Variable speed control for centrifugal pumps

• US 5,240,380 A
• Filed: 05/21/1991
• Issued: 08/31/1993
• Est. Priority Date: 05/21/1991
• Status: Expired due to Fees

• Current Assignee: Sundyne Corporation
• Original Assignee: Sundstrand Corporation (Rtx Corporation)
• Inventors: Mabe, William J.
• Primary Examiner(s): Bertsch, Richard A.
• Assistant Examiner(s): Scheuermann, David W.
• Application Number:
  US07/703,761
• Time in Patent Office: 833 Days
• Field of Search: 417/20, 417/43, 417/44, 417/45
• US Class Current: 417/43
• CPC Class Codes: F04D 15/0066 by changing the speed, e.g. of the driving engine

Abstract

A control system (10) for a variable speed centrifugal pump (12) in which pump pressure as a function of flow rate for a constant speed of operation of the pump has a range of flow rates in which the pump pressure increases as a function of increasing flow rate which is unstable in accordance with the invention includes a sensor (14) for sensing an operational parameter of an output flow pumped by the pump; a variable speed drive (16) for driving the pump at a commanded rotational speed in response to a commanded speed signal; and a controller (22), responsive to the sensed operational parameter, for producing the commanded speed signal (N) as a function of pump speeds at which the pump pressure does not increase with increasing flow rate.

Claims

1. A control system for a variable speed centrifugal pump operative throughout a flow range extending from a minimum to a maximum flow rate in which pump pressure as a function of flow rate for a constant speed of operation of the pump has a range of flow rates in which the pump pressure increases as a function of increasing flow rate which is unstable comprising:

a sensor in fluid communication with output flow pumped from the pump for sensing only a single operational parameter of the output flow pumped by the pump;

a variable speed drive for driving the pump at a commanded rotational speed in response to a commanded speed signal; and

a controller, responsive to the sensed operational parameter, for producing the commanded speed signal as a function of pump flow to vary pump speed from a speed producing the flow rates in which the pump pressure increases as a function of increasing flow rate to the commanded rotational speed to produce pump operation throughout the flow range to produce only flow rates for which pump pressure decreases as a function of increasing flow rate to produce stable pump operation.

2. A control system in accordance with claim 1 wherein:

the pump has an impeller with radial blades.

3. A control system in accordance with claim 1 wherein the variable speed drive comprises:

a variable speed electric motor for driving the centrifugal pump; and

an electrical power drive for supplying an electrical power signal to the variable speed electric motor to cause the electric motor to rotate at the commanded rotational speed.

4. A control system in accordance with claim 1 wherein:

the operational parameter is flow rate.

5. A control system in accordance with claim 1 wherein:

the controller utilizes an equation expressing pump speed as a function of flow rate which is solved by the controller in response to the operational parameter to produce the commanded speed signal.

6. A control system in accordance with claim 5 wherein:

the operational parameter is flow rate.

7. A control system in accordance with claim 1 wherein:

the controller utilizes a table of individual speeds each associated with a flow rate with the controller producing the commanded speed signal by matching the operational parameter to a flow rate and outputting the speed, associated with the matched flow rate, as the commanded speed signal.

8. A control system in accordance with claim 7 wherein:

the operational parameter is flow rate.

11. A control system in accordance with claim 1 wherein:

the controller utilizes a table of individual speeds each associated with a flow rate with the controller producing the commanded speed signal by matching the operational parameter to a flow rate and outputting the speed, associated with the matched flow rate, as the commanded speed signal.

12. A control system in accordance with claim 11 wherein:

the operational parameter is flow rate.

9. A system comprising:

a variable speed centrifugal pump operative throughout a flow range extending from a minimum to a maximum flow rate in which pump pressure as a function of flow rate for a constant speed of operation of the pump has a range of flow rates in which the pump pressure increases as a function of increasing flow rate which is unstable;

a sensor in fluid communication with output flow pumped from the pump for sensing only a single operational parameter of the output flow pumped by the pump;

a variable speed drive for driving the pump at a commanded rotational speed in response to a commanded speed signal; and

a controller, responsive to the sensed operational parameter, for producing the commanded speed signal to vary the speed of the pump as a function of pump flow to vary pump speed from a speed producing the flow rates in which the pump pressure increases as a function of increasing flow rate to the commanded rotational speed to produce pump operation throughout the flow range to produce only flow rates for which pump pressure decreases as a function of increasing flow rate to produce stable pump operation.

10. A control system in accordance with claim 9 wherein:

the operational parameter is flow rate.

13. A control system in accordance with claim 9 wherein:

the controller utilized an equation expressing pump speed as a function of flow rate which is solved by the controller in response to the operational parameter to produce the commanded speed signal.

14. A control system in accordance with claim 13 wherein:

the operational parameter is flow rate.