A method of converting an unbalanced valve to a balanced valve, the method comprising: obtaining an unbalanced valve comprising a valve body and an unbalanced valve cartridge; providing a balanced valve cartridge comprising: a retainer having a central bore including a first end and a second end, an inner surface, at least one opening in the inner surface forming a fluid inlet, and an internal threaded portion; a valve seat disposed within the central bore proximate the first end of the central bore; a movable valve plug at least partially disposed within the central bore, the movable valve plug selectively opening and closing the first end of the central bore by sliding within the central bore to cooperate with the valve seat, the movable valve plug having a hollow center portion and an angled vent portion, the angled vent portion having a fluid inlet on the downstream side of the valve seat and an outlet connected to the hollow center portion; a filter disposed within the central bore between the inner surface of the central bore and the valve plug; and an end cap disposed at the second end of the central bore, the end cap closing the second end of the central bore, the end cap including a blind bore facing the valve plug, the blind bore receiving one end of the valve plug so that the blind bore is fluidly connected to a downstream side of the valve seat by the hollow center portion of the valve plug and the angled vent portion of the valve plug, wherein an outer surface of the end cap includes a threaded portion cooperating with the internal threaded portion of the retainer to attach the end cap to the retainer; wherein the end cap plugs the second end of the central bore and traps the filter against the valve seat, thereby fixing the filter within the central bore and trapping the filter and valve plug between the end cap and the retainer, and sealing the valve seat against the retainer; removing the unbalanced valve cartridge from the valve body; and removably disposing the balanced valve cartridge into the valve body which includes threading the outer surface of the end cap into the retainer. obtaining an unbalanced valve comprising a valve body and an unbalanced valve cartridge; providing a balanced valve cartridge comprising: a retainer having a central bore including a first end and a second end, an inner surface, at least one opening in the inner surface forming a fluid inlet, and an internal threaded portion; a valve seat disposed within the central bore proximate the first end of the central bore; a movable valve plug at least partially disposed within the central bore, the movable valve plug selectively opening and closing the first end of the central bore by sliding within the central bore to cooperate with the valve seat, the movable valve plug having a hollow center portion and an angled vent portion, the angled vent portion having a fluid inlet on the downstream side of the valve seat and an outlet connected to the hollow center portion; a filter disposed within the central bore between the inner surface of the central bore and the valve plug; and an end cap disposed at the second end of the central bore, the end cap closing the second end of the central bore, the end cap including a blind bore facing the valve plug, the blind bore receiving one end of the valve plug so that the blind bore is fluidly connected to a downstream side of the valve seat by the hollow center portion of the valve plug and the angled vent portion of the valve plug, wherein an outer surface of the end cap includes a threaded portion cooperating with the internal threaded portion of the retainer to attach the end cap to the retainer; a retainer having a central bore including a first end and a second end, an inner surface, at least one opening in the inner surface forming a fluid inlet, and an internal threaded portion; a valve seat disposed within the central bore proximate the first end of the central bore; a movable valve plug at least partially disposed within the central bore, the movable valve plug selectively opening and closing the first end of the central bore by sliding within the central bore to cooperate with the valve seat, the movable valve plug having a hollow center portion and an angled vent portion, the angled vent portion having a fluid inlet on the downstream side of the valve seat and an outlet connected to the hollow center portion; a filter disposed within the central bore between the inner surface of the central bore and the valve plug; and an end cap disposed at the second end of the central bore, the end cap closing the second end of the central bore, the end cap including a blind bore facing the valve plug, the blind bore receiving one end of the valve plug so that the blind bore is fluidly connected to a downstream side of the valve seat by the hollow center portion of the valve plug and the angled vent portion of the valve plug, wherein an outer surface of the end cap includes a threaded portion cooperating with the internal threaded portion of the retainer to attach the end cap to the retainer; wherein the end cap plugs the second end of the central bore and traps the filter against the valve seat, thereby fixing the filter within the central bore and trapping the filter and valve plug between the end cap and the retainer, and sealing the valve seat against the retainer; removing the unbalanced valve cartridge from the valve body; and removably disposing the balanced valve cartridge into the valve body which includes threading the outer surface of the end cap into the retainer.