A solenoid pump, comprising: a solenoid having a coil and a pole piece positioned in a solenoid body; a base including an inlet port and an outlet port, the base connected to the solenoid body such that the base and the solenoid body cooperate to define an internal chamber; a retainer body disposed inside the internal chamber that includes an armature cavity; an armature slidably disposed in the coil of the solenoid and the armature cavity for movement along a longitudinal axis between an energized position and a de-energized position; a diaphragm mounted in the armature cavity that is connected to the armature such that the diaphragm deflects from a first position to a second position in response to movement of the armature along the longitudinal axis from the de-energized position to the energized position; an inlet check valve positioned in the internal chamber and arranged in fluid communication with the inlet port that permits fluid flow in only a first direction moving from the inlet port toward the diaphragm; an outlet check valve positioned in the internal chamber and arranged in fluid communication with the outlet port that permits fluid flow in only a second direction moving from the diaphragm toward the outlet port; a fluid flow path extending through the retainer body from the inlet check valve to the diaphragm and from the diaphragm to the outlet check valve that transports fluid from the inlet check valve to the outlet check valve as the diaphragm oscillates between the first and second positions; and a diaphragm support sleeve, positioned in the armature cavity, that abuts and supports at least part of the diaphragm, wherein at least part of the armature is received in the diaphragm support sleeve. a solenoid having a coil and a pole piece positioned in a solenoid body; a base including an inlet port and an outlet port, the base connected to the solenoid body such that the base and the solenoid body cooperate to define an internal chamber; a retainer body disposed inside the internal chamber that includes an armature cavity; an armature slidably disposed in the coil of the solenoid and the armature cavity for movement along a longitudinal axis between an energized position and a de-energized position; a diaphragm mounted in the armature cavity that is connected to the armature such that the diaphragm deflects from a first position to a second position in response to movement of the armature along the longitudinal axis from the de-energized position to the energized position; an inlet check valve positioned in the internal chamber and arranged in fluid communication with the inlet port that permits fluid flow in only a first direction moving from the inlet port toward the diaphragm; an outlet check valve positioned in the internal chamber and arranged in fluid communication with the outlet port that permits fluid flow in only a second direction moving from the diaphragm toward the outlet port; a fluid flow path extending through the retainer body from the inlet check valve to the diaphragm and from the diaphragm to the outlet check valve that transports fluid from the inlet check valve to the outlet check valve as the diaphragm oscillates between the first and second positions; and a diaphragm support sleeve, positioned in the armature cavity, that abuts and supports at least part of the diaphragm, wherein at least part of the armature is received in the diaphragm support sleeve.