Automatic actuator for variable speed pump

Claim 1

An automatic speed-control actuator system for variable-speed fluid pumps operable to change the pump speed for preventing unacceptable low pressures at a pump inlet and unacceptable high pressures at a pump outlet, comprising: a. a pump means having an inlet and an outlet; b. a drive means connected to said pump means for driving said pump means; c. a speed adjusting means in conjuction with said drive means for varying the speed of said drive means; d. an actuator means connected to said speed adjusting means and being operable to vary said speed adjusting means for any of increasing, decreasing, and idling the speed of said drive means and thus the flow of liquid through said pump means; e. a power source; f. switching means sensitive to and actuated by present pressures at the inlet and at the outlet of said pump means; said switching means comprising; a circuit including first, second, third, and fourth pressure-actuated switches; said pressure-actuated switches being arranged in said circuit such that in their normal unactuated positions a decrease-speed signal is applied from said power source to said actuator means for causing said drive means to run at an idling speed; said first pressure-actuated switch being operable to be actuated to cause said decrease-speed signal from said power source to said actuator means to be removed when pressure at said inlet reaches a first preset pressure; said second pressure-actuated switch being operable to be actuated when pressure at said inlet reaches a second preset pressure, which is greater than said first preset pressure, to cause an increase-speed signal from said power source to be applied to said actuator means for increasing the drive means speed at a slow rate; said third pressure-actuated switch being operable to be actuated to remove said increase-speed signal applied to said actuator from said power source when the outlet pressure increases to a desired third preset pressure, which is greater than said second preset pressure, allowing said pump means to continue to operate and discharge fluid at the third preset pressure as long as fluid flow to said inlet is unchanged; said fourth pressure-actuated switch being actuated by an increase in pressure at said outlet to a fourth preset pressure causing a decrease-speed signal from said power source to be applied to said actuator means and in turn cause a decrease in pressure at said outlet until said fourth pressure-actuated switch deactuates; a decrease in pressure below said third present pressure causing said third pressure-actuated switch to deactivate and again apply an increase-speed signal to said actuator means, thus causing said actuator control system to modulate between said third and fourth preset pressures by control of said third and fourth pressure-actuated switches; said first pressure-actuated switch being deactivated when an insufficiency of fluid at said inlet causes a pressure drop below said first preset pressure thus preventing any increase-speed signal from being applied to said actuator means and causing a decrease-speed signal to be applied until the pressure rises above said first preset pressure at which point said actuator control system will modulate on inlet pressure; g. said switching means connected to said actuator means and to said power source for applying signals from said power source to said actuator means to vary said speed adjusting means and thereby cause said pump means to change its pumping rate in response to pressure conditions at said pump means inlet and outlet for maintaining normal pumping operations under pressure conditions between a minimum preset suction pressure at said inlet and a maximum preset discharge pressure at said outlet; said pump means speed being automatically regulated under varying inlet conditions to achieve a maximum pumping rate while not exceeding selected discharge pressures at the outlet and not creating an excessive vacuum at the inlet.