WO1991010615A1

WO1991010615A1 - Positive displacement device

Info

Publication number: WO1991010615A1
Application number: PCT/GB1991/000047
Authority: WO
Inventors: Alan Harper
Original assignee: Alan Harper
Priority date: 1990-01-12
Filing date: 1991-01-14
Publication date: 1991-07-25
Also published as: GB9000753D0

Abstract

A positive displacement device comprising a pressure vessel (11, 12) characterised in that the pressure vessel (11, 12) contains a pressurisable interior wall (15, 15'); a reservoir (13, 14) within the vessel (11, 12) which serves to define: a driving volume (16, 16') bounded by the interior wall (15, 15') and the pressure vessel (11, 12); and a driven volume (17, 17') within the pressure vessel (11, 12); the reservoir (13, 14) being bounded at least in part by a resilient wall; a pressurising unit (20) for applying fluid pressure to the interior of the driving volume (16, 16'); a supply inlet (25, 25') extending from the outside of the, or each, housing (11, 12) into the driven volume (17, 17') of the reservoir (13, 14); a supply outlet (25, 25') extending from the driven volume (17, 17') of the, or each, reservoir (13, 14) to the outside of the housing (11, 12); an outlet duct (29, 29') extending from the, or each, supply outlet (25, 25') to a mixing device (30); and a flow control unit (20) regulating flow along each the, or each, supply outlet (25, 25').

Description

POSITIVE DISPLACEMENT DEVICE

This invention relates to a positive displacement device. It is particularly intended for a device to be used in pumping one or more streams of hquid material. In this context 'liquid material' is intended to cover both heterogenous hquid materials, such as slurries, as well as homogenous hquid materials . As will hereafter become apparent it is particularly applicable to the pumping of mechanically, chemically or biologically aggressive hquid materials .

According to the present invention there is provided a positive displacement device comprising:

1 at least one pressurisable housing having a pressurisable interior wall;

2 a reservoir within the or each housing which serves to define : a driving volume bounded by the interior wall and the outside of the reservoir; and a driven volume within the reservoir; the, or each, reservoir being bounded at least in part by a resilient wall;

3 a pressurising means for applying fluid pressure to the interior of the, or each, driving volume;

4 a supply inlet extending from the outside of the, or each, housing into the driven volume of the reservoir;

5 a supply outlet extending from the driven volume of the, or each, reservoir to the outside of the housing;

6 an outlet duct extending from the, or each, supply outlet to a mixing device; and

7 flow control means regulating flow along each the, or each, supply outlet.

In a first preferred version of the present invention the supply inlet and outlet are common to a point from the interior of the reservoir to a location outside the housing.

In a second preferred version of the present invention or the first preferred version thereof there is provided a purging duct extending from the outside of each housing to the interior of the reservoir whereby the reservoir can be subjected to a purging or other action independently of the supply inlet. In a third preferred form of the present invention or any preceding preferr version thereof incorporating at least two pressurisable housings the operation of the pressurising means for one driving volume can be made to differ from that for the other, or another, driving volume so that ratio of material fed to the mixing device from one outlet duct relative to that fed to the mixing device from the other, or another, outlet duct can be varied. Typically the pressurising means is a hydraulic system.

An exemplary embodiment of the invention will now be described with reference to the accompanying drawing of which the sole figure is of a production unit for use in the manufacture of fibre reinforced plastics material.

The unit includes two rigid housings 11, 12 incorporating, respectively, reservoirs 13, 14 fabricated from an elastomeric material. Since the corresponding parts of each housing 11, 12 are similar in form and function only those associated with housing 11 are hereafter described in detail. Th corresponding item for housing 12 is identified with a similar reference numeral to that used in the context of housing 11 with the addition of an apostrophe (') .

Reservoir 13 isolates interior wall 15 of the housing 11 from the interior of t reservoir 13 so as to establish a driving volume 16 and a driven volume 17. Being fabricated from resilient material allows for material within driven volume 17 to be pressurised (positively or negatively with respect to ambien atmospheric pressure) by the application of a suitable over or under control pressure of hydraulic hquid in the driving volume 16. This control pressur is fed into interior of housing 11 to the driving volume 16 by way of a contr duct 18 from a pressure cylinder 19 in a hydraulic pumping unit 20.

The pumping unit 20 is powered by a pump 21 and variable linkage 22 whereby the pressure generated in pressure cylinder 19, and fed by way of control duct 18 into driving volume 16. A control arrangement for the unit and the variable linkage enables the pressure in the driven volume 17 to be varied relative to the pressure in driven volume 17' . Pumping unit 20 incorporates a hydraulic reservoir 23 coupled to the remainder of the unit 2 by duct 24. The reservoir is of sufficient size to ensure that sufficient hydraulic fluid is available to deal with the full capacity of the housings 11, 12.

Supply inlet 25 extends from T-junction 26 into the interior of driven volume 17. The T-junction 26 is also coupled by way of: pipe 27 to a source of hqui material to be transferred by way of the production unit (flow being regulated by way of valve 28) ; and flexible line 29 extending to a dispensing outlet which in this case is a mixing nozzle 30.

Mixing nozzle 30 enables components for a catalysed mixture of resin to be individually dispensed from the driven volumes 17, 17', mixed and injected into a mould into which fibre reinforcement has already been located. Once polymerisation has occurred the mould is opened and the moulded component removed. The mixing nozzle can equally well be used to dispense resin into mould having no fibre reinforcement in it when it is required to produce an un-reinforced product.

The upper part of the housing 11 has a vent valve 31 located in it to provide for the complete venting of the housing should it be required. There is also provided in the upper part of the housing a purge duct 32 whereby the reservoir 13 can be purged.

In operation the hydraulic system made up of driving volumes 16, 16', contr ducts 18, 18' and working chambers of unit 20 are rendered hydrau cally tight with the removal of any air entrapped within the cylinders, ducting, pump and reservoir system. Each driven volume 17, 17' is filled with the appropriate stream of hquid resin mixture components by opening the valve 28, 28' and applying a sub-atmospheric pressure to the driving volumes 16, 16' by way of control ducts 18, 18' so withdrawing hydraulic fluid from driving volumes 16, 16' so causing reservoir 13, 14 to expand to draw in the resin mixture.

The hydraulic pump unit 20 serves two purposes. Firstly to draw hydraulic fluid from the cyhnders so as to create reduced pressure in the driving volumes 16, 16' . Secondly to provide for the controlled pressurisation of th driving volumes 16, 16' so as to provide for the accurate displacement of the contents of the reservoirs 13, 14.

It can be seen that the ratio of the flow of hydraulic fluid along ducts 18, 18' can be proportioned to provide for the appropriate ratio of subsequent hquid flows by way of ducts 29, 29' to the mixing nozzle 30 and so to a mould fed by way of the nozzle . Valves S allow for a further proportioning or regulation where necessary.

The embodiment has a number of advantages over known single or double acting positive displacement pumps or other mechanical positive displacement pumps. In particular it provides for the metering/ pumping of problematic hquid material. Such materials include abrasive slurries and chemically activ materials (such as those which are oxidizable, corrosive, inflammable or contaminatable) .

The embodiment could be adapted to make use of a replaceable reservoir, rather than a permanently mounted one. This could be particularly advantageous when dealing with a noxious material since an operative would not need to contact the contained material or be subject to emissions from it. Once emptied by use of the driving volume as described earlier the replaceable reservoir would be removed for re-charging and replaced by a freshly charged reservoir or with a permanent reservoir when a less problematic material is to be used in the production process.

Typically the embodiment avoids restrictions common to conventional pumps such as arise from moving parts and dynamic seals in contact with the pumpe medium. Hydraulic fluid is used to convey the metering linkage from the mechanical drives and acts to 'squeeze' the pumped medium within the bladders in the desired proportions . There is little chance of bursting a reservoir such as reservoir 13, 14 as the whole system is designed to be hydrauhcally tight and therefore equal pressures would exist on either side of the reservoir walls.

The embodiment is concerned with the metering of resin components. In the resin transfer moulding industry matrix materials used incorporate fillers an can have very high viscosities. In addition their chemistry requires the application of special non-corrosive pump systems. The present embodiment also serves for handling adhesive materials .

The embodiment makes use of two relatively large capacity reservoirs with sufficient capacity to provide sufficient working material for several production runs without refilling. In an alternative embodiment use can be made of a set of relatively small capacity reservoirs to provide a continuous for by reciprocating the reservoirs in turn between input and output of the hquid materials.

Vent valves 31, 31' enable the reservoirs to be de-gassed. This has been found to be a distinct advantage in an earher unit developed by the present applicant and marketed under the trade mark HYPAJECT (Registered Trade Mark) .

Liquid having been loaded into the reservoirs can be placed under a sub- atmospheric pressure. Thus by withdrawing hydraulic fluid in the driving volumes or still maintaining at least 95% vacuum in the hydraulic system a 90% vacuum to be maintained by way of vent valves 31, 31' . A further advantage of vent 31, 31' is that where necessary it will enable the pump internals to be readily purged with an inert gas to eliminate oxygen from the system.

The described embodiment makes use of a hydraulic system to develop pressure within driving volumes 16 to pressurise driven volume 17. As an alternative other fluids including gases or vapours, or a combination of them, may be used such as gas or vapour can be used to transmit the driving pressure.

Since the driving volume envelops the driven volume the fluid used for driving can also be used as a heat transfer or heat insulating material for establishing an effective operating temperature for material contained in the or each driven volume. The driving material can be circulated through a heat exchange device to ensure that during the residence time of the driving fluid in the driving volume the material to be expelled from the driven volume is enclosed within a fluid bulk at an appropriate temperature. As shown in the figure this bulk extends around the upper and lower parts of the container. It will be appreciated that the temperature of the bulk material in the driving volume can be above or below ambient atmospheric temperature. Typically the temperature could be one tending to inhibit polymerisation in the material in the driven volume. A heat exchange device could be located outside the pressurised housing or incorporated in the housing (or devices could be provided in both locations) to regulate the temperature of the bulk driving fluid to optimise the temperature of the driven material.

Claims

A positive displacement device comprising at least one pressurisable housing having a pressurisable interior wall characterised by:

1 a reservoir (13, 14) within the or each housing (11, 12) which serves to define : a driving volume (16, 16') bounded by the interior wall (15,

15') and the outside of the reservoir (13, 14) ; and a driven volume (17, 17') within the reservoir (13, 14) ; the, or each, reservoir (13, 14) being bounded at least in part by a resilient wall;

2 a pressurising unit (20) for applying fluid pressure to the interior of the, or each, driving volume (16, 16') ;

3 a supply inlet (25, 25') extending from the outside of the, or each, housing (11, 12) into the driven volume (17 , 17') of the reservoir (13, 14);

4 a supply outlet (25, 25') extending from the driven volume (17, 17') of the, or each, reservoir (13, 14) to the outside of the housing (11, 12) ;

5 an outlet duct (29, 29') extending from the, or each, supply outlet (25, 25') to a mixing device (30) ; and

6 a flow controller (S) regulating flow along each the, or each, supply outlet (29, 29') .

A positive displacement device as claimed in Claim 1 characterised in that the supply inlet (25 , 25') and outlet (25, 25') are common to a point from the interior of the reservoir (13, 14) to a location outside the housing (11, 12) .

A positive displacement device as claimed in Claim 1 or Claim 2 characterised by a purging duct (32, 32') extending from the outside of each housing (11, 12) to the interior of the reservoir (13 , 14) whereby the reservoir (13, 14) can be subjected to a purging or other action independently of the supply inlet (25, 25') .

A positive displacement device as claimed in any preceding claim characterised by at least two pressurisable hnkages (18, 18' , 22, 22') such that the of the pressurising of one driving volume (16) can be ma to differ from that for the other (16') , or another, driving volume so that ratio of material fed to the mixing device (30) from one outlet duct (29) relative to that fed to the mixing device (30) from the other , or another, outlet duct (29') can be varied.

A positive displacement device as claimed in any preceding claim characterised in that the pressurising unit (20) regulates a hydrauhc system. ^'