Controlled inlet valves for metering pumps
BACKGROUND OF THE INVENTION 
     The present invention relates to controlled inlet valves for metering pumps. 
     To inject metered amounts of liquid into another liquid, it is known to use a metering pump which consists of a cylinder in which moves a piston. The piston draws the liquid to be metered from a container and pumps it into a second container which holds the other liquid. The second container may in particular be an injector device as described in French Patent Application No. 72.39699. 
     However, if a valve of a conventional type which opens under atmospheric pressure is used at the inlet when the fluid pressures involved are very low, this results in the valve closing in an unsatisfactory fashion and the metering action being such that the metering device operates incorrectly. 
     It is an object of the invention to provide a device which shall minimise or overcome these disadvantages by the use of a positively controlled valve. 
     SUMMARY OF THE INVENTION 
     The invention consists in a controlled inlet valve for a metering pump, which pump consists of a cylinder in which moves a piston to which a reciprocating movement is imparted, wherein a member is mounted to slide in said pump cylinder, one of the ends of said member having an obturator which co-operates with a sealing gland arranged at the inlet opening to the cyclinder, the said slidable member being selectively coupled at its other end to the piston and being subject to the urging of an elastic member which is capable of thrusting the obturator back to the closed position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention shall be more clearly understood, reference will now be made to the accompanying drawings which show the embodiment thereof by way of example and in which: 
     FIG. 1 is a longitudinal section through a metering pump fitted with an intake valve according to the invention, which is shown in the closed position, and 
     FIG. 2 is a similar view of the pump when the inlet valve is in the open position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, in FIGS. 1 and 2 is shown a metering pump, which consists of a cylinder 1 in which a piston 2 is mounted to slide. The said cylinder has at one of its ends a threaded portion 3 onto which a cap 4 is screwed, the cap 4 being provided with an inlet tube 5 which is connected in a known manner to a container for liquid to be metered which is not shown in the drawings. 
     Between the cap 4 and the body 1 is clamped a sealing gland 6 made of an elastic material which has a circular lip 6a which defines an inlet opening in which an obturator 7 is engageable. The obturator 7 is formed by a stud attached to a tubular member 5 in which an end 2a of piston 2 is mounted to slide. 
     At the opposite end from obturator 7, tubular member 8 is subject to the urging of a coil spring 9 which bears against a sealing gland 10 made of an elastic material. Sealing gland 10 has a circular lip 10a which fits round piston 2 and forms an outlet valve, the said gland being held clamped between cylinder 1 and a shoulder 11 on a container 12. Cylinder 1 is mounted on container 12 by means of a threaded portion 13 provided at its other end, which corresponds to the outlet for the liquid. 
     In the tubular obturator member 8 are provided two longitudinal slots 14, 14a in which move the ends of a pin 15 attached to the end 2a of piston 2, the ends of the said pin 15 being capable of coming to bear against an annular base 8a on the tubular member which forms the end, of slots 14, 14a. 
     An annular gap 16 is provided between tubular member 8 and piston 2 to allow the liquid to flow out. 
     The device according to the invention operates in the following way: 
     When piston 2 is moved in the direction of arrow F (FIG. 1), i.e. during the delivery period, tubular member 8 is subject to the urging of spring 9, which forces the obturator member 7 into the opening 18 defined by the circular lip 6a on the sealing gland, thus positively closing the inlet tube 5 for the liquid to be metered. 
     Pin 15 moves in slots 14, 14a without acting on the tubular member 8 in which piston 2 is sliding. 
     The liquid which was admitted to cylinder 1 during the previous stroke is pumped by piston 2 and flows through the annular gap 16 into the chamber 17 which is formed between the piston and the cylinder. 
     Being under pressure, the liquid lifts the circular lip 10a which deforms elastically to allow it to pass into container 12. 
     When piston 2 is moved in the direction of arrow F1, there is produced in cylinder 1 a slight reduction in the pressure intended to assist in the intake of the liquid, the relevant part of the travel of piston 2 being that in which the pin 15 moves in slots 14, 14a without carrying the tubular member 8 along with it. At the end of this part of the travel of the piston, the ends of pin 15 come up against the annular base 8a (FIG. 2) of the tubular obturator member 8, which is thus coupled to piston 2 and carried along with it in direction F1 in opposition to spring 9, which is compressed. 
     The movement of tubular member 8 causes obturator 7 to be drawn out of the circular lip 6a and the inlet opening 18 to be opened so as to allow liquid to enter cylinder 1. 
     When piston 2 is moved back in the direction of arrow F, tubular member 8 again becomes subject to the urging of spring 9, which causes obturator 7 to be inserted in the opening 18 defined by the circular lip 6a, and the cycle described above begins again.