CN1004822B - multistage centrifugal pump - Google Patents

Abstract

In order to eliminate the locking of the rotating parts of the pump body of the multistage centrifugal pump, the multistage centrifugal pump (2) used for heat medium, such as the water supply pump used for large power stations, has an external cooling system for its shaft seal system. When the pump is stopped or its operation ceases, the pump cooling system (7, 8, 9, 10, 11) is shut off by various auxiliary valves (13). The clogging of the water pump can be detected, for example, by detecting the motor current with (14), with the tachometers (16, 18) connected to the pump (2) or the pump drive (15), or by detecting the output pressure of the pump.

Description

Multi-stage centrifugal pump

The invention relates to a multistage centrifugal pump for a heat medium, in particular to a shaft seal system with an external cooling system, for example, a feed water pump for a large power station is a pump with the heat medium.

The danger of such pumps is: when the motion is stopped under thermal conditions, the rotating parts of the pump can latch due to temperature induced twisting and warping, which prevents the pump from restarting. In order to make the pump ready to start under various operating conditions, a back-up operation is required. It is often the case that the pump is stopped due to a load condition and must be restarted in a short time. In this case, the pump is at rest and the temperature inside the pump is very high, so that locking of the rotating parts is avoided anyway. Therefore, an additional system is required during normal operation, which is also operated during standby operation to ensure proper cooling of the seals, bearings and cover. Similar considerations apply when the centrifugal pump must often be started in cold or half-warm conditions.

In order to make the temperature distribution in the pump uniform and maintain the temperature within a desired limit to prevent warping of the various parts in the pump due to temperature differences, there are generally several methods including circulating the pump using a separate circulation pump, injecting hot water at the input or output end, pumping the water from the inside of the pump, and continuously idling at a low speed to remove the temperature difference formed in the pump. The auxiliary equipment required for these methods is not only very complex but also increases the source of failure.

The object of the present invention is to provide a reliable means for preventing the blocking of the rotating parts for a water pump of the above-mentioned type.

The invention relates to a multistage centrifugal pump for a thermal medium, comprising a shaft seal system with an external cooling system and a control device for detecting the locking state of the centrifugal pump. The invention is characterized in that the control device comprises hydraulic, electric or mechanical transmission means and detection means, detects the state of rotation of the pump, and controls one or more shut-off valves which are part of a system for detecting or controlling the pump, which shut-off valves are caused to shut off the cooling system of the pump when the pump is stopped, and in that the supply or collecting line of the cooling system is provided with an electromagnetic valve for controlling the flow of cooling water, and in that the shut-off valves are provided with remote control means.

The simple solution to this problem reliably avoids the locking of the rotating element when it is not in operation. The cooled part will heat up as a result of the complete pump cooling system being switched off, but it is ensured that the temperature of the cooled part does not exceed the permissible limit, because of the radiation effect of the pump surface. The closing avoids any convection of temperature differences in the entire system, so that no disadvantageous temperature layers can be formed, and the occurrence of blocking due to temperature differences in the mass is prevented. The complex compensation systems normally used in standby operation become completely redundant.

The control device preferably comprises hydraulic or electric and/or mechanical transmission means for detecting the condition of the pump. A pressure gauge, relay or tachometer can detect a pump failure while a trigger signal drives a shut-off valve.

A further advantageous embodiment is that the shut-off valve has a remote drive, while the shut-off valve is part of a system for detecting or controlling the water pump, which ensures a very reliable operation since this combination avoids operator mistakes and ensures that the shut-off valves are opened, for example, when the water pump is started, so that the operation is reliable.

The cold water flow can be controlled by installing an electromagnetic valve on a main supply pipeline or a water collecting pipeline of the water pump cooling system. In this case one or several simple solenoid valves are sufficient to replace the expensive and complex systems normally used. Shutting off the main circuit of the water pump cooling system reliably prevents thermosiphon through the heat exchanger or cooling chamber while avoiding the attendant high temperature differentials that cause severe warping and latching of rotating parts.

Embodiments of the present invention will be described in more detail by the following examples and the accompanying drawings.

Fig. 1-3 show various arrangements of shut-off valves for centrifugal pump cooling systems.

Referring to fig. 1, an electric motor 1 drives a centrifugal pump 2. The pump shaft 3 outside the pump body is guided by bearings and sealing tubes 4, 5. The cooling chamber 6 of the seal box 5 communicates with the main supply line 8 of the water pump cooling system via a cooling line 7. A cooling line 10 branches off from line 8 to a heat exchanger 9. The lubricant and coolant in the slip ring seal 12 are cooled by the heat exchanger 9. The used supercooled water is discharged through the header pipe 11.

To prevent the blocking of the rotating parts due to the stop of the pump 2, a shut-off valve 13 is used to cut off the main supply line 8. The shut-off valve is in this embodiment a solenoid valve 13. When the control device 14 associated with the motor 1 detects that the motor has stopped pumping, the valve 13 is immediately closed. Thus, a malfunction of the water pump can be reliably detected, and the trigger signal drives the shut-off valve.

The configuration of fig. 2 is similar to that of fig. 1, except that the centrifugal pump 2 is driven by a turbine 15. Several shut-off valves 13 are located on the cooling lines 7 and 10. One or more tachometers or similar instruments 16, 18 are also used to detect the operating conditions of the turbine 15 and the pump 2. If the turbine is running, the tachometer 16 can detect the turbine speed and if the turbine speed is lower than the centrifugal pump idle speed, i.e. the pump is unloaded, the control device 14 closes the valve 13.

A tachometer 18 is mounted on the pump shaft 3 to allow for the detection of a water pump fault, whether motor driven or turbine driven, as well as a triggering signal to actuate one or more valves 13. It should be noted that either tachometer 16 or 18 may be used alone or in combination, with one omitted.

Referring to fig. 3, a valve 13 mounted on the main supply line 8 and communicating with the pump output connection 17 is used to shut down the cooling system. The valve 13 operated by the hydraulic cylinder 19 is closed when the output pressure of the pump is equal to or less than the pump intake pressure plus, for example, 5 bar. A pressure difference of 5 bar is an additional safety factor that can vary according to the design specifications actually adopted.

When the pump resumes the water supply, the pressure on the pump's low-use cylinder 19 causes the hydraulically driven valve 13 to open. The various possible closing methods in the above-described embodiments may, of course, be combined in different ways.

Claims (2)

1. A multi-stage centrifugal pump for heat medium, comprising a shaft seal system with an external cooling system and a control device for detecting the locked state of the centrifugal pump. The present invention is characterized in that the control device includes a hydraulic, electric, or mechanical transmission device and a detection device for detecting the dynamic state of the pump and controlling one or more shut-off valves, the shut-off valves being an integral part of the system for detecting or controlling the pump, and shutting off the pump's cooling system when the pump stops operating. A solenoid valve is disposed in the supply pipe or water collection pipe of the cooling system to control the flow of cooling water. 2. The multi-stage centrifugal pump according to claim 1, wherein the shut-off valve has a remote control device.

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