Historically, this application has always caused problems for Severn Trent, as they were unable to source a pump that would draw the thick sludge (12% ds) through the suction pipe work continuously without cavitating and subsequently failing.
The VRM pump at Itchen Bank has now been operating successfully for the past 6 months. The secret of the success is in the slow, gentle pumping action which can create up to 9 metres suction head.
The VRM pump manufactured and installed by EMS features an electric motor driving though a reduction gearbox to a crankshaft, connecting rod and piston assembly (very much like an upside down internal combustion egine). The piston, which is directly connected to the sludge ram, slides up and down inside a lubriacted housing and imparts a direct, vertical motion to the sludge ram. The piston sliding inside the lubricated housing sustains all the lateral forces that arise as a result of the eccentric crankshaft motion. This ensures that the lateral forces are not transferred to the sludge ram and ram seals, thereby allowing a very long pump stroke, whilst extending the expected working life of both the ram and sludge seals.
The pump has been specified with a selctable two speed option for summer or winter flow rates.