JPS5832994A - Overheat preventing method for speed control system pump - Google Patents

Abstract

PURPOSE:To aim at economic operation, by setting up overheat preventing escape piping provided with a built-in solenoid valve as well as a pressure signal generator in a pump discharge line, while providing the pump with a rotational speed signal generator so as to cause signals from both these generators to be inputted into an arithmetic unit, through which a minimum flow of liquid discharge corresponding to a rotational speed variation that satisfies a specific formula is released through the escape piping. CONSTITUTION:A rotational speed signal Ni from the rotational speed signal generator installed to a pump and a pressure signal Hi from the pressure signal generator installed in the discharge line are inputted in to an arithmetic unit, and when these relationships between them are found to be Hi>=alphaNi<2> (alpha:constant), a solenoid valve is fully opened, then the valve is kept up in a full-open state until the condition of Hi<=betaNi<2> (beta: constant) is satisfied and when it is satisfied, the valve is, in turn, fully closed. On the other hand, when Hi<alphaNi<2> is the case, the solenoid valve is kept up without being fully opened; solenoid valve operation is achieved after some time waiting for finding of the condition of Hi<=betaNi<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 both at 100% rotation speed and at low rotation speed, which results in a wasteful flow of liquid that is returned to the liquid tank at low speeds. In addition, if the amount of liquid to be returned is large, the power of the pump shaft increases, resulting in unnecessary power consumption.

The present invention was made to eliminate the above-mentioned defects, and its purpose is to reduce the amount of liquid for minimum flow for overheating prevention.
Superheating of a speed-controlled pump that is adjusted according to the pump speed and eliminates the need to wastefully release pumped liquid from the discharge line when the pump is operated at low speed, which is favorable for operational economy. The aim is to provide a method to prevent this.

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

In FIG. 1, 1 is a pump discharge line equipped with a pump P and a check valve 2, and on the downstream side of the pump P and check valve 2 of this pump discharge line 1, a pressure transmitter 4,
The pump P is provided with a rotation speed transmitter 3, and demand valves 1a, lb, 10.1d, and ie are connected to the discharge side of the pump P.

An overheating prevention relief piping 5 is bypassed from between the pump P and check valve 2 of the pump discharge line 1 and the pressure transmitter 4, and a part of the pumped liquid is transferred to the discharge side by this overheating prevention relief piping 5. The liquid is then refluxed to the liquid tank 6 on the suction side. Further, a solenoid valve M 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 rotation speed N1 detected by the rotation speed transmitter 6 and the pressure H1 of the pump discharge line 1 detected by the pressure transmitter 4 are sent to the calculation device 9. is input.

Then, H=αN (in this formula, H: total head (m), α: constant, N: number of revolutions per minute (
The solenoid valve M of the overheat prevention relief pipe 5 is controlled to open and close so as to release the liquid amount of 4 minimum flows accompanying the change in the rotational speed that is satisfied by the formula (rpm). In other words, in the total head curve when flowing out at the minimum 70- in Fig. 2, is there a minimum flow at the H-Q curve? . Decide and then
=αQ2 (H=α1) is replaced with H=αN2, so that an arithmetic expression of H=αN2 can be obtained.

In addition, the rotation speed when the differential is 1100% rotation is set to No (
rPm), then the rotational speed N1 (rpm) at low speed rotation is
) is N1 in N□

(indicates the minimum flow liquid volume at low speed rotation)
The total lift H:J (changes with 2, so the rotation speed in the minimum flow changes on the curve shown as H=αN2 (where α: constant, N: revolutions per minute (rpm)).

Also, H = βN (where β: constant, H: total head (m)
, N: revolutions per minute (rpm)) indicates changes in the electromagnetic 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 70- 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 = Once - (1" Ω - 1) 427Cη Here, △t: Temperature rise (℃) H: Total head when pump is operating (2)) C: Specific heat of pumped liquid η: When pump is operating Pump efficiency 6) Although the allowable temperature rise depends on the suction temperature and NPSH, it is generally best to keep it within 10 to 15°C. In the temperature rise curve shown in Figure 3, the temperature rise value △t changes depending on the pump characteristics, and if the temperature rise limit is determined, the discharge amount that can be used to reach the minimum flow? . is determined.

Further, FIG. 4 is a block diagram showing the opening/closing control of the solenoid valve V of the present invention.

Now, the rotation speed signal N1 detected by the rotation speed transmitter 3 and the pressure signal H of the pump discharge line detected by the pressure transmitter 4
1 is input to the arithmetic device 9, and the arithmetic device 9 causes the solenoid valve M to be fully opened via the command device 10 if Ht2αN12;
2, then fully close the solenoid valve V via the command device sum,
Also, when H1 = βN12, the solenoid valve V is kept fully open.

On the other hand, according to the above calculation result, if Hl-αN1 is not satisfied, the solenoid valve V is not fully opened and Hl =
βN12 is applied to the arithmetic unit 9, and the following H1-βN1
The opening/closing control of the solenoid valve M is performed in the same manner as in the case of .

As described above, the present invention provides a pressure transmitter in the pump discharge line, a rotation speed transmitter in the pump, and
A method for preventing overheating by providing a relief pipe for overheating prevention in the pump discharge line and controlling the opening and closing of a solenoid valve on the overheating relief piping, the method comprising: controlling the number of revolutions detected by the number of revolutions transmitter and the pressure; A signal of the pressure of the pump discharge line detected by the transmitter is input to a calculation device, and the calculation device releases the minimum flow amount of liquid as the rotation speed changes, satisfying the formula H=αN2. Since the solenoid valve is controlled to open and close, 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, which reduces the liquid volume and power. Both of these methods can be used as an economical method for preventing overheating of a pump, and have the advantage of being particularly suitable for speed-controlled pumps that frequently operate 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. 3 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, 6...Rotation speed transmitting device 1, 4...01. Pressure transmitter, 50.・90. Relief piping for overheating prevention・9...Calculation unit, P...
・Pump, M...Solenoid valve. Others −q=−J: @Eko − ::′□1

Claims (1)

[Claims] A pressure transmitter is provided on the pump discharge line, a rotation speed transmitter is provided on the pump, and a relief piping for overheating prevention is provided on the pump discharge line, and a solenoid valve on the overheating prevention relief piping is controlled to open and close to prevent overheating. A method of In the formula, H: total head, -α: constant, N: rotations per minute). A method for preventing overheating of a speed-controlled pump, characterized in that: