Liquid pump control

A control circuit for controlling cyclic operation of a circulation pump, the control circuit comprising:

• an intermittent actuating means for intermittently producing a pump signal, the intermittent actuating means being operatively connected with the circulation pump for pumping a circulation fluid through a fluid receiving apparatus, the intermittent actuating means including a first timer for producing the pump signal at selected, regular intervals;
• a pressure monitor for monitoring the pressure of the circulating fluid;
• and,
• a low pressure shutdown means for terminating operation of the circulating pump unless the monitored circulation fluid pressure attains a first preselected pressure within a preselected time period, the low pressure shutdown means includes,
• A. a second timer which is operatively connected with the first timer to be actuated by the pump signal to commence timing said preselected time period, the second timer causing a time controlled switching means to conduct the pump signal for the preselected time period;
• and,
• B. a pressure controlled low pressure switch which passes the pump signal around the time controlled switching means in response to the monitored circulation fluid pressure exceeding the first preselected pressure such that the circulation pump continues to be activated by the pump signal;
• and,
• C. a bypass switch connected electrically in series with the time controlled switching means, the pressure controlled low pressure switch bypassing the bypass switch and the time controlled switching means, the bypass switch conducting the pump signal in response to sensing a pressure below a second preselected pressure, the second preselected pressure meeting or exceeding the first preselected pressure such that the pressure controlled low pressure switch closes as or before the bypass switch opens.