Displacement pump and control system

Abstract

A pump system includes a positive displacement pump, such as a diaphragm pump, an electric motor directly coupled to the positive displacement pump, and a programmable controller configured to maintain a desired current to the electric motor. The programmable controller is adapted to sense the current to the motor and to maintain constant current. It has been found that constant current provides constant torque and constant torque achieves constant fluid discharge pressure from the pump. The programmable controller utilizes an absorbed power formula to determine the correct current to achieve the necessary torque for a desired fluid discharge pressure. The programmable controller includes a power saving mode with minimal current and the pump is “dead headed” with no flow. The system is operated with a method that maintains constant fluid discharge pressure as well as having a power saving mode.

What is claimed is: 
     
         1 . A pump system, comprising:
 a positive displacement pump;   an electric motor directly coupled to the positive displacement pump; and   a programmable controller configured to maintain a desired current to the electric motor.   
     
     
         2 . The pump system according to  claim 1 , wherein the programmable controller comprises a current sensor. 
     
     
         3 . The pump system according to  claim 1 , wherein the positive displacement pump comprises a diaphragm pump. 
     
     
         4 . The pump system according to  claim 1 , wherein the programmable controller controls current according to an absorbed power formula. 
     
     
         5 . The pump system according to  claim 1 , wherein the programmable controller comprises a power saving mode. 
     
     
         6 . The pump system according to  claim 5 , wherein the programmable controller detects acceleration from the power saving mode and is operably configured to apply the desired current. 
     
     
         7 . The pump system according to  claim 1 , wherein the controller comprises a variable frequency drive controller. 
     
     
         8 . The pump system according to  claim 1 , wherein the system is configured for connecting to an fluid system solely with a current connection to the motor and a fluid connection to the pump. 
     
     
         9 . A method for controlling a positive displacement pump with a system including an electric motor and a programmable controller to achieve a desired constant fluid discharge pressure, the method comprising:
 programming the controller to control the system in a power saving mode with minimum current and torque with the pump having no flow;   determining current and torque requirements for the desired constant fluid pressure;   providing constant current to the motor corresponding to a torque for the desired constant fluid pressure;   maintaining the current for the corresponding torque and fluid discharge pressure.   
     
     
         10 . The method according to  claim 8 , further comprising returning the system to a power saving mode when demand ends. 
     
     
         11 . The method according to  claim 8 , wherein the torque automatically accelerates when there is demand on the pump and wherein the programmable controller senses the acceleration and returns to the current for the desired constant fluid discharge pressure.