JPH0816478B2 - How to calibrate pump head characteristics - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a turbo pump having a head characteristic which is obtained by an impeller having a small radiant velocity component, has a steep downward slope, and has a lift characteristic that conforms to the similarity rule, and a pump. The present invention relates to a method for calibrating secular change in pump head characteristics in a pump system including a device for detecting the number of rotations of the pump and a device for detecting pressures at the inlet and outlet.

(Prior Art and Problems to be Solved) In a general centrifugal pump of conventional design, as shown in FIG. 7, the gradient of the curve of its lift characteristic becomes a gentle curve, and therefore, the minute change amount ΔH of the lift is reduced. On the other hand, since the value of the minute change amount ΔQ of the flow rate becomes large, the accuracy of the flow rate instruction with respect to the pressure (total head) is poor. Furthermore, in the case of centrifugal pumps of general design, the JIS standard stipulates that the similarity rule may be used within 20% of the upper limit of the rotational speed, but this is similar in other rotational speed ranges. It means that the rule is not met. Therefore, when the number of revolutions used is wide, the calculated value and the measured value do not match.For each number of revolutions, for example, 30m.pm or 50r.pm are measured and the head characteristics are stored in the computer. This is impractical, which results in enormous memory capacity and thus requires a large computer, which is impractical.

Further, in the case of a turbo hoop, it is usual that the impeller, the casing, etc. are worn or corroded and the lift characteristics are changed during long-term use. As mentioned above, since the similarity range of the general design centrifugal pump is narrow, the calibration must be performed at the pump installation site for each rotation speed, and all the lift characteristics at each rotation speed must be calibrated. Not
Practically impossible.

On the other hand, the applicant of the present invention has filed Japanese Patent Application Laid-Open No. 61-229989 (Japanese Patent Application No.
60-50576), Japanese Patent Application No. 63-34070, and an axial flow turbo pump with a small number of blades, and Japanese Patent Application No. 63-34070, a radial turbo pump. The common point of these turbo pumps is that the inlet guide device allows the fluid to flow into the impeller without resistance without causing a sudden change in the flow direction at the impeller inlet. The velocity component Cm in the flow direction impeller is
It is smaller than Cm by about 1/10 and the direction change of the flow velocity at the exit when leaving the blade is very gentle.

When a turbo pump having an impeller with a small radiative velocity component as described above is used, first of all, its lift characteristics are linear as shown in FIG. 1 (in the case of a single-blade axial flow turbo pump). It has been found that a sharp downward slope characteristic of is shown. As can be seen from comparison with the curve of the lift characteristic of the centrifugal pump of the conventional design (FIG. 7), the curve of the slope to the lower right shows that the magnitude of the minute change amount ΔQ of the flow rate with respect to the minute change amount ΔH of the same head. Since it is extremely small, the accuracy of indicating the flow rate with respect to the pressure (total head) is high. Secondly, according to the turbo pump described above, as shown in FIG. 1, it was found that the pump head curve at each rotation speed conforms to the similarity rule.
This will be described later.

It is an object of the present invention to provide a method that allows easy on-site calibration of aging of pump head characteristics.

(Apparatus for Solving the Problems) In order to achieve the above object, the method according to the present invention comprises:
Attach a valve to the pump system outlet and completely close the valve in the initial stage,
The pump is rotated near the reference speed using the liquid that is actually used to measure the cut-off pressure, which is stored as the cut-off pressure converted to the reference speed, and the valve is closed during calibration to perform the same operation. Number of pump cut-off pressures and the difference between the pump cut-off pressure at the calibration reference speed measured during calibration and the difference between the pump pressure curves stored in advance stored in parallel by the amount of this difference. Become.

(Example) Hereinafter, the method of the present invention will be described with reference to the accompanying drawings.

As described above, the applicant previously applied for the turbo pump has two conditions necessary for maintaining reliability and accuracy for a long period of time when attempting to indicate or control the flow rate by using its lift characteristic. That is, the two conditions are satisfied: the pump head characteristic shows a straight line or a steep downward-sloping characteristic close to a straight line, and the pump head characteristic conforms to the similarity law in a wide rotational speed range required when used with a variable speed device. . There are two types of turbo pumps filed by the applicant, a radial type and an axial flow type. The structure of the axial flow type turbo pump having a single-blade impeller will be described with reference to FIG.

In this single vane type impeller 22 of the turbo pump 20, a frusto-conical hub 23 fixed to the drive shaft 21 has a blade inlet having an inflow surface substantially perpendicular to the impeller axis so as to smoothly remove the fluid. From the inlet to the outlet so that the blade 24 is continuously wound around the week surface of the hub 23 for one or more turns to the outlet side, and the centrifugal force is generated from the inlet to the outlet. They are arranged so that they gradually incline forward toward the line. The flow paths between the blades adjacent to each other on the peripheral surface of the hub 23 are formed so as to have substantially the same cross section from the inlet to the outlet. This impeller is characterized in that the wrapping angle of the blade with respect to the plane perpendicular to the axis is small, so that the radiant velocity component Cm of the fluid in the blade becomes about 1/10 of that in the conventional case.

A suction casing 27 having an annular suction chamber 27a is attached to the inlet side flange of the pump casing 25. The suction casing 27 has an inlet port 28 opening to the emotion suction chamber 27a. An inlet guide vane member 26 as an inlet guide device is removably mounted downstream of the suction casing 27, sandwiched between the suction casing 27 and the pump casing 25, adjacent to the blade inlet side of the impeller 22. The inlet guide vane member 26 has two inlets 29a and 29a of the fluid passage opening in the suction casing 27 in the circumferential direction.
a ′ are provided symmetrically, and the fluid passages 29 are formed so that their cross-sectional areas gradually decrease in the axial direction while rotating 180 ° in the circumferential direction from the respective inlets.
30 approaches toward the blade entrance of the impeller, and finally comes to be adjacent to the blade entrance surface as shown in the lower part (solid line) and the upper part (phantom line). In this configuration, the fluid that has entered from the inlet port 28 flows into the suction chamber 27a of the suction casing 27, and then from the inlets 29a and 29a 'of the inlet guide vane member 26, respectively, and while swirling 180 °, It is forcibly guided in the axial direction so as to gradually come closer to the blade inlet, and finally can naturally flow into the blade inlet of the rotating impeller.

Further, a ring-shaped outlet guide vane member 31 as an outlet guide device is removably attached to the inside of the pump casing 25 by an adapter 32 adjacent to the blade outlet side of the impeller 22. Fluid passage of this outlet guide vane member 31
33 is formed such that the cross-sectional area thereof gradually increases from the inlet 34 of the fluid passage adjacent to the blade outlet of the impeller toward the outlet, and the discharge of the pump casing 25 on the outlet side of the outlet guide vane member. It is connected to the passage 25a. Reference numeral 35 is a discharge port tangentially connected to the discharge passage 25a of the pump casing 25.

FIG. 1 is a graph showing the lift characteristic of the axial-flow single-blade turbo pump. As described above, the turbo pump shown in FIG. 2 has the impeller with a small radiant velocity component, so that the pump head curve thereof conforms to the similarity rule as shown in FIG. 1, and the calculated value and the measured value match. I understand what to do. That is, the curve indicated by the alternate long and short dash line is a curve showing the law of similarity, 6,000, 8,000 based on the measured value at 4,000 rpm.
Calculated according to the similarity rule at 0 ... In the heading curve obtained by plotting the value of It can be seen that the values of match well.

FIG. 3 shows a pump system for instructing or controlling the flow rate using the above-mentioned pump head lift characteristic. 1 is a motor, 2 is the above-mentioned turbo pump connected through a coupling,
3 is a rotation speed sensor for measuring the rotation speed of the pump, 4
Is a pressure sensor connected to the inlet of the pump 2, 5 is a pressure sensor connected to the outlet of the pump, 6 is a shutoff valve connected to the pump discharge pipe, 7 is a computer, 8 is a device for displaying a flow rate, Reference numeral 9 indicates an inverter as a variable speed device required when the pump is used over a wide range of rotation speeds. The motor 1 is connected to an inverter 9, the rotation speed sensor 3, pressure sensors 4 and 5 are connected to a computer 7, and the computer 7 is connected to a flow rate display device 8.

In the pump system shown in FIG. 3, in the method of instructing the flow rate using the lift characteristic of the turbo pump 2, the rotation speed detected by the rotation speed sensor 3 and the pump lift characteristic previously stored in the computer 7 are shown. Calculate the pump head characteristic at that number of revolutions using the formula and this characteristic,
The pump flow rate is actually calculated from the total head pressure obtained from the pressure difference between the inlet and outlet detected by the pump inlet pressure sensor 4 and the outlet pressure sensor 5, and this value is displayed by the flow rate display device.

FIG. 4 shows a pump system for controlling the flow rate by using the total lift curve of the turbo pump. Similar parts to those in FIG. 3 are provided with similar reference numerals. The difference from FIG. 3 is that the computer 7 is connected to the control unit 10, and this control unit is connected to the inverter 9 as a variable speed device. Actual measurement values are fed back to the computer 7 by the rotation speed sensor 3, the inlet pressure sensor 4, and the outlet pressure sensor 5, and based on these values, the flow rate is calculated from the total head characteristic of the rotation speed as described above. Control unit 10
To the inverter 9, and the inverter controls the rotation speed of the motor 1 and hence the pump 2.

Generally, in the case of turbo pumps, the lift characteristics are usually degraded due to wear and corrosion of the blades, casing, etc., so this degraded characteristic should be regularly checked on site to calibrate it easily. It is necessary that the subsequent flow rate instruction and control can be performed with the calibrated characteristics. Therefore, in the present invention, as shown in FIG. 3 and FIG. 4, a valve 6 capable of completely closing the pipe line is provided at the pump discharge port, and the valve 6 is completely closed to shut off the valve when the flow rate is zero. The pressure is confirmed and this value is used to calibrate the value of the pre-stored equation representing the pump head characteristic.

In the actual process, at the site where the pump was installed, at the beginning,
The dead pressure is measured by rotating the pump in the vicinity of the reference speed using the liquid actually used, and is stored or recorded as the dead pressure converted to the reference speed. After that, perform the same operation at the time of calibration, and set the pump cutoff pressure at the initial reference speed and
Calculate the difference between the calibration reference speed measured at the time of calibration and the dead pressure of the pump, and simply shift the initial pump head characteristic downward in parallel by the amount of this difference, and the characteristic curve becomes the characteristic curve at the time of calibration. . The reason is that a turbo pump having an impeller with a small radiant velocity component is used, and therefore the lift characteristic curve when the wear or the gap changes as shown in FIGS. 5 and 6 is the first lift characteristic curve. This is because it changes parallel to.

It should be noted that the characteristics other than the deadline for calibrating the secular change may be previously investigated and stored in advance, and the characteristics may be determined accordingly. As an example of this preliminary investigation, FIG. 5 shows an axial flow single-blade turbo pump (Japanese Patent Application No. 60
-50576, Japanese Patent Application No. 63-34070), the characteristics of the pump head against changes in the gap between the impeller and the casing are shown in the graph.
In the case of this type of turbo pump, the gap between the casing and the tip of the impeller has a great influence on the pump head characteristics due to the blades that are open on one side. Show. In addition, FIG. 6 shows that after measuring the reference lift characteristics of the above-mentioned axial flow type turbo pump with fresh water, abrasive sand, for example, silica sand with a uniform grain size, is mixed with water and allowed to flow in the pump to obtain the lift characteristics. The results of examining changes in From these two graphs, it can be seen that, in the case of the above-described axial flow type turbo pump, the lift characteristics move almost in parallel. In the case of these examples, the H value at the point of Q = 0 can be simply lowered for the entire range by the amount of decrease (lifting mAq) when measured with the above-mentioned actual liquid to obtain the calibration characteristic.

FIG. 7 shows changes in the lift characteristics when the gap a between the open blade and the casing and the gap b between the back blade and the casing of the impeller of a general centrifugal pump are widened. Although it is possible to calibrate even in the case of the general characteristic curve of the centrifugal pump as shown in FIG. 7, the curves are not parallel to each other and spread out, so that there is a problem in that the accuracy is poor.

(Effect of the Invention) Since the present invention is configured as described above,
The following effects are achieved.

In the method of the present invention for calibrating the secular change of the head characteristic of the turbo pump, a valve is attached to the outlet of the pump system, the valve is completely closed in the initial stage, and the pump is rotated in the vicinity of the reference speed by using the liquid actually used. Then, the cutoff pressure is measured and stored as the cutoff pressure converted to the reference speed.The valve is closed during calibration and the same operation is performed, and the cutoff pressure of the pump at the initial reference speed and the calibration reference rotation measured at the time of calibration are stored. The difference between a certain number of pump shutoff pressures can be calculated and the pre-stored pump head curve can be shifted parallel downwards by this amount, which makes it extremely easy to perform regularly at the site where the pump is installed. The calibration can be performed in a short time, and thus a long-term accurate, accurate and reliable pump system can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing a pumping curve of a single-blade turbopump having an axial flow shape, which has a pumping head characteristic which is steep to the right and which conforms to the law of similarity, and FIG. FIG. 3 is a vertical cross-sectional view of an axial flow type turbo pump showing the pump head characteristic, FIG. 3 is a schematic diagram of a pump system for carrying out the method of indicating the flow rate, and FIG. 4 is a pump for carrying out the method of flow rate control. Schematic of the system, fifth
FIG. 6 is a graph of the lift characteristic with respect to the change of the impeller having a small radial velocity component and the casing gap, FIG. 6 is a graph showing the change of the lift characteristic due to wear, and FIG. 7 is corresponding to FIG. 5 of the conventional centrifugal pump. It is a graph which shows the lift characteristic with respect to the change of the gap of an impeller and a casing. 2,20 ...... Turbo pump 3 …… Pump speed detection device 4 …… Pump inlet pressure detection device 5 …… Pump outlet pressure detection device 6 …… Valve 9 …… Pump variable speed device 22 …… Impeller 24 ...... Feather

Claims (1)

[Claims] Claim: What is claimed is: 1. A turbo pump having a head characteristic which is obtained by an impeller having a small radiant velocity component and which is steeply descending to the right and which conforms to the similarity law, a device for detecting the rotational speed of the pump, an inlet of the pump, and In a method of calibrating the secular change of the lift characteristic stored in advance in a pump system equipped with a device for detecting the pressure of the outlet, a valve is attached to the outlet of the pump system, and the valve is completely closed at the beginning, Using the liquid to be used, rotate the pump near the reference speed to measure the cutoff pressure, store it as the cutoff pressure converted to the reference speed, and close the valve during calibration to perform the same operation. It is characterized in that the difference between the cutoff pressure of the pump and the cutoff pressure of the pump at the calibration reference speed measured at the time of calibration is calculated, and the pump head curve stored in advance is shifted downward in parallel by the amount of this difference. Person .