respective valve for example ports 37 and 38 in valves 16 and 17 could be appropriately sized for this purpose as is fully developed in the referenced patents signals from a sensing pump may be employed simply for information and can be read by any convenient means such as an osciloscope or can be used to activate a desired function such as a second pump in a two pump system using circuit discriminator means discrimination for example to determine whether a pump should be operated or not may be based upon signal strength in which the function is activated by a signal which exceeds a predetermined level or by signal timing by which activation is limited to the open period of timed gating means or by a combination of both in which a signal to cause activation must be both early enough and of sufficient magnitude it should be kept in mind that the purpose of this system is to discriminate between a liquid in the bore and a gas or vapor or mixture of the two as a consequence of this information suitable response may be taken it is evident that in pumping the device of fig1 with or without the orifices 35 or 36 the reaction of the plunger will be different for oil than for air and that for best discrimination it is best practice to have as much separation both in magnitude and in timing between the two as possible fig2 graphically shows these circumstances plotting relative signal strength versus time in milliseconds the time beginning with the energizing of coil 25 initially it will be noted that when the pump is delivering air the curve 40 will be substantially the same whether either or both of the orifices.