Abstract: The use of a probe for the control of foam build up in a fermenter, which probe comprises a guard electrode (13), first and second insulators (14 and 15) separated by the guard electrode, a detecting electrode (12) separated from the guard electrode by the first insulator, and a plug (18) and socket (17) for connecting the probe to a power source, the second insulator being provided with fermenter mounting means in the form of a flange (16), a sensor comprising the aforementioned probe for use with an antifoam supply regulator, a foam control system and a method of controlling the build up of foam in a fermentation vessel.

Abstract: A wellhead assembly for a beam pumped production well comprises a stuffing box for providing a seal around a polished rod of the beam pump assembly and a flapper type safety valve for sealing off the wellhead in case of polished rod failure. The safety valve comprises a wear plate which is pressed against the polished rod and means are provided for monitoring the amount of wear of the wear plate on the basis of the angular orientation of the safety valve relative to the stuffing box.

Abstract: A well for the solution mining of salt from an underground salt formation, comprising a borehole (12) extending from the earth's surface downwards into the formation, a casing (10) that is cemented in said borehole down to the upper level of said formation and separate conduct means provided within said casing and extending through the borehole downwardly beyond said casing, respectively for introducing leaching water into the salt formation and for withdrawing pregnant leach liquor from said formation, which conduct means have adjustable effective lengths, said conduct means each comprising a tubing string (13, 14), the two strings extending parallel through said casing and at least one of said strings carrying a tailpipe (18, 19) of smaller diameter, which tailpipe is axially telescopic in said string, can extend downwardly beyond said string and carries a liner assembly (20, 21, 22, 23) at its upper part that can engage the inner wall of said string at any desired location above the bottom end of the strin