US20070177990A1

US20070177990A1 - Centrifugal pump casing relief system

Info

Publication number: US20070177990A1
Application number: US11/341,289
Authority: US
Inventors: Louis Zacherl
Original assignee: Applied Drives and Systems Inc
Current assignee: Applied Drives and Systems Inc
Priority date: 2006-01-27
Filing date: 2006-01-27
Publication date: 2007-08-02
Also published as: CA2575925A1; US20080304955A1

Abstract

In a fluid flow network including a centrifugal pump, a system and kit for monitoring said centrifugal pump and relieving the pump of fluid when the pump is operating at no-flow conditions. The system comprises a fluid conduit connected to the pump, at least one sensor for indicating when the pump is operating at no-flow conditions. The sensor is selected from the group consisting of: temperature sensors, pressure sensors, and motor current sensors. The system has a fluid control means located in the fluid conduit. An electric snap-action valve is included that has an inlet connected to the fluid conduit and an outlet and a diaphragm. The diaphragm is movable between a first position and a second position. A power supply is included.

Description

BACKGROUND OF THE INVENTION

The present invention relates to centrifugal pumps and, more specifically, systems and devices to monitor operating parameters of centrifugal pumps to prevent damage to the centrifugal pumps.
Centrifugal pumps are relatively simple pumps used for fluid movement within piping systems. The pumps operate efficiently requiring only one moving part. However, care must be taken to insure that the pump is being operated within proper parameters. Specifically, care must be taken to insure that the pump is not operating at a “no-flow” condition, which can lead to damage of the pump and burning out of the motor driving the pump.
If a centrifugal pump is operating at a “no-flow” situation, fluid flow will have stopped through the pump. A small amount of fluid can remain in the pump and become trapped within the pump. This fluid will be churned by the spinning impeller of the centrifugal pump. Because there is only a small amount of fluid within the pump, the temperature of the fluid can increase quickly, and the fluid will begin to boil. The boiling fluid will increase the pressure within the system. The increasing temperature and pressure feed off of each other, and the pressure can quickly increase to uncontrollable levels. Such increases will lead to damage to the piping system and the pump, such as damage to the seals located at the joints, and the rise of the fluid temperature can lead to spontaneous tripping of “dry pipe valves” in fire protection systems. Other components, such as the pump seals, gauges, pressure switches, valve packings, flow switches, etc., may also be damaged by the pressure and temperature rise at no-flow situations.
Regulation of the pump is usually done by monitoring the pressure of the pump, the temperature of the fluid within the pump, or the electrical current feeding the pump motor. Normally, a separate fluid path is provided through the pump to assure a minimal flow of fluid to prevent overheating of the trapped fluids. Such a device to control the fluid flow is generally referred to as a casing relief valve.
The amount of time between the cessation of fluid flow through the pump and the onset of damages depends on many factors, such as liquid temperatures, the design and speed of the impellers located in the pump, fluid vapor pressure, and fluid volume in the volutes. Time before the onset of damages can range from over ten minutes to less than ten seconds, depending on the pump configuration. As the flow slows and stops within an operating pump, the pump parameters may change. For instance, the discharge pressure will rise, the motor current will decrease, the fluid temperature rises, and the speed of the motor shaft increases.
The discharge pressure on a centrifugal pump is a function of two sources: the inlet fluid pressure and any additional pressure added to the inlet pressure by the pump, with the additional pressure being dependent on fluid flow through the pump. Generally, centrifugal pumps produce the highest pressure rises or changes from the inlet pressure to the discharge pressure at a zero flow rate (“no-flow”), or churn condition. The amount of additional pressure the pump contributes decreases as flow increases through the pump.
If the inlet pressure changes, the discharge pressure will change by the same amount. Several factors can lead to these fluctuations in pressure, including seasonal factors, number of pumps being employed, demand, and pipe size, to name a few. As an indicator for no-flow situations, one should monitor the difference between inlet and discharge pressure.
As noted above, the motor current also varies, with the current being approximately fifty percent of the full load at churn, to nearly one hundred percent of current load at full flow. Motor currents below a certain level can indicate little or no fluid flow through the pump. Motor currents of a running motor will fall below churn levels only if the fluid in the volutes flashes to vapor. Current levels are not affected by either the inlet pressure or the fluid temperature, but can be altered by variations in the voltage of the power source, with lower voltages resulting in higher current levels.
Generally, it has been preferred to determine the temperature of the fluid with the use of a sensor device, such as a transducer or a switch, by placing the sensor directly into the fluids located in the centrifugal pump. The fluid temperature is measured directly, and the sensor device can immediately and automatically adjust to temperature changes. Pressure or voltage changes do not alter the sensors. However, such sensors may have problems of reacting quickly enough for a rapidly rising or falling temperature.
The most common packaging configuration for a centrifugal pump is to mount a “horizontal split case”pump and an electric motor on a common steel base plate. The drive shafts of the two devices are connected using a coupling that will allow for some misalignment between the pump and the motor.
If the coupling is removed and the motor is then started, the motor will draw approximately twenty percent of the maximum continuous current, commonly referred to a full load current. If the coupling is then reinstalled and the pump restarted with the discharge valve closed, the motor will then draw approximately fifty-five percent of the full load current. The value of the current rises as flow is added to the pump by opening the discharge valve.
Centrifugal pumps are preferably driven by three-phase induction motors, commonly referred to as “squirrel cage” motors. Squirrel cage motors use a differential slip to allow for changes between the “synchronous” speed (usually 1800 RPM and 3600 RPM) and an operating speed that is typically 25 to 100 RPM lower than the synchronous speed. As the speed changes, the mechanical load will change; a greater load equals a greater slip. A greater slip means a higher rotor current for the pump, producing higher torques to drive the load, which translates into a lower flow through the pump. Devices that monitor the pump load are not generally commonly used.
The present state of the art to prevent overheating in a pump uses a casing relief valve located on the discharge side of the pump. Fluid pumped through this valve may be discharged to a drain or recycled into a fluid storage. Some relief valves may pump the fluid back into the inlet of the pump, which increases the potential for the pump to overheat. Such devices use a mechanical pressure detector and an internal valve to release fluids at churn conditions. The simplest design uses a plunger and a compressed helical spring to seal the valve. As pressure rises, the plunger is pushed backward, allowing fluid to flow through into the by-pass line of the valve. As pressure falls back to normal levels, the plunger will reseal the valve.
The described relief valve has some drawbacks. Since the valve is operated by discharge pressure (as opposed to pressure differential) it may not open at proper times. For instance, if the inlet pressure is rather low, the spring and plunger may not activate, even if there is a significant change in the pressure, since the outlet pressure may still be lower than the pressure necessary to activate the plunger. Likewise, the flow amount is a variable dependent on the differential between the pump discharge and the valve trip pressure. A lower discharge pressure relates to a lower flow rate, which increases the possibility of pump damage. Also, the spacing between the valve and the plunger is based upon the pressure differential. If the differential is low, the space will be small, which potentially may lead to small particles becoming entrapped between the plunger and the valve, which could prevent the valve from being resealed. The result is a constant fluid leak, which, eventually, can lead to general failure of the valve,
While it has been known to monitor such variables to prevent pump damage or fatigue, to date there has been no simple arrangement to monitor up to all three of these variables within a single system. Thus, it would be advantageous to develop a system that would monitor centrifugal pumps while minimizing problems that could lead to failure of the monitoring system and the pump.

SUMMARY OF THE INVENTION

Within a fluid flow network including a centrifugal pump, the present invention comprises a system and kit for monitoring the centrifugal pump and relieving the pump of potentially damaging fluid when the pump is operating at no-flow conditions. The system comprises a fluid conduit connected to the pump, at least one sensor for indicating when the pump is operating at no-flow conditions. The sensor is selected from the group consisting of: temperature sensors, pressure sensors, and motor current sensors. The system has a fluid control means located in the fluid conduit. An electric snap-action valve, preferably a solenoid operated valve, is included that has an inlet connected to the fluid conduit and an outlet and a diaphragm. The diaphragm is movable between a first position and a second position. A power supply is included. The method of installing the system and/or kit is also included in the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a centrifugal pump arrangement according to the present invention installed in a piping system.
FIG. 2 is a perspective view of a possible fluid control valve according to the present invention.
FIG. 3 is a perspective view of an alternative fluid control device according to the present invention.
FIG. 4 is a perspective view of a temperature sensor used according to the present invention.
FIG. 5 is an exploded view of a solenoid valve used according to the present invention.
FIG. 6 is a perspective, partially exploded, view of a possible motor configuration used with the present invention.
FIG. 7 is a perspective view showing an initial step of installing the pump regulator system of the present invention.
FIG. 8 is a perspective view showing a further step of installing the pump regulator system of the present invention.
FIG. 9 is another further step of installing the pump regulator system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention which may be embodied in other specific structures. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.
The present invention provides a pre-engineered set of components that addresses the shortcomings of the prior art discussed above with respect to centrifugal pumps. The components are included as kit that will allow the end user to easily install the components and efficiently monitor the specific pump. The kit provides the basis for a method of monitoring the centrifugal pump and providing relief for the pump when the internal temperature and/or pressure of the pump reaches critical conditions, or the sensor indicates that the temperature and/or pressure may reach critical conditions. The components include 1) a valve, orifice, or other similar device to determine the volume of fluid flow that will flow through the pump; 2) a valve to regulate the fluid flow; 3) a sensor to detect a specific variable when the pump is churning, with the variables being either pressure, temperature, or motor current; and 4) a means to allow the sensor to operate the fluid regulation valve. The kit may also include various pipes, connectors, and other hardware to assist in installing the valves and sensors. Likewise, instructions may be included with the kit.
The present invention provides an easy to use, reliable, predictable system that will reduce problems associated with “no-flow” situations through the centrifugal pumps. Whereas previous designs and arrangements required the placing of components and piping in specific, fixed locations due to mechanical constraints of the pump itself, the separate detection and operation valves of the present invention allows the user to place the valves in locations where they would be most advantageous. The flexibility of installation maximizes the ability to monitor the operation of the pump. Furthermore, the system does not need to interact with other systems or components to operate, and may include a back-up power source, if necessary. The components included in the kit do not require any special tooling or skilled labor to install.
FIG. 1 is a perspective view of a pump relief system 10. The system 10 is showed installed in connection with a fluid flow network 12 (shown generally in phantom), which employs a centrifugal pump. As is known in the art, the system 10 is connected to a fluid conduit or flow path that operates independently from the normal fluid flow in the network 12. This allows the system 10 to provide fluid flow when problems arise with the centrifugal pump, such as “no-flow” conditions, thereby preventing or minimizing potential damage to the centrifugal pump. The system generally comprises a fluid flow device, which may be in the form of a conventional, manually operable gate valve 14; a solenoid operated fluid regulator valve 15, and a sensor 25, depicted as a temperature sensor 25 in FIG. 1. As fluid passes through a fluid conduit or pipe 22 in communication with the pump 12, the sensor 25 can individually monitor fluid flow conditions of the pump 12 as shown in FIG. 1, or it is possible to include other sensors such as pressure or motor sensors that can work in tandem to provide more checks for the pump. It is understood that the fluid conduit 22 refers to the entire length of pipe used in connection with the system 10, and should not be limited to a specific shape or arrangement. The present invention allows for several various arrangements of the individual sensors.
Fluid Flow Control
FIG. 2 provides a perspective view of the fluid flow device 14, which, as shown, is generally referred to as a manually operable gate valve. The gate valve 14 is a simple mechanical device used for regulating the volume of fluid flow through the system 10. A handle 24 is turned to either increase or decrease fluid flow through an internal conduit 26, thereby regulating the amount of fluid passing through a centrifugal pump during churn conditions. The design of the gate valve 14 allows for wide adjustments of fluid flow.
FIG. 3 provides an alternative fluid flow device, commonly referred to as a pipe union 114. The pipe union 114 has an internal restrictor plate 116 with a predetermined orifice 118 that regulates the amount of fluid passing through the conduit 26. The pipe union 114 is preferably constructed of a first half 120 and a second half 122. The restrictor plate 116 is located between the first half 120 and the second half 122. The three pieces 116, 120, and 122 are held together with a threaded union section 124. If necessary, the restrictor plate 116 can be replaced with another plate having a differently sized orifice if the flow is determined to be lower or higher than necessary.
As FIGS. 2 and 3 show, various flow control devices may be used for the present invention and the present invention should not be limited to a specific part or device.
Sensors
FIG. 4 shows a perspective view of the conventional, commonly available, temperature sensor 20. The sensor 20 comprises a probe 40 that will be directly inserted into the piping system, as will hereinafter be described. An electrical connector 42 is attached to the top of the probe 40, preferably permanently affixed to the probe 40. A threaded area 44 area on the probe 40 allows the sensor 20 to be secured to the pipe 22, again as will be later described, and in connection with the views of FIGS. 1, 7, and 8. The probe 40 must be in contact with fluid within the pipe 22 at or near the area very close to the area where actual heat may be generated in the system. The sensor 20 should be installed relatively near the impeller of the pump, or the sensor 25 will not accurately portray the temperature. The temperature sensor preferably includes a switch that is fixed to operate at 140° F (60° C.), which is a temperature similar to the discharge temperature of a residential fluid heater, with a temperature differential for the sensor being fixed at approximately 15° F. (or an approximate range of 12°-18° F.). The sensor 25 preferably operates a pilot duty metallic switch (not shown).
While a temperature sensor 25 was generally discussed above, pressure sensors and motor current sensors could be used in place of the temperature sensor, or may be used concurrently in a single system. Whichever type of sensor is used, it will operate on similar principles. The sensors are designed to complete an electrical circuit, allowing a current to flow from the power source to a solenoid valve coil, with the circuit being activated when the sensor registers a predetermined value for the related variable.
As with the temperature sensor 25 described above, a conventional pressure sensor (not shown) used in the system would preferably include a pilot duty metallic switch. The pressure sensor can be located and installed at any point in the piping 22 that is connected directly to the pump's discharge. That is, there should be no check valves or other devices located directly between the sensor and the pump's discharge. The pressure sensor will also be adjusted for a particular installation. Preferably, the inlet pressure for the pressure sensor is constant, which will result in a constant discharge pressure from the system. If the inlet pressure is variable, a pressure sensor must be adjusted accordingly, to insure that the solenoid 16 operating the valve 18 properly opens, even at relatively low pressures.
A motor current sensor as may be used in the present system, as will later be described, is preferably a solid state electronics module, and usually installed within the motor control center.
Solenoid Operated Valves
FIG. 5 provides a partially exploded view of the solenoid operated valve 15 used in the present invention. The solenoid 18 has a coil 19 for operating the solenoid armature 21 that is arranged for separable electrical connection wit an electrical connector 20 to be mounted onto the valve 15. The connector 20 is secured to an electrical cord 54, which is routed to a power supply 50 (see FIGS. 1 and 6).
The solenoid operated valve 15 is preferably a piloted diaphragm operated device. The valve 15 controls the pressure as it passes a diaphragm 32. A carburetor 35 may be included with the valve 16 as a pressure release. As the coil 19 is energized by means of the solenoid armature 21, a diaphragm 74 is pulled towards the coil 30, which provides complete opening or closing of the valve 16. The valve 16 is preferably a “snap action” valve.
Referring further to FIG. 5, the solenoid operated valve 15 can be either a normally open or a normally closed valve. The valve 16 comprises a top section 70 and a bottom section 72. A spring 76 provides resistance and is seated upon the diaphragm 74 to provide pressure for securing the diaphragm 74 in place. A normally open version of a valve 15 allows fluid flow when the coil 19 is de-energized, whereas a suction of a normally closed valve 15 allows fluid flow when the coil is energized. Determination of which valve type to use generally is based upon whether or not fluid should be flowing should there be a power outage.
Power Supply
FIG. 6 illustrates a power supply 50 used in the present invention. The power supply 50 houses a motor 52. The power source 50 is electrically connected to the solenoid 19 of the valve 15 and the sensor 20 with standard electrical cords 54 (see FIG. 1). A motor current sensor 56 (see FIG. 6) for monitoring the motor used with the pump 12 may also be connected to the motor 55. The sensor 56 is preferably self-powered by the flow of current (preferably a 2.5 amp minimum flow) through the sensor 56 to the motor 52. The sensor 56 is connected to the output of the motor 52, preferably with a two-conductor cable 58, commonly known and used with electrical connections. The motor current flow through the sensor 56 is preferably detected using a conventional current transformer (not shown), which is used to detect the magnetic field of the motor current. The sensor 56 will test for two conditions: 1) whether or not the motor current is high enough to assure that the motor is running, and 2) whether or not motor current is low, thereby indicating no fluid movement in the system. When the sensor 56 indicates that the current is high enough to indicate that the motor is running and low enough to indicate that there is no fluid flow, the electrical output of the sensor 56 is activated, thereby energizing the solenoid valve 15.
Installation
FIGS. 7-9 show various stages of installing the system 10. In FIG. 7, a first section of pipe 60, having a threaded conduit 62, is connected to the pump 12. The threaded conduit 62 will receive the sensor 25, as shown in FIG. 1. A second section or sections 64 of pipe 22 connect the pipe section 60 to the gate valve 14, and a third pipe section 66 connects the gate valve 14 to the solenoid valve 16. To insure proper fluid flow, the gate valve 14 and the solenoid operated valve 15 are preferably installed within 2 to 4 inches from one another. FIG. 8 shows the connector 18 being secured to the coil 19 of the solenoid valve 15. In FIG. 9 there is shown a discharge section 68 of the pipe 22 connected to the solenoid valve 15, and the sensor 25 being finally connected to the system 10, as further shown in FIG. 1. The pipe section 68 may lead to a drain or connected to recirculate the fluid into the general piping system.
FIGS. 7-9 show one possible way of installing the kit components and should not be considered as limiting. For example, one possible preferable alternative way is to install the power supply, next the sensor or sensors and thereafter the valves. When starting the installation process, the system installer must be sure to verify that all of the electrical connections are secure. After energizing the electrical supply, the operator must slowly open the fluid supply to the system, which will properly pressurize the gate valve 14 and/or the solenoid operated valve 115. The centrifugal pump should then be started and allowed to run. When it has been determined the pump is running properly, the operator may adjust the individual sensor to the specific operating conditions.
When installing the power supply 50, it is preferable to mount the supply 50 on a freestanding vertical structure 59, with the orientation being as shown in FIG. 6. The supply 50 should be mounted at least 12 inches off of the floor. Power should be turned off to the supply until it has been established that the sensors and valves are properly installed.
When installing the temperature sensor 25, any fluid pressure on the pump itself should be released before installation of the sensor 25. The sensor 25 is then threaded into the pipe section. The sensor 25 should be installed in an upright, vertical position. An electric connector 54 is attached to the sensor 25 (see FIG. 4) and then routed to the power pack 40 (see FIG. 4).
As previously stated, the system is tailored for an individual pump's needs. For example, the size of the fluid control valve 14 is determined by the amount of fluid that is flowing through the system. It should also be determined what variable the system will be monitoring so that the proper sensor will be included with the kit for the system. This will be taken into account when deciding how no-flow conditions will be detected in the system. An extra, back-up battery may be included in the system in case of power failure. Another factor to consider is whether the solenoid operated valve 15 will be open or closed if power fails for the system.
The present invention provides a simple and easy to use method for providing a fluid flow detector system for protection of a centrifugal pump. Essentially, the present invention allows for a custom made sensor system. It has not been previously contemplated to provide the end user with such a system selected from a component kit. The invention allows for the end user to receive an easy to install system that is tailored for an individual's needs. Likewise, the end user can obtain a kit including selected temperature, pressure, or motor sensors, or a combination of all three. By providing an individual sensor together with an individual solenoid valve, the present system will provide a resultant product that can monitor fluid flow through a centrifugal pump in an optimal fashion.
The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.

Claims

1. In a fluid flow network including a centrifugal pump, a system for monitoring said centrifugal pump and relieving said pump of fluid when said pump is operating at no-flow conditions, said system comprising:

a fluid conduit connected to said pump;

at least one sensor for indicating when said pump is operating at said no-flow conditions, said sensor intersecting said fluid conduit, said sensor selected from the group consisting of: temperature sensors, pressure sensors, and motor current sensors;

a fluid control means located within said fluid conduit;

an electric snap-action valve having an inlet connected to said fluid conduit and an outlet and a diaphragm, said diaphragm having a first position and a second position; and

a power supply;

said power supply, said sensor and said electric snap-action valve forming an electrical circuit, said electrical circuit activating said snap-action valve to move said valve from said first position to said second position.

2. The system according to claim 1 wherein said fluid control means comprises a gate valve.

3. The system according to claim 1 wherein said fluid control means comprises a pipe union.

4. The system according to claim 1 wherein said first position of said diaphragm allows fluid flow through said electric snap-action valve and said second position of said diaphragm prevents fluid flow through said snap-action valve.

5. The system according to claim 4 wherein said fluid control means comprises a gate valve.

6. The system according to claim 4 wherein said fluid control means comprises a pipe union.

7. The system according to claim 1 wherein said first position of said diaphragm prevents fluid flow through said electric snap-action valve and said second position of said diaphragm allows fluid flow through said snap-action valve.

8. The system according to claim 7 wherein said fluid control means comprises a gate valve.

9. The system according to claim 7 wherein said fluid control means comprises a pipe union.

10. A method for monitoring a centrifugal pump within a fluid flow network and relieving said pump of deleterious effects caused by an increased pressure and/or temperature in said pump, said pump communicating with a fluid release valve connected to a fluid conduit, said method comprising:

selecting a sensor to monitor a variable of said pump;

providing a fluid control device;

providing an electrical solenoid operated valve having an inlet connected to said fluid conduit and an outlet and a solenoid operated diaphragm, said diaphragm having a first position and a second position;

providing a power supply;

attaching said sensor to said fluid conduit or said network;

attaching said fluid control device and said solenoid operated valve to said fluid conduit;

forming an electrical circuit by attaching said sensor and the solenoid operated valve to said power supply; and

moving said diaphragm from said first position to said position second position by completing said electrical circuit to the solenoid of said solenoid operated valve.

11. The method of claim 10 wherein said step of attaching said fluid control device and said solenoid operated valve further comprises attaching said fluid control device and said solenoid operated valve to said fluid conduit at a distance of four inches or less to one another.

12. The method according to claim 10 further comprising the steps of:

selecting a second sensor to monitor a second variable of said pump; and

attaching said second sensor to said fluid conduit or said network.

13. The method of claim 10, wherein said step of moving said diaphragm results in allows fluid flow through said solenoid operated valve.

14. A kit to be used for monitoring the deleterious effects of increased pressure and/or temperature within a centrifugal pump, said kit comprising:

at least one electronic sensor to monitor a variable of the centrifugal pump, said variable being selected from the group consisting of: temperature, pressure, and motor current;

a fluid control device;

an electronic snap-action valve;

a power supply; and

electrical connectors for connecting said sensor, said power supply, and said electronic snap-action valve.

15. The kit according to claim 14 wherein said fluid control device comprises a gate valve.

16. The kit according to claim 14 wherein said fluid control device is a pipe union.

17. The kit according to claim 14 further comprising installation instructions for said kit.

18. The kit according to claim 14 further comprising at least two of said sensors.

19. The kit according to claim 18 further comprising installation instructions for said kit.