PROCEDURE FOR THE STARTING UP OF PUMPS

Abstract: The invention is concerned with a procedure for use with a pump (6) for the movement of liquid, powered by an internal combustion engine, which pump is not capable of pumping air (gas) and thereby drawing liquid up into itself at start-up when elevated significantly above the body of liquid from which it is to pump; in which procedure the internal combustion engine also powers a hydraulic pump (3) which in turn drives by hydrostatic transmission an immersed pump (10) which pumps liquid up to the pump (6) during the start-up phase.

Description: Procedure for the starting up of pumps The present invention is concerned with a procedure for starting up a pump for the movement of liquid, which pump is not capable of drawing liquid up to itself at start-up when located significantly above the body of liquid from which it is to pump, but can act as self-sucking once it has begun pumping liquid. It is often necessary in practice for a pump to be located above a body of liquid, so that the pump must draw liquid up to itself through a feed line, because bodies of liquid are for natural reason often situated at a lower level than their surroundings and because solutions involving an immersed pump or a pump located in a basement alongside or below the body of liquid (thus providing gravity feed) are expensive and advanced solutions which are suitable only for permanent installations, and then only with an electric motor as prime mover. In the case of a large mobile pump powered by an internal combustion engine, location at a level that would allow gravity feed is impossible in most cases. Pumps are well-known which are capable of pumping air or other gas and hence of drawing up liquid from a lower level at start-up. Examples of such pumps are various forms of piston pump, screw pump etc. A common feature of such pumps is that they are precisely constructed, with highly finished interior surfaces which slide against each other so as to ensure gas tightness. The drawback of these self-priming pumps is that they are ill-suited to liquids contaminated with e.g. grit, soil, grass, straw etc., as the said sliding surfaces are easily damaged, thus destroying the pump's gas pumping capability. Other service conditions that damage the sliding surfaces are cavitation and dry running, whereof the latter often generates heat. A class of pumps which is particularly simple, inexpensive and suitable for use with highly contaminated liquids such as are found in agriculture, civil construction, street cleaning etc., is the so-called turbo-pumps, being based on a hydrodynamic principle and lacking the aforesaid sliding surfaces. The variant known as the centrifugal pump is particularly popular. The said turbo-pumps can indeed function as self-sucking once they are filled with liquid and the gas initially present in them has been expelled. However, they normally cannot pump gas so as to draw liquid up into themselves from a lower level in the start-up phase. A conventional method of solving this problem is to fit a non-return valve at the lower end of the pump's feed line and to fill the pump and the feed line with liquid from above. This is done once only when the pump is first started up. The said procedure is cumbersome and is particularly ill-suited to mobile pump applications where the feed pipe must be continually emptied (such is the case, for example, if the pump is mounted on a tanker and is used to fill the tank at one location, then to empty it at a second location, then to fill it again at the first location, etc.). Another problem that often arises in intermittent operation in a fixed location is that impurities in the liquid are deposited in the non-return valve and prevent it from sealing perfectly when the pump is at rest, as a result of which the pump has emptied of liquid by the next time it has to be started. The purpose of the present invention is to solve the above-mentioned problems in pumps which are not capable of drawing liquid up into themselves at start-up when elevated significantly above the body of water from which they are to pump, primarily because of their inadequate capacity to pump air. The invention provides a solution to these problems and is defined by the characterising part of claim 1. The procedure of the invention is more particularly explained with reference to an example of embodiment (see Fig. 1). To an agricultural tractor (1, Fig. 1), which is equipped as standard with a power take-off shaft (2) for mechanical power transmission from the tractor's internal combustion engine and with a hydraulic system — comprising oil tank, hydraulic pump (3) powered by the said internal combustion engine, valves (4), and quick-release couplings for an external hydraulic system (5) — there is connected via the power take-off shaft a large centrifugal pump (6) of 25-50 kW driving power, whose feed line (7) extends down into the liquid tank (8). At the lower end of the feed line there is fitted a simple, more or less tight-sealing non-return valve (9) and an immersible centrifugal pump (10) powered by a hydraulic motor and having its discharge above the non-return valve, said centrifugal pump obtaining its hydraulic fluid from the tractor's built-in hydraulic system via either one of hoses (11) or (12) (the other hose serving as the return line for the hydraulic fluid). Before starting up the centrifugal pump (6), the centrifugal pump (10) is started first, whereupon the non-return valve (9) closes to downward flow and the feed line (7) and the centrifugal pump (6) fill up with liquid. Then the centrifugal pump (6) is started up with the aid of the tractor's power take-off shaft, whereupon the non-return valve (9) opens and the hydraulically powered pump (10) may be switched off if desired. The procedure has been put into practice in a number of trials and has been found to work excellently. The pumps may also be started in the reverse order to that mentioned above. In the event of cavitation in the feed line or some other condition causing the pump (6) to "lose hold", it is very easy to restart by a simple manipulation of the tractor's hydraulic valves (4). In practice there are many circumstances that make the procedure according to the invention an advantageous one. A hydraulically powered immersed pump with sufficient capacity to quickly fill the feed line (7) and the pump (6) can be made very simple, inexpensive and easily handled (weighing just a few kilograms). The power source is in many cases available at low cost, since the internal combustion engine (most often a diesel engine) required to drive the large pump connected to the power take-off shaft is manufactured in very large series for vehicular applications and in such cases is equipped as standard, or at least prepared to be equipped, with a small hydraulic pump for various servo systems attached to the intended vehicle. The invention may of course be varied within the terms of the claims. A simplified variant is to fit at the lower end of the feed line (7, Fig. 1) a specially designed centrifugal pump (13, Fig. 2) — driven by a hydraulic motor (13d)- — which pump replaces both the pump (10, Fig. 1) and the non-return valve (9, Fig. 1), in which case all the pumped liquid passes through said pump (13). In a generalised procedure according to the invention it is often desirable, for reasons of efficiency of power transmission and ease of handling, to make the immersed hydraulically powered pump small compared to the pump that is powered directly by the internal combustion engine. Therefore the pump (13) must be designed to transmit a considerably greater flow of liquid than it would be capable of pumping itself. This is achieved by making the pump housing (13a, Fig. 2) and its discharge opening (13b) considerably wider than the impeller (13c). A solution as described above wherein all the pumped liquid passes through the pump (13) also permits said pump to operate continuously, thus helping to increase the total capacity and prevent cavitation in the feed line.

Claims: Claims: 1. A device for use in a centrifugal pump for the movement of liquid (6, Fig. 1), said pump being powered by a tractor (1, Fig. 1) via a power take-off shaft (2, Fig. 1) and possessing at least one feed line (7, Fig. 1), to the immersed lower end of which is connected at least one hydraulically driven pump (10, Fig. 1) which obtains its hydraulic fluid from a hydraulic pump (3, Fig. 1) powered by the tractor (1), said immersed pump (10) serving to fill the feed line (7) and the centrifugal pump (6) with liquid when the pumps are started up; which device is characterised in that the immersed pump (10) is a centrifugal pump which at all times transmits all the liquid which passes through the centrifugal pump (6) even when the latter is in full operation after the above-mentioned start-up phase. 2. A device according to claim 1, characterised is that the immersed, hydraulically driven centrifugal pump consists of a purpose-designed centrifugal pump (13, Fig. 2) whereof the housing (13a, Fig. 2) and its discharge opening (13b, Fig. 2) are substantially wider than the impeller (13c, Fig. 2) so that more liquid can easily pass through the pump than said pump is capable of pumping itself.

Inventors: OLSSON BENGT, OLSSON, BENGT
Applicants: OLSSON BENGT, OLSSON, BENGT
Application year: 1997
Main classification: F04D9
IPC codes: F04D9, F04D13