referring now to the figures , and most particularly to fig1 , 2 , and 3 , a prior art piston paint pump 30 may be seen . the particular pump shown in fig1 is a model 1920 , available from the assignee of the present invention . fig2 shows an illustration from the owner &# 39 ; s manual wherein the user is directed to insert a spout 32 of an oil can 34 into an aperture 36 in a cover 38 of a pump housing 40 for periodic lubrication . fig3 shows an exploded view of the front of a paint pump ( with the cover removed ) in which a paint pumping piston 42 is received in and passes through a nut or bushing 44 . the lubrication is to be applied to the piston in the region where it projects from the bushing 44 , to minimize wear that would otherwise occur between the paint pumping piston 42 and the bushing 44 . with the paint pumping piston 42 and bushing 44 recessed within housing 40 , such prior art lubrication was found to be inconvenient . referring now to fig4 through 8 , an on - board lubrication system 46 according to the present invention may be seen . system 46 is preferably permanently installed in or on the pump 30 , more particularly , in or on the pump housing 40 , and most desirably on the cover 38 . system 46 preferably includes a lubricant reservoir 48 located internal to the housing 40 of the pump 30 . reservoir 48 has an inlet 50 and an outlet 52 . system 46 also includes a lubricant dispensing mechanism 54 having an inlet 56 connected to the outlet 52 of the reservoir 48 and mechanism 54 has an outlet 58 for delivering a predetermined minimum amount of lubricant to the paint pumping piston 42 adjacent the bushing 44 per activation . the system 46 also may have an actuator 60 located exterior of the housing 40 for activation by a user . in one embodiment , the present system provides about 0 . 01 cubic inches of liquid lubricant per stroke of the actuator 60 . user instructions for that system recommend that the user initially activate the actuator between 2 and 5 times to lubricate the piston 42 . user instructions go on to recommend pressing the actuator 60 once for every eight hours of pump operation . the lubricant dispensing mechanism 54 preferably has a housing 62 containing an inlet check valve 64 , an outlet check valve 66 , a lubricant delivery piston 68 and a return spring 70 for piston 68 . each check valve may be formed by a ball having a spring urging the ball against a seat to block flow in one direction i . e ., from the ball towards the seat , and to permit flow in the opposite direction i . e ., from the seat towards the ball . the seat may be formed in an end of a threaded fitting received in the housing 62 , it being understood that the threads are omitted from some of the figures for simplicity . the lubricant reservoir 48 may be a hollow tube connected to a fitting 74 projecting through the housing 40 ( more particularly the housing cover 38 ) and in fluid communication with inlet 56 of the mechanism 54 ( through the inlet check valve 64 ). the fitting 74 is secured to cover 38 by a conventional nut 76 , with it being understood that fitting 74 has external threads ( not shown ) mating with internal threads ( also not shown ) on nut 76 . nut 76 may be made of any suitable material , for example , nylon . a cap 78 ( also with internal mating threads , not shown ) is received on a projecting end of fitting 74 exterior of cover 38 . a breather valve 80 is attached to cap 78 to prevent a vacuum from forming in reservoir 48 as the lubricant is drawn from the reservoir 48 . referring now also to fig9 - 18 , various views of the housing 62 may be seen . housing 62 has a first mounting aperture 82 and a second mounting aperture 84 to secure the mechanism 54 to the cover 38 using conventional machine screws . a stepped bore 86 is sized to receive the lubricant delivery piston 68 , while allowing the actuator portion 60 to project out of the housing 62 . although not shown in these views , it is to be understood that bore 86 is threaded to receive a threaded plug 88 , shown schematically in fig8 and in section in fig1 . it is also to be understood that inlet 56 and outlet 58 are each threaded to receive respectively , inlet check valve fitting 90 and outlet check valve fitting 92 , each of which are threaded , as shown in the section views of fig1 and 18 . housing 62 may be formed of any suitable material , such as aluminum . inlet check valve 64 includes the inlet check valve fitting 90 , which provides a valve seat 91 on an inboard end thereof , and a ball 94 and spring 96 . outlet check valve 66 includes the outlet check valve fitting 92 and a ball 98 and spring 100 . a valve seat 102 for outlet check valve 66 is provided by a step in the bore of outlet 58 in housing 62 . referring now to fig1 , the lubricant delivery piston 68 has a stem 104 forming actuator 60 , and a groove 106 to retain an o - ring 108 ( shown in fig1 ) to seal the piston 68 against the bore 86 . referring now to fig2 , outlet check valve fitting 92 is shown in more detail in cross section . fitting 92 has a through bore 110 and a first end 112 which has external threads 114 to mate with the internal threads of outlet 58 in housing 62 . through bore extends from the first end 112 to a second end 116 which may have an enlarged perimeter or drip lip 118 . drip lip 118 prevents oil from running back from the second end 116 towards the first end 112 . fitting 92 also serves as a discharge nozzle and , when installed , is located adjacent to and directed at the paint pumping piston 42 proximate the bushing 44 . fitting 92 may be made of any suitable material , such as brass . referring now most particularly to fig2 - 25 , details of a breather valve and cap assembly 120 may be seen . assembly 120 ( shown in fig2 ) is preferably made up of the cap 78 and breather valve 80 . fig2 and 22 show a rear and section view , respectively of the cap 78 , which has a central through bore 122 and an offset through bore or breather hole 124 . cap 78 has internal threads indicated by dashed line 126 sized to mate with external threads ( not shown ) on fitting 74 . cap 78 may also have flutes 128 projecting radially and extending axially on the exterior of cap 78 . cap 78 may be made of any suitable material , such as nylon breather valve 80 is shown in a side view in fig2 , in a section view in fig2 , and is shown installed in cap 78 in fig2 . breather valve 80 has a stem 130 connecting an umbrella - like flange 132 to an enlarged head 134 . breather valve 80 may be made of any suitable material sufficiently soft to function as a vacuum breaker valve , and is available as a fluorocarbon part from vernay laboratories , inc . of 120 e . south college street , yellow springs , ohio 45387 as model va 4687 . in operation , flange 132 will lift away from cap 78 to permit ambient air to enter the lubricant reservoir 48 via breather hole 124 when lubricant is drawn from the reservoir 48 thus preventing a vacuum from forming in the reservoir 48 . referring now to fig2 , 27 , 28 and 29 , a second embodiment of the present invention may be seen . in this embodiment , a larger reservoir 140 ( preferably formed of a transparent or translucent material , such as a polypropylene polymer ) is used to store the lubricant . a fill fitting 142 is provided on the top of the cover 38 , and may include a cap and breather as described above with respect to the first embodiment . with this embodiment , a window or opening 144 in cover 38 may be provided to enable a user to view the level of lubricant ( typically oil ) remaining in the reservoir . fill tube 146 preferably has an 0 - ring 148 to seal against a reservoir lid 150 . a piston 152 has a spring 154 to return the piston to the rest position after an extension 156 is depressed to deliver lubricant as described above . in this embodiment , a cylinder 158 has an inlet port 160 closed when the piston 152 is actuated . a poppet 162 serves as an outlet check valve and is urged against a valve seat 164 by a spring 166 acting against poppet valve cap 168 . the outlet tube delivers the lubricant to the interface between the paint pumping piston and its supporting bushing , as described above with respect to the first embodiment . it is to be understood that all materials in contact with the lubricant ( typically a lubricating oil ) must be compatible with and not degraded by the lubricant used . initially the reservoir 140 may be filled with separating oil , available from wagner spray tech corporation , 1440 fernbrook lane , plymouth , minn . 55447 , as part number 0516915 . optionally , the reservoir may be refilled with light household oil , if desired . referring now to fig3 - 35 , a third embodiment of the present invention may be seen . in this embodiment ( which is similar to the second embodiment ) a reservoir 170 is preferably formed of a transparent or translucent polymer material , and may have a cover 172 permanently bonded to a main housing 174 ( as shown in fig3 ) after a breather valve 176 is installed , as shown in fig3 . with this embodiment the window or opening 144 in cover 38 may be provided as with the second embodiment . a fill tube 178 may have an o - ring 180 to seal the proximal end of the fill tube 178 against the reservoir cover 172 . a fill tube cover 182 may be used to close the distal end of the fill tube after lubricant is stored in the reservoir . referring most particularly to fig3 and 35 , a cylinder 184 ( corresponding to cylinder 158 in the second embodiment ) has inlet port 160 closed by the piston 152 when the piston 152 is actuated . the piston moving in front of and blocking the inlet port serves as an inlet check valve in this embodiment . the poppet 162 serves as the outlet check valve and is urged against the valve seat 164 by spring 166 acting against poppet valve cap 168 . the outlet tube 186 ( whose position is represented by dashed circle 188 in fig3 ) delivers the lubricant to the interface between the paint pumping piston and its supporting bushing , as described above with respect to the first and second embodiments . a spring 190 provides a return force for piston 152 when actuator or pushbutton end 192 of piston 152 is released by a user . the reservoir 170 , cover 172 , and fill tube 178 may each be made of a polypropylene polymer , while the fill tube cover 182 , valve cap 168 , poppet 162 and piston 152 may each be made of an acetal polymer , such as is available under the trademark delrin from dupont . referring now most particularly to fig3 and 37 , fragmentary section views with the fill tube cover 182 both installed and removed from the fill tube 178 may be seen . cover 182 may have a slot to permit rotation using a conventional flat bladed screwdriver . when cover 182 is rotated , a pair of dogs are released from cam surfaces in an upper end of the fill tube 178 . one dog 194 and a corresponding cam surface 196 may be seen in fig3 . it is to be understood that cover 182 has a flange 198 with an outside diameter that is sized to closely interfit with an inlet diameter of an inlet end of fill tube 178 to prevent leakage of liquid lubricant in the event that the paint pump is tipped or positioned to orientations other than as shown in fig1 , for example , for transportation or storage . this invention is not to be taken as limited to all of the details thereof as modifications and variations thereof may be made without departing from the spirit or scope of the invention . for example and not by way of limitation , oil is the preferred lubricant for the practice of the present invention , however , other similar lubricants are to be included within the scope of the present invention .