A connection device (1; 101) configured for connecting a separation system with a separation device, said connection device comprising: a separation device inlet connection configured for connection to a separation device inlet; a separation device outlet connection configured for connection to a separation device outlet; a separation system inlet connection configured for connection to a separation system inlet; a separation system outlet connection configured for connection to a separation system outlet; a first fluid path connecting the separation system inlet connection with the separation device outlet connection; a second fluid path connecting the separation system outlet connection with the separation device inlet connection; a bypass fluid path connecting the separation system inlet connection with the separation system outlet connection; an inlet valve provided in the second fluid path in connection with the separation device inlet connection, said inlet valve being operable to provide an open state allowing fluid flow through the separation device inlet connection and a closed state preventing fluid flow through the separation device inlet connection; an outlet valve provided in the first fluid path in connection with the separation device outlet connection, said outlet valve being operable to provide an open state allowing fluid flow out through the separation device outlet connection and a closed state preventing fluid flow through the separation device outlet connection; and at least one bypass valve (35; 35a, 35b) provided in the bypass fluid path, said at least one bypass valve (35; 35a, 35b) being operable to provide an open state allowing fluid flow through the bypass fluid path and a closed state preventing fluid flow through the bypass fluid path, wherein a fluid can be flowed from the separation system outlet connection, through the bypass fluid path to the separation system inlet connection while a connected separation device is bypassed when at least one of the inlet and outlet valves (31, 33) is provided in a closed state and the at least one bypass valve (35; 35a, 35b) is provided in an open state; and wherein said bypass valve (35; 35a, 35b) is positioned in the bypass fluid path at a distance from the first and/or second fluid path (23, 35) of no more than 3 times a diameter of the first, the second and/or the bypass fluid path (23, 25, 27). a separation device inlet connection configured for connection to a separation device inlet; a separation device outlet connection configured for connection to a separation device outlet; a separation system inlet connection configured for connection to a separation system inlet; a separation system outlet connection configured for connection to a separation system outlet; a first fluid path connecting the separation system inlet connection with the separation device outlet connection; a second fluid path connecting the separation system outlet connection with the separation device inlet connection; a bypass fluid path connecting the separation system inlet connection with the separation system outlet connection; an inlet valve provided in the second fluid path in connection with the separation device inlet connection, said inlet valve being operable to provide an open state allowing fluid flow through the separation device inlet connection and a closed state preventing fluid flow through the separation device inlet connection; an outlet valve provided in the first fluid path in connection with the separation device outlet connection, said outlet valve being operable to provide an open state allowing fluid flow out through the separation device outlet connection and a closed state preventing fluid flow through the separation device outlet connection; and at least one bypass valve (35; 35a, 35b) provided in the bypass fluid path, said at least one bypass valve (35; 35a, 35b) being operable to provide an open state allowing fluid flow through the bypass fluid path and a closed state preventing fluid flow through the bypass fluid path, wherein a fluid can be flowed from the separation system outlet connection, through the bypass fluid path to the separation system inlet connection while a connected separation device is bypassed when at least one of the inlet and outlet valves (31, 33) is provided in a closed state and the at least one bypass valve (35; 35a, 35b) is provided in an open state; and wherein said bypass valve (35; 35a, 35b) is positioned in the bypass fluid path at a distance from the first and/or second fluid path (23, 35) of no more than 3 times a diameter of the first, the second and/or the bypass fluid path (23, 25, 27).