GB2057587A - Method and apparatus for the transfer of viscous liquids and liquid slurries - Google Patents

Abstract

A double-acting hydraulic cylinder 41 is used as a flow limiting device for a transfer barrier 11 and also as a position indicator. The invention has particular application to the metering of abrasive liquid slurries in the making of fibre filled polyurethanes. Slurry is pumped from a pressurised reservoir 29 via the transfer barrier 11 to apparatus 27, e.g. a viscometer, manually actuated valves 23, 25 controlling connection between the transfer barrier housing 15 and the apparatus 27 and reservoir 29 respectively. <IMAGE>

Description

SPECIFICATION Method and apparatus for the transfer of viscous liquids and liquid slurries This invention relates to the transfer of viscous liquids and liquid slurries.

It is known to pump liquids using a 'transfer barrier' in which a benign fluid, such as a hydraulic oil, is used to pressurise and expel a difficult fluid, the two fluids being separated by an expansible membrane. The attraction of this type of pump is that it has no sliding parts and the membrane being under no load, is potentially long wearing.

However damage can be caused to the membrane if excessive pressurising fluid is supplied and the membrane is ruptured by being forced down an outlet port.

According to the present invention we provide a method for the transfer of a viscous liquid or liquid slurry feedstock using a transfer barrier in which an expansible membrane divides a housing into a liquid feedstock chamber and a fluid receiving chamber, the method comprising filling the liquid feedstock chamber with a viscous liquid or liquid slurry feedstock and pumping a fluid, such as a hydraulic oil, into the fluid receiving chamber to expand the membrane thereby expelling feedstock from the feedstock chamber and transferring it to connected apparatus to which the feedstock is to be supplied, the volume of fluid pumped to the receiving chamber being controlled by means external of the transfer barrier and being not greater than the volume of the transfer barrier housing.

The method of the invention may be used for pumping any viscous liquid or liquid slurry feedstock but of particular interest to us is the pumping of polyurethane components, especially fibre-filled polyols. It is an advantage of this invention that the method can be used for pumping highly abrasive fibre-filled polyols at high pressures eliminating the need for pressure-tight sliding components which form part of the pumps hitherto used for this purpose.

In a further aspect of our invention we provide apparatus for the transfer of a viscous liquid or liquid slurry feedstock, the apparatus comprising a transfer barrier in which an expansible membrane divides a housing into a liquid feedstock chamber and a fluid pumping chamber, the liquid feedstock chamber being provided with a delivery port connectable to apparatus to which liquid feedstock is to be supplied; and, connected to the fluid pumping chamber, a hydraulic cylinder swept by a piston for propelling fluid to the fluid pumping chamber which piston is drivable by fluid supplied from a fluid metering device, the swept volume of the cylinder being not greater than the volume of the transfer barrier housing.

Advantageously the piston can be used to indicate the stage of operation of the transfer barrier. Thus in a preferred embodiment of our invention a piston rod attached to one side of the piston extends through the cylinder in fluid-tight manner, the externally projecting part of the rod providing means for indicating the position of the piston in the cylinder and hence the stage of operation of the transfer barrier. The projecting end of the rod may itself be the indicator means or an indicator, e.g. a pointer, may be attached to the projecting part of the rod and be used in conjunction with a scale.

Conveniently the projecting piston rod can be used to actuate a switch, for instance by means of a fitted cam, to halt the supply of hydraulic fluid to the hydraulic cylinder from the metering device.

It is a particular advantage in having a piston rod attached to the piston that the hydraulic cylinder acts as a pressure converter. Thus if the rod extends from that end of the cylinder to which the transfer barrier is connected, because of the different effective areas of the piston faces, the pressure of the hydraulic fluid supplied by the metering device will be intensified on transmission by the piston to the transfer barrier. Thus by appropriate dimensioning of the piston considerably higher pressures can be generated than the pressures delivered by commercially available pumps used in the metering device. It is a consequence, of course, that the flow rate will be reduced. Conversely, by reversing the cylinder the flow rate can be increased but at the expense of a reduced delivery pressure.The ability to reverse the cylinder adds to the flexibility of operation of the apparatus of this invention.

Currently, there is considerable interest in the use of glass-fibre reinforcement in polyurethane foam products of high modulus and consequently in transferring and mixing at high pressure fibrefilled polyols with high fibre loadings. The apparatus of the present invention provides a means of metering fibre filled polyols to high pressure polyurethane mixing guns of the type well known to those skilled in this field. In addition, there is a need for fundamental work to be done on the flow properties of these fibre-filled materials at the rates of shear likely to be experienced in practical production machines and processes. No viscometry equipment presently exists which is capable of handling these materials at these shear rates.It is therefore a further advantage of the apparatus of this invention that it can be used to supply a viscometer to carry out the desired measurements on the materials.

To further illustrate the invention, one embodiment of it will be described, by way of example only, with reference to the accompanying drawing which is a diagrammatic cross-section through pumping apparatus of the invention being used in conjunction with a feedstock reservoir to supply a viscometer.

In the drawing a 4 1. capacity transfer barrier 11 comprises an expansible membrane 13, shown both in an inflated state (solid line) and in a deflated state (broken line), which divides a housing 1 5 into a liquid feedstock chamber 17 and a fluid pumping chamber 1 9. A delivery port 21 is connected through manually operated 50 mm diameter ball valves 23 and 25 to a viscometer 27 and a 40 1. feedstock reservoir 29.

The valves have chrome-plated, hardened steel balls with nylon seats and are operated only under low pressure conditions. The reservoir 29 is fitted with a stirrer 31 driven by a motor 33 and has a compressed air inlet 34, a pressure gauge 35 and a closable charge-hole 37. The fluid pumping chamber 19, which is fitted with a pressure gauge 39, is connected via port 20 to a 3.6 1. capacity double-acting hydraulic cylinder 41. The cylinder is swept by a piston 43 having attached thereto a poston rod 45 which extends through a fluid-tight seal 47 in the upper end of the cylinder. The lower end of the cylinder is connected to a metering unit (not shown) for pumping hydraulic oil to the cylinder in the direction 'A'. The maximum output of the metering unit 41 1. per minute at 270 bar and this gives a maximum output of 37 1. per minute at 300 bar from the upper end of the hydraulic cylinder.A cam 49 attached to the piston rod 45 co-operates with a microswitch 51 which controls a let down valve in the metering unit. A bleed valve 53 is located at the upper end of the cylinder.

The operation of the apparatus is next described, by way of example, for pumping a fibrefilled polyol to a viscometer but it will be understood that it can be used in a similar manner for pumping other liquid feedstock and for supplying, for instance, a polyurethane mixing head instead of a viscometer.

The reservoir 29 is charged with a fibre-filled polyol through charge-hole 37 and the stirrer 31 started to keep the suspended fibre evenly dispersed. The reservoir is pressurised to 10 bar with air introduced through an inlet 34. The pressure is monitored using pressure gauge 35.

The fluid pumping chamber 19 is filled with hydraulic oil as also is the cylinder 41 on both sides of the piston 43. Any entrapped air is bled from between the piston and fluid pumping chamber through bleed hole 53. Similarly air entrapped between the cylinder and metering unit is bled away by means not shown.

To fill the transfer barrier, the ball valve 25 is opened and the ball valve 23 to the viscometer 27 closed. Fibre-filled polyol flows from the reservoir under pressure through the ball valve 25 and into the liquid feedstock chamber 17, collapsing the membrane 13 and forcing hydraulic oil out of the fluid pumping chamber 19. The membrane at this stage assumes an appearance notdissimilarfrom that indicated by the broken line. The oil forced from the fluid pumping chamber causes the piston 43 to descend in the cylinder 41 forcing hydraulic oil to return to a metering unit tank (not shown).

The quantity of oil trapped in the fluid pumping chamber is such that the piston reaches the bottom of its travel before the membrane is damaged by being forced into the connecting port 20. When the liquid feedstock chamber 1 7 is full the valve to the reservoir is closed and that to the viscometer opened.

A metering unit pump (not shown) is started and when a 'dispense' button (not shown) is pressed hydraulic oil passes into the cylinder 41 at a predetermined rate forcing the piston upwards.

This in turn forces oil (at a lower rate because of the effective difference in area of the piston faces) into the fluid pumping chamber and an identical flow of material is thereby pumped from the liquid feedstock chamber into the viscometer. When sufficient oil has passed to nearly empty the polyol from the transfer barrier, the cam on the piston rod actuates the microswitch which, in turn, instantaneously operates the let-down valve to the metering unit dropping the hydraulic pressure to tank pressure and ending the 'shot'.

Calibration of the flow rate of material through the viscometer can be done by calibrating the metering unit. An adjustable valve is provided on the metering unit which allows back pressure on the metering pump to be adjusted so that the timed calibration shots can be carried out under the same pressure loading conditions as those attained during the 'shot' through the viscometer.

The measured flow rates are then scaled to allow for the differential area effect of the piston.

Leakage past the piston will be negligible since the differential pressure across the piston in this particular embodiment is small.

Claims (6)

1. A method for the transfer of a viscous liquid or liquid slurry feedstock using a transfer barrier in which an expansible membrane divides a housing into a liquid feedstock chamber and a fluid receiving chamber, the method comprising filling the liquid feedstock chamber with a viscous liquid or liquid slurry feedstock and pumping a fluid, such as a hydraulic oil, into the fluid receiving chamber to expand the membrane thereby expelling feedstock from the feedstock chamber and transferring it to connected apparatus to which the feedstock is to be supplied, the volume of fluid pumped to the receiving chamber being controlled by means external of the transfer barrier and being not greater than the volume of the transfer barrier housing.

2. A method as claimed in claim 1 in which the liquid slurry feedstock is a fibre-filled polyol.

3. A method as claimed in claim 1 substantially as herein described with reference to the drawings.

4. Apparatus for the transfer of a viscous liquid or liquid slurry feedstock, the apparatus comprising a transfer barrier in which an expansible membrane divides a housing into a liquid feedstock chamber and a fluid pumping chamber, the liquid feedstock chamber being provided with a delivery port connectable to apparatus to which liquid feedstock is to be supplied; and, connected to the fluid pumping chamber, a hydraulic cylinder swept by a piston for propelling fluid to the fluid pumping chamber which piston is drivable by fluid supplied from a fluid metering device, the swept volume of the cylinder being not greater than the volume of the transfer barrier housing.

5. Apparatus as claimed in claim 4 in which a piston rod attached to one side of the piston extends through the cylinder in fluid-tight manner, the externally projecting part of the rod providing means for indicating the position of the piston in - the cylinder and hence the stage of operation of the transfer barrier.

6. Apparatus as claimed in claim 4 substantially as herein described with reference to the drawings.