This invention relates to a rotary machine, preferably pump or compressor comprising a screw with a driving unit, a housing provided with suction and delivery openings and a prism shaped membrane body arranged between said housing and said screw

The types of pump most widely used nowadays are rotary turbine pumps, screw pumps, also piston pumps with reciprocating elements, and membrane pumps.

Of these, those types suitable for rather high delivery performance are the turbine pumps, while those with rather high lift capabilities are piston pumps. At the same time, turbine pumps have characteristically low lift and piston pumps characteristically low delivery. Accordingly, neither of these pump types has favourable performance characteristics in terms of practical requirements.

Of the other two types of pump, the membrane pumps are suitable rather for low performance requirements with regard both to lift and to delivery and, at the same time, because of the need for reciprocating motion and the need to provide them with rectification valves, they may be viewed as mechanisms relatively complicated and expensive in their construction. A further disad¬ vantage is the pulsating nature of the delivery.

Varieties of screw pumps would be optimal for small and medium power and delivery applications and, by virtue of this more widely used. This type of pump is, however, also rather complicated and expensive in their construction. Furthermore, they are vulnerable to the possible corrosive and erodent influence of the fluids being delivered, and to unfavourable lubrication and fric¬ tion characteristics, since the delivery of the fluid has to be performed by parts with fitting surfaces produced with the most costly machining work. For this reason, the double screw pump is suitable for continuous operation only when delivering fluids which are suitably clean and lubrifying.

A single screw pump variety comprises characteristically a housing, provided with a two-start rib spiral on its internal surface which is in moving contact with the rotating screw, and the requirement is that these two parts make also planetary movements with respect to each other, which either demands complicated costly design or, otherwise, or involves very unfavourable, high level of friction relatively high rate of wear in the mechanism.

The housing should necessarily be made in this latter case with a rather thick wall and of a very deformable structural material for the necessary planetary motion to be made possible; but, in this design, high and asymmetrical pressure and frictional forces arise which, in turn, result in significantly increased energy input due to reduced efficiency and which may lead to relatively early damage, depending on the character of the fluid being delivered.

To date, several inventions have been submitted intended to achieve the delivery of liquids or gases using a screw and a membrane element connected to this and in moving contact with each other (see e.g. US-PS 2.752.860 and 3.951.576 as well as UK-PS 800 154).

A fundamental shortcoming of the designs described in the above documentation is that they are not capable of generating the delivery and lift values necessary for fulfilling the minimum practical standards required, not even for very short duration. Thus, they cannot be considered even utilizable, i.e. mechanisms of technical nature, because of their low performance, very short working life and their completely uneconomical nature resulting from these factors. For this reason, the practical use of these types is unknown, even for peripheral, subsidiary purposes despite the long period of time which has elapsed.

It is possible to produce also a pump of relatively simple construction on a rotary, volumetric displacement principle and of favourable performance characteristics and self priming operation, with a screw driven directly by a motor, and prism-shaped membrane body connected to this and arranged within a tube-like housing and sealingly fastened to the housing, a pump which

does not contain reciprocating elements, nor require valves, and in which the friction between the surfaces sliding over each other may be greatly reduced and planetary movement of parts with respect to each other in respect of the component parts. Demand on the parts may be reduced also by a design where the surfaces sliding over each other are not affected by the physical or chemical influences of the fluid being delivered, as a result of which it may be manufactured economically and utilized on many fields.

The sides, formed as plane faces, of the prism membrane employed in this screw-membrane pump are joined to each other at distances corresponding with the external diameter of the screw and with rounded segments in order to reduce to an acceptable value the tensions caused by deformation demands arising during operation and, thereby, to attain the desired working life.

However, with such joining by way of rounded segments of the sides of the membrane body, the useful volume of the delivery chambers and so, the delivery of the machine is reduced and reduced more with greater radii of the segments that is: the longer the life for which we wish to design the pump.

The object of the invention is primarily to provide a membrane screw pump which may be designed for long life without reduction of the delivery indeed such that it may be possible to increase both the lift and the delivery together. The invention achieves this objective by improved joining the sides of the prism-shaped membrane to each other. As a result of this, the magnitude of the critical working tensions in the membrane may be reduced and, at the same time, the volume of the delivery chambers between the housing and the membrane may be increased, as can the speed of the machine. According to the present invention the rotary machine, preferably ferably pump or compressor is comprising a screw coupled with a driving unit, a housing provided with suction and delivery openings and a prism-shaped membrane body arranged between said housing and said screw, wherein the side walls of the prism-shaped membrane are connected to each other by curved segments arranged outside the space defined by the outer diameter of the screw and/or by the inner surfaces of the membrane.

ln the machine the inner surfaces of the membrane are preferably plain or convex surfaces and the developed length of the convex walls of the membrane is about equal to the inner perimeter of the housing. The curved segments are generally concave surfaces. The walls of the membrane are of resilient homogeneous material and may be provided with reinforcing coils springs, filaments or textile inserts, wherein these filaments or coil springs extend in directions corresponding to the pitch of the screw.

According to an advantageous embodiment the walls of the membrane are consisting of zones of different elastic modulus or of zones of different wall thicknesses, wherein the zones extend in directions corresponding to the pitch of the screw.

The invention is based on the following recognitions:

Fundamentally more favourable results are made possible by the innovation wherein the rounded segments are formed outside the space formed by the external diameter of the screw and/or by the inner surfaces of the membrane.

In this way, the total effective displacement volume will not be less, compared with that of the earlier designs, even when using rounded segments of larger radii, thus the desired working life may be attained while simultaneously maintaining greater displacement. In other words, these important characteristics may be created at more favourable levels, without any reduction caused by one to the detriment of the other.

Additionally, by forming the sides of the prism membrane to curve in towards the axis with convex shape the effective cubic capacity, and thus also the displacement, may be increased still further.

A further recognition relating to ability to increase performance is that, in order to counteract external demands for flexibility arising in the parts unsupported between the crests of the screw, in the vicinity of the edges of the sides of the prism membrane, namely in the section of the membrane body subjected to the

fluid pressure it is preferable to form the walls of the membrane with a convex shape and/or to reinforce these with embedded fibre or textile insert.

With this design, it is possible to increase the lift to a significant extent, for which purpose it is recommended that a pre-stressed fibre or textile insert, or one made of low extensibility material be used for increased reinforcement of the convex parts.

A further recognition, relating to the foregoing, is that the filaments or coil springs extend in directions corresponding to the pitch of the screw, in which case, the membrane sides are not subjected to tensile stress during operation, thus nor do the tensions arise which would otherwise be substantial. Further, since the tensions caused by bending are fractional by comparison, therefore this choice of design is equally favourable with regard to the working life, also.

A further, related recognition is that fibre or textile reinforcement of very low extensibility and high strength can be embedded into the membrane by which means the lift and the working life can both be increased several times. As a result, the importance of the strength characteristics of the structural material of the membrane is decreasing.

It follows that this construction can be applied satisfactorily, for example, to the delivery of corrosive fluids or other materials needing special attention. With the above structure it is possible to embed fibre or textile of good thermal conductivity (metals or carbon) which may contribute to maintaining lower working temperatures, e.g., in the membrane.

Higher values may be attained both for the volumetric and for the lift performance, but also for the working life by producing the membrane wall from materials of differing elastic properties, assembling strips of several materials of differing properties or thicknesses.

Another design possibility with similar effect is embedding preferably pre- stressed a row of coil springs into the sides of the membrane made of homogeneous structural material or made as described in the foregoing, set in a suitable direction.

The strength properties of the membrane wall, so produced, are favourably dependent upon direction the values parallel to the axis of the screw are higher than those in a direction perpendicular to this, i.e. the extensibility of the membrane wall is greater in the latter direction, and these properties contribute to their fitting more efficiently into the grooves of the screw.

Another possible method for achieving a more efficient fit into the grooves is creating, inside the membrane body during assembly, a pressure lower than that in the delivery chamber (preferably a vacuum). The best and simplest method of maintaining this condition is employing a motor whose housing is open only at its drive end, and so the internal spaces of the two parts may be joined by a safe static seal.

In the case of more simple construction, without fastenings, it may be preferable to partially remove the load from the membrane body during prolonged storage or standstill, which may be achieved by a system where the internal pressure is reduced to the required level only during operation. This can be carried out e.g. by providing a separate pump, which provides for decreasing the inner pressure during operation meanwhile in standstill the lubricant can flow back to the inner space of the membrane.

Slip is produced only between the surfaces of the screw and the inner surface of the membrane body. These surfaces can be produced as lapped faces and lubricant can be arranged between them.

Due to the above, both friction and energy consumption can be reduced considerably with respect to the usual screw pumps or compressors. Accordingly, a multiple working life can be achieved. Furthermore, both the production and the operation of the machines according to the invention are extremely efficient, meanwhile the pollution of the environment can also be reduced by applying a great number of them.

The machine, according to the invention can be used for delivering different fluids being corrosive or erodent and it can be adapted to different purposes by applying appropriate material for the parts of the machine. The machine is also

suitable for being applied as a feeding pump as well as a compressor for producing pressurised air.

The machine of the invention may be a pump or compressor and is very advantageous compared to other designs for pumping corrosive and erodent fluids, or for compressing gases.

The membrane body may be made of a laminate material and, where applicable, have a corrugated internal and/or external surface.

It is suggested that there be a lubricant in the spaces between the screw and the membrane body and, at the same time the screw is provided with channels for circulation of the lubricant.

The essence of the invention is therefore an improved membrane body arranged between the moving parts of the pump. Due to this improved membrane body, the loading of the operating parts can be reduced and the machine comprises only three relatively small parts, whereby the machine operates in a new, improved way, due to the construction of the parts and to the presence of the membrane body.

Further details and advantages of the invention will be described by way of example example and with the accompanying drawing. In the drawing

Fig. 1 is the longitudinal section of a pump according to the invention and

Fig. 2 is section ll-ll of Fig. 1.

In the housing 1 of the pump on Figs. 1 and 2 there is a screw 2 provided with an outer thread having an ace rounded profile. Between the housing 1 and the screw 2 is arranged the prism shape membrane 3 prepared with a special, star formed cross section. Shoulder 6 of the elastic prism-shaped membrane 3 is clamped between flange 1 1 of housing 1 and the front surface of the housing of the motor 17.

There are ribs 8 at the edges of the side walls 4 of the membrane 3 and these ribs are inserted into the grooves 9 of the housing 1.

Screw 2 is connected to the shaft 16 of the driving motor 17.

In view of the fact that the distance between the side walls 4 of the membrane 3 and the longitudinal axes of the screw 2 is similar to the core diameter of the screw, side walls 4 follow the surface of the screw 2. In this way, the side surface of the membrane 3 and the wall of the housing 1 define a number of delivery chambers 10, these chambers making the fluid advancing from the suction opening to the delivery opening.

Due to the wall thickness of the membrane the pump can provide any needed pressure. In the case of the embodiment shown in Figs. 1 and 2 the fluid enters the delivery chambers 10 through suction opening 14 and leaves the pump through delivery opening 15.

The walls 4 of the membrane 3 are connected to each other by segments 5 arranged outside the space defined by the outer diamater of the screw 2. Due to the above fact the bending movements have a greater space along these segments during operation and accordingly the bending stresses are reduced. This will result in a longer service time.

At the same time the clamping of the membrane 3 according to the invention enables to apply deeper threads, which in turn goes with an increased delivery. In order to improve the operation of the pump, the space between the screw and the membrane body is filled with lubricant, which can circulate through channels 12 and 13. Accordingly, the friction between the moving parts is considerably reduced.