Abstract:
A fluid delivery system comprising a pump arranged to draw fluid, in use, from a reservoir ( 1 ) and dispense it through a dispensing tube ( 4 ), the pump comprising a cylinder ( 21 ) in which a piston ( 22 ) is reciprocally movable; an inlet into the cylinder; a one-way inlet valve ( 17 ) for controlling flow through the inlet; an outlet from the cylinder and leading to the dispensing tube; and an outlet valve ( 27 ) controlling flow through the outlet, wherein the piston is arranged to selectively contact the outlet valve to maintain it open during the initial portion of its downstroke and to allow it to close for the remainder of the downstroke.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a US National Stage of International Application No. PCT/GB2010/051110, filed 6 Jul. 2010, which claims the benefit of GB 0912065.0, filed 10 Jul. 2009, both herein fully incorporated by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a fluid delivery system. 
     BRIEF SUMMARY OF THE INVENTION 
     It has been designed particularly for use with an automatic soap dispenser for use in a domestic environment. The soap dispenser is a battery-operated device with a replaceable reservoir of soap or the like which is placed in an upturned configuration over a base unit. The reservoir has an outlet with a valve at its lower end which prevents leakage of the liquid from the reservoir. The base has a spigot which enters the outlet thereby opening the valve to allow the liquid to flow into the base. 
     The base is provided with a battery compartment, a motor, a pump system, a dispensing tube and a sensor. When the user&#39;s hands are sensed by a sensor, the motor is activated to operate the pump and dispense liquid from the dispensing tube. 
     The present invention is directed to a fluid delivery system for use in the base unit which can prevent or significantly reduce unwanted dripping from the dispensing tube. 
     Although the fluid delivery system has been designed for use in such an application, it can be broadly applied to any fluid delivery system for dispensing fluid via a dispensing tube where it is necessary to prevent or reduce dripping. 
     One dispenser which can do this as disclosed in EP 1 604 600. This discloses the possibility of an ancillary piston and cylinder which operate downstream of the check valve, so that, upon the downstroke of the piston, the ancillary piston sucks fluid into the ancillary cylinder. It also discloses a piston having a pair of annular flexible disks which are arranged to reciprocate in cylinders of different dimensions. Downward movement of the piston increases the size of the chamber between the two disks, thereby generating a suction force which sucks back some of the dispensed product to reduce or prevent dripping. 
     According to a first aspect of the present invention there is provided a fluid delivery system comprising: 
     a pump arranged to draw fluid, in use, from a reservoir and dispense it through a dispensing tube, the pump comprising a cylinder in which a piston is reciprocally movable; 
     an inlet into the cylinder; 
     a one-way inlet valve for controlling flow through the inlet; 
     an outlet from the cylinder and leading to the dispensing tube; and 
     an outlet valve controlling flow through the outlet, wherein the piston is arranged to selectively contact the outlet valve to maintain it open during the initial portion of its downstroke and to allow it to close for the remainder of the downstroke. 
     Because the piston holds the outlet valve open during the initial portion of its downstroke, liquid is sucked back through the outlet. It is therefore sucked back along the dispensing tube and dripping is prevented or reduced. By making use of existing components to do this, namely the piston and outlet valve, the invention provides a solution without having to employ additional devices, or specially made components of complex construction. 
     The outlet valve could be in the top wall of the cylinder and be arranged such that it moves downwardly with the piston, and has an orifice which only communicates with the outlet, once the piston has moved more than a predetermined distance below top dead centre. However, more preferably, the outlet valve comprises a valve element positioned in an orifice at the side wall of the cylinder and biased to a closed position in which the valve element projects into the cylinder, the valve element being arranged to be opened by the piston moving in the cylinder past the outlet valve element and pushing the projecting part of the valve element out of the cylinder against the action of the resilient biasing force. The inlet valve element may be biased into position. However, it is preferably a floating valve element. 
     The dispensing tube may have any configuration as the suction caused by the piston will create a back pressure which will maintain the liquid in the dispensing tube to some extent. Preferably, the dispensing tube comprises an upward portion extending away from the piston leading into a curved transitional portion, the curved transitional portion leading to a generally downwardly facing outlet. Preferably, the piston is configured to suck the liquid back to a location, which is back beyond the point where it could flow out of the outlet under gravity. 
     The invention preferably extends to a dispenser for soap and the like having a replaceable reservoir of liquid, the reservoir having an outlet orifice at its lower end and a reservoir outlet valve for controlling the flow from the outlet, a base unit having a spigot which engages with the outlet in the reservoir to open the valve, the base unit being provided with a fluid delivery system according to a first aspect of the present invention, the one-way inlet valve being arranged to control the flow of liquid through the spigot and into the cylinder. 
     The dispenser may be manually operated in which case the piston is moved by a hand-operated lever mechanism. However, preferably, the base unit is provided with a motor, a control circuit and a sensor to detect the presence of movement in the vicinity of the dispensing tube, the control circuit being arranged to drive the motor to move the piston when movement is detected. The dispenser may be a wall-mounted unit or one which is integrally built into a surrounding unit. However, it is preferably a free-standing unit, in which case the base unit preferably also comprises a battery compartment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An example of a fluid delivery system in accordance with the present invention will now be described with reference to the accompanying drawings, in which; 
         FIG. 1  is a cross-sectional view of dispenser for which the fluid delivery system is primarily designed; and 
         FIGS. 2A to 2K  are schematic representations of the fluid delivery system showing various stages of operation. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The dispenser is a hands-free dispenser which is generally suitable for domestic use. The dispenser is primarily intended to dispense liquid soap, but may also be used to dispense other liquid or semi-liquid products (ideally with a viscosity greater than water), such as hand cream, body lotion, moisturiser, face cream, shampoo, shower gel, foaming hand wash, shaving cream, washing up liquid, toothpaste or a sanitising agent such as alcohol gel. 
     The dispenser comprises two main parts, namely a refill  1  and a base unit  2 . The refill  1  provides a reservoir of liquid to be dispensed and is fitted to the base unit  2  as set out below. 
     The base has an interface into which liquid is dispensed from the refill unit as described with reference to the remaining drawings. The interface is in fluid communication with a dispensing tube  4 . A pump as described below with a motor  5  is selectively operable to pump a metered dose of the liquid along dispensing tube  4  and out of dispensing head  6  as described in detail with reference to the remaining drawings. 
     The base has an infrared transmitter  7 A which transmits an infrared beam through a window  8  to a receiver  7 B to sense the presence of a user&#39;s hands in the vicinity of the dispenser. Control circuitry reacts to a signal from the proximity sensor to activate the pump. The illustrated sensor is a break beam sensor, but may also be a reflective sensor. Although an infrared sensor is shown, any known proximity sensor such as a capacitive sensor may be used. The device may be mains powered or battery powered. Alternatively, it may be a manually operated pump device in which a user pushes a lever to displace the product. 
     The base unit  2  comprises a cowling  10  which forms a cup-shaped housing surrounding a significant portion of the refill to protect and support it. A spigot  11  projects through the base of the cowling  10 . 
     The refill  1  comprises a bottle  12  with a cap  13  attached at its lower end. At the lower end is an outlet  14  into which the spigot is inserted. The outlet  14  is closed by a valve element  15  which is resiliently biased onto the top of the annular wall of the outlet. The valve  15  is lifted from its seat upon insertion into the base  2  by the spigot  11 . This opens up a flow path around the top of the spigot. An air Inlet valve  16  provides a vent which allows air into the bottle to replace lost liquid without interfering with the flow of liquid out of the dispenser. 
     The invention is concerned with the mechanism of the pump in the base unit and this will now be described with reference to  FIGS. 2A to 2K . 
     As shown in  FIG. 2A , an inlet valve element  17  is provided within a spigot  11 . This inlet valve element  17  has a conical upper wall which seats on a complimentary valve seat  18 . It could equally be a ball valve. The valve element  17  is retained to float within a spigot  11  by a cylinder housing  19 , an upper portion of which projects into the spigot  11 . This is sealed to the spigot by an O-ring  20 . 
     The cylinder housing  19  defines a cylinder  21  in which a piston  22  is reciprocally mounted. The piston  22  is provided with an annular sealing ring  23  and a piston rod  24  which couples with a rotatable cam (not shown) driven by the motor  5  ( FIG. 1 ). The cylinder  21  has an inlet orifice  25  flow through which is controlled by the previously described inlet valve element  17  and an outlet orifice  26  flow through which is controlled by an outlet valve element  27 . 
     The end of the outlet valve element  27  closest to the cylinder  21  is relatively narrow and is arranged to slide within a retainer  28 . At this point, the valve element  27  is provided with, a plurality of elongate grooves  29  to allow the passage of liquid. At the opposite end, the outlet valve element  27  is wider and is dimensioned to slide within outlet channel  30 . At this point, the valve element has a plurality of notches  31  which also allow for the flow of liquid. Below the enlarged portion is an O-ring  32  which lands on conical seat  33  in order to seal the outlet. 
     The outlet valve element  27  is biased towards the cylinder  21  (to the left as shown in  FIG. 2A ) by a spring  34 . The outlet chamber  30  leads to the dispensing tube  4  which has an outlet  35 . Relating back, to  FIG. 1 , this outlet  35  effectively provides the dispensing head  6 . 
     The operation of the system will now be described. 
     In  FIG. 2A , the piston is shown before first use and in an unprimed condition with the piston  22  In the uppermost position and the inlet  17  and outlet  27  both open. It should be noted that this is not the normal position that the piston will return to at the end of a cycle as described below. 
     With the piston in this unprimed condition, the refill  1  is inserted into the base unit  2  as shown in  FIG. 1 . When the sensor  7 A,  7 B detects the presence of movement in the vicinity of the dispensing head  6 , the motor  5  drives the piston downwardly as shown in  FIG. 2B . In this position, liquid is drawn down past the inlet valve  17  and into the cylinder  21 . During this initial movement, the outlet valve element  27  remains open, so that liquid fills the chamber  36  surrounding the outlet valve element and may even flow further into the outlet chamber  30 . 
     As soon as the piston  22  reaches the position shown in  FIG. 2B  in which it is beneath the outlet valve element  27 , the spring  34  urges the outlet valve element  27  into the closed position as shown in  FIG. 2B  in which the sealing ring  32  lands on seat  33  to seal the outlet. Further downward movement of the piston via the position shown in  FIG. 2C  to the position shown in  FIG. 2D  fills the cylinder  22  with liquid. 
     The piston  22  reaches bottom dead centre and then reverses as shown in  FIG. 2E . The increase in flow pressure that this generates closes the inlet valve  17  as shown in  FIG. 2E . As the piston continues its upward stroke as shown in  FIG. 2F , the liquid pressure on the outlet valve  27  overcomes the biasing force provided by the spring  34  and liquid L enters the outlet housing  30 . Continued upward movement of the piston  22  forces the liquid L up the dispensing tube  4  as shown in  FIG. 2G  and ultimately out of the outlet  35  as shown in  FIG. 2H  until the piston reaches top dead centre. 
     The pump is now primed. The piston  22  then reverses as shown in  FIG. 2I . At this point, the outlet valve element  27  is prevented from closing as the tip of the valve element is obstructed by the side wall of the piston  22  while moving to the closed position. This downward movement of piston  22  re-opens the inlet valve element  17  sucking liquid in through inlet  25  as well as sucking liquid back down the dispensing tube  4  around the valve element  27  as shown in  FIG. 2J . 
     Once the piston  22  passes the outlet valve element  27 , the valve element  27  closes and liquid is drawn into the cylinder  21  until the piston approaches bottom dead centre just above the position shown in  FIG. 2K  (approximately 75% of the downstroke). This is the at rest position L of the pump during normal use. In this position, the cylinder  21  is filled with liquid and the dispense tube  4  is full of liquid L up to a level which is beneath uppermost part of the lower surface of the discharge tube. Thus, the liquid has been sucked back to a location at which it cannot flow through the outlet under gravity. When movement is detected by sensors  7 A,  7 B to trigger the next dispensing operation, the piston first travels down to bottom dead centre (the remaining 25% of its stroke) to fully prime the cylinder before completing a full upstroke to dispense the liquid and 75% of the downstroke to return to the “at rest” position of  FIG. 2K .