This is a U.S. national phase application under 35 U.S.C. §371 of International Application No. PCT/EP2007/054660 filed May 14, 2007 and claiming priority of European Application No. EP 06 113 845.9 filed May 12, 2006.
The present invention relates to a gear pump comprising a housing with at least two intermeshing gears each with a shaft supported by slide bearings lubricated with pumping medium, the pumping medium getting from a suction side to a pressure side and a return duct being provided, which leads pumping medium flowing to the outside via the slide bearing back to the suction side, and with a valve, which includes a movable and a stationary part, for the adjustment of a pressure difference in function of an adjustment path, which indicates a position between the stationary and the movable part.
Substantially, gear pumps consist of a housing with two intermeshing gears, which are arranged on shafts, at least one of the shafts being connected to a drive. The shafts are supported by slide bearings lubricated with pumping medium, which slide bearings are immediately arranged next to the internal space of the pump. The pumping medium used for the lubrication of the slide bearings gets from the pressure side via the gap of the slide bearing and a return duct into the suction side of the gear pump.
Gear pumps in particular, which are used for the conveying of low-viscous polymers and prepolymers and which comprise a dynamic sealing—in the form of a labyrinth sealing (sealing of threaded mandrel) for example—and subsequent static sealing—a packing sealing with or without sealing medium, for example—, must be ensured that always a positive pressure with respect to the suction side is present ahead of the dynamic mandrel sealing, since otherwise—in using a sealing medium—this can get into the pumping medium, which is highly undesirable. The positive pressure is necessary in order to get a sufficient filling of the sealing gap of the dynamic sealing. Thus, a penetration of sealing medium can be prevented into the main stream of the pumping medium.
On the other side, the pressure should not be too high in front of the dynamic mandrel sealing, since otherwise pumping medium can get outside via the dynamic mandrel sealing or—if a static sealing is present—the pumping medium gets in contact with this sealing, whereby a destruction of the static sealing must be expected.
Furthermore, it must be ensured that the return duct can be closed at the static sealing during maintenance work. For this reason, a valve has been provided in the return duct, by which a penetration of air into the suction side of the gear pump can be cut off.
However, the known valve is not suitable to meet the afore-mentioned conditions for the adjustment of the pressure of the pumping medium in front of the dynamic mandrel sealing. Thus, due to the adjustment characteristic of the known valve, it is uttermost difficult to adjust a pressure of a pumping medium in front of the dynamic sealing in complying with the afore-mentioned pressure conditions, since the range is very small, in which an adjustment must be made.
Therefore, the present invention has the object to provide a gear pump, which does not have the afore-mentioned drawbacks.
This object is solved by the present invention wherein the valve of the gear pump has an adjustment range, in which the pressure difference in function of the adjustment path has a slope between 0.05 and 2.5 bar per percentage of a maximum adjustment path, and wherein the adjustment range is at least 50% of the maximum adjustment path. Further embodiments of the present invention are described below.
The present invention relates to a gear pump consisting of a housing with at least two intermeshing gears, each with a shaft, which is supported by slide bearings lubricated with pumping medium. A pumping medium is conveyed from a suction side to a pressure side, and a return duct is provided, which leads pumping medium flowing to the outside via the slide bearing back to the suction side, and with a valve having a movable and a stationary part for the adjustment of a pressure difference in function of a adjustment path, which indicates a position between the stationary and the movable part. According to the present invention, the valve comprises an adjustment range, in which the pressure difference in function of the adjustment path comprises a slope between 0.05 and 2.5 bar per percentage of a maximum adjustment path. Furthermore, the adjustment range comprises at least 50% of the maximum adjustment path.
It arises as unit for the slope “bar per percentage of the maximum adjustment path xmax”. This unit is valid for all values indicated in this description for the slope for the course of the pressure difference in function of the adjustment path.
Therewith, a considerable improvement of the adjustment possibility of the pressure is obtained in the transition range between the slide bearing and a dynamic sealing of a drive shaft directed to the outside. In general, a good-natured adjustment characteristic has been obtained.
An embodiment of the gear pump according to the present invention is characterized in that the pressure difference in function of the adjustment path comprises a slope between 0.05 and 2 bar per percentage of the maximum adjustment path, particularly between 0.05 and 1.75 bar per percentage of the maximum adjustment path.
A further embodiment of the gear pump according to the present invention is characterized in that a closing range is provided, in which the pressure difference in function of the adjustment path is higher than 2.5 bar per percentage of the maximum adjustment path, the closing range comprising preferably 10 to 15% of the maximum adjustment path.
In a further embodiment of the present invention, the valve is contained in the return duct.
Alternatively, to the preceding embodiment of the present invention, the valve is contained in a feeding duct, which leads from the pressure side to the region arranged behind the slide bearing, viewed from the gears.
In an embodiment of the present invention, the valve comprises a pressure adjustment section, which mainly serves for the pressure adjustment. Furthermore, the valve comprises a closing section, by which the duct containing the valve can be opened or closed, respectively.
In a further embodiment of the present invention, the movable part is insert-able into the stationary part.
In another embodiment, the movable and the stationary part contact each other in the closing section if the duct containing the valve is closed.
In another embodiment of the present invention, the valve comprises a pressure adjustment section, which serves mainly for the adjustment of the pressure, and a closing section, in which the duct containing the valve can be opened or closed, respectively, the adjustment characteristic running linearly in the pressure adjustment section in a first approximation.
In a further embodiment of the present invention, the stationary part is an exchangeable sleeve.
In another further embodiment of the present invention, the valve comprises the following dimensions:
In another embodiment of the present invention, the movable part is merely translatory displaceable.
In another embodiment of the present invention, a mandrel lifting drive is provided in order to displace the movable part in a translatory manner.
In another embodiment of the present invention, the movable part facing the end of the suction side is tapered, globular or flat.
A further embodiment of the present invention is characterized in that the movable part comprises one of the following cross-sections:
Finally, a further embodiment of the present invention consists in that the closing section is provided after the pressure adjustment section in flow direction of the pumping medium.
The present invention is further explained with the aid of exemplified embodiments, which are shown in figures.
In
The slide bearings are lubricated in the gear pump depicted with the pumping medium M. Thus, the pumping medium M penetrates from the pressure side 3, preferably via a groove of the bearing lubrication 14, into a bearing gap of the slide bearing section I and causes a lubrication of the shaft 8. The dynamic sealing, which is subsequent to the slide bearing and the static sealing being subsequent to this, prevent that pumping medium M can get to the outside. It has to be paid attention to that no sealing liquid gets into the return duct 4, due to a high vacuum in the transition region between the slide bearing section I and the sealing section II (dynamic sealing), since the sealing liquid would then mix with and contaminate the pumping medium M. At the same time, the pressure may not be too high in the said transition region, since the pumping medium is pressed into the packing of the stuffing box and degrades there, which can lead to a destruction of the static sealing.
As already mentioned above, the use of a damper screw in the return duct 4 is already known. Primarily, this damper screw has been used for the complete closing of the return duct 4, like it always must be done for a temporary shutdown of the gear pump, for example. In addition, in each case it has been tried to comply with the afore-mentioned conditions in relation to the pressure ratios behind the slide bearing section I during operation of the gear pump. This is very difficult to achieve with a damper screw as it has been used in the known manner.
In
With the aid of the embodiment according to
Particularly, the valve 5 according to the present invention is characterized in that both functions to be fulfilled by the valve, namely the opening/closing of the return duct 4 as well as the pressure adjustment in the transition region of the slide bearing section I to the dynamic sealing section II (
The pressure ratios in flow direction ahead and behind the valve 5 are identical to a large extent for a valve 5 that is completely open. By inserting the pintle 20 into the sleeve 21, the cross-section for the pumping medium M is firstly reduced. Therewith, a first increase of the pressure difference Δp results across the valve 5. This is the initial position for many implementations, i.e. this is the position with the smallest possible pressure difference Δp.
The cross-section surface is not changed anymore due to a further penetration of the pintle 20 into the sleeve 21—i.e. a width of gap S1, which is present between the pintle 20 and the sleeve 21, remains unchanged to a large extent—but it is only the penetration depth (in the following also called effective length or adjustment path) of the pintle 20 into the sleeve 21, which leads to a change of the pressure difference across the valve 5. Therewith, for the first time, an adjustment characteristic is obtained, which makes a large adjustment range possible for the pressure difference Δp across the valve 5. Therewith, an adjustment of the optimum pressure in the transition region between slide bearing section I and dynamic sealing section II is substantially easier.
For the further explanation of the invention, calculations were made, whose results can be summarized in the following formula, which is based on a couple of model assumptions for simplification:
whereas
For the known damper screw, for which the preceding calculations are also valid, primary, the short annular gap, which can be characterized by the gap height S1, is reduced at the short end. This reduction has an effect on the calculations in the third power, which leads to a very high pressure change for small changes of the gap width S1.
In contrast thereto, an almost linear increasing of the pressure difference Δp is achieved with the device according to the present invention by advancing the pintle 20 into the sleeve 21, because—as can be explained with the preceding formula—the gap width S1 is only changed in a minor manner and only the adjustment path x is changed essentially. Therefore, the course of the pressure difference Δp in function of the adjustment path x is linear for a comparative long adjustment path in a first approximation. A change of the course takes place in that position, which is depicted in
Now, by pushing the pintle further into the sleeve, the distance in the tapered region of the pintle 20 is thus smaller than the gap width S1 in the cylindrical-shaped section. Therewith, the pressure difference Δp across the valve increases disproportionally (i.e. the meaning of the effective length x decreases for the determination of the pressure difference Δp), and the distance (i.e. the gap width S1) determines now the pressure difference Δp across the valve in the third power. In other words, the function “opening/closing” now is active, which follows a strong nonlinear law and let the pressure difference Δp increase correspondingly strongly.
From the preceding explanations, the implementation of both functions “opening/closing” and “pressure adjustment” can be localized inside the valve 5: thus, the function “pressure adjustment” is locally allocated to a closing section 22 and the function “opening/closing” to a closing section 23, whereby the function “opening/closing” and, essentially, the function “pressure adjustment” is separately implemented. Therewith, the meaning of the expression “essentially” points to the fact that a certain overlapping is present in that region, in which it comes to a quasi elongation of the effective length. This is indicated by a dashed-lined elongation of the pressure adjustment section 22. In relation to the overall length of the pressure adjustment section 22, the overlapping is small. The overlapping range amounts to a maximum of 20% of the pressure adjustment section 22, for example, in particular, a maximum of 10% of pressure adjustment section 22.
Based on the preceding rather general remarks, a big diversity of embodiments of the outer shape of the pintle 20 and/or the inner shape of the sleeve 21 can be obtained. The embodiments are examples, which are shown in
It has been shown that the dimensions have to be adjusted as follows:
It is pointed out that the adjustment characteristic can particularly be adjusted with a variation of the gap width S1 across the adjustment section 22.
The uttermost steep course 50 of the adjustment characteristic for gear pumps with the known damper screw is clearly visible in
The principle according to the present invention is further explained by referring to the gradients of the course of the pressure difference Δp in dependence on the adjustment path x with the aid of
Again, two adjustment characteristics are depicted in
As unit for the slope arises “bar per percentage of the maximum adjustment path xmax”. This unit applies for all values for the slope given in this description.
An adjustment range shows values for the slope g, which lie between 0.05 and 2.5, which makes an easy and comfortable (i.e. good-natured) adjusting of the pressure conditions for a gear pump possible.
Embodiments with more good-natured behaviour comprise slope values between 0.05 and 2.0, particularly between 0.05 and 1.75 or less. Slope values, which are bigger than 2.5, are not suitable for an adjustment of the pressure conditions. Hence, slope values bigger than 2.5 are allocated to the closing range. Finally, the slope values, which are smaller than 0.05 are as well not suitable in order to adjust the pressure conditions of a gear pump, since already for small changes of the pressure difference Δp, long adjustment paths x are necessary. For this reason, ranges with slope values, which are smaller than 0.05, are allocated to a residual range, in which the desired adjustments are referred to as useless.
The use of the afore-mentioned definitions for the courses of the pressure difference in function of the adjustment path x according to
It clearly results from the comparison of the courses according to
In
A further embodiment of the present invention is depicted in
It is noted that the pintle 20 is shown in the completely opened as well as in the completely closed position in
It is conceivable for all embodiments of the pintle as well as of the sleeve to provide a cross-section deviating from a rotation-symmetry. Thus, it is particularly conceivable that the pintle and/or the sleeve comprise one of the following cross-sections:
Furthermore, the end of the pintle pointing in direction of the suction side can be embodied differently. Particularly, the end can be embodied tapered—and namely pointed or truncated—, globular or flat.
Finally, it is also conceivable that the pressure adjustment section 22 (
The valve 5 according to
Finally, a special feeding unit 60 is depicted in
The known damper screws described initially perform a rotation around its own axis during the translatory displacement of the pintle 20. Therewith, the sealing, making sure that no pumping medium M flows in direction of feeding unit, are not only stressed by the actual translatory feeding movement, but, in addition, also by the rotation around the own axis. During the pressure adjustment and particularly also at a closing or opening of the return duct, respectively, the sealing is stressed so strongly that their life expectancy is susceptible to being restricted.
A further aspect according to the present invention leads to a considerable improvement of this problem. Thus, in using a mandrel lifting drive 61, it is possible that a mere translatory movement can be obtained. Thus, the sealing 63 are no more stressed by the combination of own rotation and translation of the pintle 20, but merely only by the actual translatory movement, which is necessary for the adjustment of the pressure or for the opening/closing of the valve. Therewith, the glide path of the sealing is reduced.
Further, the feeding unit 60 according to the present invention makes possible a substantial larger lift (maximum length L or maximum adjustment path x, respectively) so that the pressure adjustment characteristics can be implemented making an extremely fine adjustment possible.
Finally, the use of the mandrel lifting drive 61 allows an easier handling during the adjustment process. While the adjustments for the known damper screw must have been made very close to the rotating drive shaft, the adjustment of the embodiment according to the present invention can be carried out with a mandrel lifting drive 61 perpendicularly to the rotating drive shaft. Therewith, the access to the adjustment device is substantially improved and the danger of an injury of operating personnel by the rotating drive shaft is reduced.
Although, the feeding unit 60 is especially suitable in combination with the valve or the depicted embodiments according to the present invention, respectively, also a combination of the feeding unit according to the present invention with known valves leads to the advantages mentioned in connection with the mandrel lifting drive. For this reason, the feeding unit according to the present invention has to be looked at independently from the valve according to the present invention and hence deserves protection independent from the valve.
Number | Date | Country | Kind |
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06113845.9 | May 2006 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2007/054660 | 5/14/2007 | WO | 00 | 9/24/2008 |