Cargo pumps
Page 73
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The company that claims to have pioneered the use of helical gears in gearor rotor-type pumps, now known as Varley-FMC Ltd., has introduced a new range of displacement pumps suitable for many uses including road tanker cargo handling.
The new pumps no longer have two rotors or double-helical teeth, but embody three rotors each with single-helical gears, The new units are claimed to be capable of twice the throughput of a twin-rotor pump of the same dimensions running at the same shaft speed.
A single shaft mounted centrally in the pump casing protrudes through the casing, at which point it is sealed by either a stuffing box or a mechanical seal. This and two other shafts— situated on a common centreline laterally in the casing—are carried in heavy-duty roller bearings designed to be lubricated by the product being handled. Fluid displacement is achieved in the same manner as in a doublerotor pump, but considerable research and development has resulted in the flow pattern within the casing being virtually free from cavitation—the bogy of displacement pumps.
A relief valve is built into the casing in such a way that the whole assembly can be reversed in order to provide for differing shaft rotations. Alternatively, the company provides a full-flow reversing valve affording three operating conditions: straight-tostorage gravity feed by-passing the pump, and from receptacle to receptacle in both directions, permitting the pump to operate with maximum efficiency irrespective of direction of rotation.
One of the features of the new pump is that the porting in the cases" is arranged so that the pipework can emerge from the rear of the pump, avoiding the main chassis members of the vehicle.
The models produced suitable for road tanker operation are designated type GP and have a 4in, bore size. The dry weight without a reversing valve is 2281b. The reversing valve adds 41Ib to this. The units are built for a maximum shaft speed of 1,000rpm. a maximum pressure of 150psi and maximum temperature of 250 deg F. They will handle fluids with viscosity ranging from 28 to 5,000 second Redwood. The pump cases are manufactured in either cast iron or aluminium.
Made by: Varley-FMC Ltd., Ferry Lane, Brentford, Middx.