The invention relates to a pump system for pumping liquids, comprising a submerged pump, which is connected to a pressure pipeline and can be driven by means of a hydraulic drive comprising a hydraulic pump and a hydraulic motor, which are connected to one another by a hydraulic circuit, the hydraulic pump delivering a hydraulic medium at high pressure to the hydraulic motor, from which the hydraulic medium is discharged at low pressure.

Hydraulically driven submerged pumps of this kind are used in fire-fighting. To this end, the submerged pump can be placed in a body of water, such as a river, lake or the like, at a greater or lesser distance from the fire. The hydraulic unit, which may contain a diesel engine, is placed on the bank and drives the water pump via the hydraulic lines. The water can be transported over great distances by means of a pressure pipeline. For greater distances to be covered, a plurality of these pump systems can be connected in series.

The hydraulic lines and the pressure pipeline may have a considerable length and therefore have to be treated carefully. It is therefore continuously necessary to ensure that the lines do not become blocked, since the extinguishing apparatus would then cease to function. However, this is not easy in the sometimes chaotic conditions when fighting a fire, and as a result, it is scarcely possible to avoid vehicles driving over the lines and blocking them.

A further drawback of blocking the hydraulic drive is that oil leakages can then occur. This does not have to lead directly to problems for the feed line, since the latter is protected by a pressure-relief valve on the side of the hydraulic pump. However, the problems are greater for the discharge line; under normal operation, there is scarcely any load on this line, while in the blocked state considerable increases in pressure can occur. As a result of unexpected high pressures of this nature the discharge line or the housing of the hydraulic motor can crack, as can the housing of the liquid pump, as a result of which the oil is lost into the environment.

Not only does this destroy a significant part of the pump system, more importantly the extinguishing apparatus ceases to function. In such an event the environment also suffers serious damage. This problem is all the more serious if such an accident were to take place in a vulnerable environment such as a water-catchment area.

The object of the invention is therefore to provide a pump system which does not have this drawback. This object is achieved in that protection means are provided for protecting the circuit against excess pressure in the hydraulic medium discharged from the hydraulic motor.

The pump system usually comprises a hydraulic circuit with a feed line for feeding hydraulic medium at high pressure to the hydraulic motor from the hydraulic pump, as well as a discharge line for discharging hydraulic medium at low pressure from the hydraulic motor to the hydraulic pump. The protection means according to the invention can be used here in various manners. According to a first possibility the protection means are connected to the discharge line.

According to a second possibility, which is suitable for a pump system in which the hydraulic pump has leakage discharge means for discharging hydraulic medium released owing to leakage in the hydraulic motor, the protection means are connected to the leakage discharge means. This may, for example, be the leakage line.

In both the abovementioned possibilities, the protection means may comprise a pressure-relief valve as well as a container which is connected to the pressure-relief valve and in which the oil can be collected.

The expandable member is preferably a bellows. For further protection, a shut-off valve may be incorporated in the feed line, which valve can be actuated by the hydraulic medium in the discharge line in order to shut off the feed line in the event of a predetermined pressure in the discharge line being exceeded.

A signalling means may also be provided for visually signalling that the excess-pressure protection has come into operation. A provision of this kind is useful for an embodiment in which the submerged pump together with the hydraulic motor form a separate unit which floats in the liquid, and the hydraulic pump with associated drive, such as a diesel engine, form a unit which can be placed on land. It can then easily be seen on land, even from some distance, whether the protection has come into operation. The invention will be explained in more detail below with reference to an exemplary embodiment depicted in the figures, in which:

Figure 1 shows a view of the liquid pump system according to the invention.

Figures 2-7 show circuit diagrams of the pump system.

The pump system according to the invention comprises a submerged pump, which is denoted overall by 1 and is situated in a body of water 2, such as a lake, river or the like, as well as a hydraulic unit 3 which is situated on the land . Hydraulic unit 3 and submerged pump 1 are connected to one another by means of a hydraulic feed line 5 and a hydraulic discharge line 6. Furthermore, the submerged pump 1 is connected to a pressure pipeline 7. through which the pumped water is transported.

The submerged pump comprises a housing 8, in which a hydraulic motor 9. which drives the actual pump 10, is situated. This pump has an inlet filter 11 on the suction side and a coupling 12, to which the pressure pipeline 7 is connected, on the delivery side. The hydraulic unit contains a diesel engine 17, to which a hydraulic pump 18 is connected. The hydraulic pump 18 forces hydraulic oil via feed line 5 to the hydraulic motor 9. from where the oil flows back to the hydraulic pump 18 via discharge line 6, thus executing a circulating motion.

As regards the submerged pump 1, these components can be seen in the circuit diagrams shown in Figures 2 and 3«

If, in operation, the hydraulic discharge line 6 were to become closed, for example due to a heavy weight being applied to it, the pressure in the motor 9 or the liquid pump 10 would increase, which would ultimately lead to the housing of the motor or the liquid pump breaking. As a result of this the hydraulic oil would pass into the body of water 2, which must be avoided for environmental reasons. In order to prevent breakage of this kind in the event of the hydraulic discharge line 6 becoming closed off, in accordance with Fig.2b a bellows 13 is connected to the discharge line 6 via a pressure-relief valve I . The pressure at which this pressure-relief valve 14 opens, may, for example, be 20 bar. In the event of pressure building up in the hydraulic discharge line 6, the pressure-relief valve 14 will therefore open above this pressure after which the hydraulic oil which cannot be discharged via the discharge line 6 will collect in the bellows 13. It can thus be ensured that hydraulic oil is collected for a period of time in the bellows 13, during which time measures can be taken to switch off the drive unit 3. for example via an oil-level switch in the hydraulic tank.

In the embodiment of Figure 2a which is largely identical to that of Figure 2b, a leakage line MO is used. In this embodiment, the pressure-relief valve l^/bellows 13 unit is connected to the leakage line

In the circuit diagram of Figure 3. an extra safety valve 15 is included which is actuated via line 16 which is connected to the hydraulic discharge line 6. As soon as pressure in the hydraulic discharge line 6 becomes too high, as described above, the safety valve 15 is switched into the closed position, as a result of which the hydraulic feed line 5 is blocked. It can thus be ensured that the hydraulic feed is completely switched off if the pressure in the discharge line 6 should rise too high. The bellows 13 then only serves to collect the small leakage losses beyond the safety valve 15 in the event that the discharge line is 100# blocked. Normally, the pressure from the discharge line will fall rapidly if there is no more feed.

In the embodiment shown in Figure , a hydraulic motor 9 s used having an external leakage connection 20, which is connected to the discharge line 6. This discharge line 6 is also connected to a container such as a bellows 13 via a first pressure-relief valve 21 which opens at, for example, 10 bar, as well as a second pressure-relief valve 22 which opens at, for example 15 bar.

A safety valve 23, which switches over for example at 20 bar is arranged between the hydraulic motor and the connection point of the leakage connection 20 and the bellows 13.

In this embodiment, any oil which has leaked out of the hydraulic motor 9 is discharged via the leakage connection 20 through the discharge line 6. In this case too, as soon as the discharge line 6 is blocked firstly the pressure-relief valves 21 and 22 will respond and the bellows 13 will be filled. In the event of the pressure in the discharge line 6 increasing still further, the discharge from the hydraulic motor 9 will be shut off. The small amounts of medium which have leaked out can still be collected in the bellows 13. In the embodiment of Figure 5. a hydraulic motor 2k is used having an internal leakage discharge. In the feed line, a safety valve 25 is used which responds, for example, at 20 bar.

The bellows 13 is connected first of all to the discharge line 6 via the pressure-relief valve 26 which responds, for example, at 2 bar. The control line of the valve 25 is also connected to the discharge line 6. In the event of rising pressure in the discharge line 6, this embodiment will firstly shut off the feed line 5. and in the event of the pressure rising still further, the pressure-relief valve 26 opens and the hydraulic medium is collected in the bellows 13.

In the embodiment of Figure 6, a hydraulic motor with internal leakage discharge is again used, while a nonreturn valve 27 with pilot control is arranged in the feed line « f the pressure in the discharge line 6 rises, the connection between the lines 28 and 29 is interrupted by valve 37. which is connected to the discharge line 6 via line 38, while line 29 is immediately connected to the bellows 13 via pressure- relief valve 30• As a result, the nonreturn valve 27 is closed very quickly, while in the event of mounting pressure in the discharge line 6 the hydraulic medium is also collected in the bellows 13. Finally, Figure 7 shows a variant with a hydraulic motor 31 which can operate in two opposite directions of rotation, so that rotor 32 can exert a delivery action and a sucking action. The lines 33. 3^ here function alternately as feed line or as discharge line. An external leakage line 35 is also provided. A safety valve 35. 36 is incorporated in both lines 33. 3^. both of which valves can be switched by the pressure in the leakage line 39- The bellows 13 is connected to the leakage line 39-

In embodiments of this kind, both the line 33 and line 3* are equipped for high pressure, for example 300 bar. As soon as the line 33 or 3^ which is acting as the discharge line is compressed, there will therefore be no leakage in this line. The oil will seek a way out via the leakage line 39. and this line can get rid of the excess oil into the bellows 33. In the event of increasing pressure in the leakage line 39. both the feed line and the discharge line 33 or 3^ will also be shut off.