JPH0735085A - Movable vane pump - Google Patents

Abstract

PURPOSE:To restrain the instability of Q-H characteristic (quantity of discharge/ net pump head) resulting from a sudden, substantial separation by installing the pump-suction-side outlet of a balance pipe on the inner surface of a suction casing immediately in front of an impeller. CONSTITUTION:Water that is guided to the outside from behind an impeller 1 via a balance pipe 7 provided inside the thick-blade portion of a diffuser 2 is allowed to flow through a balance pipe 8, a header 9 provided around the outer peripheral portion of a suction casing 3, and a nozzle 10, and is ejected immediately in front of the impeller 1. As a result, a uniform radial distribution of meridional flow rate can be made and a stable pump characteristic can be obtained without instability in Q-H characteristic. Also, since the angle at which a fluid flowing out of the balance pipe 7 collides with a main flow is made smaller, pump efficiency can be enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a movable vane pump applied to a drainage pump of a city and a circulating water pump for cooling water of a condenser of a thermal power plant.

[0002]

2. Description of the Related Art The structure of a conventional movable vane mixed flow pump is shown in FIG.
(Turbo Machinery Association: Turbo Pump, January 1991, Nippon Kogyo Publishing Co., Ltd., p.121). The impeller 1 is attached to a hollow pump shaft. A rod is inserted in the pump shaft, and constitutes a blade operating mechanism 5 that moves in the axial direction to change the blade angle of the movable blade 1. The impeller hub is sealed from around to prevent water from entering the blade operating mechanism. Therefore, the impeller cannot have a balance hole for balancing the axial thrust. Therefore, the following method is adopted. That is, the impeller back surface 12
A slit portion 6 is provided between the casing ring and the outer circumference of the impeller. Water flowing into the room on the back side of the impeller from this slit part is discharged to the external suction tank 13 through a balance pipe (not shown) provided on the inner surface of the diffuser hub, and the pressure on the back side 12 of the impeller is pumped. As the pressure is close to the pressure at the mouth, the axial thrust acting on the impeller is reduced.

[0003]

In the movable vane mixed flow pump as shown in FIG. 4, the water flowing into the back surface of the impeller is discharged to the outside through the balance pipe, resulting in a complete leakage loss and reduced efficiency. On the other hand, a suction bell mouth 3 is usually installed at the suction port of the pump. With such a flow path shape, the meridional flow velocity immediately in front of the impeller 1 tends to be faster on the shroud side and slower on the hub side due to the influence of the bend from the bellmouth to the mixed flow portion of the impeller as shown in FIG. Indicates. Therefore,
In the impeller designed on the assumption that the shroud uniformly flows into the hub, the separation in the partial flow rate region is delayed, so that an unstable portion may occur in the Q-H characteristic as shown in FIG.

[0004]

[Means for Solving the Problems] Pressure water flowing into the rear surface of an impeller for balancing thrust in the axial direction is blown out to a suction casing immediately before the impeller through a balance pipe.

[0005]

[Action] Water blown out into the suction casing immediately before the impeller through the balance pipe flows into the flow passage at the impeller inlet with a vertical component, so that the flow passage is narrowed and the meridian surface on the shroud side acts. The increase in flow velocity is suppressed.
Therefore, the radial distribution of the meridional velocity is made uniform. In addition, since the balance tube outlet is oriented so that a slight reverse pre-swirl is given, separation of the flow in the partial flow rate region starts from a relatively large flow rate and the Q-H characteristic becomes unstable. The likelihood of performance occurring is reduced.

[0006]

EXAMPLE An example of the movable vane pump of the present invention is shown in FIGS. FIG. 2 is a view showing the AA cross section of FIG. The outlet hub of the impeller 1 is provided with a radial slit portion 6 between the impeller 1 and the casing ring so that a pressure difference is maintained between the impeller outlet portion 11 and the impeller rear surface 12. The water flowing into the impeller back surface 12 is guided to the header pipe 9 provided on the outer peripheral portion of the suction casing 3 through the balance pipe 7 provided on the thick blade portion of the diffuser and the pipe-shaped balance pipe 8 provided on the outside of the pump. Get burned. Nozzles 10a, 10b, 10c, 10d, etc. are provided on the circumference of the suction casing 3 at equal intervals and communicate with the header pipe 9. The direction of the nozzle 10 is set to be slightly opposite to the rotating direction of the impeller as shown in FIG.

The total cross-sectional area of the nozzle outlet is set to be slightly smaller than the cross-sectional area of the balance pipe inlet, and the pressure of the header pipe 9 is set to be slightly higher than the pressure of the pump suction port. However, if this pressure difference is set too large, the residual axial thrust acting on the impeller becomes large and the function of the balance tube is lost, so the nozzle diameter is set in consideration of the residual axial thrust.

FIG. 3 shows a development view (a) of the impeller blades of the pump and a velocity triangle (b) (c) at the inlet of the impeller shroud at the design point flow rate. Figure 3
FIG. 3B shows the case of the conventional technique, and FIG. 3C shows the case of the present embodiment. At the same flow rate, in the conventional pump, the meridional flow velocity is faster than the other cross sections, as shown in FIG. On the other hand, in the present embodiment, since the flow is restrained by the jet flow from the nozzle 10, the meridional flow velocity decreases. Therefore, Cm ₁ <C
m ₁ ′. Further, since water is ejected from the nozzle 10 in the direction opposite to the rotation of the impeller, the flow flowing into the impeller is
As shown in FIG. 3C, a circumferential component velocity Cu _{1 in the} direction opposite to the rotation of the impeller is given. Therefore, the relative inflow velocity vector W ₁ to the impeller is the same as in the case of the conventional technique (see FIG.
Compared to the relative inflow velocity vector W ₁ ′ in (b)), the inflow angle β ₁
Becomes smaller. The difference between the blade angle β _b and the inflow angle β ₁ is the angle of attack with respect to the blade. Since the meridional flow velocity decreases in proportion to the flow rate, the angle of attack with respect to the blade increases in the partial flow rate region. That is, in the case of the present embodiment, the angle of attack at which peeling starts is reached at a relatively large flow rate in the partial flow rate region, and peeling starts.

On the other hand, the instability of the Q-H characteristic of the pump is
It is considered that the blade separation is delayed in the partial flow rate range, does not occur even at a small flow rate, and eventually becomes a further smaller flow rate, causing large separation and abrupt decrease in the total pump head. However, in the pump of the present embodiment, as described above, the design angle also has an appropriate angle of attack, and since the peeling develops early in the partial flow rate region, the large peeling does not proceed at once. Therefore, in this pump, since the total head is not drastically lowered, instability does not appear in the Q-H characteristic, and a stable pump characteristic with a right downward slope is obtained.

Another embodiment of the present invention is shown in FIG. The direction in the meridian plane at the outlet of the balance tube is set to be slightly axial rather than perpendicular to the flow path. With this configuration, the collision angle between the flow flowing out from the balance pipe and the main flow becomes small, so that the loss due to collision is reduced and the efficiency of the pump can be improved.

[0011]

According to the present invention, the outflow water from the balance chamber behind the impeller is jetted immediately before the impeller through the balance pipe and the nozzle provided in the suction casing connected to the balance pipe, resulting in the meridian plane. The radial velocity distribution can be made uniform. Therefore, the separation of the flow on the shroud side of the impeller does not occur at an excessively small flow rate, but a small separation starts at a flow rate relatively close to the design point and the Q-H characteristic of QH characteristics caused by the occurrence of a sudden large separation occurs. Instability can be suppressed and stable characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a movable vane pump of the present invention.

2 is a cross-sectional view taken along the line AA of the pump shown in FIG.

FIG. 3 is an explanatory view of impeller blades of the pump of the present invention.

FIG. 4 is a vertical sectional view of a conventional movable vane pump.

FIG. 5 is a meridional flow velocity distribution map at the impeller inlet of a conventional movable vane pump.

FIG. 6 is a QH characteristic diagram of a movable vane pump.

FIG. 7 is a vertical sectional view showing another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Movable vane impeller, 2 ... Diffuser, 3 ... Suction casing, 4 ... Pump shaft, 5 ... Blade operating mechanism, 6 ... Casing ring, 7 ... Balance pipe, 8 ... External balance pipe, 9 ... Header pipe, 10 ... Nozzle, 11 ... impeller downstream part, 12 ... impeller back part, 13 ... suction tank.

Claims (1)

[Claims] 1. A movable vane pump in which pressure water on the back face of an impeller is made to communicate with a pump suction side by a balance pipe in order to balance axial thrust of the movable vane pump. A movable blade pump, which is installed on the inner surface of the suction casing immediately before the impeller.