GB2098273A - Submersible land drainage pumps - Google Patents

Abstract

In the past, for draining marsh land, it has been customary to use pumps carried by support structures of massive construction, or sometimes pumps driven by tractors, both having attendant disadvantages. A land-drainage pump assembly of the invention comprises a submersible, unitary, transportable casing 10 containing a hydraulic motor 12 and at least one jump 13 arranged for in-line drive from the motor and having a rigid or semi-rigid discharge pipe which rests against a ditch or channel bank. The hydraulic motor is preferably fed from a power unit situated on the bank and the pump, which may be of the centrifugal or axial flow type, is provided with a cutting tooth to chop up debris. <IMAGE>

Description

SPECIFICATION Submersible land drainage pumps This invention is concerned with pumped drainage of low-lying land and similar situations, such as irrigation. In such situations it is normal civil engineering practice to build a support structure for a pump using massive construction, with foundations in a sub-soil, at a suitable position along a channel or ditch. The construction of such a support structure is expensive, frequently difficult, and sometimes, as in the case of deep peaty soils, virtually impossible. It is also inflexible, since the pumping position cannot easily be changed. Moreover, when attempting to cater for widely differing flow rates, it has been the practice to use different sizes of pump, leading to expense in design and construction.

According to the invention a pump assembly comprises a unitary transportable casing within which is secured a pump arranged in line with a hydraulic drive motor, and a rigid or semi-rigid discharge pipe also secured to the casing, the arrangement being such that the pipe can rest against a ditch or channel bank at the angle of repose of the material of the bank.

In one form of the invention the casing of the pump assembly has a number of pumps arranged in line, with a common drive from a single motor, the pumps being separated axially sufficiently to permit ingress of fluid to their intakes. Preferably each pump has a shaft extension terminating in a drive connection and extending through the eye of the pump and a corresponding drive connection on the other side.

The employment of a unitary casing which may be of welded steel construction,'coupled with hydraulic drive, enables the entire pump assembly to be assembled ready for use and then lowered onto its operative position. It may also be easily withdrawn for any servicing that may be necessary. The casing provides support on soft soil bottoms so as to prevent the pump or pumps from sinking below the silt level, and its shape is preferably such that it continues to provide adequate support at various angles. It may have one or more inlet openings, preferably protected by grid-work to protect the pump from large pieces of debris such as polythene sacks, and the pump itself may have a "chopper" construction wherein the blades, or a separate blade, cooperates with a fixed abutment to reduce smaller debris to a size that the pump can handle.

Such a pump is usually, or can be arranged to be, operated intermittently so that debris which blocks the grid-work can be forced clear by the return surge of water through the pump when the pump is stopped.

Other features of the invention will be apparent from the following description of examples thereof taken in conjunction with the accompanying drawing in which Figure 1 is a perspective view of part of a field drainage system to which the invention has been appiied, Figure 2 is an elevation of an example of a pump assembly according to the invention, and Figure 3 is a side elevation of one of the pump units of Figure 2.

Referring first to Figure 1 which shows a typical installation according to the invention, a pump assembly 1 is submerged in the water in a drainage ditch 2, the pump or pumps being operated by a hydraulic motor which has pressure fluid supplied and exhausted via pipes 3 from a pump 4 driven by a motor 5 housed in a building 6 which is situated on the bank of the ditch. The pump assembly 1 discharges water through a riser 7 lying on the sloping end of the ditch into an outfull pipe 8 which discharges into a high level drain 9. The motor 5 may conveniently be a diesel engine and may be controlled so as to start and stop automatically to keep the level of water in the ditch 2 from rising above a pre-determined level and from falling below a further pre-determined level.Part of the building 6 may be occupied by a large fuel tank so the system can operate for long periods without attention.

Figure 2 shows a pump assembly such as that of Figure 1 but in more detail. A casing 10 is formed as a unitary structure and is shown cut away to reveal the contents. The structure is composed of steel plates welded together and is provided with a transverse wall 11 through which extends the drive shaft of a hydraulic motor 12.

This is the motor referred to in connection with Figure 1. A centrifugal pump 1 3 having its own bearings, indicated at 14, has on its shaft a coupling 1 5 arranged to couple to the shaft of the pump driving motor 12. The pump 13 has an involute casing of steel plate within which is located an impeller 1 6 (see Figure 3). The impeller is constructed of a back disc 1 7 with heavy steel weided-on curved blades 1 8 and the eye of the pump is formed by a bolted-on plate 1 9 which has an upstanding tooth 20 closely adjacent the edges of the blades 18.The nozzle of the pump has a cross-section commensurate with the casing width and the size of the eye and is arranged to emerge at an angle which may be of the order of 450 and corresponds to the angle of repose of the material of a ditch side or end in the conditions in which the assembly is to be used. In order to reduce the fluid friction the throat of the pump is enlarged as shown, to mate with a riser 7 of larger cross-section.

The pump 13 may be provided as shown with a shaft extension 21 arranged to key into a coupling 1 5a of a further pump 1 3a, and any number of pumps that may be required can be added, up to the limits imposed by the casing size and the power output of the hydraulic motor 1 2. In each case, however, a separate riser is preferably used for each pump.

The casing 10 has a flat bottom 22 but the edges, along the long sides, are sloped upwards as shown at 23. The casing thus provides a large bearing surface to take the weight of the whole assembly on even the softest of ditch bottoms, but due to the sloping portions can easily be adjusted to match up to slopes of various angles. As an alternative the bottom may be curved, or composed of a number flats together forming an effective curved surface. The casing, with its hydraulic motor and pump or pumps, and the riser or risers form a convenient unit that can be easily lifted from the water for servicing, ar lowered into position with the riser lying along the surface of a ditch wall. Suitable tackle may be left attached to the riser or the casing or both, to enable this to be done.

The pump 13 is of rugged, inexpensive construction and a typical example of a single pump having an impeller diameter of 12 inches with an intake diametter of 9 inches and a 7 inch throat is capable of delivering 70,000 gallons of water per hour against a head of 10 feet. It has been found preferable to maintain a low speed of about 700 r.p.m. in these conditions so as to prevent cavitation around the pump inlet, and the use of a hydraulic drive greatly facilitates this choice of speed. In the conditions referred to above, it has been found that a drive horse power of about 7 is required, but in the event that greater flow is required, additional pumps may be added as shown without much increase in the power requirement.The effect of the tooth 20 in conjunction with the blades of the impeller is to chop up pieces of small debris to a size that the pump can deal with, and the entry of larger pieces of debris, such as plastic sacks and the like, is inhibited by the presence of gridwork 24 across the intake end of the casing 10. For high pressure applications the back of the tooth 20 may be extended or a bolt-on plate, such as 25, provided, to avoid loss of water from that region before it reaches the throat.

In the case of a drainage system, such as might be used to maintain a low water table in land that would otherwise be marshy, for example low lying peaty land, water-level switches may be used to operate a control system for the main driving motor 5 to achieve the desired result of maintaining the level between pre-determined values. Since, in such a system the operation tends to be intermittent any accumulation of large items of debris that would totally obstruct the intake to the casing, will be displaced when the pumping is interrupted, due to the back surge of water from the riser or risers.

The use of hydraulic drive combined with single or multiple pumps driven by a common motor provides a system in which design and construction costs can be kept very low over a variation in system requirement up to a factor of many times the minimum. In the example quoted earlier in the text, a single hydraulic motor may be used at quite a low pressure of hydraulic fluid, say 500 Ib/sq.in. It will be appreciated that the transmitted power may be easily increased up to 5 or more times by the simple expedient of operating the hydraulic pump and motor at a higher pressure. Moreover, in some systems it may also be possible, where water courses are -suitably arranged, to operate several groups of hydraulic motor/water pump combinations from a single power unit.

Although the invention has been described in relation to the use of centrifugal pumps, it will be appreciated that other types, such as axial flow pumps may be used, if desired.

Claims (9)

1. A land-drainage pump assembly comprising a submersible unitary transportable casing, within said casing a hydraulic motor and a pump arranged for in-line drive from said motor, a pump outlet discharging into a rigid or semi-rigid discharge pipe secured to the casing and arranged in relation thereto such that it can rest against a ditch or channel bank at the angle of repose of the material of the bank.

2. An assembly according to claim 1 wherein the lower part of the casing is shaped to provide adequate support for itself and its contents on the softest bottoms of a drainage ditch or channel at various angles.

3. An assembly according to claim 2 wherein the bottom of the casing is arranged as a series of connected flats, such that at any angle of repose the principal support is provided by not more than two adjacent flats.

4. An assembly according to any one of claims 1,2 or 3 wherein the pump has a drive connection driving the impeller through a back plate and has a shaft extension extending through the eye of the pump and terminating in a further drive connection.

5. An assembly according to claim 4 wherein a number of pumps is provided within the casing and each pump has a separate discharge pipe.

6. An assembly according to any one of the preceding claims wherein the casing is provided near its upper surface with a grid to intercept larger items of debris before they can reach the pump intake.

7. In combination a land-drainage pump assembly as claimed in any one of the preceding claims, and lying on a ditch or drainage channel bottom with its discharge pipe arranged on a ditch bank so as to discharge into an adjacent higher level drain, a power unit on the top of the bank comprising a motor driving a hydraulic pump, and hydraulic pipe connections between said hydraulic pump and the motor of said assembly.

8. A combination as claimed in claim 7 wherein two or more pump assemblies are located near each other and are driven from a common hydraulic power unit.

9. An assembly as claimed in any one of claims 1 to 6 and substantially as herein described.