The invention relates to a piston for sucker-rod pumps having a cylindrical piston body with a through hole, and an upper valve body and a lower valve body are fluidly connected to the through hole, and a rod coupling element is provided.

Most of the production wells operating in the oil mining industry are operated by deepwell pumping, as the number of so-called ascending wells operating by self-pressure is negligible. Early pumping solutions include sucker-rod pumping, which dates back a century and is still common today, with the majority of pumped wells using this method.

The sucker-rod pump is basically made of a cylinder, a piston and two ball valves. One of the valves is a moving valve attached to the piston, while the other, the foot valve, is a stationary valve attached to the cylinder. The piston can be used in both sucker-rod pumps and production tubing pumps. In both cases, the cylinder can be fixed to the production tubing at a specified depth, in the case of a sucker-rod pump, the complete pump can be installed in a planting sleeve, while the cylinder of the production tubing pump is fixedly connected to the bottom of the production tubing with a thread. The piston is placed in the cylinder by means of the sucker-rod.

Two-stage deep-well pumps with ring valves or ball valves are usually used in production wells pumping sandy or gaseous products, where two lower and upper valves are placed in the piston. The advantage of a piston with this arrangement is that it better prevents sand from settling between the cylinder and the piston during necessary operational shutdowns and increases the efficiency of pumping gaseous products. The cylinder of the two-stage pump has valve cages both at the bottom and top of the pump body, usually attached with a thread. The function of the valve cage is, on the one hand, to guide the valve ball exactly back to the valve seat during its movement, and on the other hand, to allow the product through its openings. However, the disadvantage of the solution is that the outer surface of the piston, which is composed of at least three different parts, namely the shell of cylinder body and that of the lower and upper cages, does not necessarily form a single surface sliding in the cylinder, so their operation in wells producing solid material and gaseous fluid is not reliable, the piston is frequently jammed, and reduction in efficiency during pumping of gaseous product is common. Another disadvantage is that the valve ball wears off the relatively thin-walled valve cage, which serves as the upper ball housing and as a connecting element between the rod and the piston at the same time, so that in the case of a production tubing pump, the piston, while in the case of a sucker-rod pump, the entire deep-well pump may remain in the well.

Such a deep-well pump is described, for example, by CN111677657 publication document, where the external sliding surface of the piston made of several pieces does not form the same cylinder surface, as it is made up of several elements, and therefore deviations in the diameters of the assembled elements are inevitable. The cage acts as a valve body, recalling the danger of the piston breaking off.

Publication CN 106640610 also presents a multi-piece piston, which is also disadvantageous in the case of production wells that also transport solids. The piston consists of a hollow piston body, as well as the lower and upper valve cages connected with threads below and above the body, therefore the outer shell surface of the piston does not form a uniform cylinder surface here either, the deviations in the diameters of the assembled elements are inevitable again. There is a taper on the lower part, but due to the smaller diameter of the lower valve cage, there is a large gap between the cylinder liner and the lower part of the piston, which is why solid material can get wedged there. In the upper part, the cage does not eject the product in the right direction, there is no taper in the right direction, thus there is no effect to avoid wedging of solid material along the working length of the piston, and there is also a large gap between the wall of the cylinder and the upper cage. They try to exclude solid contamination by means of different sealing rings, but this cannot be done along the entire length of the piston.

The deep-well pump disclosed by the publication No. US4395204 is equipped with a multi-piece piston and is therefore not advantageous for wells also producing solids. The outer shell surface of the multi-piece piston does not form a single cylinder surface here either, as it is made up of several elements, so differences in the diameters of the assembled elements are inevitable in this case, too. Soft sealing rings are only located a certain distance below the upper part of the piston, which is also a major source of danger of jamming, since the metallic sealing surface cannot fit tightly to the cylinder wall. The piston can be bound in the cylinder, since the fixing of axial position is not given along the entire length, since there is no sealing ring surface in its lower part. The piston can only have a single valve, it is not possible to install an upper valve. It is not equipped with a self-cleaning mechanism since there is no tight cylinder-piston connection along the entire working length. Between the nut securing the valve seat and the lower part of the piston there is that harmful gap, which poses a serious risk for the collection of solid material and then for jamming of the piston. Due to its design it is not suitable for position independent start-up, as during the operation of the pump solid material may occur in the product in both directions, which may flow between the cylinder and the wall of the piston. If, for example, the piston has to be started on the upstroke the solid contamination falling back, and if the piston has to be started on the downstroke, the solid material stuck to the cylinder wall or in the upflowing product can cause problems. The pistons mentioned above are therefore not self-cleaning, so they can get jammed, their position-independent start is not possible, and in case of significant wear of the rod coupling element, i.e. the valve cage, the piston or the entire pump can remain in the well.

Our object with the solution according to the invention is therefore to provide a piston for a deep- well rod pump, where the outer shell surface of the piston forms a single, gap-free cylinder surface, which is a working and sealing surface along its entire length, thus the piston has self-cleaning properties, therefore the risk of its jamming in the cylinder is minimal, and it can be started regardless of the shutdown position in any case, and the rod coupling element is not exposed to significant wear, therefore the breaking off of the piston or the entire pump can be avoided.

We achieved our object by providing a piston for a sucker-rod pump, having a cylindrical piston body with a through hole, and an upper valve body and a lower valve body are connected to the through hole, and a rod coupling element is provided, wherein an upper valve pocket and a lower valve pocket are machined in the through hole, and the lower valve body is fixed in the lower valve pocket , the upper valve body is fixed in the upper valve pocket between the lower valve body and the rod coupling element fixed in the upper valve pocket , and the valve pockets of the piston are provided with an internal chamfer between the closer end of the piston and respective valve pocket, so that a smallest distance between the shell of the piston and the internal surface of the chamfer measured perpendicularly to the shell of the piston is at most 0.1 mm. These chamfers enable the flow of the product in proper direction.

The angle of the chamfer formed at the end of the piston is between 10° and 45°. The height of the rod coupling element and the height of the upper valve body are at most equal to the height of the upper valve pocket.

The height of the lower valve body is at most equal to the height of the lower valve pocket.

The rod coupling element is provided with a rod-side threaded head.

The difference between the surface hardness of the shell of the piston body and the inner surface hardness of a pump cylinder is at least 200 HV, preferably at least 400 HV, so that the shell of the piston body has a lower surface hardness than the cylinder.

The internal chamfers of the piston between the valve pocket and the closer end of the piston are preferably formed at the same angle at both ends of the piston, and the distance between the valve pockets and the closer end of the piston is the same at both ends of the piston.

The angle of the chamfers formed at the ends of the piston is between 20° and 40°.

The upper valve body and/or the lower valve body is threadedly fixed in its valve pocket.

The upper valve body and/or the lower valve body is fixed in the valve pocket by a tight fit.

The piston for deep-well rod pump according to the invention minimizes the number of cases of removal of the pump from landing due to the piston being jammed, since the solid material in the product cannot be wedged between the piston and the cylinder wall.

The piston according to the invention is described in detail below with reference to the attached drawing. In the drawing:

Figure 1 shows a suitable embodiment of the body of the piston according to the invention in a longitudinal cross section,

Figure 2 shows the upper valve body,

Figure 3 shows a rod coupling element, and

Figure 4 shows the design of the lower valve body.

Figure 1 shows an advantageous embodiment of the piston 1 according to the invention in a longitudinal section, where the piston 1 is formed with a cylindrical, one-piece piston body la. The piston 1, in the case of a deep-well rod pump assembly, fits into a cylinder 2 firmly fixed in a production tubing T, and in the case of a production tubing T pump, it fits into the production tubing T itself, in which it performs an alternating movement during the deep-well pumping operation consisting of upstrokes and downstrokes. From this point of view, the arrangement according to Figure 1 shows a deep-well rod pump assembly, so that a cylinder 2 is attached to the inside of the production tubing T. In the figure, it can be observed that the piston 1, unlike the state-of-the-art solutions, is made of a single piece. A through hole 3 is formed along the axis t of the piston 1, from which a cylindrical lower valve pocket 5a with a height h and a cylindrical upper valve pocket 4a with a height H are machined near the front surfaces 4h, 5h of the piston 1. The diameter of the section of the through hole 3 between the valve pockets 4a, 5a is therefore preferably smaller than the diameter of the valve pocket 4a, 5a. The inner cylindrical surface of both valve pockets 4a, 5a is provided with threads 4m, 5m.

One of the basic conditions for starting up the piston 1 from a stationary state, from any position, is that the product cannot flow between cylinder 2 and the wall of the piston 1, because the solid particles transported by the product can cause the piston 1 to get stuck. If the piston 1 has to be started upwards from the bottom, then solid particles fallen back in the production tubing T, if piston 1 has to be moved downwards, then solid particles stuck to the cylinder wall can get between cylinder 2 and the wall of the piston 1. Therefore, between the cylindrical surface of the valve pocket 4a, 5a of the valve body and the front surfaces 4h, 5h of the piston 1, the valve pockets 4a, 5a of the valve body of the piston 1 are formed with internal chamfers 4e, 5e, so that a smallest distance 7 between the shell ) of the piston 1 and the internal surface of the chamfer 4e, 5e measured perpendicularly to the shell ) of the piston 1 should be as small as possible, preferably not more than 0.1 mm. According to our experience, the angle a of the chamfer 4e,5e formed on the ends 4,5 of the piston 1 should be preferably between 10° and 45°, and preferably between 20° and 40°. The chamfer 4e, 5e diverts the product from the wall of the cylinder 2 into the direction of the axis t of the piston 1. This can greatly prevent the solid particles transported in the product from getting between the shell P of the piston 1 and the surface of the cylinder 2 causing a bind, which leads to the stoppage and severe damage of the pump. Since during the downstroke and the upstroke, solid contamination from the product can get between piston 1 and cylinder 2 with the same probability, and the flow rate of the product is also similar, the internal chamfers 4e, 5e of the piston 1 between the valve pockets 4a, 5a and the closer front surfaces 4h, 5h of piston 1 are formed preferably, but not necessarily, at the same angle a along the two front surfaces 4h, 5h of the piston 1, and the distance 7a between the valve pockets 4a, 5a and the closer front surface 4h, 5h of the piston 1 is preferably the same.

The hardness of the shell P of the piston body la and the inner surface of the cylinder 2 are preferably different. The difference in the surface hardness of the sliding elements is at least 200 HV, preferably at least 400 HV, so that the surface hardness of the shell P of the piston body la is lower. For example, if the hardness of the shell P is 500 HV, the hardness of the inner surface of the cylinder 2 is expediently at least 700 HV, preferably at least 900 HV. With this measure it can be achieved that the wear of piston body la, which is connected to the rod and is therefore easier to replace, is faster.

A cylindrical upper valve body 8 provided with an external thread as shown in Fig. 2 is threaded to the thread 4m of the valve pocket 4a, so that a though hole of valve seat 9 of the upper valve body 8 and the through hole 3 of the piston 1 form a continuous flow passage. In a further, advantageous embodiment, instead of threading the upper valve body 8, the upper valve body 8 can also be fixed in the pocket 4a by tight fit. In this case, the inner surface of the pocket 4a and the outer surface of the valve body 8 are smooth cylindrical surfaces. The valve seat 9 is fitted with a valve ball 13, and a hole 11 is formed at the end of the valve body 8 opposite the valve seat 9 eccentrically with respect to the axis t in order to maintain the flow capacity. Above the valve seat 9 there is a cylindrical ball chamber 12 receiving the valve ball 13. A part of the ball chamber 12 next to the valve seat 9 has a conical shape, which serves to precisely guide the valve ball 13. The height Hl of the upper valve body 8 is smaller than the height H of the pocket 4a.

A cylindrical rod coupling element 14 with an external thread shown in Figure 3 is connected to the thread 4m of the pocket 4a of the upper valve body 8, the form of which is similar to that of the well-known valve cage in the prior art practice, but it does not contain either any valve ball 13 or valve seat 9. In a further, advantageous embodiment, the rod coupling element 14 can be fixed in the valve pocket 4a of the upper valve body 8 by a tight fit instead of a threaded connection. In this case, the inner surface of the pocket 4a and the outer surface of the rod coupling element 14 are both smooth cylindrical surfaces. The rod coupling element 14 is located directly above the upper valve body 8 and at the same time prevents its rotation around the axis t. The height H2 of the rod coupling element 14 is such that it is located below the chamfer 4e, i.e. H1+H2 < H. The rod coupling element 14 is provided with a threaded head F near the rod, and with at least one hole W between the height H2 and the threaded head F, and its sole surface S is open in the direction of the valve body 8 and forms a flow passage with the hole 11 of the valve body 8.

The cylindrical lower valve body 15 with an external thread shown in Figure 4 is connected to the thread 5m of the valve pocket 5a, so that the valve seat 16 of the lower valve body 15 and the through hole 3 of the piston 1 form a continuous flow passage. In a further, advantageous embodiment, the lower valve body 15 can be fixed in the pocket 5a with a tight fit instead of a threaded connection. In this case, both the inner surface of the pocket 5a and the outer surface of the valve body 15 are smooth cylindrical surfaces. The shape of the valve body 15 is similar, ideally identical to that of the upper 8 valve body. The valve seat 16 is fitted with a valve ball 17, and a hole 18 is formed at the end of the valve body 15 opposite to the valve seat 16. Above the valve seat 16 a cylindrical ball chamber 19 is provided, and a valve ball 17 is arranged in the ball chamber 19. The height hl of the lower valve body 15 is less than or equal to the height h of the valve pocket 5a.

In summary, in the cylindrical piston body la of the piston 1 for a sucker-rod pump according to the invention a through hole 3 is formed. An upper valve body 8 and a lower valve body 15 are connected to the through hole 3, and a rod coupling element 14 is provided. The upper valve pocket 4a and the lower valve pocket 5a are machined in the through hole 3, and the lower valve body 15 is fixed in the lower valve pocket 5a, the upper valve body 8 is fixed in the upper valve pocket 4a between the lower valve body 15 and the rod coupling element 14 fixed in the upper valve pocket. The valve pockets 4a, 5a of the piston 1 are provided with an internal chamfer 4e,5e between the valve pockets 4a, 5a and the closer end of the piston 1, so that a smallest distance 7 between the shell P of the piston 1 and the internal surface of the chamfer 4e,5e measured perpendicularly to the shell P of the piston 1 is at most 0.1 mm. These chamfers enable the flow of the product in proper direction. The height H2 of the rod coupling element 14 and the height Hl of the upper valve body 8 are at most equal to the height H of the upper valve pocket 4a. The height hl of the lower valve body 15 is at most equal to the height h of the lower valve pocket 5a. The rod coupling element 14 is provided with a rod-side threaded head F. The difference between the surface hardness of the shell P of the piston body la and the inner surface hardness of a pump cylinder 2 is at least 200 HV, preferably at least 400 HV, so that the shell P of the piston body la has a lower surface hardness than the cylinder 2. Since the lower valve body 15 and upper valve body 8 of piston 1 are preferably formed of the same design, the production of the piston 1 according to the invention requires only the use of a single type of valve body 8,15.

The most important advantage of the piston 1 according to the invention as compared to the pistons 1 of the deep-well rod pumps according to the state of the art is that due to the appropriately sized and positioned edges 4e, 5e, it is self-cleaning, i.e. the majority of the solid particles transported by the product cannot get between the cylinder 2 and the wall of the piston 1, and microscopic particles that get between the walls of the cylinder 2 and the piston 1, despite this measure, cannot accumulate in the joint gap of the piston 1, because the outer shell surface of the piston 1 forms a single piston body la with a gap-free cylinder surface, so that pollutants cannot accumulate in gaps, therefore the risk of its jamming in the cylinder 2 or in the production tubing T is minimal, and it can be started up regardless of the shutdown position in any case, and the rod coupling element 14 is not exposed to wear, therefore the break off of the piston 1 or of the entire pump can be avoided. The piston 1 according to the invention can be used for both production tubing and socker-rod pumps and can be manufactured in arbitrary or standardized sizes.