JPS5949480B2 - Piping structure with pump - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to pump piping, and aims to suppress the magnitude of pressure pulsations induced in the piping by specifying the length of the discharge pipe, thereby preventing the generation of noise and vibration. It is something.

In a rotary pump such as a centrifugal pump, it is known that pressure pulsations occur when a vane passes through the beginning of the pump casing.

This pressure pulsation propagates to the discharge (suction) piping and is reflected at points where the water flow rapidly decreases, such as the collection pipe of the discharge (suction) pipe or the pressure water tank, and the reflected wave of this pressure pulsation is subsequently transmitted to the pump. This generates a standing wave of pressure pulsation by interfering with the pressure wave of pressure pulsation generated by the pressure pulsation.

The wavelength λ of the pressure pulsation/standing wave is determined by the speed of sound propagating in the pipe and the ratio of the rotation speed of the pump x the number of blades, and the frequency is 100 to 200 H2 in a general pump.
This is a low frequency range that is extremely uncomfortable.

On the other hand, according to experiments conducted by the present inventors, the distance between the standing wave of pressure pulsation and the pump and the collective piping or water tank (the length of the piping)
It has been confirmed that pressure pulsation changes significantly depending on

As will be described later, depending on the distance, the pressure pulsation value becomes three times or more than the minimum value.

In recent years, as noise regulations have become stricter, pumps have become larger, and pump stations have become closer to home areas, noise countermeasures for pumps and pump stations have become important issues. This was obtained based on the basics.

In the piping of a pump that has a collecting pipe or a water tank on the suction or discharge side, the present invention relates to the discharge or suction flange of the pump and the collecting pipe or water tank, where λ is the wavelength of a standing wave of pressure pulsation generated by the pump. The pump is installed at a position where the length of the piping between the inlet and the inlet satisfies λ L = -(2n-1) x (1±0°05), where n is an integer. It is.

Next, the present invention will be described in detail with reference to the drawings.

Figure 1 is a schematic diagram of the piping at a pumping station. A suction pipe 1 is connected in series with a suction pipe 2, a pump 3, and a discharge pipe 4. Multiple pipes are connected in parallel depending on the water supply capacity, and the discharge A discharge manifold pipe 5 is connected to one end of the pipe 4.

Figure 2 is a schematic diagram of a pump device used to pump water into an aquarium.
The suction pipe z1 pump 3/ and the discharge pipe 4 are connected in series, and the end of the discharge pipe 4' is connected to the water tank 6.

In a rotary pump such as a centrifugal pump, pressure pulsations are generated as the impeller rotates as described above, and this is propagated to the discharge piping and suction piping, resulting in pressure pulsations as shown in Fig. 1 A1 or A'.
It is reflected at a point where the flow changes rapidly, such as the point B in FIG. 2 or the point B in FIG.

As a result, the reflected wave and the traveling wave interfere to generate a standing wave of pressure pulsation.

The strength of the standing wave of pressure pulsations is closely related to the pump and the location where the pressure pulsations are reflected.

Distance L1 between pump 3 and point A in Figure 1 or pump 3
It has been confirmed that the strength of the standing wave changes depending on the distance between the pump 3' and the point A', or the distance L between the pump 3' and the point B in FIG. 2 (the same applies to the suction pipe side).

The wavelength λ of pressure pulsations and standing waves is determined by the speed of sound propagating through the pipe,
It is expressed as the ratio of pump rotation speed x number of blades.

According to many experiments conducted by the inventors, a resonance phenomenon occurs when the pump is located at a node of a standing wave, and a resonance phenomenon occurs when the pump is located at an antinode of a standing wave. When the pressure becomes the minimum value and the resonance phenomenon occurs, the strength of the pressure pulsation is four to five times as strong as when the pressure is at the minimum value.

FIG. 3 shows a case where the pump 3 is located at a node of the standing wave W. In this case, resonance occurs and the pressure pulsation increases significantly as indicated by W.

FIG. 4 shows a case where the pump 3 is located at the antinode of the standing wave W.

FIG. 5 shows the relationship between the intensity of pressure pulsation and the wavelength in both of the above cases, and the curve ■ shows the case in FIG. 3, that is, the case where the distance L=nλ.

On the other hand, curve ■ is for the case in Figure 4, where distance L = "(2n-1)
The case is shown below.

Now, if the value of the pressure pulsation of curve (■) is 1, then the value of curve (2) is 4.

Figure 6 shows the pulsation rate △P/P and the piping distance and wavelength ratio L/
It shows the relationship with λ, and it can be seen that L/λ shows the minimum value between 1.0 and 1.5.

Comprehensive consideration of the above experimental data reveals that if the distance between the point where the pressure pulsation is reflected and the position of the pump is L2' (2n-1) in relation to the wavelength λ, then it is stationary. It can be seen that the wave pulsation rate ΔP/P becomes the minimum value.

The distance was measured on the pump side at the beginning of the winding of the pump casing, and on the other end at the junction between the discharge piping and the discharge collecting pipe (Figure 1), or at the junction between the discharge piping and the water tank (Figure 2). ).

However, since it is generally difficult to measure the position of the start of winding of the pump casing, there is no substantial problem in measuring from the surface of the discharge flange or suction flange.

If the value of the distance is exact, the effect will be great.

However, it is better for actual equipment to have a tolerance within a certain range.

This tolerance is ±5% calculated from the wavelength λ.
This is a good value, and when it deviates from this value, the pulsation rate increases rapidly as shown in FIG.

As described above, in the piping of a pump having a collecting pipe or a water tank on the suction or discharge side, when the wavelength of the standing wave of pressure pulsation generated by the pump is λ, The pump is installed at a position where the length L of the piping between the collecting pipe or the water tank inlet satisfies λ L = - (2n-1) x (1 ± 0.05), where n is an integer. , pressure pulsations that inevitably occur in rotary pumps can be prevented from resonating in the piping.

Therefore, since vibration and noise can be prevented, the pump equipment can be operated quietly.

Furthermore, since there is no need to provide a special noise prevention structure to the building or the pump itself, equipment costs can be reduced.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams of the water supply equipment, with FIG. 1 showing the case where a discharge collecting pipe is used, and FIG. 2 showing the case where a water tank is used. 3 and 4 show the relationship between the pump installation position and standing waves, and FIG. 5 shows the magnitude of pressure pulsations in FIGS. 3 and 4, respectively. FIG. 6 is a diagram showing the relationship between the ratio of pipe length and wavelength and pulsation rate. 1...Suction collecting pipe, 2.2...Suction piping, 3 t3
'-...Pump, 494'...Discharge piping, 5...Discharge collecting pipe, 6...Water tank.

Claims (1)

[Claims] 1. In a pump piping having a collecting pipe or a water tank on the suction or discharge side, when the wavelength of the standing wave of pressure pulsation generated by the pump is λ, The pump should be installed in a position where the length of the piping between the collecting pipe or the water tank inlet satisfies the following: λ L-=-(2n-1) x (1±0.05), where n is an integer A piping structure with a pump featuring the following.