having a seating surface 108 a valve member 109 is accommodated in the tubular housing 105 the valve member comprises a head 110 and a stem 111 which comprises a tubular portion 111a provided with windows 111b and 111c the head 110 is biased against the valve seat 107 by a light spring 112 which is disposed circumjacent the stem 111 and acts between a flange 116 on the top of the tubular portion 111a and a shoulder 117 formed in the tubular housing 105 between the cylindrical portion 106 and the valve seat 107 in use the float collar 101 is mounted in a length of casing towards the bottom thereof once the casing is in position mud is pumped down the casing the mud displaces the valve member 109 downwardly from valve seat 107 thereby permitting the mud to pass through the fill valve 102 the mud then passes downwardly to the bottom of the casing radially outwardly and then upwardly in the annular space between the casing and the wellbore the mud removes debris from the annular space and carries it to the surface after several hours the flow of mud is stopped and conditioning fluid is pumped down the casing to prepare the annulus.