the threaded nippies of the pistons suitable adhesive is employed permanently to join the pistons to the brass piece 350 although fig3 and 5 merely show projecting stop pin portions 368 on the cross pieces the preferred configuration is illustrated in fig6 wherein the stop member is in the form of a hardened steel ball 370 seated within the bore 371 and resistance welded thereto along the interface 373 as shown in fig1 and ground off across the face 372 as shown in order to reduce its weight and also to provide clearance between the inner ends of the two armatures the opposed inner faces of the pump bodies 344 and 346 provide reaction surfaces against which two wedge shaped and vertically slidable stops means 374 and 376 engage it is against the surfaces of these two stop means that the stop pins engage during the working strokes of the pumps at this point it is well to elucidate certain novel feature which accrue in consequence of the combinational arrangement as described to this point as noted the electromagnets of each pair are closely spaced and as a result the armatures are strongly influenced thereby by arranging the electromagnets between the pivot and displacing ends of the armatures the close spacing of the electromagnets of each pair still allows sufficient movements of the liquid displacing members to effect the requisite pumping action for example in a prototype fuel injection system having a maximum pump stroke of 2 mm each pump delivered a maximum of 40 mm 3 of fuel per stroke up to a maximum of 85 injections per second the rapidity with which each pump performs its.