the position of the Arretierungsteils 8 is impaired.

Subsequent to the position shown in FIG. 6, the release part then takes the again Position of Fig. 2, but with the moving part in the direction Pressing position is moved by the constantly running pump. As soon as the Pressing has been achieved, the pump turns off automatically. This even if, as a rule, the release button 14 is still pushed. At the same time the return valve 1 moves automatically into its open position, against the action of the compression spring. 7

Figs. 7 to 9 relate to a second embodiment, which only the Arresting the acted upon by an overpressure in the open position Return valve concerns. Overpressure here means that the pressure is higher than he only about the end of the return path of the movement part to close the return valve is needed. He is so high that he is in every one Position of the return of the moving part to close the return valve suitable is.

Here, too, the hydraulic pressing device 21 has a not shown Hydraulic pump on, by means of which in a further detail also not shown hydraulic reservoir 22 hydraulic fluid, usually oil, in the hydraulic chamber 18, see. Also Fig. 8, is pumped. By means of the hydraulic pressure is a moving part 4, here a piston, against the effect of a Return spring 3 movable. The hydraulic pressure is built up until a predetermined compression pressure is reached, in which at the same time as a pressure relief valve acting return valve 1 opens.

The return valve 1 has this an initially effective comparatively very small valve surface, which in the embodiment through the hole 23 corresponds to the given cross section.

This cross-section requires to release the return valve 1 such a high Pressure, as it corresponds to the compression pressure. After lifting off the return valve 1 is given by the diameter of the piston portion 24 larger area to the effect. Therefore, the return valve 1 after his Triggered by a much lower pressure - still - in the open position held.

The movement part 4 is moved relative to a fixed part 25. The terms Movement part and fixed part can also on not shown in detail Elements of the work area of the pressing device are related. The movement part or the moving parts are for this purpose, for example, together Baking or the moving part is a knife or a die that is against a stop or a fixed counter-mold moves.

In the course of building up a pressure, which state shown in Fig. 8 is the hydraulic space 18 with increasing increasing pressure acted upon, by the already mentioned, not shown pump and the piston of the moving part 4 is until reaching a pressing pressure pressurized by increasing pressure.

The return valve 1 has a locking receptacle 26, which in the embodiment by a circumferential groove in a piston portion of the return valve 1 is formed. It is further provided a locking part 27, the under Effect of a spring 28 is biased to the return valve 1 out. The locking part 27 has a locking projection 8, which in the method of Return valve 1 retracts into its open position in the locking receptacle 26.

The return valve 1 is in turn biased in its closed position by the action of the spring 20.

Back of the return valve 1, in extension of a shaft of the Return valves 1, a handle 29 is further formed, with which the Return valve can be moved by hand in its open position. It but can not be closed by hand when engaging the Arretierungsvorsprungs 8 become.

The locking member 27 in turn cooperates with a release member 11, the is designed as a valve piston. The release part 11 has an urging projection 30, which is in the travel of the moving part 4, here the piston, protrudes.

The release part 11 further has an actuating tip 31 which is provided with an actuating molding 32 cooperates on the locking part 27. In the embodiment are the operating tip 31 and the Betätigungsausformung 32 each cone-shaped.

When starting from the initial position in Fig. 7 oil in the hydraulic chamber 18 is pumped to move the moving part 4, the moving part moves 4 against the action of the spring 3, as shown in Fig. 8. The same with a release of the actuating projection 30 moves the Arrestierungsteil 27 by the action of the spring 28 to the locking projection 8 abuts the peripheral surface of the piston portion 33, in the closing direction of the return valve 1 is formed in front of the locking receptacle 26. Of the Piston portion 33 corresponds in diameter to the free diameter of the cylinder 34 in which the return valve 1 moves.

In the initial position shown in FIG. 7, the locking projection 8 by the action of the spring 3, which the movement part 4 on the Beaufschlagungsvorsprung 30 presses and so the release part 11 zurückverfährt, under training of a free-standing 35 retracted from the piston portion 33.

Now, as shown in FIG. 8, the hydraulic pressure up to the injection pressure is constructed is, with beyond going bias, as shown in Fig. 8 can be seen, the locking projection 8 to the peripheral piston surface of the piston portion 33 is approached. Taking into account the angular relationship between the release part and the locking part, given by the conical surfaces 31 and 32, the bias of the Arretierungsvorsprungs 8 on the piston portion 33 so high that the pressure in the cylinder chamber 18 to is surpassed by the action of the spring 28 towards the injection pressure.

The latter is not necessary. It could also be that the effect of the spring 28 is much lower. Then the lock would only in the course of the back process of movement 4, under a substantial lower pressure in the cylinder chamber 18, the locking projection in move the locking recess 26.

Once the pressure has been reached and the return valve 1 has opened, this state is shown in Fig. 9, the locking receptacle 26 is in coverage to the locking projection 8, so that this by the action of the spring 28 retracts (or, as indicated above, retires later in time when the Pressure in the cylinder chamber 8 has fallen so far that the action of the spring 28 is sufficient, but the moving part 14 is not yet back to the stop is).

As a result, further the release part 11, which under no spring preload is, but only by the spring 28 and prevailing in the cylinder chamber 18 Oil pressure is applied, further back process. It is even further in the trajectory of the moving part 4 before.

The oil from the cylinder chamber 18 can by the indicated line 36, the when opening the return valve released by the piston portion 24 is, drain into the reservoir 22.

Now, if the moving part 4 on the end face of the Beaufschlagungsvorsprungs 30 of the release member 11 abuts, this is due to the action of the spring 3 in Direction encountered on the locking part 27 and drives so on the transmission surfaces 31, 32, the locking member 27 against the action of the spring 28 back.

The return valve 1 can then by action of the spring 20 back into his Closing position according to FIG. 7 or FIG. 8 method.

The third embodiment is shown in FIGS. 10 to 12.

Here, in principle, the above-described locking part with the release part functionally summarized.

The return valve 1 corresponds to the above-described return valve 1. In this respect, reference is made to this.

The same is the fixed part 25 with the moving part 4 with acting on it Return spring 3 is the same design.

In the illustration of FIG. 10, the basic position is shown, when closed Return valve 1 and with the locking projection 8 in a distance position to the associated piston portion 33 of the return valve. 1

The locking projection 8 is in the embodiment of Figs. 10 to 12th initially under bias by the spring 36. The locking projection 8 is with a directly acting through the cylinder space 18 in the hydraulic pressure acted upon piston part 37 connected. Next, however, is the locking projection movable within the piston part 37. He stands within the piston member 37 under the action of a spring 38, which the locking projection 8, depending on a pressure acting on the piston part 37 pressure, biases against the return valve 1.

When, according to the state described in Fig. 8, in the second Embodiment, a compression pressure is built up, cf. Fig. 12, that is Piston part 25 this - increasing - exposed to compression pressure. This pressing pressure overcomes the action of the spring 36, so that the piston member 37th is moved together with its shaft 39 on the return valve 1 point.

The piston part 37 can proceed until the shaft 39 at the end 40 the associated cylinder bore 41 comes to a stop. In this condition is already the end face of the Arretierungsvorsprunges 8, the return valve 1 is assigned to the circumference of the piston portion 33 of the Return valve 1 encountered. In the course of the increasing process of the piston part 37, the locking projection 8 is moved back, wherein the spring 38 comes into effect.

For this purpose, the locking projection 8 passes through a bore 42 in the piston section 39 of the piston part 37.

In the hollow-shaped piston portion 39, the locking projection 8 movably guided by means of a piston portion 43, on which the Return valve 1 side facing away from the spring 38 acts.

As soon as the specified compression pressure is reached and thereby the return valve 1 is moved to its open position, the Arretierungsvorsprung occurs 8 in the recess 26, basically as in the second Embodiment already described. This state is shown in FIG. 12 shown. The further prevailing pressure in the cylinder chamber 18, caused by the spring 3, holds the locking projection 8 in the locked position Only when the moving part 4, here the piston, on the End wall 44 of the cylinder chamber 18 comes to rest, the pressure drops in the Cylinder chamber 18 from, so that the piston member 37 under the action of the spring 36 in the position of FIG. 10 moves. As a result, the locking projection 26 moved out, so that due to the action of the spring 20, the return valve be moved to its closed position, as shown in FIG. 10 again can.

All disclosed features are essential to the invention. In the revelation The application is hereby also the disclosure of the associated / attached Priority documents (copy of the advance notification) in full included, also for the purpose, features of these documents in Claims of the present application to include.

Claims (19)

Method for operating a hydraulic Verpressgerätes, in particular hand-pressing device, wherein the pressing device comprises a hydraulic pump, a moving part, a fixed part and a return valve, wherein further the moving part is moved by the construction of a hydraulic pressure in a Verpressstellung and the return valve automatically only at a predetermined , Hydraulic pressure corresponding to an injection pressure moves into an open position, wherein further the moving part is designed to automatically move back under the action of a return spring from the injection position to an end position and the return valve is designed to close only after the moving member has reached the end position , characterized in that on the return valve with a for achieving the required during the return movement of the moving member closing force upon reaching a pre-selected return position or when reaching a predetermined R cklaufstellung of the moving member is acted. A method according to claim 1 or in particular according thereto, characterized in that a mechanical locking of the return valve is carried out in the open position. Method according to one or more of the preceding claims or in particular according thereto, characterized in that a magnetic locking is carried out. Method according to one or more of the preceding claims or in particular according thereto, characterized in that an electromechanical lock is made. Hydraulic pressing device, in particular hand-pressing device, wherein the pressing device comprises a hydraulic pump, a moving part (4), a fixed part and a return valve (1), wherein the moving part (4) by the construction of a hydraulic pressure in an injection position is movable and the return valve ( 1) automatically moves into its open position only at a predetermined, corresponding to an injection pressure hydraulic pressure, wherein the moving part (4) is designed to automatically return under the action of a return spring of the injection position in an end position and the return valve (1) is designed to only to close after the moving part (4) has reached the end position, characterized in that the return of the moving part (4) before reaching the end position by a triggering device, acting on the return valve (1), is sustainable. Pressing device according to Claim 5 or in particular according thereto, characterized in that the triggering device consists of a pull or pressure part connected to the return valve (1). Pressing device according to one or more of claims 5 or 6 or in particular according thereto, characterized in that on the return valve (1) an electromagnet acts. Pressing device according to one or more of the preceding claims 5 to 7 or in particular according thereto, characterized in that the return valve is acted upon by a biasing force sufficient for moving into the closing position at each time of the return movement of the moving part. Pressing device as claimed in any one of the preceding claims 5 to 8 or in particular according thereto, that the opening position of the return valve is until a predetermined return position of the moving member is locked. Pressing device according to one of the preceding claims 5 to 9 or in particular according thereto, characterized in that the open position of the return valve (1) is mechanically locked. Pressing device according to one of the preceding claims 5 to 10 or in particular according thereto, characterized in that a separate release part is provided to release the locking projection, which moves out the locking projection from the locking receptacle. Hydraulic pressing device with a hydraulic pump, a moving part (4) and a fixed part (9) and a return valve (6), wherein the moving part (4) moves from a starting position to a pressing position, that return valve (6) automatically in response to one of the injection position Hydraulic pressure moves into an open position and the moving part (4) under the action of a return spring (5) zurückfahr, characterized in that the open position of the return valve (6) until reaching a predetermined return position of the moving part (4) is locked. Pressing device according to claim 12 or in particular according thereto, characterized in that the return valve (6) has a latching receptacle (10) into which a locking projection (12) engages when being locked. Pressing device according to one or more of the preceding claims 12 or 13 or in particular according thereto, characterized in that the locking projection (12) is under spring bias in the locking position. Pressing device according to one or more of the preceding claims 12 to 14 or in particular according thereto, characterized in that a separate release part (16) is provided which moves the locking projection (12) out of the latching receptacle (10). Pressing unit, characterized to 15 or in particular according to one or more of the preceding claims 12 so that the release part (16) cooperating with a ramp of the Arretierungsvorsprungs (12). Pressing device according to one or more of the preceding claims 12 to 16 or in particular according thereto, characterized in that the release part (16) can be acted upon by the movement part (4). Pressing device according to one or more of the preceding claims 12 to 17 or in particular according thereto, characterized in that the moving part (4) is a piston and that the release part (16) projects into the travel path of the piston. Pressing device according to one or more of the preceding claims 12 to 18 or in particular according thereto, characterized in that the release part (16) is spring biased into its release position and that the spring preload is exceeded by the hydraulic pressure prevailing during compression and return of the moving part (4) ,

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