JPS5832993A - Overheat rreventing method for speed control system pump - Google Patents

Abstract

PURPOSE:To release and disperse only a minimum flow of pump discharge, by setting up overheat preventive escape piping provided with a built-in solenoid valve in a pump discharge line, while controlling the solenoid valve so as to achieve its opening/closing motion in response to a flow signal from a discharge flow detecting device divided into more than two pressure stages for discrimination in accordance with the ON-OFF condition of a discharge pressure detecting device. CONSTITUTION:A flow signal Qi of the pump discharge line is inputted into a control unit and discriminated by a decision whether a pressure detecting device is ON (a certain condition is satisfied above a certain setting value) or OFF and after that, when it is Qi<q1 (a minimum flow of liquid discharge at pump low speed rotation), a solenoid valve is fully opened, then it is kept in a full-open state till reaching a status of Qi>qo (a minimum flow of liquid discharge at pump 100% rotational speed) and when it has reached this status, the solenoid valve is fully closed.

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 minimum flow amount of liquid for superheat prevention according to the pump speed, the flow rate is detected and when the flow rate falls below a certain level, the superheat prevention valve is opened to allow minimum flow.

However, the conventional method for preventing overheating of speed-controlled pumps is to maintain a constant flow rate at a minimum of 70- at both 100% rotation speed and low rotation speed, so it is difficult to return more liquid than necessary to the liquid tank during low-speed rotation. In addition to causing 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 was made in order to eliminate the above-mentioned defects, and its purpose is to adjust the minimum flow liquid amount for overheating prevention 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 pumping.

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 flow rate detection means 3 such as a flow meter and a Pressure detection means 4 such as a pressure switch
is provided, and demand valves 1a, 1 are provided on the discharge side thereof.
b, ic, 1d, and 1e are arranged in series.

An overheating prevention relief piping 5 is installed between the pump P and check valve 2 of the pump discharge line 1 and the flow rate detection means 6 and pressure detection means 4, and this overheating prevention relief piping 5 A part of the pumped liquid is returned from the discharge side 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 control device, into which a signal of the flow rate Q1 of the pump discharge line 1 detected by the flow rate detection means 6 is inputted. Then, the flow rate signal Q1 input to the control device 9 is combined with the on/off conditions of the pressure detection means 4, and the pressure stage is divided into two sides and determined, and as a result, the solenoid valve of the overheat prevention relief pipe 5 is determined. Controls opening and closing of M.

Next, Figure 2 shows the total head curve when discharging at minimum flow.If the minimum flow liquid volume at 100% pump rotation speed is 0 (m/m1n), then at low speed rotation Minimum flow liquid volume of 9.1 (m/m1n)
Is he in g-1? . ×fj (here, N0 indicates the rotation speed (rpm) at 100% rotation, and N1 indicates the rotation speed (rpm) at low speed rotation)? . teeth? It may be smaller than 1.

Next, FIG. 3 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=H- (Rule 1-1) 427Cη Here, △t: Temperature rise ('C) H: Total head in pump operating state (2)) C: Specific heat of pumped liquid η: In pump operating state Pump efficiency (%) The allowable temperature rise depends on the suction temperature and NPSH, but is generally 10 to 15 degrees Celsius.
It is better to keep it in check. In the temperature rise curve in Figure 6,
The temperature rise value △t changes depending on the pump characteristics, and when the temperature rise limit is determined, the minimum flow liquid volume? 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 flow rate detection means 3 is inputted to the control device 9,
Pressure detection means 4 is turned on.

Depending on the OFF condition, the solenoid valve M operates as follows.

First, if the pressure detection means 4 is turned ON (the condition that the pressure is higher than a certain pressure set value is satisfied) and Qi<t1', the solenoid valve M is fully opened, and then the control device 9
〉? . ′, then the solenoid valve M is fully opened, and Ql〉? .

If not, keep the solenoid valve M fully open. On the other hand, when Ql<g, 1', the solenoid valve M is not fully opened and is directly applied to the control device 9 of \Qi>t Control takes place.

Further, the pressure detection means 4 is turned off, and Qi<
If 't1, the solenoid valve ■ is fully opened, and furthermore, the control device 9 allows Ql>? . If so, fully open solenoid valve M, and Ql again.
〉? . Otherwise, keep solenoid valve M fully open. On the other hand, when Qi<tl, the control device 9 for \Q1> persimmon is directly applied without fully opening the solenoid valve M.
Thereafter, the opening/closing control of the solenoid valve M is performed in the same manner as when Qi<yl.

In the above embodiment, the pressure detecting means 4 is of a two-contact type, but the pressure detecting means 4 is of a multi-contact type H.
It is more economical to increase the pressure conditions such as 1, N2 sH3, . . . .

Also, instead of the pressure detection means 4, a rotation speed detection means such as a rotation switch is provided to detect the minimum flow under the rotation speed condition.
It is also possible to change.

As described above, the present invention provides a flow rate detection means and a pressure detection means in a pump discharge line, and also provides a relief pipe for overheating prevention in the pump discharge line, and controls the opening and closing of a solenoid valve on this relief piping to prevent overheating. In this method, a flow rate signal detected by the flow rate detection means is input to a control device, and the flow rate signal is turned on to the pressure detection means.

Claims (1)

[Claims] A method of preventing overheating by providing a flow rate detection means and a pressure detection means 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 the relief piping for overheating prevention. , the flow rate signal detected by the flow rate detection means is inputted to a control device, the flow rate signal is divided into two or more pressure stages depending on the ON/OFF' conditions of the pressure detection means, and the opening/closing control of the electromagnetic valve is controlled. A method for preventing overheating of a speed-controlled pump, characterized by: