EP2018479A1

EP2018479A1 - Gearwheel pump

Info

Publication number: EP2018479A1
Application number: EP07729112A
Authority: EP
Inventors: René Triebe; Stefan Weber
Original assignee: Maag Pump Systems AG; Maag Pump Systems Textron AG
Current assignee: Maag Pump Systems AG
Priority date: 2006-05-12
Filing date: 2007-05-14
Publication date: 2009-01-28
Also published as: WO2007131994A1; US8038422B2; JP5027216B2; US20090169408A1; JP2009536992A; EP1855007A1

Abstract

The invention relates to a gearwheel pump, composed of a housing having at least two gearwheels, which engage into one another, with in each case one shaft, which shafts are mounted in feed-medium-lubricated plain bearings, wherein a feed medium (M) is fed from a suction side to a pressure side, and a return duct is provided which leads feed medium which flows outward through the plain bearing back to the suction side, and wherein a valve (5) having a stationary part and a moveable part (20, 21) is provided. According to the invention, the valve (5) has a setting characteristic which runs, as a first approximation, linearly at least in one region, wherein the setting characteristic is defined by a differential pressure (?p) across the valve as a function of a setting path (x) in the valve (5). In this way, a significant improvement is obtained in the capability for setting the pressure in the transition region between the plain bearing and a dynamic seal of a driveshaft which is guided outward.

Description

Zahnradpυmpe

The present invention relates to a gear pump according to the preamble of claim 1.

Gear pumps consist essentially of a housing with two intermeshing gears, which are arranged on shafts, wherein at least one of the shafts is connected to a drive. The shafts are mounted in medium-lubricated sliding bearings, which are arranged immediately adjacent to the pump interior, wherein the fluid used for lubrication of the sliding bearing passes from the pressure side via the sliding bearing gap and a return channel to the suction side of the gear pump.

In particular, in gear pumps, which are used for the promotion of low-viscosity polymers and prepolymers and a dynamic seal - for example in the

Form of a labyrinth seal (threaded shaft seal) - and subsequent static seal - for example, a packing seal with or without barrier medium - must ensure that before the dynamic shaft seal always a positive pressure compared to

Suction side is present, otherwise - when using a barrier medium - this can get into the fluid, which is highly undesirable. The positive pressure is necessary to obtain a sufficient filling of the sealing gap of the dynamic seal. So can a penetration be prevented by blocking medium in the main flow of the pumped medium.

On the other hand, the pressure before the dynamic shaft seal should not be too large, otherwise pumped medium can pass through the dynamic shaft seal to the outside or - if a static seal is present - the fluid enters into contact with this seal, which with destruction of the static seal must be expected.

It must also be ensured that the return duct can be closed during maintenance work on the static seal. For this reason, a valve was provided in the return passage, with the one

Ingress of air on the suction side of the gear pump can be prevented.

However, the known valve is not suitable, the above conditions for adjusting the

To meet delivery medium pressure before the dynamic shaft seal. Thus, it is extremely difficult due to the adjustment of the known valve, a fluid pressure before the dynamic seal in compliance with the above-explained

To set pressure conditions, since the area in which a setting must be made, is very small. The present invention is therefore based on the object to provide a gear pump, which does not have the disadvantages mentioned above.

This object is achieved by the measures specified in the characterizing part of claim 1. Further embodiments of the invention are specified in the dependent claims.

The invention relates to a gear pump, consisting of a housing having at least two intermeshing gears, each having a shaft which are mounted in lubricated slide bearings, wherein a fluid is conveyed from a suction side to a pressure side and a return passage is provided by the sliding bearing externally flowing fluid returns to the suction side, and wherein a movable and a stationary part comprehensive valve for adjusting a pressure difference in function of a Einstellweges, which indicates a position between the stationary and the movable part, is provided. According to the invention, the valve comprises an adjustment range in which the pressure difference as a function of the adjustment path has a gradient between 0.05 and 2.5 bar per percent of a maximum adjustment travel. Furthermore, the

Adjustment range at least 50% of the maximum adjustment path.

The unit for the slope is "bar per percent of the maximum adjustment path x _ma χ". This unit applies to all values given in this description for the Slope for the course of the pressure difference as a function of the adjustment path.

This results in a substantial improvement in the setting possibility of the pressure in the transitional region between the slide bearing and a dynamic seal of an outwardly guided drive shaft. Generally, a good-natured adjustment characteristic has been obtained.

An embodiment of the inventive gear pump is characterized in that the pressure difference in function of the adjustment in the adjustment range has a slope between 0.05 and 2 bar per percent of the maximum adjustment, in particular between 0.05 and 1.75 bar per percent of the maximum adjustment.

A further embodiment of the gear pump according to the invention is characterized in that a closing region is provided in which the pressure difference as a function of the adjustment path is a gradient greater than 2.5 bar per percent of the maximum adjustment travel, the closure region preferably comprising 10 to 15% of the maximum adjustment travel ,

In yet another embodiment of the present invention, the valve is contained in the return passage.

As an alternative to the above embodiment of the invention, the valve is contained in a supply channel which is separated from the pressure side leads in an area arranged by the gears from the slide bearing area.

In one embodiment of the present invention, the valve has a pressure adjustment section which is primarily for pressure adjustment. Furthermore, the valve has a closing section with which the channel containing the valve can be opened or closed.

In a further embodiment of the present invention

Invention, the movable part is insertable into the stationary part.

In yet another embodiment, the movable and stationary parts contact each other in the closing section when the channel containing the valve is closed.

In another embodiment of the present invention, the valve has a pressure adjusting portion mainly for pressure adjustment and a closing portion in which the passage containing the valve can be opened and closed, and in the pressure adjusting portion, the adjusting characteristic is linearly approximated in the first approximation.

In a further embodiment of the present invention, the stationary part is an exchangeable sleeve.

Yet another embodiment of the present invention, the valve has the following dimensions: x: 0.5 * D ... 5 * D, in particular 3 * D;

Sl: 0.008 * D ... 0.08 * D; di: di <D, di = D / l.5 ... D / l.2; where x is the displacement, D is the diameter of the movable part, that is the passage opening in the shooting section and Sl is the gap width between the stationary and the movable part.

In a further embodiment of the present invention, the movable part is only translationally displaceable.

In a further embodiment of the present invention, a screw jack is provided to translate the movable member.

In yet another embodiment of the present invention, the movable part at the suction-side end is conical, spherical or flat.

A further embodiment of the present invention is characterized in that the movable part has one of the following cross sections: polygon, in particular a triangle, quadrangle or hexagon;

- oval;

- round. Finally, another embodiment of the present invention is that the closing section is provided in the flow direction of the conveyed medium after the pressure setting section.

The present invention is based on

Embodiments shown in figures, further explained. Showing:

1 shows a section along a rotation axis of an outwardly guided drive shaft of a gear pump in a schematic representation,

2 to 4 different embodiments for a valve according to the invention,

5A, 5B and 5C possible adjustment characteristics for the various embodiments according to the

2 to 4,

6 shows a further embodiment variant for a valve according to the invention,

Fig. 7 shows a section along a rotation axis of an outwardly guided drive shaft of another embodiment of a gear pump in a schematic representation and 8 shows a valve according to the invention with a translationally displaceable movable part.

In Fig. 1 is a section through a gear pump is shown, wherein the sectional plane on the one hand along the axis of rotation 13 of a shaft 8 and on the other hand perpendicular to a plane which is spanned by the two shafts of the gear pump extends. The second, not visible in Fig. 1 shaft is therefore behind or in front of the illustrated shaft 8. A medium M, which is for example a polymer or a so-called prepolymer is supplied from a suction side 2 and with a gear 1, i. in the tooth spaces, on a pressure side 3 transported. On the pressure side 3, the pumped medium M is pressed by the intermeshing of the teeth of the two gears from the tooth gaps. The gear 1 is mounted on a shaft 8 or it forms together with the shaft 8 a workpiece.

Fig. 1 shows that shaft portion which is guided to drive the gear pump to the outside. Starting from the gear 1 follows first a slide bearing section I, in which the shaft 8 is supported or mounted in the housing 9. Subsequent to the plain bearing section I follows a dynamic seal (sealing section II), which is realized here as a so-called labyrinth seal in the form of a return thread, and a static seal (seal section III), which is here realized with stuffing box packings with a barrier medium. The sliding bearings are lubricated with the pumped medium M in the illustrated gear pump. Thus, conveying medium M penetrates from the pressure side 3, preferably via a bearing lubrication groove 14, into the bearing gap of the slide bearing section I and effects lubrication of the shaft 8. The dynamic seal adjoining the slide bearing and the static seal adjoining this prevent the conveying medium M from moving Outside can kick. It is important to ensure that, due to a high negative pressure in the transition area between the

Slide bearing section I and the seal section II (dynamic seal) no barrier liquid enters the return channel 4, since then mix the barrier liquid with the pumped medium M and this would be contaminated. At the same time, the pressure in said transition region must not be too high, since otherwise the pumped medium is pressed into the stuffing box packing and degraded there, which can lead to the destruction of the static seal.

As has already been explained, the use of a throttle screw in the return channel 4 is already known. This throttle screw was used primarily to completely close the return duct 4, as must be done, for example, in a temporary shutdown of the gear pump each. In addition, it has always been attempted to satisfy the above-described conditions with respect to the pressure conditions after the sliding bearing section I during the operation of the gear pump. This is with a simple throttle screw, as used in a known manner, very difficult to accomplish.

FIGS. 2 to 4 show valves 5 according to the invention which are located in the return duct 4 (FIG

Use come. The valves are all characterized by a comparison with the known throttle screw improved adjustment.

Based on the embodiment according to FIG. 2, in which a valve 5 is shown in a section, the inventive principle is explained. A movable part 20, also referred to as a journal, is displaceable in a stationary part 21, also referred to as a sleeve, according to arrow 24. In this case, the sleeve 21 can be designed so that it can be inserted or inserted as a separate part in the return channel 4, or the return channel 4 has a corresponding shape in the region of the valve 5 to be realized. The advantage of a replaceable sleeve 21 is a rapid adaptability of the valve 5 to changed circumstances, for example, when an optimization to a specific fluid must be made. Corresponding adjustments can also be made on the side of the pin 20.

The inventive valve 5 is characterized in particular by the fact that the two functions to be performed by the valve, namely the opening / closing of the return channel 4 and the pressure setting in Transition region of the sliding bearing portion I to the dynamic sealing portion II (Fig. 1), are realized substantially separately. This does not mean that no overlaps between the functions are possible, but that there is a high degree of independence between the functions. In the following, the relationships and the operation of the valve are explained:

In a fully open valve 5 are the

Pressure ratios in the flow direction before and after the valve 5 are substantially identical. By introducing the pin 20 into the sleeve 21, the cross-sectional area for the pumped medium M is initially reduced. This results in a first increase in the pressure difference Ap over the valve 5. In many applications, this is the initial position, i. this is the position with the smallest possible pressure difference Δp.

With the further penetration of the pin 20 in the sleeve 21, the cross-sectional area is no longer changed - ie, a gap width Sl, which is present between the pin 20 and the sleeve 21, remains substantially unchanged - but it is now only the penetration depth (hereinafter also called effective length or adjustment path) of the pin 20 in the sleeve 21, which leads to a pressure difference change across the valve 5. For the first time, an adjustment characteristic was obtained which enables a large adjustment range for the pressure difference Δp across the valve 5. This creates a setting of the optimal pressure in the transition area between Sliding bearing section I and dynamic sealing section II much easier.

To further illustrate the invention, calculations have been made, the result of which can be summarized in the following formula, which for simplicity is based on some model assumptions:

in which

Δp resulting pressure difference over the

Valve

Q Flow rate η Viscosity x effective length or adjustment path D Pintle diameter Sl gap width

In the known throttle screw, for which the above calculations are also valid, primarily the short annular gap, which can be characterized by the gap height Sl, is reduced at the short end. This reduction flows into the calculations in the third power, which leads to a very large change in pressure with little change in the gap width Sl.

In contrast, in the inventive device with the further advancement of the pin 20 in the sleeve 21st an almost linearly increasing pressure difference Δp achieved because - as can be explained with the above formula - the gap width Sl is only slightly changed and essentially only the adjustment path x is changed. The course of the pressure difference .DELTA.p in function of the adjustment path x is therefore linear over a relatively long adjustment in a first approximation. A change in the course occurs in the position shown in FIG. In this position, the effective length x (adjustment) is virtually extended without the pin 20 continues in the

Sleeve 21 is pushed. The conical pin 20 and the conical sleeve 21 have in this position at a distance from each other, which corresponds to the gap width Sl in the cylindrical portion of the pin 20 and the sleeve 21 approximately. This is the effective length

(Setting path x), which is flowed through by the conveying medium M in the valve with the same gap width Sl, extended by the corresponding dimensions in the conical region of the pin. As a result, the pressure difference Δp increases in proportion to this new effective length, resulting in a first disproportionate increase in the pressure difference Δp.

If now the pin pushed further into the sleeve, the distance in the conical portion of the pin 20 is smaller than the gap width Sl in the cylindrical portion. Thus, the pressure difference Δp above the valve increases disproportionately (ie the meaning of the effective length x decreases in the determination of the pressure difference Δp), and the distance (ie Slit width Sl) now determines in the third power the pressure difference Ap above the valve. In other words, the function "open / close" is now active, which follows a strongly nonlinear legislation and the pressure difference .DELTA.p corresponds to increase sharply.

From the foregoing, the realization of the two functions "open / close" and "pressure adjustment" can be located within the valve 5: Thus, the function "pressure adjustment" is locally assigned to a pressure adjustment section 22 and the function "open / close" to a closure section 23, whereby the function "open / close" and the function "pressure adjustment" are realized essentially separately from each other. The meaning of the phrase "substantially" indicates the fact that there is a certain overlap in the area in which there is a quasi extension of the effective length. This is indicated by a dashed extension of the pressure adjustment section 22. In proportion to the total length of the pressure adjustment section 22, the overlap is small. The overlapping area is, for example, at most 20% of the pressure setting section 22, in particular not more than 10% of the pressure setting section 22.

Based on the above rather general embodiments, a large variety of configurations of the outer shape of the pin 20 and / or the inner shape of the sleeve 21 can now be obtained. As examples are the embodiments that are shown in Figs. 3 and 4. While in the embodiment according to FIG. 3, the gap width Sl is rather constant in the pressure adjustment section 22, the gap width Sl varies in the embodiments according to FIGS. 2 and 4, wherein the variation in the gap width Sl in one case by the outer shape of the pin 20 (FIG. as in Fig. 2) is generated and in the other case by the inner shape of the sleeve 21 (as in Fig. 4). The variation of the gap width Sl by the design of the pin and / or the sleeve can thus be used to obtain targeted adjustment characteristics.

It has been shown that the size ratios are to be set as follows:

x 0.5 * D ... 5 * D, in particular 3 * D;

Sl 0.008 * D ... 0.08 * D; di di <D, di = D / l.5 ... D / l.2;

It should be noted that in particular with a

Variation of the slit width Sl on the adjustment section 22, the adjustment characteristic can be adjusted.

Fig. 5A shows the adjustment characteristics of a known throttle screw (reference numeral 50) and various valves according to the invention (reference numerals 51, 52, 53 and 54), wherein the abscissa of the adjustment path x of the pin 20 relative to the sleeve 21 is indicated. Here, the origin represents the completely closed Valve dar. On the ordinate the pressure difference Ap is entered.

In Fig. 5A, the extremely steep curve 50 of the adjustment characteristic for gear pumps with the known throttle screw is clearly visible. In contrast, the courses 51 to 54 are significantly flatter, so that a simpler and more precise pressure setting is already apparent from this. As a first approximation, the curves 51 to 54 are linear within a setting range. The linear range corresponds to the pressure adjusting portion 22 (Fig. 2). The differences between the progressions 51 to 54 can be made, for example, by different gap widths Sl (i.e., the gap width Sl is not constant over the effective length x) in the pressure adjustment portion 22

(Fig. 2) obtain, as indicated for example in Figs. 2 to 4. In particular, the course 54 shows a pronounced linearity, which is a consequence of a constant gap width Sl, as is the case, for example, in the embodiment according to FIG.

Fig. 5B shows two further courses 55 and 56, wherein the course 55 were determined for a low-viscosity and the course 56 for a highly viscous pumped medium using the same valve. As in the determination of

Also, the pressure p to be set is in the same operating range B as the gradients 55 and 56. The setting range x and the adjustment ranges E55 and E56 resulting from the operating range and the ranges 55 and 56 are different due to the difference Viscosities of the fluids differ. As can be clearly seen from the curves 55 and 56, in the adjustment ranges E55 and E56, in the first approximation, there is a linear relationship between the adjustment path x and the pressure difference Δp. While in the course 56 in the

Setting range E56 even a linear relationship between the adjustment x and the pressure difference .DELTA.p exists, the curve 56 due to the slight curvature in the adjustment only in a first approximation on a linear relationship. To illustrate this

Facts were connected in Fig. 5B, the two endpoints in the adjustment range E55 by a dash-lined line.

Based on FIG. 5C, the principle according to the invention is further explained by giving details of the gradients of the course of the pressure difference Δp as a function of the adjustment path x.

FIG. 5C again shows two adjustment characteristics, on the one side being a steep curve 100 of the pressure difference Δp as a function of the adjustment path x of a known valve and on the other side a flat profile 200 of a valve according to the invention. Again, the value 0 for the adjustment path x is to be used at the origin of the course. The valve is in this position in the fully closed state. On the other hand, the pin is maximally moved back out of the sleeve, in which case the adjustment path X _max is. Since% units are used, the value for x _{max is} 100%. The at this maximum adjustment path X _max remaining pressure difference Δp corresponds to the residual pressure drop across the fully opened valve. Below the curve for the pressure difference Δp as a function of the adjustment path x, closing regions SBioo and SB200A are now given adjustment ranges EB100 and EB200 as well as so-called residual ranges R100 and R200 for the course 100 of the known valve, respectively for the profile 200 of the valve according to the invention , These areas are (partially overlapping) sections of the abscissa (ie adjustment path x) of the illustrated course. These ranges are defined by the gradients (gradients) of the courses, wherein the slope of a course Δp is defined by their derivation after x as follows:

Gradient g =

The unit for the slope is "bar per percent of the maximum adjustment path x _max ". This unit applies to all slope values given in this description.

An adjustment range that allows simple and comfortable (and also good-natured) adjustment of the pressure ratios in a gear pump has values for the pitch g, which are between 0.05 and 2.5.

Variants with even more benevolent behavior have slope values between 0.05 and 2.0, in particular between 0.05 and 1.75 or less. Slope values that are greater than 2.5, are not suitable for adjusting the pressure conditions. As a result, slope values greater than 2.5 are assigned to the closure area. Finally, slope values smaller than 0.05 are also not suitable for adjusting the pressure ratios in a gear pump since large adjustment paths x are already necessary for small changes in the pressure difference Δp. For this reason, ranges with slope values less than 0.05 are assigned a residual range in which the desired settings are designated as useless.

The application of the abovementioned definitions for the pressure difference profiles as a function of the adjustment path x according to FIG. 5C yields the ranges registered under the curves 100 and 200. While the closure region SBioo, the adjustment region EBioo and the remainder region Rioo result for the course 100 of the known valve, the closure region SB ₂ OO / the adjustment region EB ₂₀₀ and the remainder region R _2O O ₂ result for the course 200 for the valve according to the invention.

From the comparison of the courses according to FIG. 5C for a known and a valve according to the invention, it is clear that the setting range EB ₂ oo, which is essential for a simple and accurate setting of a desired pressure in the gear pump, is much greater than the setting range EB ₁ 00 of the known valve. The adjustment range of a valve according to the invention covers at least 50% of the maximum adjustment path x _max , Preferably, it is 50% to 90% of the maximum adjustment path x _max , more preferably 80% of the maximum adjustment path x _ma χ. In contrast, known valves have setting ranges that do not cover more than 15% of the maximum adjustment path x _ma χ. Thus, while the largest portion of the adjustable adjustment paths x are in the adjustment range in the inventive valve, the largest portion of the adjustable adjustment paths x in the known valve in the remaining area, which is not usable.

In the embodiment of the valve according to the invention shown in FIG. 5C, the setting range EB ₂₀₀ covers

80%, the closing range SB ₂ oo approx. 10% and the remaining range R ₂₀₀ likewise approx. 10% of the maximum setting range x _ma χ.

In contrast, the known valve according to FIG. 5C has a setting range EB ₁₀₀ of approximately 15%, a closing range SB100 of approximately 10% and a residual range R10 ₀ of approximately 80%. Characteristic of the known valve is in particular an overlap of the closing area SB ₁₀₀ with the

Adjustment range EBioo- Therefore, in the case of the known valve, the setting of the differential pressure Δp actually takes place in the closing range SB ₁₀₀ , in which a pressure differential adjustment is particularly difficult due to the extremely steep course 100 (gradient g >> 2.5).

FIG. 6 shows a further embodiment according to the invention. The pumped medium M which has flowed through the bearing gap is directed onto the suction side via a return channel 4 extending at right angles (FIG. 1). the gear pump is returned, wherein the return channel 4 on the one hand as a bore in a housing part 9a and a groove in a housing part 9b is executed. In the vertex of the rectangular course of the return channel 4, a feed unit 60 is provided, by means of which a pin 20 is inserted into the formed as a bore return channel 4. In contrast to the embodiments according to FIGS. 2 to 5, in the case of that according to FIG. 6, the arrangement of the two functions "opening / closing" and "pressure setting" is reversed: the pressure adjustment takes place on the side of the end of the journal 20 and the function " Opening / closing "on the side of the feed unit 60. This also existing gear pump can be equipped in a simple manner with a novel valve without the pump housing must be changed.

It should be noted that in Fig. 6, the pin 20 is located in the fully open and in the fully closed position. Overall, the pin 20 can be moved over a maximum length L (maximum displacement x).

In all embodiments of the pin as well as the sleeve is conceivable to provide a deviating from a rotational symmetry cross-section. For example, it is conceivable that the pin and / or the sleeve has one of the following cross sections: - Polygon, in particular a triangle, quadrangle or hexagon;

- oval;

- round.

Furthermore, the pointing in the direction of the suction end of the pin can be designed differently. In particular, the end may be conical - pointed or blunt -, spherical or flat.

Finally, it is also conceivable that the pressure setting section 23 (Fig. 2) is divided into subsections so as to be able to obtain a further variation in the setting characteristics. Each subsection can be customized to meet specific needs.

Fig. 7 shows, based on the representation according to FIG. 1, a further embodiment variant for a gear pump. In contrast to that according to FIG. 1, the gear pump has a supply channel 15, which connects the pressure side 3 with the region between the sliding bearing and the dynamic seal. Furthermore, the valve 5 is not arranged in the return channel 4 but in the feed channel 15. Incidentally, the

Gear pumps constructed identically, which is why reference is made to the description of FIG. 1 for further explanation. The valve 5 according to FIG. 7 is in turn used for pressure adjustment or for opening / closing the supply channel 15, the above explanations regarding the valve 5 and the corresponding adjustment characteristics also being valid here.

Finally, in Fig. 8, a special feed unit 60 is shown, which is particularly in connection with the embodiments described above for

Adjustment of the adjustment x in the novel valves suitable.

The known throttle screws described above lead during the translational displacement of the

Pivot 20 a rotation about its own axis. Thus, the seals, which ensure that no fluid flows M in the direction of feed unit, not only claimed by the actual translational feed motion, but also by the rotation about its own axis. During the pressure setting and in particular also when the return channel is closed or opened, these seals are stressed so heavily that their life expectancy is severely restricted.

Another aspect of the invention leads to a substantial improvement of this problem. Thus, the use of a Spindelhubgetriebes 61 it allows that a pure translational movement can be obtained can. Thus, the seals 63 are no longer claimed by the combination of self-rotation and translation of the pin 20, but only by the actual translational movement, which is necessary to adjust the pressure or to open / close the valve. The sliding path of the seal is thus reduced.

Furthermore, the feed unit 60 according to the invention allows a substantially larger stroke (maximum length L or maximum displacement x), so that

Pressure adjustment characteristics can be realized, which allow a very fine adjustment.

Finally, the use of the Spindelhubgetriebes 61 allows easier handling during the adjustment process. While in the known throttle screw settings had to be made very close to the rotating drive shaft, the setting in the inventive variant with a

Spindelhubgetriebe 61 are made perpendicular to the rotating drive shaft. Thus, the access to the adjustment device is significantly improved and reduces the risk of injury to operating personnel by the rotating drive shaft.

Although the feed unit 60 according to the invention is particularly suitable in combination with the valve according to the invention or the various embodiments shown, a combination of the invention also results Feed unit with known valves to the advantages mentioned in connection with the screw jack. For this reason, the feed unit according to the invention is considered to be independent of the valve according to the invention and therefore deserves protection independent of the valve.

Claims

claims

1. Gear pump, consisting of a housing (9) with at least two intermeshing gears (1) each with a shaft (8), which are stored in fluid-lubricated slide bearings (I), wherein a fluid (M) from a suction side (2 ) is conveyed to a pressure side (3) and a return channel (4) is provided which flows through the sliding bearing (I) to the outside

Recirculating medium (M) to the suction side (2), and wherein a movable and a stationary part (20, 21) comprising valve (5) for adjusting a pressure difference (Δp) in function of a Einstellweges (x), a position between the stationary and the movable part (21, 20) indicates is provided, characterized in that the valve (5) comprises an adjustment range (EB ₂₀₀ ), in which the pressure difference (Δp) in function of the adjustment (x) a slope between 0.05 and 2.5 bar per percent of a maximum adjustment path (x _ma χ), and that the adjustment range (EB ₂ oo) at least 50% of the maximum adjustment path (x _ma χ) includes.

2. Gear pump according to claim 1, characterized in that the pressure difference (Δp) in function of the adjustment

(x) in the adjustment range (EB ₂₀₀ ) has a slope between 0.05 and 2 bar per percent of the maximum adjustment travel (x _ma χ), in particular between 0.05 and 1.75 bar per percent of the maximum adjustment travel (x _ma χ).

3. Gear pump according to claim 1 or 2, characterized in that a closing area (SB ₂ oo) is provided, in which the pressure difference (Δp) in function of the adjustment (x) a slope greater than 2.5 bar per percent of the maximum adjustment path (x _m ax) is, wherein the closing area (SB2 ₀₀ ) preferably 10 to 15% of the maximum adjustment path (x _ma χ) includes.

4. Gear pump according to one of claims 1 to 3, characterized in that the valve (5) in the return channel

(4) is included.

5. Gear pump according to one of claims 1 to 3, characterized in that the valve (5) in a supply channel (15) is included, which from the pressure side (3) in one of the gears (1) as seen from the plain bearing ( I) arranged area leads.

6. Gear pump according to one of claims 1 to 5, characterized in that the valve (5) has a

Pressure setting section (22), which is mainly used for pressure adjustment, and that the valve (5) has a closing portion (23), with which the valve (5) containing the channel (4, 15) can be opened or closed.

7. Gear pump according to one of claims 1 to 6, characterized in that the movable part (20) in the stationary part (21) can be inserted.

8. Gear pump according to one of claims 1 to 7, characterized in that the movable (20) and the stationary part (21) in the closing section (23) touch when the valve (5) containing the channel (4, 15) closed is.

9. gear pump according to one of claims 1 to 8, characterized in that the stationary part (21) is an exchangeable sleeve.

10. Gear pump according to one of claims 1 to 9, characterized in that the valve (5) has the following dimensions: x: 0.5 * D ... 5 * D, in particular 3 * D; Sl: 0.008 * D ... 0.08 * D; di: di <D, di = D / l.5 ... D / l.2; where x is the displacement, D is the diameter of the movable part (20), di the passage opening in the shooting section (23) and Sl is the gap width between the stationary (21) and the movable part (20).

11. Gear pump according to one of claims 1 to 10, characterized in that the movable part (20) is only translationally displaceable.

12. Gear pump according to claim 11, characterized in that a Spindelhubgetriebe (61) is provided to translate the movable part (20) translationally.

13. Gear pump according to one of claims 1 to 12, characterized in that the movable part (20) on the Suction-side end facing conical, spherical or flat.

14. Gear pump according to one of claims 1 to 13, characterized in that the movable part (20) has one of the following cross-sections:

- Polygon, in particular a triangle, quadrangle or hexagon;

- oval; - round.

15. Gear pump according to one of claims 1 to 14, characterized in that the closing section (23) is provided in the flow direction of the conveying medium (M) after the Druckeinstellabschnitt (22).