EP2982863B1 - Reciprocating piston pump for cryogenic liquids - Google Patents

Description

• einen Pumpenzylinder mit einer Laufbüchse und einer Zylinderkopfkammer,
• einen Pumpenkolben, der in der Laufbüchse linear beweglich geführt ist,
• ein Einlassventil, das in einem Einlassbereich der Zylinderkopfkammer angeordnet ist und dem Einlass der kryogenen Flüssigkeit dient, und
• ein Auslassventil,das in einem Auslassbereich der Zylinderkopfkammer angeordnet ist und dem Auslass der kryogenen Flüssigkeit dient.

Der Pumpenkolben ist dazu ausgebildet, sich in der Laufbüchse zwecks Bewirkung des Pumpvorganges hin- und herzubewegen und die Zylinderkopfkammer durch die Hin- und Herbewegung des Pumpenkolbens zu bilden bzw. zu vergrössern und zu verkleinern.The invention relates to a reciprocating pump for cryogenic liquids according to claim 1, wherein the reciprocating pump has substantially the following structural features:

• a pump cylinder with a liner and a cylinder head chamber,
• a pump piston, which is guided linearly movable in the liner,
• an intake valve disposed in an inlet region of the cylinder head chamber and serving the inlet of the cryogenic liquid, and
• an exhaust valve disposed in an outlet portion of the cylinder head chamber and serving the outlet of the cryogenic liquid.

The pump piston is adapted to reciprocate within the liner for effecting the pumping action and to form, enlarge and reduce the cylinder head chamber by the reciprocating motion of the pump piston.

Wear resistance is a problem with cryogenic reciprocating pumps - as with all piston pumps - especially when the piston pumps are operating at very high pressures. The wear-sensitive area are the sealing or piston rings on the pump piston. In this area, therefore, the combination of materials between liners and piston rings is of particular importance, because high abrasion resistance and good sliding properties are important here. To make matters worse, of course, that one works in the extreme low temperature range and that the type of medium to be pumped (for example, liquid oxygen) may under certain circumstances further limit the number of usable material combinations.

Piston pumps for cryogenic liquids which operate at very high pressures are known, for example, from US Pat CH-703 376 and the US-2003/0080512 known. In the former, it is mentioned that the sealing rings arranged in a region close to the piston head or in the vicinity of the cylinder head chamber consist of a combination of PTFE and bronze rings, the latter still exists a little more detail, stating that the bronze content of the rings is greater than 50%, that a tungsten disulphide content of about 5% is used, and that, by the way, PTFE is also used. It is known that combinations of stainless steel liners and low friction bronze & PTFE compound piston rings are common in this field of technology.

On the other hand, it is also known that today hard-chrome coatings are often used for particularly wear-resistant surfaces. For example, in the general state of the art for piston engines, such as in DE102007038188A1 a wear-resistant coated machine element, in particular a piston ring with a hard chrome layer applied to the surface. Under machine elements in this publication but also impression cylinder, piston and the like understood. Obviously, however, the applications specifically mentioned are those in the high-temperature range, namely for reciprocating engines. Basically, the hard chrome layer is introduced to reduce wear due to friction as possible, but this is because of the main field of application for piston engines, of course, mainly to achieve a high fire resistance. The latter, however, is not important for cryogenic applications.

Finally, the shows US 20130118424 in that chromium as a coating material is partly already used in piston pumps for cryogenic media because of its high wear resistance. Thus, this publication shows that a piston of such a piston pump is indeed provided in a piston tip remote sealing area, but not in a piston tip near the piston ring area with a hard chrome coating. It seems to be inferred from this disclosure as a whole only that the hard chrome coating in the sealing area together with a scraper apparently was therefore chosen to damage the seals that Partially caused by pollution particles in the cryogenic media, to avoid as possible.

Furthermore, it is off CA 734 207 A a reciprocating pump for cryogenic liquids, wherein the pump piston of the reciprocating pump has a chromium-based coating.

The further document DE 16 20 112 U discloses a piston pump in which, among other things, the liners of the cylinder have a hard chrome plating.

Furthermore, the document discloses DE 10 2008 011 456 A1 a piston pump for conveying cryogenic liquids in the field of automotive engineering. Boron nitride in aluminum oxide and graphite-filled Teflon in aluminum oxide can be used as material combinations for the piston or bushing, for example, and instead of the aluminum oxide, chromium nickel steel can also be used.

The object of the invention is therefore to provide a reciprocating pump for cryogenic liquids, which has particularly low-wear and at the same time particularly low-friction materials or material combinations in the highly loaded piston ring or sealing region and which is also particularly simple.

This object is achieved by the feature combination of claim 1.

The solution is that the liner has a chromium-based low-friction inner coating, at least in a region close to the cylinder head, and the pump piston is piston-less and, at least in the liners, a chromium-based low-friction Has outer coating. Of course, piston ringless basically means a significant design simplification.

It is proposed to use chromium-based low-friction coatings for the liners as well as for the pump piston, which have a layer thickness of <0.01 mm and a chromium content of> 98%. Other but basically similar chromium-based low-friction coatings with different layer thicknesses, different layer structure, similar chromium shares and possibly different residual amounts of other metals are of course also possible, but still poorly tested in the current state of development. The proposed thickness and composition has already yielded good results in experiments.

Chromium coatings are therefore not only hard, they also have a very low coefficient of friction. In general, however, further considerations must be taken into account when choosing the material combinations, as tolerances and surface roughness also influence the achievable result. So you have to assume in non-piston machines assume that you must provide closer tolerances between the pump piston and the piston sleeve to achieve an approximately equal pump efficiency as in piston ring using machines. To reduce the risk of the pump piston and piston sleeve surfaces jamming or even sticking together, mutual friction must be kept low. With the material combination of steel and bronze or gray cast iron used so far clamping and adhesion problems could possibly be avoided, but the problem of wear of the piston would still exist and thus would probably still to a greater extent the problem of rapid drop in pump efficiency or the so associated high service life and complex maintenance. Alternative material combinations, which come into consideration for piston-ring machines in general, must therefore not only have a low mutual friction and a very good abrasion resistance, but also the mentioned Consider adhesion problems with tight tolerances. Chromium-on-chromium material combinations are suitable in principle because they have at least the first two properties.

Tight tolerances in the mating of piston sleeve and piston and smooth surfaces to achieve a low coefficient of friction thus have their own problems. Although it is known that the coefficient of friction between two materials is reduced with very smooth surfaces, the risk of adhesion also increases. It may therefore be necessary to take further measures to reduce the risk of liability. One such measure is to use a chrome-based low friction coating that has micro-bumps to reduce the mutual contact areas. In principle, a similar idea has been proposed in the engine field, but there the physical and chemical conditions are completely different, but is still either completely or at least partially presupposes the presence of a lubricant (see, eg DE-102005054622 ). The reaction is therefore not readily transferable to lubricant-free cryogenic reciprocating pumps.

Fig. 1

Eine Hubkolbenpumpe für kryogene Flüssigkeiten mit einer Laufbüchsen-Innenbeschichtung und einer Kolben-Aussenbeschichtung die chrom-basiert und reibungsarm sind.

The invention will be described in more detail below with reference to a drawing. It shows the

Fig. 1

A reciprocating pump for cryogenic liquids with a liners inner coating and a piston outer coating which are chrome-based and low-friction.

The FIG. 1 shows a reciprocating pump for cryogenic liquids with a liner inner coating and a piston outer coating which are chrome-based and low friction in a cross-sectional view. Shown in simplified form, only the pump piston area because the rest Components of the reciprocating pump are not relevant to the understanding of the present invention.

• Ein Pumpenzylinder 1 hat im Innern eine Laufbüchse 2 und eine Zylinderkopfkammer 3. Die Zylinderkopfkammer 3 ist in dieser Figur allerdings nicht ohne weiteres erkennbar, angedeutet ist deshalb lediglich der Bereich in dem sie sich im Betrieb der Hubkolbenpumpe ausbildet. In der Laufbüchse 2 ist ein Pumpenkolben 4 in einer Bewegungsrichtung P linear beweglich geführt, und zwar so, dass er eine Hin- und Herbewegung ausführt. Die Antriebsmittel für den Pumpenkolben, nämlich ein Pumpenmotor, sind nicht dargestellt, wohl aber ein Antriebsende 8 des Pumpenkolbens 4, das mit dem Antriebsmittel verbindbar ist. Weil der Pumpenkolben 4 hier in der maximalen Vorschubstellung gezeigt ist, ist das Volumen der Zylinderkopfkammer 3 in dieser Darstellung auch auf dem tiefsten Wert, nämlich praktisch gleich Null. Ein Einlassventil 5 ist in einem Einlassbereich der Zylinderkopfkammer 3 angeordnet ist und dient dem Einlass der kryogenen Flüssigkeit in die Zylinderkopfkammer 3. Ein Auslassventil 6 ist in einem Auslassbereich der Zylinderkopfkammer 3 angeordnet und dient dem Auslass der kryogenen Flüssigkeit aus der Zylinderkopfkammer 3. Einlassventil 5 und Auslassventil 6 befinden sich an dem dem Antriebsende 8 entgegengesetzten kalten Ende 9.

The reciprocating pump according FIG. 1 has essentially the following structural features:

• A cylinder cylinder 1 has inside a bushing 2 and a cylinder head chamber 3. The cylinder head chamber 3 is in this figure, however, not readily apparent, is therefore indicated only the area in which it forms during operation of the reciprocating pump. In the bushing 2, a pump piston 4 is guided linearly movable in a direction of movement P, in such a way that it performs a reciprocating motion. The drive means for the pump piston, namely a pump motor, are not shown, but a drive end 8 of the pump piston 4, which is connectable to the drive means. Because the pump piston 4 is shown here in the maximum feed position, the volume of the cylinder head chamber 3 in this illustration is also at the lowest value, namely virtually equal to zero. An intake valve 5 is disposed in an inlet portion of the cylinder head chamber 3 and serves to introduce the cryogenic liquid into the cylinder head chamber 3. An exhaust valve 6 is disposed in an exhaust portion of the cylinder head chamber 3 and serves to discharge the cryogenic liquid from the cylinder head chamber 3. Intake valve 5 and Exhaust valve 6 are located at the drive end 8 opposite cold end. 9

It should also be noted that the pump piston 4 is piston-free in a region A close to the cylinder head chamber. As mentioned, the pump piston is adapted to reciprocate in the liner to effect pumping in a pumping direction P, and to form and enlarge and reduce the cylinder head chamber 3 by the reciprocating motion of the pump piston.

Furthermore, from the FIG. 1 It can be seen that the bushing 2, in which the pump piston 4 effectively reciprocates, does not extend over the entire length of the pump cylinder 1 extends. The bushing 2 has in its interior a chromium-based low-friction inner coating. The pump piston 4, at least in the area which is in the reciprocating motion with the liner in contact, on a chromium-based low-friction outer coating. Specifically, this applies to the area near the cylinder head chamber A, ie at the cold end 9 of the piston pump.

The chrome-based low-friction inner coating of the liner 2 and the chrome-based low-friction outer coating of the pump piston 4 have, for example, a layer thickness of <0.01 mm and a chromium content of> 98%. It is thus a thin-chromium coating.

In this case, an additional tungsten disulphide (WS ₂ ) layer may be present to improve the dry lubrication properties of the thin-chromium coating.

Furthermore, as mentioned, the chromium-based low-friction coatings of bushing 2 and pump piston 4 may have micro-elevations to reduce the mutual contact surfaces.

List of reference numerals:

1

pump cylinder

2

liner

3

Cylinder head chamber

4

pump pistons

5

intake valve

6

outlet valve

7 8

drive end

9

cold end

A

Cylinder head chamber near area

P

movement direction

Claims (3)

1. A reciprocating piston pump for cryogenic liquids, comprising

   - a cylinder head chamber (3) and a cylinder liner (2) in a pump cylinder (1),

   - a pump piston (4) which is linearly guided in the cylinder liner (2),

   - an inlet valve (5) which is arranged in an inlet area of the cylinder head chamber (3), and

   - an outlet valve (6) which is arranged in an outlet area of the cylinder head chamber (3),

   wherein the pump piston (4) is configured to reciprocate in the cylinder liner (2) for effecting the pumping process,
   wherein the pump piston (4) has no piston rings and has a chromium-based low-friction outer coating at least in the area of the cylinder liner,
   characterized in that
   the cylinder liner (2) has a chromium-based low-friction inner coating at least in an area near the cylinder head, and
   that the chromium-based low-friction coatings have an additional tungsten disulfide (WS₂) layer for improving the dry-running properties.
2. The reciprocating piston pump according to claim 1, characterized in that the chromium-based low-friction inner coating and the chromium-based low-friction outer coating serve for decreasing friction and have a layer thickness of <0,01 mm and a chromium content of >98%.
3. The reciprocating piston pump according to any one of claim 1 or 2, characterized in that the chromium-based low-friction coating have micro-protrusions so as to reduce the mutual contact surfaces.

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