GB2215491A

GB2215491A - Pump apparatus for discharging liquid

Info

Publication number: GB2215491A
Application number: GB8901583A
Authority: GB
Inventors: John Fletcher
Original assignee: Drum Engineering Co Ltd
Current assignee: Gardner Denver UK Ltd
Priority date: 1988-01-29
Filing date: 1989-01-25
Publication date: 1989-09-20
Also published as: FR2627549A1; GB8802022D0; GB8901583D0

Abstract

Pump apparatus for selectively discharging liquid from a container tank (26) comprises a pump (34) operated by a hydraulic drive means (42) which is controlled by a second hydraulic drive means (44). The drive means (44) is automatically adjusted in response to variations in flow of liquid discharged by the pump along a hose (38). The flow is sensed by a valve (48) arranged to control the connection of the control line (50) to a section line (53), the pressure in the control line (50) serving to adjust the drive means (44), the latter being directly coupled to the power-take-off (46) of the vehicle gear-box. <IMAGE>

Description

DESCRIPTION IMPROVEMENTS IN AND RELATING TO PUMP APPARATUS FOR DISCHARGING LIQUID The present invention relates to pump apparatus for discharging liquid and in particular, but not exclusively, to pump apparatus for discharging liquid from transport tankers.

Transport tankers such as road tankers which are engaged in the transport and delivery of liquids, may be required to either discharge their full liquid load into a bulk storage vessel or to discharge part of their liquid load into a small storage vessel. Some road tankers, typically those used by authorised distributors, are required to carry out both duties mentioned hereinbefore and also satisfy national weights and measures requirements for the quantities of liquid delivered.

At present, vehicles have a pumping system which generally comprises a cargo pump of the fixed displacement type fitted with a relief valve usually set at 7 bar. The cargo pump is normally driven from a power-take-off unit attached to the vehicle gearbox.

Liquid product is thus pumped from a container tank via the cargo pump and is then pumped through a 3-way valve to either a bulk outlet or a hose outlet depending on the storage vessel being supplied.

The bulk outlet is used for deliveries to large storage vessels which, due to the inherently low pipework resistance may be supplied at a high flow rate of about 800 litres/minute. The total quantity delivered is then checked using a calibrated dipstick, dr the like, to measure the liquid product level remaining in the vehicle container tank.

When the cargo pump is supplying smaller or domestic type storage vessels, the liquid is delivered by way of a hose reel via a liquid quantity meter. The maximum allowable working pressure of hose reel and meter is about 7 bar and any over pressurisation therein is prevented by the operation of the cargo pump relief valve. As a result of this pressure limitation and the greater combined restriction of the hose and meter, the rate of flow is lower than for bulk liquid delivery and is in the order of 300 litres/ minute.

Several disadvantages are associated with the current pump discharge apparatus which commonly arise from the requirement for manual adjustment of the vehicle engine speed so as to the cater for the different liquid flow recuirements of bulk and hose reel delivery.

Typically, when the cargo pump is in operation and neither outlet is open, the relief valve associated with the cargo pump operates in a full bypass mode in which the total pump flow is diverted to the suction side of the pump. This may result in the cargo pump becoming overheated and also suffering excessive wear and damage.

Also, when the pump apparatus is required to deliver liquid quantities via the hose reel, the operator, who is commonly the vehicle driver, may experience difficulty in judging how fast to run the vehicle engine. Excessive speed causes the cargo pump relief valve to open due to the liquid pressure therein reaching its limit value of about 7 bar. With the relief valve in this partial bypass mode, a reduction in liquid pressure results due to the two stage action of the relief valve. This results in a reduction in the rate of flow of the liquid through the meter along with a corresponding increase in delivery time for a given liquid quantity. Damage to the cargo pump and relief valve may also occur as a result of rapid fluctuations in liquid pressure and overspeeding of the pump.

A disadvantageous effect similar to those described hereinbefore results on completion of a metered liquid delivery when an automatic shut off control of the meter causes the cargo pump relief valve to switch into full bypass mode in which the total liquid flow is directed back to the suction side of the cargo pump. The driver/operator then has to take prompt action and slow the engine or disengage the powertake-off in order to prevent the pump becoming overheated and damaged. Such overheating and damage may also occur when the shut off valve, referred to as a trigger nozzle, is closed in the event of overfilling the storage vessel. Since the driver is often some distance from the vehicle there is some delay in reducing the engine speed which delay may increase the likelihood of this overheating and damage occurring.The trigger nozzle is also often maintained in a partially open state, particularly when storage vessels are being "topped up" and a reduced liquid flow rate is required.

Again, this causes the cargo pump relief valve to remain on bypass so contributing to excessive wear and damage of the cargo pump. Also, opening and closing of the nozzle results in "kicks" occurring in the length of hose.

It would therefore be advantageous if pump apparatus could be provided which reduces or even excludes the various inherent disadvantages outlined hereinbefore. In particular, it would be advantageous if the available liquid product flow rate on metered or bulk delivery could be maximised and also if the pump could operate in an "unloaded" condition when not delivering liquid product.

It would be further advantageous if the apparatus could also protect against overspeeding and also make fine manual adjustment of the engine unnecessary, thus making control independent of the operator.

In accordance with one aspect of the present invention there is provided pump apparatus for discharging liquid from a container tank via a pump as required, wherein the operation of the pump is adjusted in response to variation in pressure of the liquid therein, whereby the pressure of the liquid is returned to a predetermined value.

In accordance with another aspect of the present invention there is provided pump apparatus for discharging liquid from a container tank via a cargo pump as required comprising a first driving means for driving the cargo pump, a second driving means for driving the first driving means, the effective driving force of the second driving means on the first driving means being automatically adjusted in response to variation in pressure of the liquid in the cargo pump.

Preferably, the second driving means is activated by a detecting means in response to liquid flow from the cargo pump and advantageously this detecting means comprises a flow sensing valve.

Preferably, the first and second driving means are hydraulically activated and also advantageously driven hydraulically. As such the first driving means comprises a hydraulic motor and the second driving means comprises a hydraulic pump which is preferably a variable displacement pressure compensated hydraulic pump.

Advantageously, the second means is driven directly by a motor =r engine and preferably by a power-take-off from a vesicle gearbox.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic representation of known pump discharge apparatus employed in a vehicle; Fig. 2 is a schematic representation of one embodiment f pump discharge apparatus emplcyed a vehicle in accordance with the present invention; Fig. 3 is a schematic representation of the hydraulic circuit of the pump discharge apparatus of Fig. 2; Fig. 4 is a cross-section through the flow sensing valve of the pump discharge apparatus of Fig. 2; and Fig. 5 is a cross-section through the bulk shut off valve of the pump discharge apparatus of Fig. 2; Fig. 6 is a section through one embodiment of a pump; Fig. 7 illustrates diagrammatically the two-speed operation of the motor; and Fig. 8 illustrates diagrammatically the construction of the pump.

The known pump discharge apparatus of Fig. 1 comprises a tank compartment 10 connected with a cargo pump 16 by way of a foot valve 12 and flow pipe 14 having a filter 15. Liquid product is pumped by the cargo pump out of either of bulk outlet 18 or a hose outlet 20 via a meter 24. A three-way valve 22 determines which of the outlets is in use at any one time. The cargo pump is driven by a power-take-off 19 from the vehicle gearbox. The cargo pump is also provided with a relief valve 17.

As mentioned hereinbefore, particular problems are associated with this apparatus since once the delivery pressure of the liquid product in the cargo pump 16 reaches a nominal value, for example in the region of 7 bar, the relief valve 17 starts to operate and liquid product is directed back to the suction side of the cargo pump 16. The rate of delivery via the meter 24 is then reduced and also the cargo pump 16 may start to overrun, particularly if the manual operator decides to try to rectify the situation by increasing the vehicle engine speed and thus the power provided by the power take-off.

Apparatus in accordance with the invention, as shown in Fig. 2, also comprises a tank compartment 26, foot valve 28, filter 32, hose outlet 38 and meter 40.

However, the cargo pump 34 is not provided with a relief valve. The cargo pump is driven by a hydraulic motor 42 which in turn is driven, via a hydraulic line 56, by a hydraulic pump 44 which is directly coupled to the power-take-off 46 of the vehicle gearbox. The hydraulic pump 44 is a variable displacement pressure compensated type. The output of the cargo pump 34 provided for the hose outlet 38 includes a flow sensing valve 48 which is activated by the flow of liquid product therethrough.

A hydraulic control line 50, for controlling operation of the hydraulic pump 44 passes from a hydraulic tank 52, via the hydraulic pump 44 and then v-a the flow sensing valve 48 back to the hydraulic tark 52 by way of a tank return line 53 and oil cooler 55. The hydraulic motor 42 is of a type with two selectable displacements so that, when the cargo pump 34 delivers liquid via a bulk outlet shut off valve 36, it may run at 1.Sxits normal speed, but with 2/3 the output torque, as on hose outlet delivery. The mode of operation of the hydraulic motor 42 is switched by way of a hydraul selector valve 51 (Fig. 3).

In operation, the hydraulic pump 44 is unloaded to supply a low pressure when the control line 50 is connected, by the flow sensing valve 48, to the tank return line 53. This corresponds to the flow sensing valve 48 being in a closed position. With the hydrauli pump 44 in an unloaded condition the hydraulic motor 42 generates a low torque and drives the cargo pump very slowly. In this mode of operation, the cargo pump produces a liquid product pressure of about 1.5 bar.

When it is required to dispense liquid product via the hose outlet 38, the meter 40 is activated and liquid starts to flow through the flow sensing valve, lifting the valve head 58 from its seat 59 (Fig. 4). This action results in the control line 50 becoming closed at the flow sensing valve, which in turn brings the hydraulic pump to its full load operating condition providing about 180 bar hydraulic pressure in the hydraulic line 56. This hydraulic pressure is limited to about 180 bar by a control valve fitted to the hydraulic pump 44.

The construction of the pump 44 enabling the aforegoing action is shown in more detail in Figure 8 wherein line 100 is connected to the flow sensing valve 48 (corresponding to line 50 of Fig.2) and line 102 is connected to the hydraulic motor 42 (corresponding to line 56 of Fig.2). Numeral 104 denotes a de-stroking piston. When the line 100 is connected to tank via the flow sensing valve 48, pump pressure is limited to 40 bar. When the line 48 is closed by the flow sensing valve 48, pressure acts on the right-hand (spring) side of a stand-by pressure valve P1 (e.g. 40 bar) and prevents it opening. This allows the working pressure to rise to the setting of a maximum pressure valve P2 (e.g. 180 bar).In either condition, pressure acts of the de-stroking piston 104 in a direction to reduce the swash angle.

A typical construction for the pump 44 (and also the motor 42) is shown in Fig.6 which includes a swash plate 106, a piston 108, a slipper pad 110, a cylinder block 112, a control valve module 114 (pump only) and a de-stroking piston 116 fed from the control valve module 114. The swash plate 106 is spring-loaded towards a maximum flow position and is de-stroked automatically when the control valve pressure setting is reached. The pump 44 therefore drives the hydraulic motor 42 at whatever speed is necessary to induce a working pressure equal to the setting of the control valve, that is, a constant torque drive is achieved which then produces a constant output pressure of the cargo pump 34.

If, in use, the trigger nozzle is partially closed, the hydraulic pump 44 senses the increases in the liquid product pressure which prevails in the cargo pump and the hydraulic fluid pressure within itself and automatically adjusts the angular disposition of its swash plates so that the hydraulic fluid pressure in the hydraulic line 56 returns to 180 bar and the optimum liquid product pressure of 7 bar again prevails in the cargo pump. A correspondingly opposite adjustment in the hydraulic pump swash plate angle would result if the liquid product pressure in the cargo pump 34 were to decrease.

A constant torque drive to the cargo pump 34 is thus maintained, which ensures that a maximum liquid product delivery rate is achieved under all conditions.

If the hose outlet 38 s closed or the meter 24 shut off, the flow sensing valve returns to a closed condition in which it reconnects the control line 50 t: the tank return line 53 and so unloads the hydraulic pump. The liquid product pressure in the cargo pump then returns to 1.5 bar. Since negligible power is being used, the cargo pump 34 and the hydraulic components can operate in this condition without experiencing overheating or wear damage problems.

When bulk deliveries are required, that is the bk outlet valve 36 and nct the hose outlet 38 is in use, the hydraulic motor is operated at 2/3 its normal displacement as mentioned hereinbefore.

the means for achieving the two-speed operation of the motor is illustrated diagrammatically in Fig.7, wherein the rotary shaft 120 is coupled to the cargo pump. When the pilot port P is connected to tank, the motor operates at maximum displacement and gives maximum torque for a given input pressure at A. With pressure applied to pilot port P on the other hand, the motor is de-stroked by means of a de-stroking piston 122 to approximately 2/3 displacement and its output torque is reduced accordingly for the bulk delivery condition.

A hydraulic selector valve 51 (Fig. 3) is operated so as to switch either the bulk outlet or hose outlet into operation and also performs four main functions.

Firstly, it opens the bulk shut off valve 36, it closes the flow sensing valve 48, it selects 2/3 hydraulic motor 42 displacement, and it closes the control line 50 to the hydraulic pump.

With the hydraulic selector valve 51 set for bulk delivery, the cargo pump is driven at approximately 1.5x its normal speed as for hose-outlet deliveries and the flow at the bulk outlet is approximately 800 litres/ minute. Additionally the liquid product delivery pressure is limited to approximately 4.5bar with a corresponding hydraulic pressure in the hydraulic line 56 of approximately 180 bar which value is controlled internally by the hydraulic pump.

In certain instances the static bulk delivery pipework may be of such a size that the cargo pump flow will only be limited by the speed at which the powertake-off driven hydraulic pump is operated, i.e. the vehicle engine speed.

Additionally, the hydraulic selector valve 51 has a third position which effectively stops rotation of the hydraulic motor 42 and simultaneously provides a hydraulic supply to a conventional hose rewind valve 124 (Fig.3). In this position a relief valve 130 set at 50 Bar is used to prevent the motor 42 stopping too suddenly.

The cross-section of one embodiment of a flow sensing valve 48 in accordance with the apparatus cf Fig. 2 is shown in Fig. 4. The valve 48 comprises e valve piston 60 slidable within a cylinder. One ed of the piston 60 has a valve head 58, which when the valve is substantially sealed therewith by means of a rubber seal 62. The end of the piston opposite the valve head 58 is located in a chamber 76 which opens into one 66" of three control ports 66, 66',66". The two control ports 66, 66' are contiguous when the valve is clcsed (as shown in Fig. 4) by way of an annular spool 6E, connected ports 70, 72 and an annular chamber 74 which the port 66' opens.When the ports 66, 66' are so contiguous the control line 50 and the tank return line 53 (Fig. 2) are connected and so the hydraulic pump is in its unloaded state. Once the meter 40 (Fig. 2) is operated, liquid product flows into the valve in the direction A and lifts the valve head 58 off its seat.

Since part 64 of the valve head 58 extends into the valve opening surrounded by the valve seat 59, there is a slight delay between the valve head lift off its seat and the valve becoming fully open. The valve head lifts off its seat when the pressure across the valve differs by approximately .3 bar. With the meter 40 (Fig. 2) non-operated, no liquid product is able to pass through the valve and so the valve remains closed. The pressure on each side of the valve is partizularly equalised due tc the flow return seals 78, 80 and 78' 80'. With the meter 40 (Fig. 2) operated the valve head 58 lifts from its seat 59 and the valve piston ED moves within its cylinder into a position in which the port 60 and annular spool groove 68 are no longer contiguous.The control line 50 is thus no longer connected to the tank return line 53 and so the hydraulic pump 44 operates in its loaded state. The movement of the valve member within the flow sensing valve thus controls the operation of the hydraulic pump 44.

In Fig. 5, the bulk shut off valve 36 is shown comprising valve piston 86, slidable within a cylinder sleeve 88. One end of the valve piston is connected to a valve head member 82 sealed (as shown in Fig. ,-) by means of a seal ring 84. The other end 90 of the piston 86 is located in a pressure chamber 89 which is contiguous with a control portion 94 of one of tte hydraulic control lines from the hydraulic selector valve 51. When the hydraulic fluid within the c-amber 89 is pressurised the piston 86 and valve head timber 82 move in the direction of C and liquid product fl-ws out of the valve in direction B.

The advantages inherent in the present invention are that the apparatus conserves energy at all times.

The hydraulic pu-=? 44 provides only sufficient w and pressure as required to drive the cargo pump. re apparatus operates without the drive being required to make adjustments to vehicle engine speed for eo er hose or bulk deliveries. When the cargo pump is not delivering liquid product from the hose outlet cr bulk outlet, the liquid product pressure is maintained at a minimum 1.5 bar with a pump speed of approximately 30 rpm. When product delivery is being controller at the hose outlet, the hose pressure is always reduce- to 1.5 bar when this outlet is closed. Also, since no relief valve is fitted to this cargo pump, the pump carrt overspeed. In particular, the present invention includes an unloading feature for the cargo pump.

Claims

1. Pump apparatus for selectively discharging liquid from a container tank by way of a pump characterised in that the operation of the pump is adjustable in response to a variation in pressure of the liquid therein, whereby the pressure of the liquid is returned to a predetermined value.

2. Pump apparatus as claimed in claim 1, characterised in that the pump is driven by a first driving means, the first driving means being driven by a second driving means wherein the effective driving force of the second driving means on the first driving means is automatically adjusted in response to the variation in the pressure of the liquid.

3. Pump apparatus as claimed in claim 1 or 2, cllarseterised in that the pump comprises a cargo pump.

4. Pump apparatus as claimed in claim 2 or 3, characterised in that the second driving means is activated by a detecting means in response to liquid flow from the pump.

5. Pump apparatus as claimed in claim 4, characterised in that said detecting means comprises a flow sensing valve.

6. Pump apparatus as claimed in any of claims 2 to 5, characterised in that the first and second driving means are hydraulically activated.

7. Pump apparatus as claimed in any of claims 2 to 6, characterised in that the first and second driving means are driven hydraulically.

8. Pump apparatus as claimed in any of claims 2 to 6, characterised in that the first driving means is driven hydraulically and the second driving means is driven directly by a motor or engine.

9. Pump apparatus as claimed in claim 8, characterised in that the second driving means is driven by way of a power-take-off from a vehicle gear box.

10. Pump apparatus as claimed in any of claims 7 to 9, characterised in that the first driving means comprises a hydraulic motor.

11. Pump apparatus as claimed in any of claims 8 to 10, characterised in that the second driving means comprises a hydraulic pump.

12. Pump apparatus as claimed in claim 11, characterised in that the hydraulic pump comprises a variable displacement pressure compensated hydraulic pump.

13. Pump apparatus as claimed in claim 11 or 12, characterised in that when the hydraulic pump is loaded so as to drive the hydraulic motor, the position of the swash plates is varied so as to maintain a predetermined pressure in the hydraulic drive to the hydraulic motor which in turn maintains a predetermined liquid pressure in the pump, so as to provide a constant torque drive to the puP3.

14. Pump apparatus as claimed in claim 13 characterised in that the hydraulic pressure in the hydraulic drive to the hydraulic motor is limited by a pressure relief valve.

15. Pump apparatus as claimed in any of claims 11 to 14 when appendant to claim 10, characterised in that the liquid is selectively discharged from the pump by way of a hose outlet or by way of a bulk outlet.

16. Pump apparatus as claimed in claim 15, characterised in that the hydraulic motor nas two selectable displacements such that when liquid is discharged via the bulk outlet, it may run approximately 1.5x the speed and 2/3 the output torque as when liquid is discharged via the hose outlet.

17. Pump apparatus as claimed in claims: 15 or 16, characterised in that either of the outputs is selected by way of a hydraulic selector valve.

18. Pump apparatus as claimed in claim 17, characterised in that the hydraulic selector valve controls the bulk outlet valve, the flow sensing valve, the hydraulic motor displacement, tme hydraulic activation of the hydraulic pump and the pressure relief valve.

19. Pump apparatus substantially as hereinbefore described with referance to and as illustrated in Figs. 2 to 8 of the accompanying drawings.