Rotary piston pump

The principle of operation of the structure

The device is designed on the basis of a rotary piston mechanism (RPM) from the engine of the famous German inventor Wankel. But to perform the function of pumping liquid and gas, the RPM is transformed as follows. For the three-vertex piston, a different working surface was chosen instead of the old one according to the Reuleaux triangle. For the inner surface of the chamber, a new surface was also applied, which gives the mechanism a more accurate functioning, its mathematical formulas are derived. According to the principle of operation, the pump belongs to volumetric devices with suction and subsequent extrusion of liquid or gas from the internal cavity.

Pump application area and advantages

The aim of the development of the pump was to be able to universally apply it for: ̶ the use in the oil production industry instead of mine piston pumps with bulky ground equipment, expensive multi-screw pumps and centrifugal pumps, mainly intended for relatively “clean” oil; ̶ maintenance of liquid or gas pumping systems, as well as for power systems (hydraulic and pneumatic) of control and management with electronic support, for example, in cars; ̶ water supply of residential buildings instead of gear, piston, centrifugal and other types of pumps. Advantages (so far calculated) of the new pump over the above: ̶ performance is 1.5 times higher (with equal dimensions and weight); ̶ pump efficiency> 0.92 (for the above ≈0.85).

Brief description of the design of the main links

The figures show two versions of the Rotary Piston Pump: ‒ variant Ⅰ with suction and delivery nozzles on the end caps; ‒ version Ⅱ with suction and discharge fittings located on the body. Fig. 1a shows the complete pump according to variant Ⅰ, in fig. 1b – the same according to variant Ⅱ. Figure 2 shows the disassembled version Ⅱ pump. In variant Ⅰ, the body-sleeve link is a single part, in variant Ⅱ, these are two different parts. The group of main links also includes a piston, an eccentric shaft and two covers. An additional brief description of the design of these links is given below. Sleeve 1 serves to accommodate the rotary mechanism. To ensure uniform pumping, the inner surface of the sleeve must be machined along a special figured surface, on which piston 2 accurately slides and rolls. Mathematical formulas for this surface are calculated and derived. Piston 2 is used to displace and suck liquid or gas when the shaft rotates. To obtain a uniform pumping, the outer surface of the piston was chosen to be special with a different guide (instead of the old guide – ∆ Reuleaux), which also has three rounded tops. The inner surface of the piston is cylindrical and serves for a movable fit on the shaft eccentric. Piston ends are flat. The eccentric shaft 3 is used to transfer the rotational energy to the rotary assembly of the pump. The inner part of the shaft is made in the form of an eccentric 5 for a movable fit of the piston 2 on it. The covers 6, 7 serve to support the shaft 3 and limit the longitudinal displacement of the piston 2 and the eccentric 5 with the shaft, which, during the operation of the pump, slide freely with their flat ends along the inner flat end of each cover. In variant Ⅰ, suction and discharge pipes are located on the outer ends of the covers. Note. The illustrations do not show auxiliary parts such as seals, bearings, supports, fasteners, etc.

General description of pump function

Based on the device design described in detail above, the sequence of operation of the pump var. Ⅱ when pumping liquids, for example. In var. Ⅰ the principle of operation is similar, but the tracing of the liquid is much simpler – the flow enters the branch pipe (fitting) or leaves it directly without circumferential channels, and the channel openings Ⅰ are IV curly and much larger. Figure 3a shows a general view of the pump in cross section for var. Ⅰ, in Fig.3b – the same for variant Ⅱ. The main lines show the fixed parts and one of the possible intermediate positions of the links of the rotary mechanism of the pump, and the thin lines show the initial position of the piston and shaft. For a simple perception of the principle of operation of the pump, one must proceed from the following conditions: – in the initial situation, one of the tops of the piston Co is on the vertical in the upper position; − shaft 3 rotates at a constant speed n3 counterclockwise. page; − the ratio of rotation speeds of piston 2 and shaft 3 is equal to: n2/ n3=1/3. At any time in the cross section of the device, the piston has at least 4 points of contact with the sleeve, which divide the space between the piston and the sleeve into parts that are variable in volume. When the shaft 3 with the cam 5 rotates through the angle α counterclockwise, the piston, having left the initial position 2o, shown in thin lines, will take the position 2α, turning around its axis by the angle α/3. Such precise rotation is ensured by a specially calculated shape of the inner surface of the liner and the outer surface of the piston under the influence of fluid pressure forces and reactions at the points of contact between the piston and the liner. At the same time, liquid is displaced from the cavities M and m, which enters the left injection fitting 11 through channel holes Ⅰ, Ⅱ and a circumferential communication channel 13. 13 l (located behind channel 13) from the right suction port 11l. With further rotation of the shaft and piston, this incoming liquid is forced out into the left injection nozzle as described above at the beginning of the process. Such pumping of liquid occurs constantly when the shaft rotates in any position of the piston. When shaft 3 rotates in the opposite direction – clockwise, the above fluid flow changes direction and pumping will occur in the opposite direction. Obviously, in one revolution, the presented pump sucks in and further squeezes out more fluid (≈2 times) than the gears of the gear pump, conventionally inserted into the internal dimensions in Fig. 3 (due to the limited height of the teeth).

Pump characteristics

Figure 3 shows schematically the relative position of the piston relative to four holes, of which Ⅰ and Ⅱ work as pumping, and Ⅲ and Ⅳ ̶ as suction when the piston and shaft rotate counterclockwise.

The characteristics of the pump in terms of supply are shown in Fig. 4.

Two types of feed characteristics are selected:

̶ figure 4a shows the specific feed by the angle of rotation of the shaft

̶ angular feed Vangle (cm3/deg.);

̶ Figure 4b shows the specific time feed, i.e. per unit of time ̶ Vvr (cm3/sec.).

The feed characteristic through a certain hole is traced along the corresponding line:

̶ feed through hole Ⅰ is shown by a solid thin line VⅠ,

̶ feed through holes Ⅱ – thin dashed VⅡ;

̶ the total flow of the pump is shown as a thickened solid line V∑.

The graphs show that at constant speed, the total feed is constant. This was confirmed experimentally on a prototype: the outgoing flow was uniform without pulsations, scattering and twisting.

The regularity of the feed characteristics is based on a shifted undeformed sinusoid y = a + b sin (x – c), from which the following formulas are derived:

Evidence of a constant flow of the pump per unit time at constant speed is the symmetry of the other two curves about their common longitudinal axis. As clearly shown in Fig.4b, at any arbitrary moment corresponding to the secant line c-c, the ordinate of the point V(cc)∑ on the line of general supply is equal to the sum of the ordinates of the points V(cc)Ⅰ and V(cc)Ⅱ on the curved lines of supply from holes. The graphs in Fig. 4 are based on the results of testing a prototype with the following data: displacement Vp = 90 cm3/rev., n = 300 rpm, operating pressure p < 5 bar, flow rate Q = 27 l/min. Hydraulic oil RANDO HD46 (viscosity 46 cSt) was pumped.