fig1 shows a tap assembly 10 according to one embodiment of the invention isolated from its mounting position , e . g . next to a sink . the tap assembly 10 has a mixing chamber housing 12 which receives two fluid inputs 14 , 16 which are connected to hot and cold water supplies ( not shown ) respectively via connectors 20 . the inputs 14 , 16 feed the base 15 of the mixing chamber housing 12 ; each input 14 , 16 supplies its own cartridge valve ( not shown ) inside the base 15 . an output conduit 18 carries mixed fluid away from the mixing chamber housing 12 to a fluid outlet 34 at the end of an output spout 32 . the output conduit 18 is a flexible pipe that loops around the bottom of the base 15 and passes through the interior of the output spout 32 , which is a hollow rigid pipe made of suitable material ( e . g . stainless steel , brass , etc . ), arranged in a goose - neck configuration . the output conduit 18 feeds fluid to the fluid outlet 34 , which is a conventional spray head . the fluid outlet 34 is detachably mounted to the output spout 32 , and can be pulled down , i . e . away from the spout 32 , to give the user flexibility in directing flow out of the outlet 34 . the output conduit 18 has extra length to accommodate this movement . the mixing chamber housing 12 is connected to control housing 26 by an upstanding rigid tube 24 . in use , as shown in fig2 , the base of control housing 26 rests on the top of a work surface 42 , where it is secured in place by a backing nut 27 . the upstanding tube 24 extends through a hole ( not shown ) in the work surface 42 so that the mixing chamber housing 12 and the loop of output conduit 18 are located out of sight below the work surface 42 . tube 24 is hollow , and control housing 26 has a passageway therethrough to allow the output conduit 18 to travel from below the work surface 42 to the output spout 32 through the same hole in the work surface 42 as the tube 24 . the tube 24 has a cut - out opening 25 which allows the output conduit 18 to be fed in below the control housing 26 . a guiding tube 22 is attached to a ring 21 mounted on the tube 24 via a lug 23 . the guide tube 22 controls the orientation and angle at which the output conduit 18 enters the tube 24 . this prevents the edges of the cut - out hole 25 from interfering with the output conduit , and also prevents kinks from forming in the conduit . two radially protruding rotatable push levers 30 , 31 are mounted in the control housing 26 to communicate with the valves in the mixing chamber housing 12 as described below . the levers 30 , 31 rotate about a vertical axis extending through the tube 24 . the levers 30 , 31 are located on top of one another , and their connections in the housing are covered by respective trim covers 28 , 29 . the upper lever 31 is arranged to control flow rate ( output volume ), whereas the lower lever 30 is arranged to control mix ratio , i . e . the relative proportion of fluid received from inputs 14 , 16 . fig3 shows the mechanism by which the levers 30 , 31 communicate with the valves in the mixing chamber housing 12 . lower lever 30 is operably coupled to the head 35 of an upstanding rotatable sleeve 36 . the base of sleeve 36 is connected to a annular block 46 , which has a depending lug 55 connected to a set of radially protruding teeth 64 , which are arranged to engage gears 58 , 60 associated with valve cartridges 52 , 54 for controlling the input mix ratio of fluid from inputs 14 , 16 ( see fig4 and 5 ). similarly , upper lever 31 is operably coupled to the head 37 of another upstanding sleeve 38 which lies inside and coaxial with sleeve 36 and tube 24 . the base 40 of sleeve 38 has a splined through hole 43 bored therein which receives a correspondingly splined projection 45 from coupling block 44 . rotation of the sleeve 38 causes coupling block 44 to rotate . coupling block 44 extends through annular block 46 and terminates in another set of radially protruding teeth 62 arranged to engage a gear 56 to operate a cartridge valve 50 associated with output flow rate ( see fig4 ). the valve cartridges 50 , 52 , 54 are housed in the base 15 of the mixing chamber housing 12 . a casing 17 attaches the base 15 to the tube 24 to prevent relative rotation therebetween , i . e . so that operating the levers 30 , 31 does not cause the entire mixing chamber housing 12 to rotate . additionally , the cover 17 protects the gear connections , which protrude from the top of the base 15 . the rotatable sleeves 36 , 38 , which act as physical control means that connect user operations above the work surface 42 to the control of valves below the work surface 42 , also have cut - out openings along their length to overlap with the cut - out opening in tube 24 . to allow for the rotation of the sleeves 36 , 38 , their cut - out openings have a wider circumferential extent . this means that they do not interfere with the output conduit 18 , even when rotated to control the cartridge valve ( s ). fig4 and 5 show the operative connections in the mixing chamber housing 12 . the base of the housing contains three standard cartridge valves 50 , 52 , 54 of the ceramic plate type . as is conventional , each valve has an input in its base , and an output near the top , and flow through the cartridges controlled by a valve which is opened and closed by rotating a control lever which projects from the top of the valve . in the illustrated embodiment , gears 56 , 58 , 60 are mounted on and rotatable with the control levers of the cartridges . inputs 14 , 16 are connected to the inputs of two of the cartridges 52 , 54 . the gears 58 , 60 of these cartridges 52 , 54 are operably connected to a common set of teeth 64 . this allows for the input cartridges to be controlled in a complementary fashion , i . e . the common set of teeth 64 rotate between two limits corresponding to 100 % ( full ) supply from input 14 and 100 % ( full ) supply from input 16 . between these limits the cartridges 52 , 54 are open / closed in a linear ( i . e . constant ) fashion so that the total input volume remains constant and only the mix ratio ( proportion of input 14 to input 16 ) varies . the outputs of the two cartridges 52 , 54 connected to the inputs 14 , 16 are both connected to the input of the third valve cartridge 50 . mixing of the fluids occurs at this point . the third valve cartridge 50 is operated to control the flow rate of mixed fluid out of the mixing chamber housing 12 ( i . e . through output conduit 18 ). thus , the set of teeth 62 which are operably connected to the gear 56 on the third valve cartridge 50 is arranged to move the gear between two limits corresponding to off , where no fluid flows through the cartridge ( i . e . the valve is closed ), and on , where the valve is fully open and maximum flow rate is achieved . fig6 to 8 illustrate a second embodiment of the invention . components which are the same as those illustrated in the first embodiment are given the same reference numerals and are not described again . in the second embodiment , the three valve cartridges of the first embodiment are replaced by a conventional single lever - type mixer valve 74 , which is sits in an outer housing 71 , secured by a ring 79 . the inputs 14 , 16 and output conduit 18 are connected to the outer housing 71 , from where they are fed to the mixer valve 74 . a lever 76 is manipulated to permit fluid from the inputs 14 , 16 to enter a mixing chamber ( not shown ) in the mixer valve 74 in variable proportions . this is achieved by rotating the lever 76 . the same lever 76 is also tiltable to control the amount of fluid released from the mixer valve 74 into the output conduit 18 . the mixer valve 74 is operated using an actuator lever 30 that is mounted on the control housing 26 above the work surface 42 . the actuator lever 30 is coupled to an upstanding sleeve 72 which extends between the control housing 26 and the mixer valve 74 . the sleeve 72 is rotatable and axially slidable relative to the tube 24 connecting the control housing 26 and mixer valve 74 . the actuator lever 30 is connected to the sleeve 72 via a v - shaped connector 73 . the actuator lever is pivoted at a fulcrum 33 to enable the sleeve 72 to be pulled up and down . the lever 30 and fulcrum mechanism 33 are mounted on a rotatable ring 28 , attached to the sleeve 72 so that the sleeve can be rotated by pushing the actuator lever 30 . fig7 and 8 show the connection between the control lever 76 of the mixer valve 74 and the base 75 of the sleeve 72 . the control lever 76 is typically a box - like structure , and is contained within walls formed by the base of the sleeve 72 so that it is rotated with the sleeve 72 . outward projections 78 on the control lever 76 are received in slanted slots 77 in the walls that contain the lever 76 . the slanted slots cause the lever to be tilted by the up and down movement of the sleeve 72 . fig7 shows an on configuration , where the sleeve 72 is at its lower position ( actuator lever 30 pulled high ) so that control lever 76 is tilted forward by the action of slot 77 against projection 78 . fig8 shows the off position with the sleeve 72 in its upper position ( actuator lever 30 pushed down ) where the control lever 76 stands upright . as before , the sleeve 72 represents a physical control means connecting the actuator lever 30 with the mixer valve 74 and has a cut - out formed therein to enable the output conduit 18 to travel into the middle of tube 24 , through the work surface 42 via the same hole as the tube 24 and sleeve 72 to enter the output spout 32 . a casing 70 attached the outer housing 71 to the tube 24 to prevent relative rotation therebetween , as described above . the casing 70 also protects the operative mechanism between the sleeve 72 and the control lever 76 . fig9 to 11 illustrate a third embodiment of the invention , where the work surface which hides the mixer valve ( i . e . the work surface through which the output conduit passes ) is a vertical wall 102 , e . g . a stud wall for mounting in a kitchen or other suitable area . again , parts in common with the first or second embodiments are given the same reference numbers . in the tap assembly 100 of the third embodiment , the housing 26 includes a flat base plate 106 which can be mounted on the wall 102 using screws 108 . the output conduit 18 enters the cut out 25 in the tube 24 behind the wall 102 and is therefore guided horizontally through the wall into a conventional spout 104 to terminate at spray head 34 . similar to the second embodiment , the third embodiment uses the single lever mixer valve 74 , but in this case , the valve 74 is held in a horizontal configuration , with the lever 76 extending substantially horizontally . the inner control sleeve 72 is movable axially ( horizontally ) and rotatably by the control lever 30 on the housing 26 using the same mechanism as the second embodiment .