JPS5832992A - Overheat preventing method for speed control system pump - Google Patents

Abstract

PURPOSE:To aim at economic prevention, for pump overheating by setting up escape piping for overheat prevention use and a solenoid valve in a pump discharge line, while controlling the solenoid valve so as to release a minimum necessary flow of liquid discharge in proportion to the discharge line's flow and pressure. CONSTITUTION:A flow signal Qi and a pressure signal Hi of the pump discharge line are inputted into an arithmetic unit and, if the status satrsfied Hi>=alphaQi<2> (alpha:constant), a solenoid valve installed in escape piping for overheat prevention is fully opened and afterward when the operated value comes to satisfy Hi<=beta Qi<2> (beta:constant), the solenoid valve is fully closed but it keeps up a fully opened state until this time. In this connection, when Hi>=alphaQi<2> is not satisfied the solenoid valve is left intact without being fully opened switching control takes place with the following result of calculation, Hi<=betaQi<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing overheating of a speed controlled pump.

Generally, in order to adjust the amount of liquid for the minimum flow for overheating prevention according to the pump speed, the flow rate is detected and when the flow rate falls below a certain level, the overheating prevention valve is opened and the minimum flow is performed.

However, the conventional method for preventing overheating of speed-controlled pumps is to maintain a minimum flow at a constant flow rate at both 100% rotation speed and low rotation speed, which results in a larger amount of liquid being returned to the liquid tank during low speed rotation. In addition to creating waste,
If the amount of liquid to be returned is large, the power of the pump shaft increases, which has the disadvantage of consuming unnecessary power.

The present invention has been made in order to eliminate the above-mentioned defects, and its purpose is to adjust the amount of liquid in the overheat prevention minimum 70- according to the pump speed, so that the pump is operated at low speed. It is an object of the present invention to provide a method for preventing overheating of a speed-controlled pump, which is suitable for economical operation and eliminates the need to release pumped liquid more than necessary from a discharge line when the pump is running.

Hereinafter, one embodiment of the present invention will be specifically described based on the drawings.

In FIG. 1, reference numeral 1 denotes a pump discharge line including a pump P and a check valve 2, and on the downstream side of the pump P and check valve 2 of the pump discharge line 1, a flow meter 6 and a pressure transmitter 4 are provided. is provided, and a demand valve 1a is provided on the discharge side thereof.

1b, 1c, 1d, and 1e are installed in series.

An overheating prevention relief piping 5 is bypassed between the pump P and check valve 2 of the pump discharge line 1, the flow meter 3, and the pressure transmitter 4, and the overheating prevention relief piping 5 prevents the pumped liquid from being pumped. A portion is returned from the discharge side to the liquid tank 6 on the suction side. Further, a solenoid valve V and an orifice 8 are provided on the overheat prevention relief pipe 5.

Reference numeral 9 denotes a calculation device, and the signals of the miscellaneous device Q1 of the pump discharge line 1 detected by the flow meter 6 and the pressure H1 of the pump discharge line 1 detected by the pressure transmitter 4 are transmitted to this calculation device. 9 is input. Then, H=ctp (in this equation, H: total head (m), α: constant, ?= minimum flow liquid volume (m/
The solenoid valve M of the overheat prevention relief pipe 5 is controlled by the command device 10 connected to the arithmetic device 9 to determine the minimum flow liquid volume t (m3/m1n) that is satisfied by the formula (m1n). Control opening and closing.

Next, Figure 2 shows the total head curve when flowing out at a minimum of 70-.What is the minimum flow volume at a pump rotation speed of 100%? 0 (m”/m1n) Toss lever, minimum flow liquid volume g-1 (m3/m1) at low speed rotation
What about n)? 1 medium g, ox shame (here, No is the rotation speed at 100% rotation, N1 is the rotation speed at low speed rotation.) Also, the total head H (m) changes by (ml) 2, so it is minimum. The amount of water in the flow? changes on the curve shown by H=αQ (where α: constant, Q: liquid volume (m3/m1n)). Also, H=βQ2 (where β: constant, H:
The curve of total head (b), Q: liquid volume (m3/m1n) shows the change in the solenoid valve closing command, and is maintained in the relationship α>β>0.

Next, FIG. 6 is an example of a temperature rise curve showing the relationship between the minimum flow and the rise in liquid temperature of the pump.

Now, if we ignore heat radiation from the pump casing to the outside and leakage from the gland, the temperature rise can be calculated using the following formula.

△t=-lower-, 190,) 427Cη Here, △t: Temperature rise ('C) H: Total head in pump operating state (m) C: Specific heat of pumped liquid η: Pump efficiency in pump operating state (%)Although the allowable temperature rise depends on the liquid suction temperature and NPSH, it is generally 10 to 15℃.
It is better to keep it in check. In the temperature rise curve in Figure 3,
The temperature rise value Δt changes depending on the pump characteristics, and when the temperature rise limit is determined, the minimum flow liquid amount t is determined.

Moreover, FIG. 4 is a block diagram showing the opening/closing control of the electromagnetic valve M of the present invention. Now, the flow rate signal Q1 of the pump discharge line detected by the flowmeter 3 and the pressure signal H1 of the pump discharge line detected by the pressure transmitter 4 are inputted to the calculation device 9, and the calculation device 9 calculates that if Hi-αQ12, then If H1=βQ12, the arithmetic unit 9 fully opens the solenoid valve M via the command device 10, and fully closes the solenoid valve M via the command device 10 if H1=βQt2. Keep it in good condition.

On the other hand, according to the above calculation result, if H1 = α (h2), the solenoid valve M is not fully opened and βQi2
The opening/closing control of the solenoid valve M is performed in the same manner as in the case of HI code αQi2.

As described above, the present invention provides a flow meter and a pressure transmitter in the pump discharge line, and also provides a relief pipe for overheating prevention in the pump discharge line, and controls the opening and closing of the solenoid valve on the overheating prevention relief piping to prevent overheating. The method includes inputting signals of the flow rate of the pump discharge line detected by the flow meter and the pressure of the pump discharge line detected by the pressure transmitter to a computing device, and the computing device What is the minimum flow liquid volume that is satisfied by the formula H = αr? Since the solenoid valve is controlled to open and close to allow the liquid to escape, even when the pump is operating at low speed, there is no need to wastefully drain the pumped liquid from the discharge line to the bypass line and release the liquid. It has the advantage of being an economical method for preventing overheating of a pump in terms of both quantity and power, and is particularly suitable for speed control pumps that are frequently operated with a small pumping amount.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and Fig. 1 is a schematic diagram of the entire device, Fig. 2 is an explanatory diagram showing the total head curve when discharging with minimum flow, and Fig. 6 is a temperature rise curve of the pump. FIG. 4 is a block diagram showing the opening/closing control of the electromagnetic valve. 1... Pump discharge line, 3... Flow meter, 4... Pressure transmitter 45... Overheat prevention relief piping, 9...・Arithmetic device, P...
...Pump, M..., solenoid valve. Representative Patent Attorney Takashi Suzue - Figure 3 Figure 1 Figure 2

Claims (1)

[Claims] A method of preventing overheating by providing a flow meter and a pressure light meter in a pump discharge line, and providing a relief pipe for overheating prevention in the pump discharge line, and controlling the opening and closing of a solenoid valve on this relief piping for overheating prevention. , the respective signals of the flow rate of the pump discharge line detected by the flow meter and the pressure of the pump discharge line detected by the pressure transmitter are input to a calculation device, and the calculation device calculates H-α19 (
According to this formula, H: total head, a: constant, 9. : indicates the minimum flow volume of 70-) is the minimum flow volume satisfied by the formula? A method for preventing overheating of a speed-controlled pump, characterized in that the electromagnetic valve is controlled to open and close so as to release water.