5  EP 3 800 012 A1 6  to 48V directvoltage)corresponding to the operating volt- age of the power tool. This embodiment has the advan- tage that the power supply does not lie around on the floor where it constitutes a potential tripping hazard but is rather part of a vacuum cleaner. 5 [0018] Smaller and lighter electric and electronic com- ponentswhichgenerate only a smallamountofheatdur- ing operation may be located in the adapter element or the adapter housing, respectively. For example, adapterelementmay comprise a rectifierfortransforming an alternating voltage of the mains power supply into a direct voltage of the power tool and/or a filter circuit for reducing interferences and suppressing electronic dis- turbances. However, it is preferred that these electric and/orelectronic components are also comprised by the power supply unit. To this end it is suggested that the power supply unit comprises a rectifier for transforming an alternating voltage of the mains power supply into a direct voltage of the power tool. Further, it is suggested that the power supply unit comprises an electronic filter elementforreducing interferencesandsuppressing elec- tronic disturbances. 10 15 20 25 the hook element could be manufactured from metal or synthetic material (e.g. plastic). [0023] In order to provide for an appealing design of the power tool, it is suggested that at least that part of the adapter housing which is notinserted into the recess upon complete insertion ofthe partofthe adapterelement tobeinserted intothe recess and stillvisible fromoutside has the same design as thatpartofthe batterypack which is not inserted into the recess upon complete insertion of the part of the battery pack to be inserted into the re- cess and still visible from outside. Hence, the power tool has almost the same look with the battery pack inserted into the recess orthe adapterelementinserted.Theonly visible difference is the first electric cable led out of the adapter housing at the rear or a side of that part of the adapter element visible after complete insertion into the recess. [0024] According to another preferred embodiment of the presentinvention,itis suggestedthatthe powersup- plyunitisadapted to complywith the ATEX 95 equipment directive 94/9/EC.The directive 94/9/EC ofthe European Parliament and the Council of 23 March 1994 refers to the approximation of the laws of the Member States of the European Union concerning equipment and protec- tive systems intended for use in potentially explosive at- mospheres. For example, this directive stipulates that the electronic power supply unit must not cause sparks during its operation. With other words, the power supply unit preferably used for operation of the power tool by means of electric energy from the mains power supply,comprises aso-called safety isolatingtransform- er adapted for use in potentially explosive atmospheres. Such power supply units are also available off-the-shelf in large numbers and at reasonable prices. [0019] In order to provide for a safe and reliable con- nection of the adapter element to the tool housing, it is suggested thatthetool housing and the adapterhousing are provided with corresponding attachment members adaptedto enterinto mutualengagementwith each other uponcomplete insertion ofthe partofthe adapterelement to be inserted into the recess and to provide for a releas- able attachment of the adapter element to the tool hous- ing. The attachment members provide for a safe and re- liableattachmentofthe adapterelementto the toolhous- ing.Ifdesired,theattachmentmembers can be manually actuated in order to release the adapter element from the tool housing and to extract the adapter element from the recess. 30 35 40 [0025] Itispossible toreleasablyconnectthe firstcable to the adapter element by means of a plug-and-socket connection. However, in order to allow a flexible use of the power tool with the adapter element inserted therein without having to fear an unintentional disconnection of the powertoolfromthe powersupply unit,itissuggested that the first cable is fixedly attached to the adapter ele- ment. The connection between the adapter element and the first cable is the one which is stressed most during an intense use of the power tool. Additionally, a kinkpro- tection element for the first cable can be provided in the form of a grommet attached to the adapter housing. [0020] Preferably,the attachmentmembers are adapt- ed to automatically enter into mutual engagement with each other upon complete insertion of the part of t adapter element to be inserted into the recess. This has the advantage that the adapter element does not have to be actively secured to the tool housing after insertion. Rather, the adapter element is automatically secured to the tool housing upon complete insertion. This may be effected by a snap lock or a spring lock or by a magnetic lock. 45 50 55 [0026] Furthermore, it is also possible that the power supply unitcomprises a firstelectricsocketforreleasably attaching the firstcable to the powersupply unit.Thefirst cable may be attached by means of a respective plug which is connected to the firstcableand inserted into the socket.The plug andsocketmay have any desired form. In particular, they may have three contacts each,one for the positive pole, one for the negative pole and one for ground. A plug-and-socket-connection (and) with only two contacts each, one for the positive pole and one for the negative pole ispreferred.The plug-and-socket-con- nection - if present - must be adapted to transmit the [0021] According to a preferred embodiment, the at- tachment members comprise at least one spring-loaded hookelementattached to one ofthe toolhousing and the adapter housing and at least one corresponding recess or opening attached to the other one of the tool housing and the adapter housing, for receiving the hook element uponcomplete insertion ofthe partofthe adapterelement to be inserted into the recess. [0022] The spring-effect of the hook element may be achieved by a separate spring element or by means of the material of which the hook element is manufactured, the material having elastic characteristics. For example, 4