JPH0112958B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention utilizes a so-called clearance control method that changes the characteristics by changing the gap between the open ends of the blades of an open impeller, so that the flow rate can be varied from maximum to minimum (0). The present invention also relates to a structure of a centrifugal pump in which the initially set discharge pressure is kept constant.

Conventionally, it has been common to use both rotational speed control and constant discharge pressure control, but this is expensive and has limited applications. As a countermeasure for this, a main shaft with a fixed impeller is supported so as to be slidable in the axial direction, and the main shaft is connected to a piston of a servo cylinder. ) The discharge pressure is introduced directly or through a throttle into the variable pressure chamber, and the constant pressure is introduced into the constant pressure chamber on the opposite side. It is also possible to make use of this characteristic) so that when the discharge pressure rises above the set pressure, the balance is broken and the gap in front of the vanes increases, and conversely, when the discharge pressure falls below the set pressure, the above gap decreases. However, since the purpose is to keep the discharge pressure constant, the discharge pressure does not originally fluctuate much more than the set pressure. Therefore, if this differential pressure is used as the power source for the servo piston, it will be difficult to use other power sources. Although there is an advantage in not requiring it, the power is insufficient, and especially when shifting the impeller in the direction of reducing the gap in front of the blades, the impeller does not reach the required position, resulting in lower performance and lower discharge pressure than the required value. A problem arises.

The present invention detects the difference between the desired discharge pressure and the discharge pressure at each discharge amount during operation, and uses a hydraulic balance promoting mechanism consisting of a solenoid valve operated by a pressure switch to adjust the pressure between the variable pressure chamber and the constant pressure chamber. In other words, as the discharge pressure increases, the pressure in the variable pressure chamber increases and the gap in front of the blade increases. Also, if the discharge pressure decreases, the pressure in the variable pressure chamber will be lowered and the gap in front of the blades will be reduced. The invention will now be described with reference to the drawings.

The main shaft 1 in Fig. 1 is supported by a pump casing 4 at its front and rear ends (left and right in the figure) by bearings 2 and 3, and between them is a first stage open impeller 5 which faces forward and opens, and which opens in the same direction. A second stage (final stage) open impeller 6 is fixed, and a concentric motor (not shown) is connected to a portion protruding forward (to the left in the figure) from the pump casing 4. The main shaft 1 is supported so as to be able to slide to the right in the figure from the illustrated state where the front clearance a between the blades 11 and 12 of each impeller 5 and 6 is the minimum. A gap b corresponding to the allowable movement distance is provided between the fit-in type volute casings 13 and 14. 1
5 and 16 are the suction ports of each impeller, 17 is the partition wall, 1
8 is a return vane, and the partition wall 17 is provided in a volute casing type intermediate casing 20 that constitutes a part of the pump casing 4. 19 is a discharge port.

A balance disk 21 is fixed to the main shaft 1 together with the impellers 5 and 6, and the outer circumference of the balance disk 21 is in contact with an annular floating disk 22. It is slidably supported by cylindrical parts 23 and 24 on the casing side. A chamber A between the floating disk 22 and the balance disk 21 is located between the boss portion of the impeller 6 and the cylindrical portion 23.
communicates with the discharge side of the blade 12 across a gap between
Therefore, the discharge pressure of the impeller 6 is applied to the A chamber. The chamber B behind (in front of) the floating disk 22 is connected to the pipe 171 through the communication hole 25, and from the pipe 171 there is a pipe 27 connected to the discharge port 19 and the suction port 15 (low pressure section).
The pipe 29 connected to the pipe 29 is branched. Piping 27
A first electrical control valve 170 is provided in the pipe 29, and a second electrical control valve 180 is provided in the piping 29.
(hereinafter referred to as pressure switch).
The pressure switch 55 is connected via a pipe 53 to a portion of the discharge pressure pipe 27 closer to the discharge port 19 than the valve 170, and when the upper limit H ₃ of the discharge pressure (Fig. 2) is detected,
The valve 170 is closed and the valve 180 is opened, and when the lower limit _H2 of the discharge pressure is detected, the valve 170 is opened and the valve 180 is closed. Suction pressure piping 2
A throttle valve 181 is provided at a portion closer to the suction port 15 than the valve 180 of No. Connecting.

By appropriately adjusting the effective area and supply pressure where the pressure on the chambers A and B sides acts on the floating disk 22,
The floating disk 22 can be made to follow the balance disk 21 regardless of the position of the balance disk 21. The impellers 5 and 6 have low pressure suction ports 15,
Although an axial thrust toward the 16 side is acting, this axial thrust can be balanced by the discharge pressure of chamber A acting on the balance disk 21, while the floating disk 22 is always pressed against the outer periphery of the balance disk 21. In order to follow the balance disk 21, even when the main shaft 1 is made slidable in the axial direction, the balance disk 2
1 function can be secured.

To explain the constant pressure setting, minimize the gap a at the open front edge of the impeller (pump performance as shown in Figure 2).
When operating at the maximum water flow rate _Qm , the discharge pressure becomes _H1 (discharge set pressure, that is, the desired discharge pressure). At this time, the valves 170 and 180 are closed, and the B chamber is sealed while maintaining a pressure that balances the forward axial thrust of the impellers 5 and 6. Also, since the liquid is incompressible and the B chamber is sealed to prevent leakage, the impellers 5 and 6 do not move.
The discharge pressure _H1 does not change. In addition, the pressure switch 55
The upper limit H ₃ and lower limit H ₂ of the discharge pressure detected by are distributed above and below the set pressure H ₁ .

Now, the gap a between the impellers is relatively large (pump performance is low as shown in S ₄ in Figure 2), the amount of water used Q ₁ , and the discharge pressure
When the water volume increases to Q ₂ when H ₁ is the operating point B, the discharge pressure will decrease to the above lower limit due to the general pump characteristic that the discharge pressure decreases as the water volume increases.
The temperature drops to _H2 (operating point C). Pressure switch 55 detects this pressure drop and opens valve 180. Valve 1
When 80 opens, the pressure in chamber B decreases, and impeller 5,
The forward axial thrust by 6 is the balance disk 21
Since this overcomes the balancing force (rearward axial thrust) by the disk 22, the main shaft 1 slides forward, and the gap a between the impellers decreases. As a result, the pump performance increases from S ₄ to S ₃ , and the discharge pressure also increases (operating point D). Valve 1
80 continues to be open, the performance further increases to _S2 , and the discharge pressure becomes the upper limit value _H3 (operating point E). The pressure switch 55 detects the upper limit value _H3 , closes the valve 180, and opens the valve 170. Thereby, the discharge pressure _H3 is introduced into the B chamber. The effective area of the disk 22 is set so that the pressure inside the B chamber is slightly lower than the discharge pressure when the B chamber is sealed, so in other words, the pressure inside the B chamber is _equal to the discharge pressure (at the operating point ), the balancing force of the disk 22 and the balance disk 21 balances the axial thrust of the impellers 5 and 6, so when the pressure in the B chamber reaches the upper limit _H3 , the disk 22 and the The balance disk 21 overcomes the axial thrust by the impellers 5 and 6 and moves in a direction (backward) that increases the gap a between the impellers. Therefore, the discharge pressure decreases.

Contrary to the above case, when the water volume decreases and the discharge pressure increases, the valve 170 opens at the same time as the discharge pressure reaches the upper limit _H3 as described above, and the pressure in chamber B increases. The impellers 5 and 6 move rearward and the discharge pressure decreases.

Note that the discharge pressure is centered around the set value _H1 and has an upper limit of _H3.
and the lower limit _H2 , but the fluctuation range _H3 - _H2 corresponds to the difference between the on and off of the pressure switch 55, and if a micro switch or the like is used for the pressure switch 55, the difference can be reduced to 0.5 m or less. In that case, the fluctuation difference H ₃ - _{H 2} is extremely small at 1% even compared to the lowest pump pressure of about 30 m, so
It's not a problem.

As explained above, according to the present invention, a balance disk type turbine pump is partially modified, and one pressure switch 55 and two electric control valves 17 are installed.
By simply adding 0.180, a constant discharge pressure pump can be obtained easily and inexpensively. The balance disk 21 is used as a piston for moving the main shaft 1, and the structure can be simplified from this point as well.

In the embodiment shown in FIG. 1, the chamber in front of the balance disk 21 is divided into chamber A and chamber B, but the pressures in chambers A and B both apply a backward force to the balance disk 21. Therefore, chambers A and B are regarded as one variable pressure chamber, and the balance disk 2
1 can be regarded as a piston. In that case B
Increasing or decreasing the pressure in the chamber will increase or decrease the pressure in the variable pressure chamber.

Furthermore, in the present invention, the variable pressure chamber B on the impeller opening direction side of the cylinder 24 is connected to the first electric control valve 1.
70 to the discharge port 19, and the second
is connected to the suction port 15 through an electric control valve 180, and the constant pressure chamber C on the opposite side of the variable pressure chamber B is set at a lower pressure than the variable pressure chamber, and the axial thrust by the impeller is balanced by the pressure difference between the two chambers. In addition, a discharge pressure switch 55 is provided so that the first and second
When the discharge pressure reaches the upper limit, the first control valve 170 is closed and the second control valve 180 is opened, and when the discharge pressure reaches the lower limit, the first control valve 170 is connected to the second control valve.
Since the second control valve 180 is opened and the second control valve 180 is closed, when the discharge pressure decreases to the lower limit, the variable pressure chamber A,
The pressure in B is lowered to the pressure in the suction port 15 to actively disrupt the pressure balance with the constant pressure chamber C, thereby increasing the thrust that pushes the main shaft 1 forward (to the left in Figure 1).
The front gap a can be quickly reduced. In other words, the conventional method uses the pressure increase characteristic of a centrifugal pump (the pressure gradually increases from a large flow rate to a small flow rate) by simply supplying discharge pressure intermittently from the discharge port 19 to the fluctuating pressures A and B. In comparison, when the discharge pressure drops below the set pressure, the inside of the variable pressure chambers A and B is
5, the problem of insufficient force to reduce the front gap a is reliably prevented, and the blades 11 and 12 quickly approach the partition wall 17 side to the required position. Therefore, there is an advantage that constant discharge pressure control can be performed with high precision.

Further, the following modifications are possible in the present invention.

(1) As shown in FIG. 3 (the same reference numerals as in FIG. 1 indicate corresponding parts), a balance piston 300 may be employed as a mechanism for balancing the axial thrust. The variable pressure chamber 39 in front of the piston 300 is connected to the pipe 171 via the passage 301, and the pipe 1
From 71, a discharge pressure line 27 with an electric control valve 59 and a suction pressure line 29 with a similar valve 150 branch off. Valves 59 and 150 are electrically connected to pressure switch 55. The constant pressure chamber 40 behind the balance piston 300 is a pressure inlet 41
It is connected to piping 52 through. The pipe 52 has a constant pressure valve 51 that can maintain a constant pressure on the secondary side (constant pressure chamber side), and is connected to the middle of the pressure switch pipe 53. 400 is an annular groove provided in the center of the inner surface of the cylindrical portion 24a, and is connected to the suction pressure pipe 29 via a passage 401 and a pipe 402 having a stop valve 403. This groove 400 is a pressure relief to prevent the pressures in the variable pressure chamber 39 and the constant pressure chamber 40 from interfering with each other, and a very small amount of water is discharged from the groove 400 to the low pressure part of the pump.

In this modification as well, the pressure switch 55 selectively opens the valves 59 and 150 to manipulate the pressure in the variable pressure chamber 39, thereby moving the impellers 5 and 6 to keep the discharge pressure constant. . Moreover, since the balance piston 300 itself has been used for a long time, a constant discharge pressure pump can be obtained with a very simple modification.

Note that when the discharge pressure is not used as a means for obtaining a constant pressure in the constant pressure chamber 40, the constant pressure chamber 40 is connected to an external pressure supply piping 64 (for example, water supply) via a set pressure piping 62 and a constant pressure setting adjustment mechanism 63.

(2) Valve 170, 180 in Figure 1 and valve 5 in Figure 2
9,150 can also be replaced with one three-way valve.

(3) A timer may be connected to valve 170 and/or valve 180 in FIG. 1 so that the opening time of the valve and/or the interval from "open" to "open" can be adjusted. In that case, the control response speed can be adjusted.

(4) One pressure switch 55 can be replaced with a combination of a pressure switch that detects the upper limit pressure _H3 and a pressure switch that detects the lower limit pressure _H2 . In that case, the pressure difference H ₃ −H ₂ can be set small.

(5) At least one impeller open to the front may be provided, and the impeller may be located at any position (for example, at the front stage).

(6) The impeller outlet may be a volute case or a guide vane.

(7) The present invention can also be applied to vertical pumps.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of the present invention, FIG. 2 is a graph for explaining the operation, and FIG. 3 is a longitudinal sectional view showing a modification. 1... Main shaft, 5, 6... Open impeller, 21, 3
00... Balance disk, balance piston (piston), 24... Cylindrical part (cylinder), A
and B, 39... variable pressure chamber, C, 40... constant pressure chamber, 55... pressure switch (balance promotion mechanism).

Claims (1)

[Claims] 1 In a single-stage or multi-stage centrifugal pump having at least one open impeller, the main shaft to which the impeller is fixed is supported slidably in the axial direction, and a cylinder chamber is formed concentrically with the main shaft around the middle of the main shaft. , the cylinder chamber is divided by a piston that moves together with the main shaft,
The variable pressure chamber on the side of the cylinder in the impeller opening direction is the first
The impeller is connected to the discharge port through an electric control valve, and is connected to the suction port through a second electric control valve, so that the constant pressure chamber on the opposite side of the variable pressure chamber is set at a lower pressure than the variable pressure chamber. The axial thrust from the vehicle can be balanced by the pressure difference between both chambers, and a discharge pressure switch is provided and connected to the first and second control valves, and when the discharge pressure reaches the upper limit, the first control is activated. A constant discharge pressure pump characterized in that a valve is closed and a second control valve is opened, and when the discharge pressure reaches a lower limit, the first control valve is opened and the second control valve is closed.