Pumps – Expansible chamber type – Mechanically actuated distributor
Utility Patent
1998-05-29
2001-01-02
Freay, Charles G. (Department: 3746)
Pumps
Expansible chamber type
Mechanically actuated distributor
C417S515000, C417S571000, C092S169100, C137S240000, C251S333000
Utility Patent
active
06168398
ABSTRACT:
FIELD OF THE INVENTION
The present invention refers to a piston pump.
BACKGROUND OF THE INVENTION
The present invention refers especially to a piston pump for conveying viscous or moderately viscous, i.e. just still flowable fluids. Such viscous or moderately viscous fluids must be conveyed and dosed e.g. in the cosmetic and pharmaceutical industry in the form of oils and creams, in the field of waste disposal technology in the form of pulpy media or sewage sludge, and, in particular, they must be conveyed and dosed in the field of food industry. The substances to be conveyed in the field of food industry are highly liquid to pulpy substances, which may occasionally also contain solid components, such as yoghurt substances with fruit, yeast substances and dregs as well as sausage substances or sausage meat.
For conveying and dosing the viscous or moderately viscous fluids mentioned hereinbefore as an example, rotating positive displacement pumps (e.g. vane pumps and lobe pumps) are known. These pumps include, however, an unavoidable gap which causes undesirable leakage. In addition, rotating positive displacement pumps are normally not suitable for conveying fluids including solid matter. Soft solid matter, e.g. pieces of fruit, is subjected to mechanical loads and broken up in rotating positive displacement pumps. In addition, rotating positive displacement pumps are very difficult to clean, especially at the point of transition from the conveyor member to the drive shaft.
Furthermore, diaphragm pumps are known for conveying and dosing viscous or highly viscous fluids. These pumps have a limited stroke so that a comparatively large diaphragm area must be chosen for conveying a sufficient amount of material, and this, in turn, results in higher forces acting on the drive unit of the pump. In addition, diaphragm fatigue will occur due to the constant cyclic stress so that cracks may form. Furthermore, diaphragm pumps show dead spots in the area where the diaphragm is fixed. Cleaning of the pump is impeded by these dead spots.
Finally, the prior art discloses piston pumps used for conveying and dosing viscous fluids. Such piston pumps have at least one inlet valve and at least one outlet valve, said valves being lifting valves. Each of said valves is coupled to a control and drive means. This control and drive means is necessary for producing the high closing forces which are srong enough to displace the fluids, which may be highly viscous in some cases, from the valve area and for locally cutting, if necessary, solid components of the substance to be conveyed. The lifting valves can be controlled mechanically or magnetically.
A piston pump of the prior art is known from the handbook “Dosieren”, publisher Gerhard Vetter, Vulkan-Verlag Essen, 1994, page 132. This piston pump includes a working space at the top end of which an inlet valve and an outlet valve are arranged on opposite sides. The inlet valve is, at its closed position, held by a seat on which said inlet valve abuts with the valve surface facing away from the working space. For the purpose of opening, the inlet valve is moved from this closed position in the direction of the working space.
It is true that this structural design of the inlet valve has the advantage that, due to the internal pressure effective in the working space when the fluid is being expelled, the valve is pressed against the seat whereby the working space is reliably sealed, but the known piston pump must have a valve space for the inlet valve in which said inlet valve can be moved from its closed position to its open position without colliding with the piston, which, when the inlet valve is being opened, is normally located in the area of its upper dead centre on the same level as the valves.
The known piston pump also includes a valve space for the outlet valve in which said outlet valve, when closed, is accommodated such that a frusto-conical valve member of said outlet valve does not collide with the piston. The valve spaces of the inlet and outlet valves prevent an almost complete evacuation of the space enclosed by the piston, the valves and the cylinder, since a residual volume of the substance to be conveyed will remain in the valve spaces even if the piston abuts, when located at its upper centre, on a cover which is arranged on the front end face of the working space and which covers the cylinder, since the piston can only sweep over the working chamber but not over the valve spaces.
Especially in the case of piston pumps used in the field of the food-processing industry, it is necessary that the whole volume of the substance to be conveyed which has been drawn into the working space is discharged when the piston carries out its stroke. Dead spots are undesirable because they make cleaning of the piston pump more difficult. It should be possible to carry out such cleaning without disassembling the piston pump. In addition, it must be guaranteed that, especially in the case of perishable foodstuff, the substance to be conveyed does not collect in the piston pump, where it may perhaps perish, for a long time. In addition, the substance of an earlier charge contained in the dead space mixes with that of a later charge, when the two charges are conveyed in succession without any intermediate cleaning step. This mixing prevents a really smooth change from one charge to the next; the mixture consisting of the first and second charge and fed by the substance of the first charge contained in the dead spot must be rejected.
SUMMARY OF THE INVENTION
The present invention is based on the technical problem of providing a piston pump which is easy to clean and which includes the smallest possible number of dead spots.
According to a first teaching of the present invention, this problem is solved with the aid of a piston pump by means of the feature that, when closed, the inlet valve is located nearer to the working space than when it is open.
On the basis of the structural design of the inlet valve according to the present invention, it is possible to arrange said inlet valve in such a way that it will delimit the working space directly at its closed position. Since the inlet valve is moved away from the working space for the purpose of opening, it is not necessary to provide a valve space in which the inlet valve can move unhindered even if the piston is located in the area of its upper dead centre. On the basis of the structural design according to the present invention, the inlet opening is, in the open condition of the inlet valve, not partially blocked by distal parts of the valve, i.e. the valve rod connected to the control and drive means of the respective valve. A cleansing fluid flowing in can therefore flow into the working space unhindered. The piston pump, especially the working space and the valve surface facing the working space, can be cleaned more easily in this way. A further essential advantage is that the inlet valve is moved away from the working space for the purpose of opening so that also the substance to be conveyed can flow unhindered into said working space.
The present invention additionally suggests a piston pump comprising at least one working space which is surrounded by a cylinder and which is adapted to be varied by a piston arranged in said cylinder, and at least one inlet valve and at least one outlet valve. The valves are implemented as lifting valves and adapted to be controlled and driven by a control and drive means. In order to provide a piston pump which is easier to clean and which includes the smallest possible number of dead spots, the present invention suggests according to a second teaching that the valve surface facing the working space should merge without any steps with the inner surface of said working space at the closed position of the valves. In this embodiment according to the present invention, the inner walls of the working space are absolutely flat when the valves are closed. Hence, the space enclosed by the piston, by the valves and by the cylinder does not have any steps. This embodiment permi
Freay Charles G.
Tilton, Fallon, Lungmus & Chestnut
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