EP2042730A2

EP2042730A2 - Improved delivery compensation unit.

Info

Publication number: EP2042730A2
Application number: EP08164843A
Authority: EP
Inventors: Diego Revelin
Original assignee: Revelin Evaristo & Figli SNC
Current assignee: Revelin Evaristo & Figli SNC
Priority date: 2007-09-28
Filing date: 2008-09-23
Publication date: 2009-04-01
Also published as: EP2042730A3; ITVI20070261A1

Abstract

The invention is a delivery compensation unit for plaster sprayers comprising a frame (3) that supports a tank (4) containing the plaster (I) to be sprayed; a pumping unit (6) for conveying the plaster (I) through suction from the tank (4) to a suction chamber (6a) and through compression from the suction chamber (6a) to a compression chamber (6b); an outlet pipe (7) connecting the compression chamber (6b) to a spray gun; ball valve means (13a, 13b) for placing the tank (4) in communication with the suction chamber (6a) and the suction chamber (6a) with the compression chamber (6b). A cylindrical container (19) closed at one end by a bottom (20) defines a compensation chamber (22) having an inlet mouth (21) connected to the chamber provided with a sliding plunger (23) and elastic mechanical means (24) interposed between the plunger (22) and the bottom (20).

Description

The present invention concerns an improved delivery compensation unit, particularly suited to be employed in plaster sprayers used in the building industry for the finishing and restoration of walls.
It is known that the plastering process requires the spreading, on the surface of the wall to be treated, of a mixture consisting of lime, sand and other substances, in order to create a smooth protective layer to which paints of different types can be applied.
It is known as well that the plastering process can be carried out either manually or using spraying devices that in fact are called "plaster sprayers".
Said plaster sprayers comprise a spray gun that the operator uses to direct the plaster toward the wall and a tank connected to the gun and containing the plaster.
Furthermore, the plaster sprayer comprises a power unit that is equipped with a motor suited to transmit motion to a plaster pumping unit and set rotating a compressor that supplies the compressed air used for spraying.
As far as the pumping unit is concerned, it comprises a plunger operated by a connecting rod that sucks plaster from the tank to convey it into a suction chamber and successively compresses it in a compression chamber that is connected to the suction chamber through valve means provided therein.
The operation of the plunger generates alternate compression and suction phases, so that the plaster is first made flow from the tank to the suction chamber and then to the compression chamber, from which it is conveyed towards the outlet pipe.
At the same time, the compressed air reaches the spray gun and facilitates spraying thanks to the Venturi effect.
The drawback posed by the plaster sprayers of the type described, belonging to the known art, lies in that, due to the alternate motion of the plunger and therefore to the succession of the suction and compression phases, delivery of the plaster is not constant.
It is known, in fact, that the alternation of compression and suction that is generated in this way assumes a substantially sinusoidal trend over time, as shown in Figure 1 related to the known art.
Consequently, the plaster outflow takes place only during compression and therefore at the level of the areas illustrated by A in the graph of Figure 1 related to the known art.
In order to overcome this drawback, pneumatic delivery compensation units are used, which consist of a compensation chamber positioned immediately above the compression chamber and filled with compressed air, through a pipe connected to the compressor.
An on-off valve allows or prevents air supply to the compensation chamber.
During the plaster compression phase in the compression chamber, part of the plaster flows into the compensation chamber so that, on the successive suction phase, the plaster accumulated in the compensation chamber flows towards the spray gun, in such a way as to ensure a certain regularity in the delivery of plaster.
Said compensation unit, in fact, makes it possible to compensate for the failed delivery of plaster during the suction phase by keeping the outflow of plaster as constant as possible.
Said result can be observed in Figure 2 related to the known art, which shows the plaster outflow from a plaster sprayer provided with compensation unit, and where it is possible to see that said outflow is more regular due to the delivery of the plaster accumulated in the compensation chamber during the plunger suction phase, as shown also by the area indicated by B.
The compensation unit described above, however, poses some drawbacks that are substantially due to the fact that it is pneumatic.
In fact, a first drawback lies in that the presence of a pressurised chamber increases the dangerousness of the plaster sprayer, above all in the case where the air present in said compression chamber reaches particularly high pressure values.
Another drawback lies in that if, upon starting the machine, the operator forgets to open the valve that feeds air to the compensation chamber, on the first pumping cycle this will be completely filled with plaster and therefore will not be able, during the following cycle, to carry out its function, i.e. ensure a compensation effect.
This, among other things, would create the further drawback of making it necessary to remove the whole compensation unit in order to clean it from the plaster, with a consequent time waste and with the need to interrupt work, and this may even happen during a critical operating phase, with an inevitable loss of money.
A further drawback is represented by the fact that it is impossible to position an overflow valve in the compensation chamber in order to be able, in case of need, to discharge the excess plaster accumulated therein, for example in case of clogging downstream of the spray pipe.
It is clear, in fact, that if this valve were added, it should remain always open, thus causing a continuous air discharge.
As an alternative, it is possible to install a settable maximum pressure valve, with the inconvenience, however, that this would make the structure of the whole compensation group more complicated from a technical point of view.
The present invention intends to overcome the drawbacks listed above.
It is a first object of the invention to provide a delivery compensation unit that during the spraying phase maintains the plaster outflow substantially constant.
It is a further object of the invention to provide a delivery compensation unit that is activated automatically when the device is started, with no need for the operator to intervene in any manner.
It is a further object of the invention to provide a delivery compensation unit that, differently from the known ones of pneumatic type, is provided with an overflow discharge system.
Another object of the invention is to provide a delivery compensation unit in which the plaster flow compensation pressure can be easily regulated.
It is another, yet not the least object of the invention, to provide a delivery compensation unit that is safer compared to the pneumatic delivery compensation units.
The objects described above are achieved by a mechanical delivery compensation unit having the characteristics illustrated in the main claim.
Further characteristics of the delivery compensation unit are described in the dependent claims.
Advantageously, the introduction of the delivery compensation unit that is the subject of the invention makes the plaster sprayer more reliable because it is less subject to stops than the pneumatic compensation units of known type.
The delivery compensation unit that is the subject of the invention can be installed also in plaster sprayers provided with a pneumatic compensation unit. The objects and advantages described above will be highlighted in greater detail in the description of a preferred embodiment of the invention that is supplied as an indicative, non-limiting example, with reference to the enclosed drawings, wherein:

Figure 3 shows an axonometric view of the plaster sprayer;
Figure 4 shows a side view of the plaster sprayer;
Figure 5 shows a sectional view of the plaster sprayer along a vertical plane;
Figures 6 and 7 show an enlarged detail of the machine shown in Figure 4 seen from two different angles;
Figure 8 shows a schematic overall view of the sequence of the plaster suction and compression phases, from the tank to the compression chamber, with reference to Figures from 8a to 8g.

The delivery compensation unit that is the subject of the invention can be seen in its whole in Figures 3 e 4, where it is shown in an axonometric view and indicated by 1, and also in Figure 5, in a longitudinal view.
Furthermore, an axonometric view of the delivery compensation unit 1 that is the subject of the invention is shown also in Figures 6 and 7, which illustrate details of Figure 4.
In the above mentioned figures, it is shown when installed in a plaster sprayer indicated as a whole by 2, of the type known per se.
It is understood that the delivery compensation unit 1 that is the subject of the invention can also be installed in plaster sprayers different from those illustrated in the drawings and described here below.
As regards the plaster sprayer 2, it can be observed that it comprises a frame 3 that supports a tank 4 containing the plaster I to be sprayed and a power unit 5 for operating a pumping unit, indicated as a whole by 6, for conveying the plaster I from the tank 4 to a spray gun, not represented herein, through an outlet pipe 7.
In particular, as regards the pumping unit 6, it can be observed in Figure 5 that it comprises a cylinder 8 with a plunger 9 sliding therein, said plunger 9 being connected to the power unit 5 by means of a rod 10.
Preferably, but not necessarily, it comprises the motor 5a that sets the plunger 9 moving according to a rectilinear alternate motion through a belt 5b and a connecting rod-crank assembly 5c and sets a compressor 5d rotating through a second belt. This generates the compressed air that is used for spraying.
The cylinder 8 communicates with a suction chamber 6a that in turn communicates with an underlying accumulation chamber 6c connected to the bottom of the tank 4 through a pipe 11.
First valve means, constituted by a first ball 13b, allow opening and closing of the first way 12 that places the accumulation chamber 6c in communication with the suction chamber 6a.
The suction chamber 6a in turn communicates with an overlying compression chamber 6b through second valve means that comprise a second ball 13a that opens and closes the second communication way 14 between the two chambers.
In the compression chamber 6b it is possible to identify also a third delivery way 15 connected to the outlet pipe 7 for conveying the plaster I to the spray gun not represented in the figure.
In the compression chamber 6b it is also possible to identify a return pipe 16 through which the plaster I returns to the tank 4, said return pipe 16 being intercepted through a rotary valve 17.
This, as shown in Figure 4, is operated manually through a handle 18 and, in normal operating conditions, is generally closed.
According to the invention, the delivery compensation unit 1 comprises a cylindrical container 19 closed at one end by a bottom 20 and communicating with the compression chamber 6b through an inlet mouth 21, as shown in Figure 6, so that the plaster I, when pushed by the compression generated by the plunger 9 in the compression chamber 6b, flows also towards the compensation chamber 22 defined by the cylindrical container 19 itself.
The delivery compensation unit 1 is also provided with a plunger 23 with rod 23a slidingly coupled in the compensation chamber 22 whose movement along the longitudinal axis y defined by the chamber itself is regulated via elastic mechanical means 24 interposed between the plunger 23 and the bottom 20, coaxially to the rod 23a, as shown in Figure 5.
According to the embodiment illustrated in Figure 5a, the elastic mechanical means 24 comprise a helical spring 25a with elastic constant selected by the operator in order to exert a controlled and predetermined thrusting action on the plunger 23.
Alternatively, the elastic means, according to the embodiment illustrated in Figure 5b, can be constituted by two springs, more precisely one external spring 25b and one internal spring 25c, which are coaxial to each other and have different elastic constants and lengths, in such a way as to start operating at successive moments during the movement of the plunger 23.
According to another embodiment, shown in Figure 5c, the elastic means can be constituted by Belleville washers 25d.
According to another construction variant of the invention, not illustrated in the drawings, the elastic means 24 can be elastomers.
In any case, the elastic means 24 can be of any type and have a diversified distribution, provided that they are mechanical.
The delivery compensation unit 1 that is the subject of the invention preferably but not necessarily comprises a drain way 26 created in the cylindrical container 19 at such a height that it is included between the plunger 23 and the bottom 20 of the container itself, at a height above the top dead center of the plunger 23 in normal operating conditions.
This drain way 26 is also connected to the tank 4 through a drain pipe 27 so that the plaster I flows back towards the tank if the plunger 23 slides beyond the set dead center, which indicates the presence of a greater quantity of plaster I in the compensation chamber 22 than would be correct in normal operating conditions.
In practice, the drain way 26 and the drain pipe 27 behave as an "overflow" system which is arranged by the manufacturer in such a position that the opening of the drain way 26 is left free when the plunger 23 exceeds a given height.
This creates an automatic safety system that opens a way for the return of the plaster I into the tank 4 if, for different reasons, there should be a stoppage downstream of the delivery way 15 and therefore at any point in the outlet pipe 7 or in the spray gun.
In this case the operator, as he/she notices that the plaster I does not flow out any longer and on the contrary returns to the tank 4, understands that the clogging is right in the section mentioned above.
As regards the bottom 20, it comprises a disc that is removably connected to the cylindrical container 19 through a suitable thread or through screws or another fixing means.
This structure facilitates the cleaning of the inside of the cylindrical container and the removal of the plunger 23 and of the elastic mechanical means 24 when necessary.
In other construction variants, the bottom 20 can be welded to the cylindrical container 19, in which case it must be possible to remove the whole cylindrical container 19 by means of a flange at the level of the inlet mouth 21.
In the embodiment illustrated and described herein, the valve means positioned between the suction chamber 6a and the compression chamber 6b and between the suction chamber 6a and the accumulation chamber 6c are balls, indicated respectively by 13a and 13b.
Further embodiments of the invention may be provided with different types of valve means.
In practice, the work carried out by the plaster sprayer 2 with the delivery compensation unit 1 of the invention is developed in different phases, as schematically shown in the sequences of Figures from 8a to 8g.
Figure 8a shows the plaster sprayer 2 at rest, with the plunger 9 at the front dead center and the tank 4 filled with plaster I up to the desired level and with the accumulation chamber 6c filled with plaster I, too.
When the power unit 5 is started, the plunger 9 moves backwards, as shown in Figure 8b, thus creating inside the suction chamber 6a a suction effect that determines the closing of the second communication way 14 through the valve 13a and the opening of the first communication way 12 through the lifting of the valve 13b caused by a vacuum effect.
In this way the plaster I flows from the accumulation chamber 6c into the suction chamber 6a according to the direction indicated by the arrows in Figure 8b.
When the plunger 9 has moved completely backwards and is at the rear dead center, as shown in Figure 8c, in the suction chamber 6a there is a certain quantity of plaster I and the suction effect fades away.
The maximum quantity of plaster I that can accumulate inside the suction chamber 6a corresponds to the volume of the cylinder 8 in which the plunger 9 moves and varies according to the position of the unit that regulates the connecting rod-crank assembly 5c.
At this point, the plunger 9 resumes its forward movement in the direction indicated by the arrow in Figure 8d and compresses the plaster I present in the suction chamber 6a making it flow, as indicated in the figure, into the compression chamber 6b, since its thrusting action lifts the ball valve 13a, opens the second communication way 14 and closes the ball valve 13b.
At the same time, the plaster I flows also through the delivery way 15 and then into the outlet pipe 7 and is finally delivered through the spray gun.
During the first pumping cycle the delivery compensation unit 1 that is the subject of the invention carries out the first step of its task, that is, lifts the plunger 23 that is moved upward by the thrust of the plaster pumped towards the bottom 20, thus compressing the elastic mechanical means 24.
The maximum height reached by the plunger 23 corresponds to the maximum pressure exerted on it by the plaster I, which is counterbalanced by the load of the elastic means 24.
Obviously, this must be set in such a way as to ensure the accumulation in the compensation chamber 22 of a quantity of plaster I that is sufficient to be sprayed during the successive phase, when the compression of the plunger 23 ends, as will be described below.
At the moment when, as shown in Figure 8e, the plunger 9 reaches its front dead center again, the compression action ends, together with the spraying action and the filling of the compensation chamber 22 that thus reaches its maximum filling level.
At this point, as shown in Figure 8f, the plunger 9 resumes its stroke to the right as indicated by the arrow, and the second communication way 14 is closed due to the downward movement of the ball valve 13a, due to a vacuum effect.
At the same time suction of the plaster from the accumulation chamber 6c through the first communication way 12 starts again.
At the same time, in the compression chamber 22 the plaster I, following the thrusting action of the plunger 23, operated by the elastic recovery of the springs, continues to be delivered through the outlet pipe 7.
At this point the importance of a correct setting of the elastic means 24 is clear, in fact theoretically the filled volume of the compensation chamber 22 should substantially ensure that the outflow of plaster in the different operating phases remains constant.
When the plunger 23, as shown in Figure 8g, reaches its bottom dead center, the compensation chamber 22 is completely empty and the spraying action due to the elastic recovery of the springs ends.
At this point the cycle is repeated starting from phase 8c and repeating exactly the sequences previously described in a cyclical way for as long as the plaster sprayer 2 keeps operating.
A constant flow of the plaster I towards the spray gun during operation is thus ensured, and the main object of the invention is thus achieved.
According to the above, it is clear that the delivery compensation unit 1 of the invention installed on the plaster sprayer 2 allows the set objects to be achieved.
In particular, the invention achieves the object to provide a delivery compensation unit that makes it possible to maintain a constant plaster flow during the spraying operation.
The invention also achieves the object to provide a delivery compensation unit that is activated automatically upon starting of the machine and that does not need any intervention by the operator as is the case with plaster sprayers provided with pneumatic compensation units where, in order to prevent the compensation unit from stopping, the operator needs to open the air supply valve.
The invention also achieves the object to provide a delivery compensation unit provided with an overflow drain system connected directly to the tank without the interposition of any valve means.
This isn't possible, either, in the plaster sprayers provided with pneumatic compensation units, since in order to do that it would be necessary to install maximum pressure check valves that, as already explained, would complicate the overall structure and in any case would not be safe.
A further object achieved is the possibility to easily regulate the plaster flow compensation pressure exerted by the delivery compensation unit through the combination of elastic elements of various types.
Lastly, the invention also achieves the object to provide a delivery compensation unit that is safer compared to the delivery compensation units of pneumatic type.
In the construction stage, the plaster sprayer and the delivery compensation unit may be modified and variants of the same, which are neither described nor represented herein, may be carried out in order to improve its functionality and make it more economic to produce.
The construction variants described herein and others not mentioned must all be considered protected by the present patent, provided that they fall within the scope of the claims expressed below.
Where technical features mentioned in any claim are followed by reference signs, those reference sings have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

Delivery compensation unit particularly suited to be used in plaster sprayers of the type comprising:
- a frame (3) that supports a tank (4) containing the plaster (I) to be sprayed;

- a pumping unit (6) for conveying said plaster (I) through suction from said tank (4) to a suction chamber (6a) and for conveying said plaster (I) through compression from said suction chamber (6a) to a compression chamber (6b);

- an outlet pipe (7) for connecting said compression chamber (6b) to at least one spray gun;

- ball valve means (13a, 13b) for placing said tank (4) in communication with said suction chamber (6a) and said suction chamber (6a) with said compression chamber (6b);
characterized in that it comprises:
- a cylindrical container (19) closed at one end by a bottom (20) in order to define a compensation chamber (22) having an inlet mouth (21) connected to said compression chamber (6b);

- a plunger (23) slidingly coupled in said compression chamber (22);

- elastic mechanical means (24) interposed between said plunger (22) and said bottom (20).
Delivery compensation unit according to claim 1), characterized in that said elastic mechanical means (24) are one or more springs.
Delivery compensation unit according to claim 1), characterized in that said elastic mechanical means (24) are elastomers.
Delivery compensation unit according to claim 2), characterized in that said one or more springs are two coaxial springs (25b, 25c) arranged one inside the other.
Delivery compensation unit according to claim 2), characterized in that said one or more springs are helical springs.
Delivery compensation unit according to claim 2), characterized in that said one or more springs are Belleville washers (25d).
Delivery compensation unit according to claim 2), characterized in that said one or more springs have a different elastic constant.
Delivery compensation unit according to claim 1), characterized in that it comprises at least one drain way (26) created in said cylindrical container (19) and included between said plunger (23) and said bottom (20) in normal operating conditions, connected to said tank (4) through a drain pipe (27).
Delivery compensation unit according to claim 1), characterized in that said bottom (20) is removably connected to said cylindrical container (19) through fixing means.
Delivery compensation unit according to claim 1), characterized in that said valve means (13a, 13b) are of the ball type.