Abstract: The present invention discloses an improved apparatus for injecting additives into a stream of fluid passing through the apparatus. The apparatus has a housing adapted for connecting to a source of fluid and to an external source of additive and also has an outlet through which the intermixed fluid and additive pass. Fluid entering the housing drives a turbine means, which converts the movement of the fluid into a rotary force. The turbine means is connected to a transmission means which changes the high-speed, low-torque rotary force produced by the turbine means to a rotary force having slower speed but higher torque. The transmission means drives a positive displacement pump means which draws additives from the external source into the fluid passing through the apparatus at a rate which is determined by the speed at which the turbine means rotates.

Abstract: In an apparatus for the pulsewise dispensing of very small amounts of liquid controlled with a measuring instrument comprising an ejecting device for the pulsewise ejection of a desired amount of liquid, a pump is provided for supplying liquid to the vessel from a reservoir. The pump includes a neck portion having an inlet at the bottom thereof and a foot portion, with at least the foot portion immersed in a liquid contained in the reservoir. The foot portion has a volume at least as great as the refill volume of the measuring vessel and a feedline to the measuring vessel is disposed within the neck portion and terminates in proximity to the bottom of the foot portion. A check valve opens and closes the foot portion inlet by means of compressed gas which is controllable by sensing devices at the measuring vessel.

Abstract: A machine is disclosed for repeatedly metering out quantities of a predetermined volume of fluid freshly mixed from a plurality of component sources. A mixing member (which may comprise simply a duct) is coupled to receive a plurality of component fluids through positive control valves. Reciprocating metering structures (cylinder-piston), connected to the valves, are driven in a controlled fashion by pressurized fluid and a reciprocating actuator. The control system incorporates sensors for detecting the positions of the metering structures as well as the valves to provide timely signals which change the valve positions and reverse the stroke. With the valves in one position, and upon movement of the actuator in one direction, fluid flows under pressure from a component source to an associated metering structure, then with the valves in another position, the actuator is reversed and the fluid is discharged from the metering structure to the mixing chamber.

Abstract: A perforated basket containing live bait is immersed in a tank of water. Upon selection by the consumer, the basket is lifted clear of the water and gravity causes the bait to fall into and fill a bait receiving pocket. The basket is then lowered leaving a predetermined amount of bait in the bait receiving pocket. At this point the bait receiving pocket is opened thereby dispensing a predetermined amount of live bait into the fisherman's bucket along with a predetermined amount of water.

Abstract: Frit material for sealing glass parts is dispensed to a sealing edge of one of such parts at a uniform desired rate through the utilization of controllably operated piston and cylinder mechanism providing constant volume displacement during the dispensing of such frit material.

Abstract: A dosing unit for highly filled synthetic-resin components, usually a polyol and an isocyanate mixed with glass fiber, barite or chalk, comprises a piston which displaces the components or one of them, especially the filled component under the control of fluid pressure. The change in the feed rate of the fluid-controlled unit is varied by varying the speed of the displacing member of the fluid-controlled unit which is preferably a piston-and-cylinder arrangement. The piston-and-cylinder arrangement has its drive piston formed with a normal seal and its dosing or metering piston formed with an adjustable seal such that a tool can be inserted through the cylinder wall to rotate a toothed member of this latter piston to adjust for wear of its seal.

Abstract: This dispensing device is for use with a mixing bowl having a discharge port. The device is connected to the bowl below the discharge port to receive mix from the bowl and includes a horizontal dispensing chamber having a discharge port at one end. A plunger mounted within the chamber includes a one-way valve passing the mix through the plunger head when the plunger moves away from the dispensing port and urging the mix out of the dispensing port when the plunger moves toward the dispensing port. The plunger is actuated by a piston and cylinder assembly which includes an adjustable stop predetermining the travel of the plunger and hence determining the quantity of mix dispensed.

Abstract: A dosing unit for highly filled synthetic-resin components, usually a polyol and an isocyanate mixed with glass fiber, barite or chalk, comprises a piston which displaces the components or one of them, especially the filled component, under the control of fluid pressure. The change in the feed rate of the fluid-controlled unit is varied by varying the speed of the displacing member of the fluid-controlled unit which is preferably a piston-and-cylinder arrangement or a membrane or diaphragm-type displacement device.

Abstract: A grease gun comprising a hollow piston rod driven by a pressure fluid upon an annular drive piston at one end of the rod, compressing a supply of grease by an annular plunger at the other end of the rod into a receiving chamber within the piston rod, which chamber cooperates with a stationary surface, upon reversely driving the piston rod, to expel the grease through a conduit from the chamber at a higher pressure than the driving fluid.

Abstract: An automatic device for supplying an elastomer or like material for an intion machine comprising an injection cylinder and a piston, wherein the piston is controlled by a hydraulic multiplier device formed by two stages, the first stage being called the downstream stage and the second stage being called the upstream multiplier stage, and wherein the device comprises a sensor for controlling the supplying of the cylinder with material so as to stock said cylinder by an electrically driven tape advance unit, the sensor being brought into play when the piston is moved in the forward direction, a pressure controller for tripping the upstream multiplier stage to multiply the pressure in the injection cylinder, the pressure controller being controlled from a pressure threshold of the fluid supply of the first downstream stage and an end of travel sensor for tripping the return of the first and second stages to make the piston return at the end of the injection.

Abstract: Fluids to be mixed and dispensed are metered out of hydraulic cylinders by movement of pistons therein. The rate of movement is controlled by movement of a recirculating ball nut connected to each piston rod, movement of the nut, in turn, being controlled by the rate of rotation of its ball screw. Each screw carries a gear, and the gears have a common drive so that the ratio of the diameter of the gears accurately controls the volumetric metering ratio of the cylinders. In one form, an inert fluid under pressure acting on the reverse sides of the pistons assists the force of the ball nut drive. In another form, two cylinders work as a pair on each fluid, inert fluid under high pressure acting on the reverse sides of the pistons of each pair to meter, mix and dispense the fluids at about two thousand to two thousand five hundred pounds per square inch.

Abstract: The invention relates to an apparatus for dosing a liquid product into water, particularly for dosing a liquid detergent product into the water stream fed to domestic washing machines. The apparatus is driven by the water pressure and therefore consists of two hydraulic pressure chambers into which the water is alternately directed. In these chambers two rigidly connected pistons are moved. The pistons are connected to the housing by membrane seals. On one side of the apparatus a pumping part with a pumping chamber is located, into which one of the pistons can move. The pumping chamber is provided with a non-return valve for unidirectionally controlling the flow of the liquid product from a reservoir and with another non-return valve for unidirectionally feeding the liquid product into the water stream in the common outlet pipe. The pistons are connected to an electrically controlled valve assembly for alternatively directing the water stream to one of the two hydraulic pressure chambers.

Abstract: A liquid dispensing pump is disclosed and is powerable by pressurized fluid intermittently applied to the pump, the pump has a pumping chamber, a pressurizing chamber, a movable member for transferring pressure to the pumping chamber, a fluid conduit to the pressurizing chamber for applying pressure to the pump, a valve in the conduit for preventing reverse flow of fluid and an open drain in fluid communication with the pressurizing chamber; any fluid used to power the pump is exhausted out of the drain both during and after pumping.

Abstract: A system for safely dispensing fluids, especially low stability fluids such as catalysts, comprises a pair of fluid operated pumps of very small volume alternately operable for drawing in individually small quantities of catalyst from an unpressurized, sanitary source of supply, and for then pressurizing and dispensing the catalyst in individually small increments; the two pumps operating alternately to provide a continuous pressurized discharge of catalyst despite the fact that only a small quantity is pressurized at any given time. Because only a small quantity of catalyst is under pressure, and the basic supply is not under pressure and is maintained in a sanitary condition, the potential for violent reaction of the low stability fluid is greatly reduced.

Abstract: A fluid operated dispensing gun for dispensing viscous material in a disposable cylindrical cartridge. The dispensing gun has a hand grip and a barrel releasably secured to the hand grip. The cartridge containing the viscous material is positioned inside the barrel of the gun and a piston-like rear wall is advanced toward the open front end of the cartridge by pressurized fluid introduced into the rear end of the barrel on the rear side of the piston-like rear wall. Fluid passageways are provided in the hand grip for providing fluid communication from a source to the rear end of the barrel. A pair of manually operated valves are provided, one valve being provided for opening and closing the fluid passageway to the rear end of the barrel and the other valve being provided for controlling the rate of flow of the fluid entering the rear end of the barrel to thereby control the rate at which the viscous material is ejected from the cartridge.

Abstract: An apparatus for proportioning and mixing liquids having a plurality of containers each containing a respective said liquid, a plurality of compression chambers individual to said containers connected in fluid communication with their respective containers, pistons individually mounted in the chambers for corresponding movement therein, a mixing head having an outlet and inlets individually connected to the chambers, and a system for sequentially pressurizing the containers to deliver their respective liquids to their respective chambers, and subsequently correspondingly pressurizing the pistons to deliver in proportioned amounts the liquids therein to their respective inlets of the mixing head.

Abstract: The quantitative supply apparatus of powder coloring agent can measure the powder coloring agent through a measuring groove provided on a rotary shaft and supply it directly to the raw material inlet opening of an injection moulding machine. The measuring groove on the rotary shaft can be adjustably changed properly in volume along a length direction. A container for the coloring agent is disposed on the top portion thereof and a hole in the bottom portion of the container is in contact, in a location covering the measuring groove, with the top portion of the rotary shaft. The coloring agent which has dropped from the measuring groove through the rotation of the rotary shaft is adapted to be introduced to the inlet opening of an ejector, and furthermore to the be supplied out of an exhaust side of the ejector to the inlet opening of the injection moulding machine through compressed air.

Abstract: A dispenser for metering a predetermined volume of acid into a water softener brine tank utilizes a generally hat-shaped diaphragm that flops from one surface of a metering chamber to the opposite surface when acted upon by either pressure or suction. The diaphragm essentially lines one-half of the chamber at a time, and its movement either draws acid into the chamber or expels the acid from the chamber.

Abstract: A manifold for use in conjunction with fluid actuable liquid dispensing apparatus is disclosed for supporting and interconnecting such apparatus, especially where numerous individual liquid dispensers are employed, for example for lubricating various points in a system. The manifold allows individual dispensers, or sets of dispensers, to be disabled, for example for repair purposes, while others may continue to operate. Several such manifolds would typically be employed in a lubricating system with each comprising a block having a plurality of separated passageways therein, including at least one actuating fluid passageway with an inlet for connection to an actuating fluid source, and an outlet for connection to the liquid dispensing device, and at least a second passageway for the liquid to be dispensed, again having an inlet for connection to a liquid source, and an outlet for connection to the liquid dispensing device.

Abstract: A hand held two part material meter-mix-dispenser apparatus has a hand held body including a base mounting an air driven cylinder means in association with a double plunger assembly and a pair of cartridge receiving barrels with means for hingedly mounting the barrels to the base so that when in hinged open position, the barrels are positioned to easily receive a pair of cartridges containing different parts of a material to be mixed and when moved into hinged closed position automatically locate such cartridges in association with the double plunger assembly for simultaneous exuding of the materials of the two cartridges through a mixing head mounted on the apparatus body. Air driven mixing means are provided in the mixing head to dynamically mix the materials under pressure being forced through the mixing head via disposable conduits running from the two cartridges during operation of the dual plunger assembly.

Abstract: Power dispensing apparatus for dispensing measured increments of colorants, lubricants, stabilizers, etc., into casting, paint, and synthetic resin, etc., industrial processes having a block with a displacement chamber and bi-directionally air powered valves controlling inlet-supply and outlet-use ports in conjunction with a displacement rod reciprocating in the chamber. A case is connected to the block and has a reciprocating piston attached to the rod. Air pressure is fed to the case to reciprocate the rod in one direction and from the case to opposite positions on the air powered valves to cause one to open and the other to close to effect dispensing an increment of material to use. Air pressure fed to the case to move the piston and rod in the other direction is also fed to the air powered valves to close the one and open the other to draw in material from supply. An adjusting screw limiting the stroke of the piston renders the apparatus variably adjustable as to the quantity dispensed.

Abstract: A method of injecting a molten material such as molten metal or plasticizing resin under pressure and an apparatus performing the same wherein the piston speed of a cylinder for injecting the molten material is made to decrease before the mold cavity is filled up to the full with the molten material, thereby peak pressure generated in the molten material filled up to the full being eliminated and further pressure vibration occurred in a pressurized oil being obviated.

Abstract: A spool-type valve system for use with a high-speed filling machine, in which a solenoid valve controlled by the main shaft of the filling machine, selectively supplies air under pressure to a respective end of a pneumatically operated piston-cylinder unit of a spool valve assembly which selectively opens and closes the pump space with respect to the reservoir for the product to be filled while simultaneously closing and opening the pump space with respect to the discharge nozzle.

Abstract: An injection molding machine comprising an injection cylinder; a displacement element axially disposed in the injection cylinder; one of the cylinder and displacement element being movable with respect to the other; an injection nozzle on one end of the injection cylinder and a feed device including a feed hopper and a plunger reciprocally mounted in the hopper on the other end of the cylinder; a pressure source for driving the plunger; and switches for varying the working position of the plunger, the plunger stroke, the stroke frequency of the plunger and the pressure of the pressure medium.

Abstract: In a batcher plant at least one pair of reciprocable pressure cylinders are provided one of which as a first pressure cylinder is connected to a source of pressure medium while the other one as a further pressure cylinder is supplied with pressure medium in dependence on the number of strokes per minute of the first pressure cylinder. Both pressure cylinders drive delivery pumps. The total amount of delivered material is controlled by the speed and the number of cycles of the piston of the first pressure cylinder while the mutual proportions of delivered material are controlled by varying the length of stroke of the further pressure cylinder. Thus, on the one hand, mutual proportions of delivered substances can be finely adjusted within very wide limits and, on the other hand, the pressure cylinders of the various batcher units may be located in considerable distances from one another so that the plant is suitable to perform the most various functions.

Abstract: A stuffing pump for handling a food product having a helical gear metering pump with means for removing air from the material moving through the metering pump and a feed conveyor in a hopper continuously feeding material to the metering pump. The feed conveyer includes a pair of counter-rotating augers in the bottom of the hopper. Independent and infinitely variable drive mechanisms are provided for the metering pump and the feed conveyer.

Abstract: Liquids and semiliquids, such as thixotropic gels, oil and greases, are delivered to a discharge means according to a method and through the use of an apparatus powered by hydraulic fluid under pressure which is controlled by a valve for passage to a hydraulic motor that is, in turn, coupled to a pump used to withdraw and pressurize the material for delivery by a conduit line to the discharge means having a discharge orifice that is either nonclosable or synchronously opened. The material is discharged by controlled pressurization which is initiated and terminated by controlling the flow of hydraulic fluid to the hydraulic motor in response to actuation of a trigger or switch on the discharge means. A discharge gun and a lubricator collar are two preferred forms of the discharge means.

Abstract: Apparatus for tempering drilling mud preparatory to testing the mud for petroleum content comprising a plurality of cylinders with heat-sinks about their exteriors, resistance heaters in the heat-sinks and temperature control means related to the heaters and heat-sinks, pistons engaged in the cylinders and shiftable longitudinally therein to draw mud into and drive mud out of the cylinders, valve controlled flow means connected with and between the cylinders and upstream and downstream sections of a mud conducting flow line and operable to conduct mud from the upstream section into the cylinders and from the cylinders to the downstream sections and operable by pressure differentials in the cylinders resulting from the movement of the pistons therein, drive means to move the pistons and means controlling operation of the drive means and responsive to the temperature of mud in the cylinders, the pistons operate to wipe and displace mud caked on the walls of the cylinders to be recombined with fluid mud, whereby

Abstract: In a die cast machine of the type wherein the piston of an injection cylinder is advanced by pressure gas admitted into the rear chamber of the cylinder while discharging pressurized liquid in the fore chamber, and the piston is retracted by pressurized liquid admitted into the fore chamber while forcing the gas in the rear chamber back into a gas accumulator, a control valve device is provided in the path of the pressurized liquid discharged from the fore chamber, and the control valve device is controlled so as to vary the flow quantity of the discharged pressurized liquid in accordance with the position of the piston during its forward movement. There are also provided two gas accumulators which are connected to the rear chamber of the cylinder through a valve device which is controlled so as to adjust the rate of increase of the pressure applied to the molten metal at the final stage of the injection casting operation.

Abstract: An injection-molding machine has a drive ram with a pressurizable chamber that can be connected either to the high-pressure side or the low-pressure side of a source of fluid under pressure. A control system operating this machine has a pressure-reducing valve with an inlet port connected to the high-pressure side of the source, an outlet port connected through a cut-off valve and a throttle to the chamber of the ram, and a pilot port pressurizable to control the pressure at this outlet port. A pressure-relief valve has an inlet port connected to the pressurizable ram chamber, an outlet port connected to the low-pressure side of the pressure source, and a pilot port pressurizable to control the pressure differential across this pressure-relief valve.

Abstract: A fluid-driven motor comprises a collapsible tube connectable at one end to a source of pressurized fluid, and a pinch-roller engaging the outer surface of the tube and collapsing same at the point of engagement, whereby the pressure within the tube drives the pinch-roller and a mechanical power output device coupled thereto. In the described preferred embodiment, the pinch-roller mounting is a rotary one and supports a plurality of pinch-rollers, the collapsible tube being supported in a semi-circular form so as always to be engageable by at least one of the pinch-rollers.

Abstract: A dispensing apparatus for viscous substances includes a unitary plastic block housing provided with a vertical bore forming a dispensing cylinder and a horizontal three way spool valve operable for controlling a dispensing piston located in the aforementioned dispensing cylinder. The dispensing piston is attached to a shaft extending centrally upwardly of the dispensing cylinder and is adjustable for controlling the stroke of the dispensing piston and thereby the quantity of material dispensed. A common source of air pressure is applied to the minor area on the shaft side of the dispensing piston as well as to the material to be dispensed. The material under pressure is normally applied to the major side of the dispensing piston via the spool valve. When the spool valve is operated the supply of material is cut off and the dispensing cylinder is connected to an exit port, whereby the air pressure behind the dispensing piston is sufficient to force a predetermined quantity of material through the exit port.

Abstract: Disclosed is a device which permits a plurality of fluids to be received in a mixing chamber simultaneously through nozzles from fluid input chambers. Actuation of a fluid cylinder opens valves so that the fluids are received under pressure in the input chambers. A second fluid cylinder then opens the mixing chamber so that the nozzles emit both fluids simultaneously which mix by impingement and thereafter are dispensed from the mixing chamber. When the valves are closed recirculation is accomplished through a plurality of ports, thereby allowing the fluids to remain at desirable temperatures and viscosity.

Abstract: Apparatus for producing a fog/spray as a coating medium for articles. The apparatus comprises a trigger actuated gun having an inlet connected to a source of hydraulically pressurized spray fluid, wherein the pressurizing medium and drive source is itself driven by a compressible fluid such as air. The compressible fluid supply line to the drive source has mounted therein a flow sensing valve which actuates an air valve for controlling atomizing air supply to the applicator gun. The atomizing air supply to the applicator gun is coupled into a gun chamber downstream of the spray orifice so that fluid sprayed through the orifice becomes fogged by the pressurized air in the chamber.

Abstract: Dispensing apparatus for semi-fluid material includes a housing having a vertical bore and a second bore connecting with this vertical bore. A piston is slidably mounted within said second bore and is movable between a first position spaced from the vertical bore and a second position adjacent to the vertical bore. Fluid pressure is applied through a first channel to a first piston surface to cause the piston to move from a first to the second position. Fluid pressure is applied through a second channel to a second piston surface to cause the piston to move back to the first position from the second position. An input aperture connects the vertical bore in the housing to an interconnecting array of branching channels which are in turn connected through a plurality of apertures to dispensing members. The channels in this array are configured such that the pressure drop between the input aperture to the array and the inputs of each of the dispensing members is equal.

Abstract: A beverage dispensing system which will deliver a precise, pre-set quantity of a selected beverage at each actuation. The system is operated by low pressure gas from a quickly replaceable source, and utilizes a controlled stroke piston pump which is driven and returned by the pressurized gas. All the valves for automatic operation of the punp are contained in the compact pump housing, but the gas and liquid sections are completely isolated to avoid contamination. The pump and valve unit contains a minimum of parts, all of which are readily accessible for cleaning and servicing. An automatic count of operations is maintained and the system shuts off when the liquid level is too low for a full serving.

Abstract: An apparatus for melting and dispensing thermoplastic material comprising a hopper, a grid melter, a reservoir and a pump. At least a portion of the hopper is enclosed within a shroud so as to define an air flow chamber around the lower end of the hopper. Air is forced through this chamber when the apparatus is in use so as to cool the hopper and prevent molten material from backing up into the hopper.

Abstract: An air-powered gun adapted to be loaded with a plastic material such as a caulking compound from a bulk container thereof, and to dispense the same through a nozzle wherein the gun is comprised of a forward loading and dispensing barrel and an oppositely extending coaxial piston-driving rear air barrel, both of which barrels are held in back-to-back receptacles in a body gripping member provided with a handle. A piston slidable in the forward barrel is connected by a shaft to a piston in the rear barrel, which shaft extends coaxially through an orifice in the body gripping member passing through the bottom of both receptacles. Two plunger valves are provided in the handle, one to direct air into the receptacle for the forward barrel, and the other, to that for the rear barrel. A removable nozzled dispensing cap is provided for the outer end of the forward barrel.

Abstract: A dispenser for flowable material comprising a pump, a dispensing head coupled to the outlet of the pump, a control valve for controlling pump operation, and a manually operable valve carried by the dispensing head for controlling the control valve. The pump includes a rolling diaphragm which is moved on the discharge stroke by fluid under pressure supplied from the control valve and is moved on the intake stroke by a spring. None of the controls for the dispenser are electrical.

Abstract: A thermoplastic material dispensing apparatus adapted to translate feedstock from a solid state to a molten state by a novel heater block structure, and to discharge the molten feedstock through a novel discharge valve in response to operation of a novel trigger device. A novel annular cooling chamber is established about the dispenser's barrel to maintain a solid/melt interface inside the barrel adjacent to the heater block structure, that zone being air cooled by inlet air taken from a single inlet air line. The inlet air from the single line also drives the dispenser's ram through use of a novel pneumatic motor/spool valve mechanism. The spool valve is manually stroked forward to extend the dispenser's ram for extruding the feedstock, and is manually stroked rearward to retract the ram for recharging.

Abstract: An improved fluid-operated dispensing apparatus for use in receiving, processing, and applying rods of hot-melt adhesive. Important characteristics of the apparatus include an air-cooling means adapted to operate when the dispensing function is not being operated, and a means for gripping the adhesive rod to assure a uniform advance through the apparatus to the heating zone. Moreover, the use of a drive piston assembly, which is annular with respect to the rod being processed, enables the manufacture of an unusually compact tool.

Abstract: A fluid dispensing system for accurately dispensing precise aliquots of fluid rapidly and efficiently. The system includes a reservoir of fluid and a pump adapted for connection to a reservoir of fluid and for transferring precise aliquots of fluid from the reservoir to an outlet orifice. An inlet tube is provided with a bore therethrough and one open end for fluid communication with a reservoir and the other open end in fluid communication with the pump. An outlet tube is provided having a bore therethrough with one open end forming the outlet orifice for the system and the other open end in fluid communication with the pump. Controls are connected to the pump to precisely regulate the amount of fluid in an aliquot transferred from a reservoir through the inlet tube, pump and outlet tube to the outlet orifice during an operating cycle of the pump.

Abstract: Apparatus for metering a predetermined timed volume of fluidic material through a dispensing circuit upon activation of a trigger, where the trigger actuates an air valve which is connected to a second time-controlled air valve. The second air valve delivers a predetermined timed shot of pressurized air to an air cylinder which is mechanically coupled to the fluidic material dispensing circuit.

Abstract: An applicator by which small, discrete, uniform quantities of molten thermoplastic adhesive can be dispensed in rapid succession comprises a body having a heated inlet chamber, which hot melt enters under low pressure, and a pump chamber. A plunger in the pump chamber is reciprocated by a pneumatic motor. A charging stroke of the plunger draws hot melt out of the inlet chamber, across a check valve and into the pump chamber. The discharging stroke expels the hot melt across an outlet check valve and through an outlet orifice coaxial with the pump chamber.

Abstract: Apparatus for spraying a predetermined amount of paint, especially electroconductive paint as used for coating metal anodes, which comprises in combination an electrostatic spray gun and a paint delivery device for the gun which operates on a single displacement diaphragm principle.

Abstract: A method of and apparatus for injection molding of materials such, for example, as thermoplastic resinous material, utilizing a rotatable and reciprocal screw extruder for plasticizing and injecting the material into a mold cavity, and wherein an injection piston in a cylinder is operatively connected to the plasticizing screw to push the screw forward to effect injection into a mold of plasticized material in front of the screw. A supply of fluid pressure is positively applied to the injection piston to provide a back pressure to act against the reaction caused by the rotation of the plasticizing screw, and this back pressure may be regulated to correspond with the rearward displacement, of the screw.