Motors: expansible chamber type – Differential – Motive fluid constantly applied to one working member face
Patent
1998-06-08
2000-08-01
Look, Edward K.
Motors: expansible chamber type
Differential
Motive fluid constantly applied to one working member face
91437, 91440, 91464, F15B 124
Patent
active
060950285
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a hydraulic unit for feeding an object at a desired feed speed a distance in a given feed direction during a working stroke and, in a return stroke, bringing the object back to the initial position at a considerably greater return speed, comprising a double-acting working cylinder with a first piston, the piston rod of which is connected to the object which is to be moved, and a receiver cylinder which is provided with a second piston and designed to be filled with oil from the working cylinder during the return stroke. The invention relates in particular to a hydraulic unit intended to move a screen unit forming part of a so-called diffuser, more specifically a pressure diffuser, for washing cellulose pulp, although the invention can very well also be used in atmospheric diffusers.
BACKGROUND OF THE INVENTION
In so-called pressure diffusers which in the cellulose industry are used for washing pulp in continuously working washing columns, the screen unit is reciprocated with the aid of a hydraulic working cylinder via a pull rod. The stroke length is normally up to approximately one meter. During the downward working stroke, the screen unit is fed slowly downwards at a speed which only slightly exceeds the sinking speed of the cellulose pulp in the column. On the other hand, the speed during the return stroke is high, normally approximately 1-1.5 m/s. The screen unit which is to be lifted during this rapid return movement can weigh more than ten tonnes and even larger installations have been planned. Furthermore, friction arises between the screen unit and the cellulose pulp in the column. The working cylinder and other parts in the hydraulic unit must therefore be of large dimensions in order to be capable of performing considerable work for a short time. This involves for example flow rates of the hydraulic oil of more than 10,000 l/min, oil quantities which furthermore have to filtered and cooled during the working cycle of the hydraulic unit. The systems which exist at present do not solve these problems in a satisfactory manner, which is hampering development within this field of technology towards increasingly large pressure diffusers and with this increasingly heavy screen units.
In order to meet the above requirements, the last fifteen years have seen the development of first the so-called float accumulator and then a hydraulic unit which comprises a so-called piston receiver. An advantage of the float accumulator is that it does not have dynamic gaskets which have to be replaced as a result of wear. In the case of greater oil quantities and cycle time, however, the gas losses become so great that gas refilling must take place frequently. The development of the piston receiver therefore constituted an improvement in this field. An example of a unit of this type is illustrated in SE 464533. Instead of gas charging, this unit has a hydraulic cylinder which presses the oil back to the tank. However, the principle has the disadvantage that the piston receiver must be completely, or at least essentially completely empty, before the next rapid return stroke is started. The emptying time must therefore be shorter than the shortest cycle time of the diffuser. This means that the hydraulic oil flow is highly discontinuous with a varying flow quantity. Apart from the fact that this involves difficulties in damping pressure peaks, the flow variation and the discontinuous manner of working also mean that filtering and cooling cannot take place optimally.
BRIEF DESCRIPTION OF THE INVENTION
The aim of the invention is to tackle the above problems and to provide an improved hydraulic unit. In particular, the aim of the invention is to solve problems in pressure diffusers in the cellulose industry but this does not preclude the possibility of the invention being applied in other fields of technology also where similar problems may arise. Further characteristics and aspects of the invention emerge from the description below of a preferred embodiment.
BRIEF DESCRIPTI
REFERENCES:
patent: 1343610 (1920-06-01), Bayles
patent: 1440730 (1923-01-01), Gartin
patent: 3606818 (1971-09-01), Hirn
patent: 5050380 (1991-09-01), Jonsson
Jonsson Allan Sven
Lam.ang.s Axel Stig
Fasth Rolf
Kvaerner Pulping AB
Lazo Thomas E.
Look Edward K.
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