A pump assembly for serial connection along a primary fluid line, the pump assembly comprising: a pump having an inlet side and an outlet side, and configured to receive a first fluid from the inlet side, and expel the first fluid from the outlet side; and a pump bypass actuatable between first and second valve states: the first valve state fluidly connecting the pump in series along the primary fluid line, and connecting an input side of the primary fluid line to an output side of the primary fluid line only via the pump; and a second valve state fluidly isolating the pump from the primary fluid line, and fluidly connecting the input and output sides (30,32) of the primary fluid line via a continuously piggable path, wherein the pump bypass further comprises: a piggable passage extending from the input side of the primary fluid line to the output side of the primary fluid line, and interrupted only by a bypass valve; a pump inlet valve disposed fluidly between the piggable passage and the inlet side of the pump; and a pump outlet valve disposed fluidly between the piggable passage and the outlet side of the pump; and wherein the piggable passage shares a passage width and a passage shape with the primary fluid line, such that a pig can run snugly through the input side of the primary fluid line, the piggable passage, and the output side of the primary fluid line, without interruption, while the bypass valve is open. a pump having an inlet side and an outlet side, and configured to receive a first fluid from the inlet side, and expel the first fluid from the outlet side; and a pump bypass actuatable between first and second valve states: the first valve state fluidly connecting the pump in series along the primary fluid line, and connecting an input side of the primary fluid line to an output side of the primary fluid line only via the pump; and a second valve state fluidly isolating the pump from the primary fluid line, and fluidly connecting the input and output sides (30,32) of the primary fluid line via a continuously piggable path, the first valve state fluidly connecting the pump in series along the primary fluid line, and connecting an input side of the primary fluid line to an output side of the primary fluid line only via the pump; and a second valve state fluidly isolating the pump from the primary fluid line, and fluidly connecting the input and output sides (30,32) of the primary fluid line via a continuously piggable path, wherein the pump bypass further comprises: a piggable passage extending from the input side of the primary fluid line to the output side of the primary fluid line, and interrupted only by a bypass valve; a pump inlet valve disposed fluidly between the piggable passage and the inlet side of the pump; and a pump outlet valve disposed fluidly between the piggable passage and the outlet side of the pump; and wherein the piggable passage shares a passage width and a passage shape with the primary fluid line, such that a pig can run snugly through the input side of the primary fluid line, the piggable passage, and the output side of the primary fluid line, without interruption, while the bypass valve is open. a piggable passage extending from the input side of the primary fluid line to the output side of the primary fluid line, and interrupted only by a bypass valve; a pump inlet valve disposed fluidly between the piggable passage and the inlet side of the pump; and a pump outlet valve disposed fluidly between the piggable passage and the outlet side of the pump; and wherein the piggable passage shares a passage width and a passage shape with the primary fluid line, such that a pig can run snugly through the input side of the primary fluid line, the piggable passage, and the output side of the primary fluid line, without interruption, while the bypass valve is open.