JPS5865983A - Overheat detecting device for feed water pump - Google Patents

Abstract

PURPOSE:To enable a feed water pump to be controlled with high reliability at a low cost, by detecting pump overheat by comparison of the discharge pressure of the feed water pump with the differential pressure generated across an orifice disposed on the suction side of the pump. CONSTITUTION:A proportional bias arithmetic unit 14 adjusts an output signal from a pressure detector 3 for detecting the discharge pressure of a feed water pump to the level of a signal from a differential pressure detector 7 for detecting the differential pressure across an orifice disposed on the suction side of the pump, and a subtractor 14 calculates the difference between both signals. Therefore, a comparator 15 detects the resulted difference signal which exceeds a predetermined value. The result of the detection is used for delivering a command signal to a device 16 for opening and closing an overheat preventing valve, an alarm device 17 or a pump trip device 18 in dependence upon its purpose. With this arrangement, a complicated function generater or root calculator may be eliminated, thereby the control of the feed water pump is possible with high reliability at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting overheating of a water supply pump, and particularly to a detection device suitable for a water supply pump whose minimum required flow rate changes depending on the pump rotation speed.

The traditional water pump overheating protection device and control device is
Since the set value of the minimum required flow rate is constant, if the set value is set too high when applied to a plant that operates with variable discharge pressure, the fluctuation of the water supply flow rate will become sharper, causing a large disturbance, and the discharge flow rate will also increase. The overheating prevention valve will not close until the temperature reaches 100°C, resulting in large losses. If the set value is set small, there is a drawback that the pump cannot be protected when the flow rate decreases under high load.

The purpose of the present invention is to improve the discharge pressure in order to reliably prevent overheating of a water supply pump that is operated in a wide range from low discharge pressure to high discharge pressure, and to reduce disturbances to a single water supply flow. The object of the present invention is to provide a detection device that can control an overheating prevention valve and protect a water supply pump with high reliability by simple calculation of the discharge flow rate.

In the conventional method, the pump discharge flow 111: is detected by opening the differential pressure applied to the five orifice plates. On the other hand, the minimum required flow rate of the pump is the square root value of the discharge pressure. Applying this principle, the orifice differential pressure,
By directly comparing the discharge pressure with the discharge pressure, the overheat protection 11- of the water supply pump can be protected and controlled with a simple device without having to perform a complex square root calculation.

Figure 1 shows a system diagram around the water supply pump. Water supply pump 5
Discharge flow from '51 tl'F, , reverse 1. Jl'2,
Output 1] Water is supplied to the boiler through stop valve 1. In the water supply pump 5, the fluid flowing inside the pump is used for cooling, and it is necessary to flow a minimum flow rate depending on the rotation speed. The water supply flow rate is determined by measuring the differential pressure generated in the orifice 6 with a differential pressure detector 17.
The flow rate is calculated by calculating the square root of this signal.
When this signal drops, the overheat prevention valve 4 is opened to ensure the minimum flow rate of the pump.

Figure 2 shows the relationship between pump discharge pressure, flow rate, and orifice differential pressure. The minimum required pump flow rate is a function (square root) of the pump discharge pressure. Further, the flow rate is the square root value of the orifice differential pressure.

Flow rate detection is performed by square root calculation on the differential pressure generated at the orifice, but the simplest and most reliable method is to focus on the fact that the pump discharge pressure and the differential pressure generated at the orifice are proportional and to directly compare both signals. In particular, when used as a protection device, it is desirable to have separate hardware from the control device; in this sense, a simple and highly reliable device can be constructed even if a pneumatic detector and arithmetic unit are used.

A specific example is shown in FIG. The output signal of the pressure detector 3 is combined with the signal level of the differential pressure detector 7 by the proportional bias calculator 13, the difference is calculated by the subtracter 14, and the comparator 15 detects that the difference signal exceeds a certain value. . This detection result is used to issue commands to the overheat prevention valve opening/closing device 16, alarm device 17, and pump trip device 18 depending on the application. By adopting this method, the function generator that converts discharge pressure to flow rate, the square root calculator that converts orifice differential pressure to flow rate, etc. can be omitted, and since these calculators are complex, they are simple and reliable. A protection and control device with high performance and low cost can be realized.

FIG. 4 shows an embodiment in which the pump overheat prevention valve 4 is of a continuous type. When used in combination with the protection device shown in FIG. 3, a control and protection device with even higher reliability and less disturbance can be constructed. r,',t,25 is the adjustment 2 which controls the valve 4.

According to the present invention, a complicated function generator and a square root calculator can be omitted, and a pneumatic detector, a calculator, etc. can be used, resulting in highly reliable and inexpensive control and protection. This has the effect that the device can be configured.

[Brief explanation of the drawing]

Figure 1 is a system diagram around the water supply pump, Figure 2 is a characteristic diagram of pump discharge pressure, water supply flow rate, and differential pressure generated at the orifice.
The figure shows an embodiment of a device for detecting overheat prevention valve opening/closing commands, pump flow rate low alarms, and pump trip commands, and FIG. 4 shows an embodiment of a superheat prevention valve continuous control device. DESCRIPTION OF SYMBOLS 1... Pump outlet stop valve, 2... Check valve, 3... Pump discharge pressure detector, 4... Overheat prevention valve, 5... Water supply pump, 6... Flow rate orifice, 7 ... Differential pressure detector, 13 ... Proportional calculator, 14 ... Subtractor, 15.
... Comparator, 16... Overheat prevention valve opening/closing device, 17...
・Alarm device, 18...

Claims (1)

[Claims] ■ In overheating prevention devices for water pumps where the minimum required water flow rate changes depending on the pump rotation speed, a water pump overheating detection device detects overheating of the water pump by comparing the water pump discharge pressure and the differential pressure.