WO2006065121A1

WO2006065121A1 - Method for mounting an expansion tank in a closed liquid circuit, and closed liquid circuit with expansion tank

Info

Publication number: WO2006065121A1
Application number: PCT/NL2005/000864
Authority: WO
Inventors: Franciscus Roffelsen
Original assignee: Spiro Research B.V.
Priority date: 2004-12-15
Filing date: 2005-12-15
Publication date: 2006-06-22
Also published as: NL1027791C2

Abstract

A method for mounting an expansion tank in a closed liquid circuit with varying temperature, which expansion tank is provided with a housing divided by a membrane into a closed- off space and a space which is brought, via an open connection, into communication with a pipe of the closed liquid circuit, wherein the expansion tank is mounted with the connection situated in a lower area of the expansion tank, the arrangement being such that the closed-off space is situated substantially above the space which is in open communication with the pipe, while between the connection to the expansion tank and the open connection to the pipe an automatically operative de- aeration device is mounted. Preferably, the de-aeration device is combined with a make-up device.

Description

Title: Method for mounting an expansion tank in a closed liquid circuit and closed liquid circuit with expansion tank.

The invention relates to a method for mounting an expansion tank in a closed liquid circuit with varying temperature, which expansion tank is provided with a housing divided by a membrane into a closed-off space and a space which is brought, via a connection, into open communication with a pipe of the closed liquid circuit, and to a closed liquid circuit with an expansion tank mounted therein.

In a closed liquid circuit, such as a pipe network for heating a building, the circulated liquid will expand upon heating and, consequently, increase the pressure in the circuit. In order to not increase the pressure too much, an excess pressure release valve is present. Upon expansion of the liquid in a closed system however, the pressure increases very rapidly. In order to prevent the excess pressure relief valve from opening in the desired temperature variation path, use is made of an expansion tank which is provided with a housing divided by a membrane into, on the one side, a closed- off space, in which a gas is present, and, on the other side, a space which is brought, via a connection, into open communication with a pipe of the closed liquid circuit. Upon expansion of the liquid, the membrane, while compressing the gas in the closed-off space, is pressed back by the expanding liquid and thus prevents the rapid and sharp increase of the pressure in the closed liquid circuit through volume increase thereof. When the liquid cools down, the gas pressure in the closed-off space will gain the upper hand and press the membrane back and, optionally, bend it towards the other side. Such an expansion tank also provides an amount, albeit a limited amount, of liquid for replacing liquid exiting the circuit through, for instance, sweating, that is to say, leaking in a scarcely perceptible manner.

Such a closed liquid circuit is generally known in practice and functions adequately. If, however, the expansion tank does not function, which is virtually always caused by the membrane springing a leak, this leads to the exceedingly unpleasant breakdown of the heating system. In practice, this may lead to a premature replacement of an expansion tank with a new expansion tank, for reasons of safety, during standard maintenance to the system. The object of the invention is to eliminate the above-mentioned problems, that is to say, to ensure that the risk of an expansion tank breaking down as well as the risk of unnecessary, that is, premature replacement of an expansion tank still functioning well is reduced to a minimum while maintaining the optimal functioning of the expansion tank in all its aspects. According to the invention, this is achieved with a method of the type described in the opening paragraph, when the expansion tank is mounted with the connection situated in a lower area of the expansion tank, the arrangement being such that the closed-off space is situated substantially above the space which is in open communication with the pipe, while between the connection to the expansion tank and the open connection to the pipe an automatically operating de-aeration device is mounted. Due to these features, the expansion tank is mounted in "standing position", as it were, instead of "suspended" from the pipe, as is the standard in practice to date. This surprisingly simple feature, with the just as surprising effect that membrane fracture is reduced to a minimum, is the result of the insight that the contaminations, sinking in the suspended expansion tank and circulated with the liquid are the cause of the membrane fracture. With a suspended expansion tank, during upwards bulging of the membrane, that is, when the circulating liquid cools down or is reduced through leakage, the referred-to contaminations will end up in the area where the membrane is fixed in the housing. That is also the area of the membrane that hinges, as it were, at change and reversal of the pressure in the closed liquid circuit. Hard and/or sharp contaminations present there can perforate the membrane in this hinging area and hence render the expansion tank inoperative. By, presently, mounting the expansion tank in a "standing" position, as a result of gravity, contaminations can no longer accumulate in the referred-to threatened hinge area of the membrane, insofar as these contaminations are still able to end up in the expansion tank, because to that end, an upward displacement would be required in an environment where little, if any, flow occurs so that in a particularly effective manner, the disastrous effect of those contaminations to the membrane is eliminated.

It is noted that from European patent publication EP 0 899 514 A and DE 100 01 542 Al, expansion tanks are known where the connection is drawn at the bottom side, but where it is not stated whether the expansion tanks should be mounted in a "standing" position instead of, as is common practice, in a "suspended" manner. A prejudice prevailing in practice against mounting in "standing" position is that in that position, the expansion tank "captures" gases present in the circulating liquid, which gases can thereupon no longer be removed from the expansion tank, so that during the compensating operation of the nearly exhausted expansion tank, gases can be pressed back into the system in an undesired manner. In the present suggestion, this drawback is entirely overcome and changed into an advantage by the provision of an automatically operating de-aeration device between the "standing" expansion tank and the closed liquid circuit, so that gases captured by the expansion tank are removed from the system through blow-off when exceeding a particular quantity.

As noted, when liquid leaks from the closed circuit, the expansion tank also has a compensatory function in order to prevent the installation from breaking down as a result of too low a pressure due to lack of liquid. As already mentioned, in an expansion tank arranged in standing position, gases separated from the liquid may accumulate under the membrane, which can also be considered to be disadvantageous to the compensatory function because of the unnoted decrease of the amount of compensating liquid available. In that case, according to a further elaboration of the invention, it can be provided that the closed liquid circuit is provided with an automatically operative make-up device for liquid. Hence, formation of liquid shortage is prevented particularly effectively and, moreover, this is done particularly efficiently as, owing to a layer of air accumulating there, the membrane is even better protected from damage or perforation by particles carried along via the circulating liquid, because then, the membrane has no contact with any floating or drifting dirt that may be present. Through increase of the air content of the expansion tank, this layer of air also entails an increase of the compensating volume, so that either with a similar expansion tank a greater compensation is possible, or the same compensation can be realised with a smaller and less expensive expansion tank, while it is ensured that no gases can be pressed back into the system and sufficient liquid is always present to ensure continuous and undisturbed functioning.

The invention also relates to a closed liquid circuit with varying temperature and provided with an expansion tank, provided with a housing divided by a membrane into an upper, closed-off space and a lower space which, via a connection, is in open communication with a pipe of the closed liquid circuit. In order to then prolong the lifespan of the expansion tank as much as possible and ensure that it can function optimally and undisturbedly, it is provided according to the invention, that, via a connection, the lower space is in open communication with an de-aeration device which, in turn, is in open communication with a pipe situated therebeneath of a closed liquid circuit, the de-aeration device being provided with an enclosed space in which a float is present which, by descending within the enclosed space, can open a de- aeration valve. To effectively prevent shortage of water, also in the long term, when the expansion tank is of relatively small design, a make-up device can be provided, comprising an enclosed space in which a float is present which, by descending within the enclosed space, can open a make-up valve.

Here, a particularly compact construction can be obtained when the float which can open the de-aeration valve is also the float that can open the make-up valve while, upon descending, the float will first open the de-aeration valve and, when descending further, it will open the make-up valve.

With reference to an embodiment represented in the drawing, albeit merely by way of non-limiting example, the invention will presently be further elucidated. In the drawing:

Fig. 1 schematically shows a closed liquid circuit in the form of a central heating installation; and

Fig. 2 shows, in enlarged scale, in cross-section, a possible connection between the expansion tank and liquid circuit. The closed liquid circuit schematically represented in Fig. 1, in the form of a central heating installation, is provided with a boiler 1, pipes 2 and radiators 3. A pump 4 is present for circulating the liquid, and an expansion tank 5 for compensating for the difference in volume of the circulated liquid upon heating and cooling down. Further, a combined, float-controlled make-up/de-aeration device 6 is present. To that end, the intended device 6 is provided with a housing 7, which is substantially cylindrical, a lower front end thereof being in open communication with a tube part 8, and thus communicating with one of the pipes 2, while an upper front end is in open communication with a tube part 16 and hence, communicates with the expansion tank 5, which is provided with a spherical housing 12 with an internal space divided in two by a membrane 13, thereby forming a completely closed-off space 14 and a space 15 which, via the tube part 16, is in open communication with the make-up/de-aeration device 6.

Gas bubbles rising from the pipes 2 through the tube part 8 and ending up, via the open connection, in the housing 7, form an air head in this housing and the space 15 communicating therewith. In the housing 1, a float 17 (Fig. 2) is present which descends in the housing 7 when the size of the air head increases through capture of gases from the circulating liquid and/or cooling down of this liquid. When descending, the float 17 will open a de- aeration valve 9 at a first level, whereupon gases from the air head will be blown-off when the pressure in the air head is higher than a blow-off pressure set by a non-return valve 18 forming part of the de-aeration valve 9. If the float 17 descends further, this will result in the make-up valve 10 being opened so that fresh liquid is brought from a pipe 11 communicating with a source, via the make-up valve 10, the open connection and the tube part 8 into the liquid circuit.

The rising of the float 17 due to adding and/or heating up of the liquid and/or blowing-off of gases from the air head results in the closure of, first, the make-up valve 10 and, upon further rising of the float 17, closure of the de-aeration valve 9, whereupon the closed liquid circuit can make use of the complete capacity of the expansion tank 5 for keeping the pressure in this closed liquid circuit within the desired values. The fact is that making-up with fresh liquid will only take place after all liquid has been pressed away from the expansion tank 5. Due to this making-up according to need, the make-up function of the expansion tank 5 has in fact become superfluous, which means that it is sufficient to provide an expansion tank which is smaller, and therefore less expensive, than an expansion tank used in a situation in which a part, for instance half, of the volume of the expansion tank must be available for make-up purposes. The expansion tank is mounted in "standing" position, that is to say that the space 15 is situated below the completely closed-off space 14 and the tube part 16 terminates in a lower area of the expansion tank 5. In Fig. 2, the situation is represented in which the liquid has been entirely or virtually entirely pressed from of the expansion tank. Further leaking away of liquid or shrinking thereof caused by temperature decrease would lead to reduction of the pressure in the system and hence to breakdown of the system with all associated adverse effects. This is prevented by de-aerating and making-up the liquid circulating system with the aid of the float 17 as described hereinabove, so that breakdown in effectively prevented. Heretofore, it was customary to arrange an expansion tank in position "suspended" from a pipe 2. In practice, such an expansion tank has proven susceptible to springing a leak in the membrane and hence, the expansion tank becoming inoperative, resulting in breakdown of the heating apparatus with all associated drawbacks.

By presently, simply, arranging the expansion tank in "standing" position instead of in "suspended" position, its life span proves to be lengthened by quite a considerable extent, that is, in principle as long as the life span of other components of the installation, such as the pipes, the radiators and the boiler. This simply obtained, considerable advantage of the modified arrangement is a result of the insight that the weak spot of the expansion tank is the membrane and that hard and/or sharp particles circulated with the liquid can descend in a suspended expansion tank and are no longer discharged therefrom. The compensatory operation of the expansion tank is based on the bending of the membrane from an initially horizontal, neutral position, in which the expansion tank is half filled with liquid and half filled with gas under pressure, to a position in which, under the influence of the expansion of heated liquid, more liquid is pressed from the pipes into the expansion tank and the gases are compressed, or to a position in which, as a result of liquid cooling down and/or liquid leaked away, virtually all liquid has been pressed out of the expansion tank, which latter position is shown in Fig. 2 and in which position, subsequently, the make-up device will enter into operation for adding liquid to the closed circuit.

In this manner, when the installation is operative, the membrane 13 will frequently move to and fro and then hinge about the attachment to the housing 12. When, with the expansion tank in suspended condition, the membrane bends upwards and outwards as a result of liquid cooling down or leaking away, the lowest point of the membrane is the annular attachment to the housing. Hard and/or sharp particles present in the expansion tank will descend to this area and may become wedged between the housing and the membrane, so that the membrane may be perforated which results in the expansion tank becoming inoperative. With an expansion tank mounted in "standing" position, the referred-to hard and/or sharp particles will not end up in the expansion tank, let alone in the hinge area situated, then, in the highest point, resulting in quite a considerable lengthening of the life span of the expansion tank.

However, a "standing" expansion tank is susceptible to "capturing" gases circulating in liquid. At first glance, this seems a disadvantage because this might decrease the compensatory make-up function of the expansion tank. However, gases captured in the "standing" expansion tank will offer a still better guarantee that sharp and/or hard particles cannot contact the membrane while during operation of the expansion tank, air will be regularly pressed from that expansion tank, for instance in the situation shown in Fig. 2, whereupon, when the membrane returns to a more neutral position, due to the liquid heating, the pressed-away gases will be replaced with liquid again.

As shown in Fig. 2, it is still more optimal to install a make-up/de- aeration device 6 which, after the expansion tank 5 has been pressed completely empty, will ensure the making-up of the amount of liquid in the installation as discussed hereinabove. In that case, the expansion tank 5 needs in fact no longer effect make-up, which means that a smaller and, therefore, less expensive expansion tank can suffice, as has been elucidated hereinabove. It is self-evident that within the framework of the invention as laid down in the appended claims, still many modifications and variants are possible. For instance, the expansion tank can also be placed next to the pipe to which is it connected, while the connection of the open communication between the pipe and the expansion tank must be maintained on the lower part thereof in order to prevent hard and/or sharp particles from contacting the membrane. Also, an expansion tank can have any other suitable design than the spherical form shown in the drawing. If desired, the installation can also be provided with other make-up and/or de-aeration devices.

Claims

1. A method for mounting an expansion tank in a closed liquid circuit with varying temperature, which expansion tank is provided with a housing divided by a membrane into a closed-off space and a space which is brought, via an open connection, into communication with a pipe of the closed liquid circuit, wherein the expansion tank is mounted with the connection situated in a lower area of the expansion tank, the arrangement being such that the closed-off space is situated substantially above the space which is in open communication with the pipe, while between the connection to the expansion tank and the open connection to the pipe an automatically operative de- aeration device is mounted.

2. A method according to claim 1, characterized in that the closed liquid circuit is provided with an automatically operative make-up device for liquid.

3. A method according to claim 2, characterized in that the make-up device is combined with the automatically operative de-aeration device while first the de-aeration device is activated before the make-up device enters into operation.

4. A method according to any one of the preceding claims, characterized in that the expansion tank is arranged above the pipe with which, through the connection, the expansion tank is brought into open communication.

5. A closed liquid circuit with varying temperature and provided with an expansion tank which is provided with a housing divided by a membrane into an upper, closed-off space and a lower space which, via a connection, is in open communication with a de-aeration device which, in turn, is in open communication with a pipe situated therebeneath of the closed liquid circuit, the de-aeration device being provided with an enclosed space in which a float is present which, by descending within the enclosed space, can open a de- aeration valve.

6. A closed liquid circuit according to claim 5, characterized in that a make-up device is arranged, which is provided with an enclosed space in which a float is present which, by descending within the enclosed space, can open a make-up valve.

7. A closed liquid circuit according to claim 6, characterized in that the float which can open the de-aeration valve is also the float that can open the make-up valve, while, upon descending, the float will first open the de-aeration valve and, when descending further, will open the make-up valve.