The invention concerns a method of locally impregnating wood with a gaseous or liquid impregnation agent, compris¬ ing drilling in the protection zone a hole which is out¬ wardly closed with a non-return valve, and injecting a quantity of impregnation agent under pressure into the cavity formed behind the non-return valve by means of an injection apparatus which, with a mouthpiece, is detach- ably connected with the valve.

Structural timber which is not protected sufficiently well is increasingly attacked by dry rot and other forms of biological forces which break down the wood. In Denmark alone, dry rot and insect damage to more than 13,000 buildings is recorded each year. The damage is concen¬ trated in particular on the areas which are so placed in the building as to be particularly exposed to moisture. These zones of risk comprise e.g. bottom rabbets in sills and transoms, bottom rails, lower corner joints at both frames and sashes as well as joints between mullions and sills. Once the wood in such a zone of risk has been des¬ troyed, it must be exchanged, and in this connection it may often be necessary to exchange major or minor portions of the entire wood structure, even if this might otherwise be completely intact.

Considering the very substantial amount of buildings which are thus attacked each year, it is of course great values which are at stake for the individual owner of the respec¬ tive building as well as for the society as a whole, and great efforts have therefore been made to develop methods and equipment for locally impregnating in particular the zones of risk with impregnating agents to thereby prevent damage of the above-mentioned type and stop commenced

attacks .

This development has led to a large number of different solutions, where it is e.g. proposed to introduce impreg- nation liquid in the wood in the form of pins, plugs, pills, capsules or in liquid form by means of suitable injection equipment. Particular interest is attached to the last-mentioned method which has been found to be both simple and effective, and which is therefore the preferred method of locally impregnating wood today.

In this case the impregnation agent is normally injected into a hole in the wood under pressure via a valve which is inserted in the hole. The purpose of this valve is i.a. to maintain the pressure in the impregnation liquid until the liquid has been distributed in the surrounding wood. However, it has been found that the air present in the cavity behind the valve constitutes a considerable ob¬ stacle to the propagation of the liquid, partly because it reduces the quantity of impregnation agent which can be injected into the cavity, partly because the impregnation agent foams because of the high pressure at which it is injected into the cavity. This foam blocks the capillaries of the wood and impedes liquid penetration through these.

The US Patent Specification 4724793 discloses a valve for injecting an impregnation agent under pressure into wood. This valve is provided with a longitudinally ex¬ tending bore which is closed at the end with a non-return valve. The valve is screwed into the the wood by means of a threaded shank portion having a hexagonal head portion. A bleeder opening is formed in the shank portion and ex¬ tends outwardly from the bore closely adjacent the head portion. When the valve is used to inject an impregnation agent into the wood, the shank portion is screwed into a threaded opening in the wood until the bleeder opening is

just slightly positioned within the threaded opening. As the impregnation agent is injected into the opening in the wood, the air in the opening will pass outwardly through the bleeder opening to the surroundings. When substan- tially all of the air has been removed from the opening in the wood, the valve is then screwed further into the open¬ ing until the head portion is closely adjacent the exte¬ rior of the wood. Additional impregnation agent is then injected into the opening in the wood through the non- return valve at the end of the bore in the valve. When sufficient impregnation agent has been pressure injected into the opening in the wood, the injector is removed and the injection operation is finished. However, it is cum¬ bersome and time-consuming to operate this known valve, in particular when considering that it is usually necessary to impregnate a wood structure via a large amount of holes, and that the operations must therefore be repeated many times. To this should be added the uncertainty and risk which the job involves, because the generally more or less toxic impregnation agent is inevitably passed direct¬ ly out to the surroundings, endangering the operating staff and other persons who might come near the impreg¬ nated wood structure. Further, the valve is not useful for repeated reimpregnations since the valve must each time be screwed into and out of the threads in the wood opening whereby the threads are liable to be destroyed in the wood which has often become relatively mouldering in the course of time.

The valves which have been used so far for injection of impregnation agent in liquid form, are moreover vitiated by various drawbacks. Thus, they are not capable of keep¬ ing tight effectively when the impregnation agent has been injected into the cavity. This entails that the positive pressure in the cavity rapidly disappears so that the pro¬ pagation of liquid partially stops, and toxic impregnation

agent often leaks through the valve, which involves envir¬ onmental and occupational risks. Moreover, the valves often do not have a sufficiently great strength and dura¬ bility to maintain their full working efficiency for a number of years, and they have therefore in many cases been found unfit for use where it is required that the impregnation is repeated at regular intervals, each of which would normally span several years.

The object of the invention is to provide a method of the type stated in the opening paragraph which ensures greater propagation of the impregnation agent in the wood than known before, and which is simultaneously simple, unharm- ful to the environment, quick and safe to work with.

This is achieved in that the method of the invention is characterized by removing the air in the cavity via the non-return valve in connection with the injection, whereby the cavity is filled completely with impregnation agent rapidly and safely, and any form of foaming is avoided, thereby increasing the zone into which the impregnation agent can penetrate, without involving any risk of pos¬ sible toxic impregnation agent leaking to the surround¬ ings, and without it being necessary to loosen the perma- nently mounted valve in case of reimpregnation.

According to the invention, the displacement of air can take place in a simple manner by passing a stream of im¬ pregnation agent through the cavity until the air in it has been expelled, following which the stream is stopped, and the impregnation agent in the cavity is pressurized.

In a particularly advantageous method of the invention, the cavity is first air-evacuated, and then the impreg- nation agent is injected into the cavity under pressure. This entails that it is not just the cavity itself which

is air-evacuated, but also the most immediate surroundings of the cavity in the wood, and it is therefore possible to inject a correspondingly larger quantity of impregnation agent, which is rapidly absorbed by the evacuated capilla- ries and cells.

Moreover according to the invention, with a view to addi¬ tionally increasing the zone which can be impregnated from a single injection point, at least one second gas or li- quid may be added to the cavity, said second gas or liquid reacting with the impregnation agent under formation of pressure gas which serves as a propellant for all the im¬ pregnation agent and also maintains the pressure in the cavity for a sufficiently long period for all the impreg- nation liquid to be expelled from the cavity.

Further, according to the invention, the hole may be drilled so that the capillaries of the wood are open along the hollow wall, thereby increasing penetration through the wall, and the cavity may moreover be bored with a greater diameter than the rest of the hole, so that it can • advantageously hold a correspondingly larger quantity of impregnation agent.

The invention also concerns a device for performing the method described above, and this device is characterized in that it comprises a valve made of an elastomeric ma¬ terial, such as rubber, and having at least one internal valve channel which, seen in the mounted position of the valve, extends all the way through the valve from the atmosphere to the cavity, and which, at any rate in one portion of this extent, is closed tightly in the rest position of the valve by an elastic bias in the elastome¬ ric material and/or by a pressure keeping the valve clamped in the hole, and that the device moreover com¬ prises an injection apparatus with a mouthpiece having a

hollow needle associated with each valve channel to drive through the respective valve channel upon filling and to open its closed portion, said portion being formed with such a cross-section that the channel is clamped tightly around the needle. The valve structure will hereby be simple and reliable in operation and maintains its working efficiency for a large number of years, so that it can be used for recurrent reimpregnations. The valve is complete¬ ly tight during the injection and afterwards effectively prevents leakage of the injected impregnation agent, so that the pressure in the cavity is maintained for the longest possible time and environmental pollution and job injuries are avoided.

Further, according to the invention, to facilitate inser¬ tion of the injection needles into the valve channels, each of these may have a portion which terminates in the insertion end of the valve, and which, at any rate in the mounted state of the valve, has a cross-section suitable for the associated needle.

Further, according to the invention, with a view to effec¬ tively anchoring the valve in the hole, the valve may be provided with a plurality of annular ribs having a slight- ly greater outside diameter than the hole. The ribs serve as a kind of barbs to maintain the valve against the posi¬ tive pressure that prevails in the cavity immediately after the injection. The ribs also serve as an effective seal against leakage of the impregnation agent between the valve and the hollow wall.

In a particularly strong and sturdy embodiment of the in¬ vention, the actual elastomeric valve may be fixedly clamped in a housing consisting of a rigid material, such as plastics or metal, and having a slightly greater out¬ side diameter than the hole at any rate partially in the

longitudinal direction.

Further, in another embodiment of the invention which is particularly simple and inexpensive, the valve may be con- structed as a solid elastomeric disc and the needles as pointed or sharp needles which, when driven transversely through the disc in connection with e.g. the first injec¬ tion, form the valve channels, which, when the needles are withdrawn again, then close tightly together under the ac- tion of an elastic bias in the material of the disc and/or by the pressure which keeps the disc clamped in the hous¬ ing.

The invention moreover concerns an injection apparatus comprising a container for impregnation agent, a feed conduit connected with the container and terminating in a feed channel in a needle, as well as a pressure pump in¬ serted in the feed conduit to pump impregnation agent from the container into the cavity upon injection. This injec- tion apparatus is characterized according to the invention in that it comprises a return channel provided in the same needle as the feed channel or in a second needle, a return conduit for the container connected with the return channel, and a check valve mounted in the return conduit and controlled by a timer so adapted that the check valve opens at the beginning of the injection and closes after a predetermined time of e.g. between 15 and 45 seconds. This entails that, in a period, the cavity will be flushed by impregnation agent which expels the air from the cavity so that the cavity can hold a correspondingly larger quantity of impregnation agent, and foaming of it is avoided.

Further, according to the invention, the device may com¬ prise at least one second container for a second gas or liquid as well as a second feed conduit which is connected with the container and in which a second pressure pump is

inserted, said second feed conduit terminating in a second feed channel arranged in the same needle as the first feed channel or in a second needle, the timer being adapted such that simultaneously with or immediately after having applied a signal to close the check valve in the return conduit, it applies a signal to connect the second pres¬ sure pump. In addition to the impregnation agent, it is hereby also possible to inject a second vapour or liquid which can e.g. react with the impregnation agent and form a propellant to press the impregnation agent deeply into the wood.

According to the invention, the injection apparatus may moreover comprise an air channel which is provided in the same needle as the feed channel or in a second needle and is connected with an air conduit leading to a vacuum pump with a check valve, inserted in front of it and controlled by a pressostate which is so adapted that at a predeter¬ mined negative pressure in the cavity it applies a signal to close the check valve and simultaneously with this or immediately after this it applies a signal to connect the pressure pump. With this structure, the air can not only be removed rapidly and effectively from the actual cavity, but also from its closest surroundings, which hereby imme- diately absorb the impregnation agent as soon as it has been injected into the cavity.

It is important in this connection that the injection takes place as quickly as possible after the conclusion of the evacuation process, since, otherwise, the evacuated air will be replaced by fresh air flowing in from the sur¬ rounding wood. To achieve this, according to the inven¬ tion, a pressure accumulator and a check valve arranged after said accumulator may be inserted in the impregnation agent feed conduit, said pressostate being so arranged that, simultaneously with or immediately after having

applied a signal to close the check valve in the air con¬ duit, it applies a signal to open the check valve in the feed conduit.

If it is desired to inject additional vapour or liquid in addition to the impregnation agent, said vapour or liquid may advantageously be added to the impregnation agent in the pressure accumulator immediately before the contents of said accumulator are injected into the cavity. With a view to this, the device of the invention may additionally comprise at least one second container for a second gas or liquid as well as a second feed conduit which is connected with said container and in which a second pressure pump is inserted, said feed conduit being connected with the pres- sure accumulator, said second pressure pump being arranged as a metering pump which supplies the pressure accumulator with a predetermined gas or liguid quantity from the se¬ cond container prior to each injection.

Advantageously, the feed conduit and/or the return conduit may moreover be provided with at least one non-return valve to effectively prevent return flow and to ensure that the generated pressure in the cavity will not be relieved. When the non-return valve is a valve of the same type as the valve inserted in the bore in the piece of wood to be impregnated, completely synchronous cooperation will be achieved between the non-return valve and the im¬ pregnation valve, so that the two valves open and close simultaneously and constantly have the same flow area, whereby the injection apparatus will operate rapidly and effectively and with extremely great precision. The ela- stomeric properties of the non-return valve are a safe¬ guard against the valve becoming inoperative because salts or impurities settle on the closing faces of the valve, such deposits being loosened when the valve expands and contracts during the impregnation operation.

The relatively fine channels of the valve may become more or less clogged by dirt or paint over the years so that the valve is not useful when the wood is to be reimpreg- nated. To remedy this problem, the device of the invention may comprise a disc with pins to be pressed into the valve channel after an injection, and this disc may additionally be adapted so that it changes its colour after a predeter¬ mined number of years to signal that reimpregnation should be repeated.

To avoid clogging of the relatively fine return or air channel in the injection needle for the air to be eva¬ cuated in connection with the impregnation operation, by left, loose chips in the cavity behind the inserted valve, the valve opening facing the cavity may be covered by a filter according to the invention, said filter having holes or meshes which are smaller than the diameter of the* return or air channel of the injection needle and/or the chips which are formed when the hole is bored and are left in a loose state in the hole.

The invention will be explained more fully by the follow¬ ing description of embodiments which just serve as ex¬ amples, with reference to the drawing, in which

fig. 1 is a side view of a first embodiment of a valve according to the invention,

fig. 2 is an axial section through the valve shown in fig. 1,

fig. 3 is a section along the line III-III in fig. 2,

fig. 4 is a section along the line IV-IV in fig. 2,

figs. 5-11 show successive process steps in zone impregna¬ tion of a piece of wood by means of the valve shown in figs. 1-4,

fig. 12 is an axial section through the elastomeric part of a second embodiment of a valve according to the inven¬ tion,

fig. 13 is a section along the line XIII-XIII in fig. 12,

fig. 14 is a section along the line XIV-XIV in fig. 12,

fig. 15 is an exploded view of the second embodiment of the valve according to the invention,

fig. 16 shows the valve shown in fig. 15 in assembled state and mounted in a hole which has been bored in a piece of wood,

fig- 17 shows the same, but during injection of an impreg¬ nation agent through the valve,

fig. 18 shows a third embodiment of a valve of the inven¬ tion, mounted in a hole which has been bored in a piece of wood,

figs. 19-22 show successive process steps in the boring of an impregnation hole with expanded cavity for the impreg¬ nation agent, and mounting of a valve of the type shown in figs. 1-4 in the bored hole,

fig. 23 is a diagram of a first embodiment of an injection apparatus according to the invention,

fig. 24 is a diagram of a second embodiment of an injec¬ tion apparatus according to the invention,

fig. 25 is a diagram of a third embodiment of an injection apparatus according to the invention,

fig. 26 is a diagram of a fourth embodiment of an injec- tion apparatus according to the invention,

fig. 27 is a diagram of a fifth embodiment of an injection apparatus according to the invention,

fig- 28 is a side view of a valve whose inwardly facing opening is covered by a filter, and

fig. 29 is a side view of the same.

Figs. 1-4 show a first embodiment of a valve which is generally designated by 1. The valve is made of an elasto¬ meric material, e.g. rubber, and has an axially extending valve channel 2, which extends longitudinally through the entire valve and which is divided into a first, substan- tially round portion 3 and a second slotted closed portion 4. The valve moreover has a plurality of annular ribs 5.

Figs. 5-11 show more fully how the zone impregnation of a piece of wood 6 takes place. It appears from fig. 5 how a hole 7 is first bored in the zone to be impregnated, by means of a drill 8 so adapted that the wood is bored with a clean cut, ensuring that the capillaries of the wood are open toward the hole so that the impregnation agent can freely penetrate into the surrounding wood.

In fig. 6, the hole is finished, and a valve 1 is ready to be pressed into the hole 7 by means of a mandrel 9 mating with the first portion 3 of the valve channel 2, so that the valve is controlled safely during insertion into the hole.

In fig. 7, the valve has assumed its position in the hole, and it will be seen how the annular ribs 5, which in the free state have a greater diameter than the hole, have been deformed and now serve as a kind of barbs keeping the valve fixedly clamped in the hole, while forming an effec¬ tive seal between the valve and the hollow wall. A closed cavity 10 is now present behind the valve to receive the impregnation agent. This cavity may typically have a size of between 3 and 7 cm ³ .

Fig. 8 shows a further fraction of an injection apparatus 11, whose structure will be described more fully below. The injection apparatus has a needle 12 formed with sub¬ stantially the same diameter as the first portion 3 of the valve channel to facilitate insertion into the valve channel. In fig. 9, the needle has now been driven comple¬ tely through the valve channel and has opened its second portion 4, which has a cross-section that is slightly smaller than the needle which is hereby surrounded snugly and tightly at this point by the elastomeric valve. As shown, the needle 12 has both a feed channel 13 to inject impregnation agent into the cavity 10 and a return channel 14 to return the impregnation agent in the cavity to the container (not shown) in which the impregnation agent is stored. The importance of this function will be explained later in connection with the description of the structure of the injection apparatus.

In fig. 10, the injection process is completed. The cavity 10 is filled with impregnation agent, and the needle 12 is about to be withdrawn from the valve channel 2, whose se¬ cond portion 4 automatically closes tightly behind the needle to ensure that the injection impregnation agent does not leak through the valve. To effectively keep the valve closed in the second portion 4, the valve channel is tightly closed at this point by an elastic bias in the

elastomeric material and/or by the pressure with which the valve is clamped in the hole.

Fig. 11 shows the final phase of the impregnation opera- tion. The injected agent has now penetrated into the sur¬ rounding wood and has impregnated it. The cavity 10 is again empty, and the valve channel is sealed with a disc 15, which has a pin 16 that is pressed into the first portion 3 of the valve channel, so that the valve channel is protected against ingress of dirt and paint, and there¬ fore, without itself being loosened, the valve is readily operational when e.g. after three years it is again neces¬ sary to impregnate the zone in question. The disc 15 may moreover be so adapted as to change its colour at the time when reimpregna ion should take place. Alternatively, the pin may directly indicate the date of the next impregna¬ tion.

Figs. 12-17 show a second embodiment of an elastomeric valve 17, which is in this case surrounded by a housing 18 of a relatively rigid material, such as metal or plastics. This structure combines the advantages of the previously described valve 1 with great resistance to outer mechani¬ cal impacts. As shown best by fig. 15, the housing 18 is composed of a front and a rear part 19, 20 which are as¬ sembled around the valve 17 by means of a bead groove lock 21, so that the valve is kept clamped safely and tightly in the housing 18.

Like the valve 1, the valve 17 has a valve channel 22 with a first, round portion 23 to facilitate insertion of the injection needle into the valve channel, and a second slotted portion 24, which is normally closed tightly when the valve is clamped in the housing. Since the valve, as shown in fig. 13, is shaped slightly oval transversely to the extent of the slot in advance, the slot will be closed

effectively when the valve is pressed into the housing which has a circular cross-section interiorly. To additio¬ nally ensure closing of the slot, there is provided a lip 25 extending outwardly in elongation with the valve with a relatively thin and flexible wall, which can easily be pressed tightly together around the slot by the positive pressure prevailing in the cavity in connection with the injection.

As shown in figs. 16 and 17, the housing 18, now in an assembled state around the elastomeric valve 17, is pressed into a hole 7 in a piece of wood 6 to be impreg¬ nated. The housing has a plurality of annular ribs 27, which have a slightly greater diameter than the hole it- self and serve to retain the valve safely in it. The hous¬ ing moreover has a through opening 26 which extends co¬ axially with the valve channel 22 and allows the needle 12 to penetrate through this channel and to inject impregna¬ tion agent into the cavity 10.

This situation is shown in fig. 17, where the slotted se¬ cond portion 24 of the valve channel 22 has been opened by the needle 12, which has hereby deformed the elastomeric valve material around the slot outwardly towards the inner cylinder wall of the housing, which provides a counter- pressure to ensure that the slot closes tightly and safely about the needle during the injection. To make room for the material displaced during said deformation, a recess 28 is provided on each side of the slot 24 in the valve 17. When the injection process is completed, the needle 12 is withdrawn from the valve channel 22, which successively closes tightly together so that the impregnation agent cannot leak from the hole 17 and the positive pressure in the hole does not disappear at once.

Fig. 18 shows a third embodiment of a valve 29 which is particularly simple and inexpensive since it just consists of a solid, elastomeric disc. This disc is retained by means of a locking ring 30 in a housing 31, which is made of a relatively rigid material, e.g. plastics or metal. The housing has a plurality of annular ribs 32 with a slightly greater outside diameter than the hole 7 and is therefore firmly positioned in it in mounted state. In this case, the valve disc 29 is not provided with valve channels in advance, and the needles of the injection apparatus 11 are therefore shaped as pointed, sharp needles 33a, 33b, which themselves can cut through the disc when the needles are driven through it at e.g. the first injection. Two valve channels 34a, 34b are hereby formed, which can be used the next time the wood is to be impregnated. When the needles 33a, 33b are drawn out of the valve channels 34a, 34b, these close tightly together because of the elasticity of the valve material and the pressure which keeps the disc clamped in the housing.

It is common to the three valve structures described above that they have an excellent operational reliability, which is obtained because of the fact that the valves completely lack mutually moving parts which, as shown by experience, can fail and get jammed, since they can e.g. be blocked by dry components from the impregnation agent. The valve channels are constantly ready for operation, and the valves can therefore be used again and again for a large number of years.

Figs. 19-22 show an example of how to make a hole 35 with a cavity 36 which has a greater diameter than the rest of the hole. The hole is first bored to full depth with a diameter suitable for a valve, e.g. the valve 1, as shown in figs. 19 and 20. For this purpose there is used a mil¬ ling cutter 37 with a shank 38 which, when the milling

cutter has bottomed, performs an orbital movement in the hole so that the innermost portion of the hole is milled to a greater diameter than the rest of the hole. This is shown in fig. 21. Finally, in fig. 22, a valve 1 is in- serted in the outermost portion of the hole 35. Since the cavity 36 can now hold a considerably larger quantity of impregnation agent than before, a correspondingly larger zone can be impregnated from the same hole.

Fig. 23 is a diagram of a first embodiment of an injection apparatus 39. The impregnation agent, which is a liquid in this case, is stored in a container 40 connected with a feed conduit 41, which terminates in a feed channel 42 in a schematically shown needle 43 which is passed through a valve 44, likewise shown schematically, in a hole 7 in a piece of wood 6 to be impregnated. A pressure pump 45, a reduction valve 46 and a non-return valve 47 are inserted in the feed conduit 41. Further, a return conduit 49 leads back to the container 40 from the return channel 48 in the needle 43, and a non-return valve 50 and a check valve 51 controlled by a timer 52 are inserted in the return con¬ duit 49.

When a quantity of the impregnation liquid in the con- tainer 40 is to be injected into the cavity 10, the pump 45 is activated and also the timer 52 which thereby opens the check valve 51. The timer 52 may e.g. be set to keep the valve 51 open for a period of 15-45 seconds, during which the impregnation liquid circulates through the ca- vity 10 and entrains all air in it. When the valve 51 is closed again after this period, while the pressure pump 45 is still working, a pressure, which is determined by the setting of the reduction valve 46 to e.g. 4-8 bars, is built up in the liquid which now fills the cavity 10 com- pletely. It is ensured by means of the non-return valves 47 and 50 that the liquid just flows in the direction

shown by the arrows in the feed conduit 41 and the return conduit 49, respectively.

As will appear, the injection apparatus 39 itself automa- tically expels the air from the cavity 10 in connection with the injection. This provides the very considerably advantage that the cavity 10 can hold a relatively larger amount of impregnation liquid, and that any form of foam¬ ing of it is avoided. It is therefore possible to impreg- nate a considerably larger zone than before from the same hole. This moreover takes place in a rapid and effective manner and without any risk of possible toxic impregnation agent escaping to the surroundings, as is the case with the conventional constructions of this type.

Fig. 24 is a diagram of a second embodiment of an injec¬ tion apparatus 53, which corresponds to the embodiment 39 shown in fig. 23, but with the addition of a further cir¬ cuit. This circuit comprises a second container 54 to store a second liquid in the shown case. The container 54 is connected with a second feed conduit 55 which continues in a second feed channel 56 in the needle 43. In the se¬ cond feed conduit 55 there are inserted a second pressure pump 57, a second reduction valve 58 as well as a second non-return valve 59 and a second check valve 60, which is controlled by the same timer 52 as the first check vavlve 51 in a manner such that the second check valve 60 opens when the first check valve 51 closes.

When the reduction valve 58 is set to a slightly greater pressure than the reduction valve 46, a certain quantity of the second liquid will also be injected into the cavity 10. The non-return valves 47 and 59 ensure during this procedure that the liquid cannot flow back in the respec- tive feed conduits 41, 55.

The second liquid or gas itself may be an impregnation agent, but is preferably so adapted as to react with the first liquid - the impregnation agent - with relatively slow generation of a pressure gas which serves to maintain the pressure in the cavity 10 for a considerably longer period of time than is normally the case. This effectively ensures that the impregnation agent is driven deeply into the surrounding wood, where pressure gas is still gene¬ rated to a certain extent to drive the impregnation agent even further into the wood.

Fig. 25 is a diagram of a third embodiment of an injection apparatus 61 which, like the first embodiment 39, has a container 40 to store the impregnation liquid, as well as a feed conduit 41 which is connected with the container 40 and terminates in a feed channel 42 in a needle 43, which is inserted into a valve 44 pressed into a hole 7 in a piece of wood 6 which is to be impregnated. Further, a pressure pump 45, a reduction valve 46, a non-return valve 47 as well as a check valve 62 are inserted in the feed channel 41. The needle 43 moreover includes an air channel

63 connected with a vacuum pump 64 via an air conduit 65 with a check valve 66, which is controlled by a presso¬ state 67 which simultaneously controls the check valve 62 in the feed conduit 41.

Use of the injection apparatus 61 causes the vacuum pump

64 to be activated, which hereby sucks air out of the cavity 10 and its surroundings in the wood via the air channel 63 and the air conduit 65 until attainment of the vacuum to which the pressostate 67 is set, the pressostate 67 applying a signal to close the check valve 66 and to open the check valve 62. Then impregnation agent is pumped from the container 40 by means of the pressure pump 45 into the cavity 10 via the feed conduit 41 and the feed channel 42 with the pressure to which the reduction valve

46 is set. By means of this apparatus it is possible not only to fill the entire cavity 10 with impregnation liquid during the injection, but also immediately to fill injec¬ tion liquid in the most immediate surroundings of the ca- vity which have been emptied of air, and which therefore instantaneously absorb the impregnation agent.

Fig. 26 is a diagram of a fourth embodiment of an injec¬ tion apparatus 68 which completely corresponds to the injection apparatus 61 shown in fig. 25, except that a pressure accumulator 69 is now inserted in the feed con¬ duit 41. This pressure accumulator 69 is filled in advance with a suitable quantity of impregnation agent under pres¬ sure by means of the pressure pump 45. The check valve 62 is closed during this procedure, while the check valve 66 opens when the vacuum pump 64 is connected with a view to evacuating the cavity 10 of air. When the pressostate 67 registers that the predetermined vacuum is reached in the cavity 10, the pressostate 67 applies a signal to close the check valve 66 and to open the check valve 62, the impregnation agent in the pressure accumulator 69 being instantaneously discharged into the cavity 10 at such a rate that no air can enter from the surrounding wood and fill the cavity.

Fig. 27 is a diagram of a fifth embodiment of an injection apparatus 70 which corresponds completely to the injection apparatus 68 shown in fig. 26, except for the insertion of a second circuit for a second liquid which is stored in a second container 71. This container is connected with the pressure accululator 69 by means of a second feed conduit 75, in which a second pressure pump 72, a second reduction valve 73 and a second non-return valve 74 are inserted. It is therefore not necessary to have a separate feed channel for the second liquid, which is instead fed to the pres¬ sure accumulator 64 in a desired quantity immediately be-

fore the contents of the accumulator are discharged into the cavity 10. As mentioned before, the second liquid itself may be an impregnation liquid, but is preferably a liquid which reacts with the first liquid - the impregna- tion agent - so as to slowly generate a pressure gas which serves to maintain the pressure in the cavity 10 and to drive the impregnation agent as deep as possible into the wood to be impregnated. Since the reaction rate is thus relatively slow, the second liquid cannot react noticeably with the impregnation agent during the very short stay in the pressure accumulator.

The non-return valves used in the circuit of the injection apparatus may advantageously be of the same type as the valves which are inserted in the impregnation hole of the wood. The circuit will hereby operate rapidly and effec¬ tively and with great precision since the uniform valves will naturally work completely synchronously and with exactly the same flow area during the injection. Non- return valves of this type will also automatically clean themselves of possible dried components from the impregna¬ tion agent, since these components will loosen .and be en¬ trained with the impregnation agent when the valve expands and contracts during the injection.

The foregoing description refers to embodiments of injec¬ tion devices which, in addition to the impregnation agent, can inject another liquid into the cavity. This is just an example since the injection apparatus of the invention can be constructed in such a manner that it can inject as many gases or liquids into the cavity as is desired. This just necessitates that the apparatus is provided with a corres¬ ponding number of additional circuits. The processes can also take place in another order. Thus, it is possible first to inject a second liquid which has the property of penetrating deeply into the wood and preparing it in a

manner which subsequently promotes the propagation of the impregnation agent.

However, in all embodiments the needle 12, 43 is provided with at least one return or air channel 14, 48, 63 to re¬ move the air present behind the valve 1, 17, 29, when the valve has been driven into the hole 7, 35 drilled in the impregnation zone.

Chips are formed during the drilling operation, some of which may be left in the hole after the insertion of the valve, which involves the risk of penetration of these chips into the relatively fine return or air channel 14, 48, 63 so that this is clogged when the air in the cavity 7, 35 is to be evacuated.

This drawback is remedied by the embodiment of a valve according to the invention shown in figs. 28 and 29. In this case there is provided a filter 77 with a number of filter holes or meshes 78 of a suitably smaller size than the return or air channel and/or of a smaller size than the chips which lie loosely in the hole 7, 35, and which are therefore either prevented from penetrating into the return or air channel and the conduit and valve system disposed behind said channel in the flow direction, or are so small that they cannot clog the channel or this system or cause other damage.

In the shown case, the filter 77 is arranged at the end of the front part 19 of the valve housing 18 shown in figs. 15-17 in the form of a substantially conical end part 79 with a bottom 80 containing the filter holes 78. The peri¬ phery of the end face 79 is provided with a plurality of evenly distributed, longitudinally and obliquely extending ribs 81, which serve to catch the hole 7, 35 upon inser¬ tion of the valve and to ensure that the valve is moved

straight into the hole, and the valve can therefore easily be fixed in correct position in the hole.

Of course, the filter can also be provided in other em- bodiments of the valve, such as the valve shown in figs. 1-4 or in fig. 18, and the filter does not have to be moulded integrally with the valve, but may e.g. be a fine mesh wire net which is mounted on or moulded together with the valve.

It is essential in any case that the filter is mounted at the end of the valve and at such a distance from the in¬ sertion end of the valve that the needle 12, 43 can be driven sufficiently far into the valve channel.