GB2338747A

GB2338747A - Two stage pump with low and high pressure output, a thermal relief valve and a filter

Info

Publication number: GB2338747A
Application number: GB9813704A
Authority: GB
Inventors: Frank William Mason; Colin Thomas Pomfret
Original assignee: Godiva Ltd
Current assignee: Godiva Ltd
Priority date: 1998-06-26
Filing date: 1998-06-26
Publication date: 1999-12-29
Anticipated expiration: 2018-06-26
Also published as: GB9813704D0; GB2338747B

Abstract

A fire fighting pump comprises a low pressure (LP) pumping stage 16,17 having a LP inlet and a LP outlet; a high pressure (HP) pumping stage 20,21 having a HP inlet 33 and a HP outlet 34; a first passage 31 providing for flow of liquid from the LP outlet 23 to the HP inlet 33; a second passage 35 providing for flow of liquid from the HP outlet 34 also to the HP inlet 33 and a stop valve 38 for preventing said flow of in said second passage 35. With the stop valve 38 open, LP liquid is provided from fitting 36, with the valve closed, the fitting 36 provides HP liquid. A pressure relief valve 42 allows circulation from the HP outlet 34 to the LP outlet 23 when no liquid is drawn from fitting 36, while a thermal relief valve 60 containing a wax capsule (64, fig 5) causes liquid above a safe temperature to be replaced. A drain valve (53,54, fig 4) is provided as is a filter 43 between the LP outlet 23 and the HP outlet 33 which can be flushed with HP liquid and is made from wedge crossection wire (47, fig 3) wound around a support structure (46, fig 3) extending from a screwed plug (45, fig 3).

Description

2338747 PATENTS ACT 1977 GMD/A95 1 OGB Title: PUMPS D2sn of Invention This

invention relates to pumps.

More particularly the invention relates to a pump intended for supplying water for fire fighting purposes. Such a pump may be installed on a vehicle to provide the pumping capacity for the well known fire appliance as used by fire brigades. When thus installed, the pump may draw its water supply from a storage tank on the vehicle or from an external source in cases where the quantity of water required to be delivered exceeds the vehicle's storage capacity. Alternatively the pump may be used in a fixed installation, e.g. on a site where a fire hazard exists.

A pump in accordance with the invention is a two-stage pump, incorporating a low pressure pumping stage and a high pressure pumping stage. The low pressure pumping stage is able to draw water from a supply and deliver it at a relatively low pressure and high volume. Some fires can only be fought satisfactorily by the delivery of large quantities of water in such a manner. By way of example, water may be de-livered at a pressure of the order of 100 psi and a flow rate of up to about 1000 gallons per minute. The high pressure pumping stage draws its supply of water from the outlet of the low pressure pumping stage, and is capable of delivering it at a pressure which might be as high as 40 bar or so, at a flow rate of up to 50 gallons per minute or so. Water under such conditions may be delivered through a relatively small bore hose or hoses to an outlet device which creates a fog or mist of water. This is very effective for fighting certain types of fire. A foam generator may. also be fed by such high pressure water.

1-1\ 2 A pump having two pumping stages as above described is known from our British Patent No. 1234587. The low pressure pumping stage is an arrangement of a centrifugal pump, while the high pressure pumping stage uses a regenerative impeller. Both are driven by a common shaft which in a fire appliance vehicle may be driven from the vehicle's engine by way of a power take-off shaft from the vehicle's transmission. There is a shut-off valve in a pipe leading from the outlet of the low pressure pumping stage to the high pressure pumping stage inlet, and when this valve is closed no water is available from the outlet of the high pressure pumping stage.

It is broadly the object of the present invention to provide improvements in a two-stage pump such as that disclosed in our patent aforesaid. Aspects of the present invention and the advantages deriving therefrorn will hereafter be described in greater detail, individually and in combination.

According to one aspect of the invention, we provide a pump comprising:

a low pressure pumping stage having a low pressure inlet and a low pressure outlet; a high pressure pumping stage having a high pressure inlet and a high pressure outlet; first passage means providing for flow of liquid from the low pressure outlet to the high pressure inlet; second passage means providing for flow of liquid from the high pressure outlet to the high pressure inlet; stop valve means for preventing said flow of liquid in said second passage means.

In a pump in accordance with the invention, in operation with the stop valve means open, water at low pressure from the low pressure outlet can always flow to the high pressure inlet but from the high pressure outlet water will be returned to the high pressure inlet and, in effect, recirculated tlu-ough _ 1 3 the high pressure pumping stage. This has the advantage that low pressure water flow will always be available from the high pressure outlet, which might be required for duties such as "damping down" after a large fire. The high pressure pumping stage will not generate any higher pressures until the stop valve means is closed, whereupon water under high pressure can be delivered from the high pressure outlet. A hose or hoses connected to a discharge fitting or fittings at the high pressure outlet can deliver low pressure water or high pressure water, as required according to whether the stop valve means is open or closed.

Preferably the second passage means is arranged to provide for flow of liquid to the high pressure inlet by way of the first passage means.

If the pump is running with the stop valve means closed, but for the time being there is no discharge of water from the high pressure outlet, it would be possible for very high pressures to be developed at the high pressure outlet, with the possibility of damage being caused. Preferably therefore there is provided pressure relief valve means which is openable in response to attainment of a pressure above a predetermined value at the high pressure outlet and providing, when open, for flow of liquid back to the high pressure inlet.

Preferably the pressure relief valve means is arranged to provide for flow of liquid back to the high pressure inlet by way of the first passage means.

During prolonged operation of the pump with water recirculating through the high pressure pumping stage, the input of energy to such water will raise the temperature thereof. Eventually the prevailing temperature of the pump could reach dangerous levels, and preferably therefore there is provided a thermal relief valve means including a thermally responsive element for causing the thermal relief valve means to be opened upon detection of a liquid temperature above a predetermined value, and when open to provide for release of liquid from the pump, conveniently fi-om the low pressure outlet.

4 The thermal relief valve means may, when open, provide for release of the heated liquid back to a water supply tank or simply to the external environment to run to waste, such liquid being replaced by fresh liquid drawn from the pump's supply to cool the pump.

When in use, to deliver large quantities of water for fire fighting or other purposes, the pump may draw its supply from a source which is not clean and which contains detritus such as dirt and grit. Whilst the low pressure pumping stage in the form of a centrifugal pump is generally able to cope with a reasonable amount of such detritus without suffering damage, the high pressure pumping stage, and equipment such as a foam generator or fogging apparatus supplied thereby, is less able to cope with dirt and grit and might suffer damage therefrom.

Preferably therefore there is provided filter means for filtering liquid flowing from the low pressure outlet to the high pressure inlet, and conveniently such filter means is provided in the first passage means.

To assist in preventing blocking of such filter means, the second passage means and/or the pressure relief valve means may be arranged such that when liquid flows therethrough, such flow of liquid is directed on to a detrituscollecting surface part of the filter means, so that any collected detritus is disturbed and displaced.

The most significant aspect of the filter means in accordance with the present invention, however, is the configuration thereof. Conventionally, filters for applications such as pumps of the present invention comprise a foraminous sheet, e.g. in the form of a cylinder through which the liquid is required to flow. The size of the individual holes is such that only particles of a size which is small enough not potentially to cause damage can pass therethrough. However, such a filter is readily blocked by particles which will just not pass through the holes but instead become lodged over and partially in the holes. If the water supply for a fire pump contains a large number of such particles, the pump performance can very rapidly deteriorate.

According to another aspect of the invention, therefore, we provide a filter comprising a supporting structure and a continuous elongate element carried by said supporting structure so as to define an elongate slot for flow therethrough of fluid to be filtered.

Conveniently the filter is of generally cylindrical configuration, the supporting structure providing for winding of the elongate element thereon.in helical configuration to define a succession of parts of a helical elongate slot.

The advantage of the filter in accordance with this aspect of the invention is that such an elongate slot or slots for flow of fluid to be filtered is much less readily blocked than are individual holes in a forarninous sheet.

Further, it is easy to clean when removed by a tangential wiping or brushing action or helical wiping, or by transverse direction of an air or liquid jet onto it as referred to above.

The filter may comprise a support structure in the form of a number of parallel support elements circumferentially spaced from one another to define a cylindrical envelope, whereon wire is wound in helical configuration. The wire may be triangular in cross-section.

Yet a further feature of a pump in accordance with the invention is the provision of a drainage valve means for drainage of liquid from the high pressure pumping stage when the pump is not in use.

Such a drainage valve means may be provided in a passage extending from the lowest point of the internal chamber provided by a casing part of the high pressure pumping stage, and comprise a valve element movable into engagement with a seating in response to pressure existing in the high pressure pumping stage when the pump is in operation, but arranged to fall from said seating under gravity when the pump is not in operation to permit draining of liquid from the high pressure pumping stage.

6 Such a valve means or the passageway in which it is provided may provide for discharge of liquid from the high pressure pumping stage to the low pressure pumping stage. Drainage of the low pressure pumping stage may be provided by means of a manually removable plug.

These and other features of the invention will now be described by way of example with reference to the accompanying drawings, of which:- Figure 1 is an elevation, partly in section, of a pump in accordance with the invention; Figure 2 is a horizontal section on the line X-X of Figure 1; Figure 3 illustrates a filter means of the pump; Figure 4 is a detail of a drainage valve means of the pump; Figure 5 shows, in different operative conditions, a thermal relief valve means of the pump; Figure 6 illustrates diagrammatically four different operative conditions of the pump; Figure 7 illustrates in greater detail two further operative conditions of the filter means of the pump.

Referring firstly to Figures 1 and 2 of the drawings, a pump is illustrated which comprises a main body 10 comprising a plurality of casing parts assembled to one another and held together by suitably disposed bolts many of which are visible in the drawings. The body includes a bearing housing part 11 which by means of spaced bearings 12, 13 supports for rotation a main pump shaft 14. At one end extending from the bearing housing 11 the shaft 14 carries a drive flange 15 for bolted connection to a complementary driving member which typically, in an installation of the pump on a fire appliance vehicle, will be drivable by the engine of the vehicle by way of a power take-off shaft from the vehicle's transmission.

At its opposite end the shaft 14 carries an impeller 16 which forms the pumping element of a low pressure pumping stage. The impeller 16 operates 7 within a volute chamber 17 defined within the adjacent casing parts of the pump. The low pressure pump is a conventional centrifugal pump, with its inlet provided by an inlet fitting 18 communicating with the centre of the impeller 16 and extending axially in line with the rotational axis of the shaft 14. The inlet fitting 18 has a connector 19 for a suction pipe. The low pressure outlet from the volute 17 extends upwardly within the body 10 and will be referred to hereafter.

The shaft 14 further carries a high pressure impeller 20 which is of the regenerative pumping type and works relatively closely within a chamber 21 defined by the body 10. High pressure inlet and outlet passages extend respectively downwardly and upwardly within the body 10, to a manifold assembly indicated generally at 22 mounted above the body 10, and some details of which are shown in greater detail in Figure 2. It will be noted, however, that the manifold assembly includes a low pressure delivery manifold 23 which provides for delivery of low pressure water from the low pressure outlet of the low pressure pumping stage to a number of delivery hoses. A delivery valve 24 and fitting for connection of one such hose 25 are shown in Figure 1.

In Figure 2 which is the section X-X tlu-ough the upper part of the manifold assembly 22, an upward extension of the low pressure outlet from the low pressure pumping stage and the low pressure delivery manifold is indicated at 30. This opens laterally into a first passage 31 which leads to a space 32 from which extends downwardly the high pressure inlet 33 leading to the high pressure pumping stage chamber 21. The high pressure outlet from the chamber 21 is indicated at 34 and this opens into a second passage 35. In one direction the passage 35 leads to a higli pressure delivery fitting 36 which has discharge ports 37 to which high pressure hose may be connected. In the direction opposite to the:Fitting 36, the passage 35 extends to a stop valve 38 which is a globe valve with a valve member 39 operable by a handle 40, and 8 thence opens into an annular chamber 41 in line with the first passage 3 1. There is also a pressure relief valve assembly 42 which is a spring- loaded device which provides for communication between the second passage 35 and the first passage 31 when a pressure in excess of a predetermined value exists in the former passage relative to the latter passage. When such a pressure differential exists, water can flow from the second passage 35 to the first passage 3 1.

A filter means 43 is provided for filtering water flowing from the first passage 31 to the space 32 to the high pressure inlet 33. The filter means comprises a filter element, shown in Figure 3, which is of cylindrical form extending from a plug 45 screwed into the manifold assembly. The filter element comprises a plurality of elongate members as indicated at 46, extending parallel to one another from the plug and forming a cage-like support structure of generally cylindrical envelope. On this support structure is wound helically a wire 47 which is of triangular shape -in cross-section ("wedge wire") with a small space between adjacent turns. This provides an opening for passage of liquid from the outside to the inside of the cylindrical filter element by way of a succession of slots in continuous helical disposition interrupted by the support members. Water flowing from the low pressure outlet 30, or through the pressure relief valve 42, or from the second passage 35 by way of the stop valve 38, must pass through the filter element from the exterior to the interior thereof to reach the space 32 and the high pressure inlet 33.

The pump also includes a drain valve means for draining down the high pressure pumping stage when the pump is not in operation. This is indicated generally at 50 in Figure 1, and is shown in greater detail in Figure 4. It comprises a passage 51 extending downwardly from the lowermost part of the chamber 21 wherein the high pressure impeller 20 rotates, the passage 51 extending into a horizontal portion 52 of larger diameter opening into a lower part of the volute chamber 17 of the low pressure pumping stage. A valve 9 seating member 53 is screwed into the passage portion 52 and holds captive therein a valve member in the form of a ball 54. The arrangement is such that when the high pressure pump is operating, as shown in Figure 4A, the relatively high pressure inside the chamber 21 causes the ball 54 to be held against the valve seating 53. When the pump is stopped, however, the ball 54 falls away from the valve seating as shown in Figure 4B, to permit water from the chamber 21 to drain into the low pressure volute chamber 17. A removable plug 55 provides for draining of the latter chamber.

The pump further comprises a thermal relief valve means which is disposed where indicated at 60 in the low pressure delivery manifold of the manifold assembly. This thermal relief valve is arranged to open upon detection of the water temperature in the passage 35 exceeding a predetermined safe limit, whereupon it permits heated water to be released either to a supply tank from which the pump draws its supply or else to the external environment, to be replaced by cool water for lowering the pump temperature. The thermal relief valve is shown in greater detail, in three operative conditions, in Figure 5, and comprises a body 61 with a cylindrical extension 62 having an array of apertures 63 circumferentially around it. The end of the extension 62 holds a wax capsule sensing device 64 with an output member 65 connected to a valve sleeve 66 which itself is of cylindrical forni with a circumferentially extending ring of apertures 67. The sleeve 66 fits closely around a hollow spigot 68 on a cap 69, the spigot having circumferentially, spaced apertures 70 thereabout. A spring in the form of a helical compression spring 71 operative between the cap 69 and the sleeve 66 biases the latter towards the wax capsule 64.

As the temperature of the wax capsule 64 increases, expansion of the wax therein drives the output member 65 towards the cap 69 and moves the sleeve 66 in the same direction against the force of spring 71. The start of such movement is shown in Figure 5B. When a certain temperature is reached, as shown in Figure 5C, the apertures 67 align with the apeitures 70 permitting water to flow from the outside of the thermal relief valve through the apertures 63, 67 and 70 to the interior of the spigot 61 and thence to be discharged to the external environment, or to a storage tank on a fire fighting vehicle.

Figure 6 shows diagrammatically four different conditions of operation of the pump as above described. Figure 6A shows the condition wherein the stop valve 38 is open. The above described recirculation of pumped water from the high pressure outlet 34 back to the high pressure inlet 33 by way of the passages 35, 31 and filter 43 takes place. Water may be delivered at low pressure both from the low pressure delivery manifold 23 and from the high pressure delivery fitting 36.

Figure 6B shows the condition when the stop valve 38 is closed. A large flow rate of water at low pressure can be delivered from the low pressure delivery manifold 23, while a relatively small flow of water at high pressure can be drawn from the high pressure delivery fitting 36.

Figure 6C shows the condition of Figure 6B but with the difference that no high pressure water is being drawn from the fitting 36. To prevent an excess pressure with the potential for causing damage from developing in the passage 35 and associated parts of the manifold assembly, the pressure relief valve 42 opens to permit water to recirculate from the high pressure outlet back to the high pressure inlet by way of the passage 31 and filter device. In Figure 6C, water is still being drawn from the low pressure discharge manifold 23.

Figure 6D shows the condition when the pump is operating as above but neither high pressure nor low pressure water is being discharged therefrom. This can lead to an increase in the temperature prevailing in the water in the pump, until at a certain temperature the thermal relief valve 60 opens to discharge water which will be replaced by cool fresh water to lower the overall temperature prevailing in the pump.

Figures 7A and 7B show on an enlarged scale part of the pump under the conditions shown in Figures 6A and 6C respectively. When either the pressure relief valve 42 or the stop valve 38 is open, water is directed on to the external surface of the filter element in the passage 3 1, thereby displacing accumulated debris from the filter and assisting in maintaining flow therethrough.

Thus the invention provides a pump which is highly suitable for providing water at high pressure and/or low pressure for fire fighting purposes. When in use, the pump can at all times provide water at low pressure and high flow rate from the low pressure delivery manifold, whilst at the high pressure delivery water is available at high pressure or low pressure according to whether the recirculation stop valve is open or closed. The pump includes an efficient design of filter and provides for flushing thereof in use. In addition the pump has further advantageous features as referred to above.

Although described above in relation to supply of water for fire fighting purposes, it is to be appreciated that a pump in accordance with the invention is usable more widely where similar or analogous requirements arise.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

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Claims

A pump comprising a low pressure pumping stage having a low pressure inlet and a low pressure outlet; a high pressure pumping stage having a high pressure inlet and a high pressure outlet; first passage means providing for flow of liquid from the low pressure outlet to the high pressure inlet; second passage means providing for flow of liquid from the high pressure outlet to the high pressure inlet; stop valve means for preventing said flow of liquid in said second passage means.
2. A pump according to Claim 1 wherein the second passage means provides for flow of liquid to the high pressure inlet by way of the first passage means.
3. A pump according to Claim 1 or Claim 2 further comprising pressure relief valve means operable in response to attainment of a pressure above a predetern-lined value at the high pressure outlet relative to the high pressure inlet and providing, when open, for flow of liquid back to the high pressure inlet.
4. A pump according to Claim -3) wherein the pressure relief valve means provides for flow of liquid to the ffi,,,,h pressure inlet by way of the first passage 0 means.

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5. A pump according to any one of the preceding claims fix-ther comprising thermal relief valve means openable upon detection of a liquid temperature above a predetermined value and providing when open for release of liquid from the pump.
6. A pump according to Claim 5 wherein said thermal relief valve means releases liquid from the low pressure outlet.
7. A pump according to any one of the preceding claims firier comprising filter means for filtering liquid flowing from the low pressure outlet to the high pressure inlet.
8. A pump according to Claim 7 wherein said filter means is provided 'm the first passage means.
9. A pump according to Clanin 7 or Claim 8, as appendant directly or indirectly to Claim 2 or Claim 4, wherein the second passage means and/or the pressure relief valve means is arranged such that liquid flowing therethrough is directed on to a detritus-collecting surface pail of the filter means.
10. A filter comprising a supporting structure and a continuous elongate 0 element carried by said supporting structure so as to define an elongate slot for flow therethrough of fluid to be filtered.
11. A filter according to Claim 10 which is of generally cylindrical 0 configuration, the supporting structure providing for winding of the elongate element thereon in helical configuration to define a succession of parts of a generally helical elongate slot.

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12. A filter according to Claim 11 wherein said support structure comprises a number of parallel support elements spaced from one another to define a cylindrical envelope, whereon wire is wound in helical configuration.
13. A filter according to Claim 12 wherein the wire is triangular is crosssection.
14. A pump according to any one of Claims 7 to 9, wherein the filter me ans comprises a filter according to any one of Claims 10 to 13.
15. A pump according to any one of Claims 1 to 9 or Claim 14 further comprising drainage valve means for drainage of liquid from the high pressure pumping stage when the pump is not in use.
16. A pump according to Claim 15 wherein said liquid is discharged from the high pressure pumping stage to the low pressure pumping stage.
17. A pump according to Claim 15 or Claim 16 wherein said drainage valve means is provided in a passage extending fi-orn a lowest point of an internal chamber provided by a casing pail of the high pressure pumping stage, and comprises a valve element movable into engagement with a valve seating in response to pressure existing in the high pressure pumping stage when the pump is in use, but arranged to fall from said seating under gravity when the pump is not in operation, to pen-nit said draining of liquid.
18. A pump substantially as hereinbefore described with reference to the accompanying drawings.
19. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.