Horizontal self-priming pump

Abstract

The application relates to the technical field of self-priming pumps, in particular to a horizontal self-priming pump which comprises a pump body, a wear plate, a flow guide component, a shaft and an impeller, the pump body is provided with a liquid inlet channel; the wear plate is arranged at the outlet of the liquid inlet channel; the flow guide component comprises a flow guide plate body and two or more than two arc-shaped guide vanes which are uniformly arranged in the circumferential direction of the flow guide plate body, the arc-shaped guide vanes are arranged in a staggered mode, a guide vane channel is formed between adjacent arc-shaped guide vanes, the inlet of the guide vane channel is communicated with the liquid inlet channel, and the outlet of the guide vane channel is communicated with a gas-liquid separation cavity; the shaft extends into the pump body and is connected with a driving device; the impeller is connected with the shaft, is arranged between the wear plate and the flow guide plate body and is located on the inner side of the arc-shaped guide vanes, and the impeller rotates to guide the fluid in the liquid inlet channel to the tip of the impeller and then to the gas-liquid separation cavity through the guide vane channel. The application is beneficial to discharging gas-liquid mixture, reducing the vibration of the pump, prolonging the service life of the pump and reducing the noise.

Description

Technical Field

[0001] This invention relates to the field of self-priming pump technology, specifically a horizontal self-priming pump. Background Technology

[0002] Self-priming pumps have advantages such as compact structure, convenient operation, stable operation, easy maintenance, high efficiency, and long service life. After normal startup, the impeller draws in the liquid stored in the inlet channel and the air in the suction pipe, which are then completely mixed within the impeller. Under centrifugal force, the liquid, carrying gas, flows towards the outer edge of the impeller, forming a white foam band of a certain thickness and a high-speed rotating liquid ring on the outer edge. The gas-liquid mixture enters the gas-liquid separation chamber. At this point, due to the sudden decrease in flow velocity, the lighter gas is separated from the gas-liquid mixture and continues to rise and be discharged through the pump body outlet. The degassed liquid returns to the storage chamber and re-enters the impeller through the return hole, mixing again with the gas drawn in from the suction pipe inside the impeller. Under the action of the high-speed rotating impeller, it flows towards the outer edge of the impeller again. As this process continues, the air in the suction pipe gradually decreases until all the gas is drawn in, completing the self-priming process, and the pump is put into normal operation.

[0003] However, during the self-priming process of a horizontal self-priming pump, after the gas forms a gas-liquid mixture in the pump's inlet channel, it flows out through the outlet section where the pump body tongue is located, enters the pump body's gas-liquid separation chamber, and discharges the gas. After liquid separation, it returns to the impeller channel to continue working until all the gas is discharged, achieving self-priming. In order to more effectively discharge the gas-liquid mixture, designers generally control the gap between the impeller blades and the pump body tongue to be very small. This results in a large reaction force generated when the tip of the impeller blade passes through the pump body tongue, leading to excessive radial force, causing large pump vibration, severely shortening the life of the pump's mechanical seal, and high pump operating noise, which affects the environment. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention provides a horizontal self-priming pump, which is provided with a wear-resistant plate and a flow guiding component. The impeller is disposed between the wear-resistant plate and the flow guiding plate body, and two or more arc-shaped guide vanes are provided on the flow guiding component to form a guide vane channel, so as to facilitate the discharge of gas-liquid mixture, reduce pump vibration, extend pump service life, and reduce noise.

[0005] To achieve the above objectives, the present invention provides a horizontal self-priming pump, comprising a pump body, a wear-resistant plate, a flow guide component, a shaft, and an impeller. The pump body is provided with an inlet channel; the wear-resistant plate is disposed at the outlet of the inlet channel; the flow guide component is disposed on the wear-resistant plate, the flow guide component comprising a flow guide plate body and two or more evenly distributed arc-shaped guide vanes disposed in the circumferential direction of the flow guide plate body, the arc-shaped guide vanes being staggered to form a guide vane channel between adjacent arc-shaped guide vanes, the inlet of the guide vane channel communicating with the inlet channel, and the outlet of the guide vane channel communicating with a gas-liquid separation chamber; the shaft extends into the pump body, and the shaft is connected to a drive device; the impeller is connected to the shaft, the impeller is disposed between the wear-resistant plate and the flow guide plate body and located inside the arc-shaped guide vanes, the impeller rotates to guide the fluid in the inlet channel to the tip of the impeller, and then delivers it to the gas-liquid separation chamber through the guide vane channel.

[0006] Furthermore, the outlet of the liquid inlet channel is provided with a tongue, which surrounds the wear-resistant plate and forms a flow guide cavity.

[0007] Furthermore, the wear-resistant plate has a wear-resistant plate return hole near the tip of the impeller. One side of the wear-resistant plate return hole is connected to the flow guide cavity, and the other side of the wear-resistant plate return hole is connected to the cavity inside the arc-shaped guide vane.

[0008] Based on the above technical solution, after the pump achieves self-priming and normal operation, the pressure near the outlet of the impeller flow channel is relatively high. If the return hole is opened at the low-pressure part of the impeller flow channel, the return pressure difference during normal pump operation will be large, the return flow rate will be large, and the volumetric loss will be significant. Setting the return hole of the wear-resistant plate near the outer diameter of the impeller flow channel can reduce the return liquid pressure difference and reduce the pump volumetric loss during normal operation.

[0009] Furthermore, a pump body reflux hole is provided at the bottom of the tongue portion of the pump body. One side of the pump body reflux hole is connected to the gas-liquid separation chamber, and the other side of the pump body reflux hole is connected to the guide chamber.

[0010] Based on the above technical solution, a pump body return hole is set at the lower end of the pump body. The liquid separated inside the gas-liquid separation chamber can pass through the bottom pump body return hole and re-enter the impeller flow channel through the guide chamber to participate in the self-priming cycle. That is, the pump body return hole introduces the pressurized medium back into the impeller flow channel from the lower end of the pump body to reduce the gas content in the return medium and achieve rapid self-priming.

[0011] Furthermore, the guide vane channel gradually narrows from the inlet to the outlet.

[0012] Furthermore, the impeller is an open impeller.

[0013] Based on the above technical solution, the horizontal self-priming pump is equipped with an open impeller that facilitates thorough gas-liquid mixing. The open impeller and the wear-resistant plate cooperate to form an impeller flow channel. Wear-resistant plate return holes are set near the outer diameter of the impeller flow channel. The number of wear-resistant plate return holes is designed according to the pump flow rate and exhaust volume requirements. The return point is located inside the impeller flow channel outlet, allowing the return liquid to achieve rapid gas-liquid mixing with air inside the impeller.

[0014] Furthermore, the arc-shaped guide vane includes a first arc-shaped guide vane and a second arc-shaped guide vane, which are evenly distributed in the circumferential direction of the guide vane body.

[0015] Based on the above technical solution, the two guide vanes are evenly arranged, which can effectively balance the radial force and further reduce the vibration of the pump.

[0016] Furthermore, the first arc-shaped guide vane has a first end and a second end that are opposite to each other, and the second arc-shaped guide vane has a third end and a fourth end that are opposite to each other. A first guide vane channel is formed between the first end and the third end, and a second guide vane channel is formed between the second end and the fourth end.

[0017] The first end is located outside the third end, and the third end is offset toward the center of the guide plate body; the second end is located inside the fourth end, and the second end is offset toward the center of the guide plate body.

[0018] Based on the above technical solution, the guide vane is inclined towards the center, which makes the inlet area large. This inclined guide vane shape can collect gas-liquid mixture well. The radial dimension of the guide vane inlet can also be cut as needed, so that the guide vane inlet size varies with the impeller diameter. Impellers with different heads can use the same guide vane blank.

[0019] Furthermore, the arc-shaped guide vane abuts against the wear-resistant plate.

[0020] Furthermore, the pump body is detachably connected to a pump cover, the pump cover is connected to the shaft, and the shaft is connected to a drive device to drive the impeller to rotate.

[0021] The beneficial effects of this invention are as follows: The horizontal self-priming pump of this invention has two or more evenly distributed arc-shaped guide vanes arranged in the outer circumferential direction of the impeller to form a guide vane channel on the outer side of the impeller. The inlet of the guide vane channel collects the gas-liquid mixture and leads it out from the outlet. That is, the guide vane channel can guide the gas-liquid mixture from the liquid inlet channel to the gas-liquid separation chamber in a directional and regular manner, thereby effectively reducing the vibration of the impeller tip, thus reducing pump vibration, extending pump service life, and reducing noise. Moreover, the evenly distributed arc-shaped guide vanes can effectively balance the radial force of the impeller, making the pump run smoothly. In addition, the outlet of the guide vane channel makes the liquid outflow smoother, accelerates the self-priming process, and thus improves the pump efficiency. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a horizontal self-priming pump in one embodiment of the present invention;

[0023] Figure 2 This is a partially enlarged view of the position of the flow guiding component and the impeller in one embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the flow guiding component in one embodiment of the present invention;

[0025] Figure 4 This is a side view of a flow guiding component in one embodiment of the present invention;

[0026] In the picture:

[0027] 100. Pump body; 110. Inlet channel; 111. Outlet; 120. Divider tongue; 121. Pump body reflux hole; 130. Pump cover; 140. Sand removal hole.

[0028] 200, wear-resistant plate; 210, wear-resistant plate reflux hole.

[0029] 300. Flow guiding component; 310. Flow guiding plate body; 320. Arc-shaped guide vane; 321. First arc-shaped guide vane; 3211. First end; 3212. Second end; 3213. Outlet; 322. Second arc-shaped guide vane; 3221. Third end; 3222. Fourth end.

[0030] 400, shaft

[0031] 500, Impeller,

[0032] 600. Sealing components,

[0033] a. Guide vane channel, a1. First guide vane channel, a2. Second guide vane channel, b. Gas-liquid separation chamber, c. Flow guiding chamber, d. Chamber body, e. Impeller flow channel, f. Guide vane flow channel. Detailed Implementation

[0034] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] See Figure 1 and Figure 2 This diagram illustrates a horizontal self-priming pump according to an embodiment of the present invention. The pump includes a pump body 100, a wear-resistant plate 200, a flow guide component 300, a shaft 400, and an impeller 500. The impeller 500, wear-resistant plate 200, and flow guide component 300 are internally disposed within the pump body 100, and the impeller 500 is mounted on the shaft 400. The pump body 100 has an inlet channel 110; the wear-resistant plate 200 is disposed at the outlet 111 of the inlet channel 110; the flow guide component 300 includes a flow guide plate body 310 and two or more evenly distributed arc-shaped guide vanes 320 disposed in the circumferential direction of the flow guide plate body 310. In this embodiment, two arc-shaped guide vanes 320 are shown, staggered to form a guide vane channel a between adjacent arc-shaped guide vanes 320. The inlet of guide vane channel a is connected to the liquid inlet channel 110, and the outlet of guide vane channel a is connected to the gas-liquid separation chamber b. The shaft 400 extends into the pump body 100 and is connected to a drive device. The impeller 500 is connected to the shaft 400 and is located between the wear-resistant plate 200 and the guide plate body 310 and inside the arc-shaped guide vane 320. The impeller 500 rotates to guide the fluid from the liquid inlet channel 110 to the tip of the impeller 500 and send it to the gas-liquid separation chamber b through the guide vane channel a.

[0036] The aforementioned horizontal self-priming pump features two or more arc-shaped guide vanes 320 arranged along the outer circumference of the impeller 500, forming a guide vane channel a on the outer side of the impeller 500. The inlet of guide vane channel a collects the gas-liquid mixture, and the outlet leads the mixture out. In other words, guide vane channel a can guide the gas-liquid mixture from the inlet flow channel 110 to the gas-liquid separation chamber b in a directional and regular manner, effectively reducing the vibration at the tip of the impeller 500, thereby reducing pump vibration, extending pump service life, and reducing noise. Furthermore, the outlet of guide vane channel a allows for smoother liquid flow, accelerating the self-priming process and thus improving pump efficiency.

[0037] In one embodiment, the outlet 111 of the liquid inlet channel 110 is provided with a tongue 120, which surrounds the wear-resistant plate 200 and forms a guide cavity c.

[0038] See Figure 1 and Figure 2In one embodiment, a wear-resistant plate reflux hole 210 is provided on the wear-resistant plate 200 near the tip of the impeller. This location near the tip of the impeller is at the outer diameter of the impeller flow channel e. One side of the wear-resistant plate reflux hole 210 communicates with the guide cavity c, and the other side communicates with the cavity d inside the arc-shaped guide vane 320. After the pump has completed self-priming and is operating normally, because the pressure near the outlet of the impeller flow channel e is relatively high, if the reflux hole is located at the low-pressure area of ​​the impeller flow channel e, the reflux pressure difference during normal pump operation will be large, resulting in a large reflux flow rate and significant volumetric loss. In this embodiment, the wear-resistant plate reflux hole 210 is located on the wear-resistant plate 200 near the outer diameter of the impeller flow channel e, which reduces the reflux liquid pressure difference and minimizes pump volumetric loss during normal operation.

[0039] See Figure 1 and Figure 2 In one embodiment, a pump body return hole 121 is provided at the bottom of the tongue portion 120 of the pump body 100. One side of the pump body return hole 121 communicates with the gas-liquid separation chamber b, and the other side of the pump body return hole 121 communicates with the guide chamber c. In this embodiment, a pump body return hole 121 is provided at the lowest point of the lower end of the pump body 100. The liquid separated inside the gas-liquid separation chamber b can pass through the pump body return hole 121 at the bottom and re-enter the impeller flow channel e through the guide chamber c to participate in the self-priming cycle. That is, the pump body return hole 121 reintroduces the pressurized medium from the lower end of the pump body 100 into the impeller flow channel e to reduce the gas content in the return medium and achieve rapid self-priming. In specific settings, the size of the return hole can be controlled according to design requirements, and the hole can be opened.

[0040] See Figure 3 and Figure 4 In one embodiment, the guide vane channel a gradually narrows from the inlet to the outlet. This arrangement allows the medium to enter the inlet of the wider guide vane channel a more smoothly and flow along the guide vane channel a to the outlet of the narrower guide vane channel a for discharge, which is beneficial for collecting the gas-liquid mixture.

[0041] See Figure 1 and Figure 3 In one embodiment, the impeller 500 is an open impeller. In this embodiment, the horizontal self-priming pump is equipped with an open impeller that facilitates thorough gas-liquid mixing. The open impeller and the wear-resistant plate 200 cooperate to form an impeller flow channel. Wear-resistant plate return holes 210 are provided on the wear-resistant plate 200 near the outer diameter of the impeller 500 flow channel. The number of wear-resistant plate return holes 210 is designed according to the pump flow rate and exhaust volume requirements. The return point is located inside the impeller flow channel outlet, allowing the return liquid to achieve rapid gas-liquid mixing with air inside the impeller.

[0042] See Figure 3 and Figure 4In one embodiment, the arc-shaped guide vane 320 includes a first arc-shaped guide vane 321 and a second arc-shaped guide vane 322, which are evenly distributed in the circumferential direction of the guide vane body 310. This arrangement, with the first arc-shaped guide vane 321 and the second arc-shaped guide vane 322 evenly distributed in the circumferential direction, can effectively collect the gas-liquid mixture and guide it into the guide vane channel a and the gas-liquid separation chamber b of the pump body. Preferably, in this embodiment, the two guide vanes are evenly distributed, which can effectively balance the radial force and further reduce pump vibration. It should be noted that in this embodiment, "evenly distributed" means that the first arc-shaped guide vane 321 and the second arc-shaped guide vane 322 have the same length and curvature, and the second arc-shaped guide vane 322 includes a structure after the first arc-shaped guide vane 321 has been rotated 180 degrees and offset in the diametrical direction.

[0043] See Figure 3 and Figure 4 In one embodiment, the first arc-shaped guide vane 321 has a first end 3211 and a second end 3212 that are opposite to each other, and the second arc-shaped guide vane 322 has a third end 3221 and a fourth end 3222 that are opposite to each other. A first guide vane channel a1 is formed between the first end 3211 and the third end 3221, and a second guide vane channel a2 is formed between the second end 3212 and the fourth end 3222, so that the inlet size of the first guide vane channel a1 is larger than the outlet size, that is, it gradually contracts and converges from the inlet to the outlet, which is more conducive to the collection of gas-liquid mixture. The first end 3211 is disposed outside the third end 3221, and the third end 3221 is offset from the center of the guide vane body 310. The second end 3212 is disposed inside the fourth end 3222, and the second end 3212 is offset from the center of the guide vane body 310, so that the inlet size of the second guide vane channel a2 is larger than the outlet size, that is, it gradually contracts and converges from the inlet to the outlet, which is more conducive to the collection of gas-liquid mixture.

[0044] It should be noted that the guide vane is inclined towards the center, which makes the inlet area large. This inclined guide vane shape can collect the gas-liquid mixture well. The radial dimension of the guide vane inlet can also be cut as needed, so that the guide vane inlet size can vary with the impeller diameter. Impellers with different heads can use the same guide vane blank.

[0045] See Figure 2Guide vane channels f are formed in the first arc-shaped guide vane 321 and the second arc-shaped guide vane 322. The guide vane channels f are connected to the outlet of the guide vane channel a. In one embodiment, an outlet portion 3213 is provided on the outer wall of the first arc-shaped guide vane 321, forming the outlet of the guide vane channel f. The outlet of the guide vane channel f is connected to the gas-liquid separation chamber b. In one embodiment, the outlet portion 3213 includes a protrusion that bends from the outer wall to the outer edge of the guide vane body 310. In this embodiment, the streamlined structure of the outlet portion 3213 can reduce the impact and resistance of the medium on the first arc-shaped guide vane 321 to a certain extent, thereby improving the efficiency of medium discharge and reducing vibration.

[0046] See also Figure 1 In one embodiment, the pump body 100 is detachably connected to a pump cover 130, the pump cover 130 is connected to the shaft 400 via a sealing assembly 600, and the shaft 400 is connected to a drive device (not shown) to drive the impeller 500 to rotate, the rotation of the impeller 500 forming an impeller flow channel e.

[0047] In one embodiment, the arc-shaped guide vane 320 abuts against the wear-resistant plate 200. Specifically, the flow guiding component 300 is pressed by the pump cover 130, and the end face of the arc-shaped guide vane 320 of the flow guiding component 300 away from the flow guiding plate body 310 abuts against the wear-resistant plate 200.

[0048] like Figure 1 As shown, in this embodiment, the shaft 400 extends into the pump body 100, and the shaft 400 is connected to a drive device. It is horizontally installed and has a pull-back structure, which facilitates the disassembly of the rotor components for replacement and maintenance. The bearing components adopt a universal standard design to improve the standardization of the pump. Through the design of universal components and reasonable hydraulic planning, the standardization of the pump is improved.

[0049] See Figure 1 In one embodiment, because the pump body 100 has a complex structure, a sand-cleaning hole 140 is provided on the end face of the pump body 100 so that sand-cleaning treatment can be performed after the pump body 100 is cast.

[0050] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0052] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0053] In this invention, unless otherwise explicitly specified and limited, "above" or "below" a second feature can mean that the first and second features are in direct contact, or that they are in indirect contact through an intermediate medium. Furthermore, "above," "over," and "on top" of a second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" a second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature. It should be noted that when an element is referred to as "fixed to" or "set on" another element, it can be directly on the other element or there may be an intermediate element present. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be an intermediate element present. The terms "vertical," "horizontal," "above," "below," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible embodiments.

Claims

1. A horizontal self-priming pump, characterized in that: include The pump body is equipped with an inlet flow channel; A wear-resistant plate is disposed at the outlet of the liquid inlet channel; The flow guiding component includes a flow guiding plate body and two or more evenly distributed arc-shaped guide vanes arranged in the circumferential direction of the flow guiding plate body. The arc-shaped guide vanes are staggered to form a guide vane channel between adjacent arc-shaped guide vanes. The inlet of the guide vane channel is connected to the liquid inlet channel, and the outlet of the guide vane channel is connected to the gas-liquid separation chamber. The arc-shaped guide vane includes a first arc-shaped guide vane and a second arc-shaped guide vane, which are evenly distributed in the circumferential direction of the guide vane body. The first arc-shaped guide vane has a first end and a second end that are opposite to each other, and the second arc-shaped guide vane has a third end and a fourth end that are opposite to each other. A first guide vane channel is formed between the first end and the third end, and a second guide vane channel is formed between the second end and the fourth end. The first end is located outside the third end, and the third end is offset toward the center of the guide vane body. The second end is located inside the fourth end, and the second end is offset toward the center of the guide vane body. A shaft extends into the pump body, and a drive device is connected to the shaft. The first arc-shaped guide vane and the second arc-shaped guide vane have guide vane channels formed on the side away from the axis. The guide vane flow channel is connected to the outlet of the guide vane passage. The outer wall of the first arc-shaped guide vane is provided with an outlet, which forms the outlet of the guide vane flow channel. The outlet of the guide vane flow channel is connected to the upper part of the gas-liquid separation chamber. The guide vane passage gradually narrows from the inlet to the outlet. An impeller is connected to the shaft. The impeller is disposed between the wear-resistant plate and the guide plate body and located inside the arc-shaped guide vane. The impeller rotates to guide the fluid in the liquid inlet channel to the tip of the impeller and send it to the gas-liquid separation chamber through the guide vane channel.

2. The horizontal self-priming pump according to claim 1, characterized in that: The outlet of the liquid inlet channel is provided with a tongue, which surrounds the wear-resistant plate and forms a flow guide cavity.

3. The horizontal self-priming pump according to claim 2, characterized in that: The wear-resistant plate has a wear-resistant plate return hole near the tip of the impeller. One side of the wear-resistant plate return hole is connected to the flow guide cavity, and the other side of the wear-resistant plate return hole is connected to the cavity inside the arc-shaped guide vane.

4. The horizontal self-priming pump according to claim 2, characterized in that: The bottom of the tongue portion of the pump body is provided with a pump body return hole. One side of the pump body return hole is connected to the gas-liquid separation chamber, and the other side of the pump body return hole is connected to the guide chamber.

5. The horizontal self-priming pump according to claim 1, characterized in that: The impeller is an open impeller.

6. The horizontal self-priming pump according to claim 1, characterized in that: The arc-shaped guide vane abuts against the wear-resistant plate.

7. The horizontal self-priming pump according to claim 1, characterized in that: The pump body is detachably connected to a pump cover, which is connected to the shaft. The shaft is connected to a drive device to drive the impeller to rotate.

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