A programmable 
electric breast pump system includes a 
vacuum pump pneumatically coupled to breast cups and a vacuum 
relief valve bypassing the 
vacuum pump. A controller receives command input from a 
vacuum level selector and a vacuum rate selector, and feedback from a 
pressure sensor measuring vacuum in the breast cups. In response, the controller cycles the 
relief valve between minimum and maximum vacuum setpoints to create a periodic vacuum pulse in the breast cups. By adjusting the vacuum min / max levels and vacuum rate, a user may change the strength of the pulse after let-down, or synchronize the frequency of the pulse with the natural 
refractory time of a lactating breast. Related methods for operating a 
breast pump mimic the suckling cycle of a 
nursing infant and may include steps for bypassing a 
vacuum pump with a vacuum 
relief valve, selecting a vacuum rate and a 
vacuum level, driving a vacuum pump at the selected vacuum rate, 
cycling the relief valve according to the 
vacuum level, and adjusting the vacuum level until the vacuum pulses in phase with a natural 
refractory time.