It is prior art to separate liquids and gases; oil, for example, is often purged from cool- ing circuits. In cooling circuits, it is normal that oil particles are carried with the cool- ing medium and around in the cooling circuit due to the high flow speed of the cooling medium gas. These oil particles have to be purged from the cooling medium before the medium flows into an evaporator or the like in order to attain high capacity in the sys- tem, For this purpose, an oil purger is normally used. The oil separation often occurs intermittently, depending on different operating conditions. The prior art oil purgers are made in different ways, but the two most common types will be described below.

One of the prior art oil purgers functions in that the oil is collected in an oil sump, and therefrom the oil is returned to a reservoir or to the compressor of the cooling system.

This returning is controlled with a float, which opens a valve when sufficient oil is pre- sent in the sump for lifting the float, and thereby most of the collected oil is returned.

This solution is mechanical with many components, is vulnerable to vibrations and in addition requires relatively much space. Furthermore, it is a drawback in this kind of purgers that a relatively large amount of oil has to be collected before the valve is opened. This drawback appears in that the oil present in the sump is carried with the cooling medium due to the high speed of the cooling medium, whereby the efficiency and the capacity of the system are considerably reduced.

Another widely used type of oil purger consists of a manually operated valve which is continuously flowed through by a fluid consisting of a mixture of cooling medium gas and oil. This valve is to be regulated manually in dependence of operating conditions.

However, often it occurs that the valve is set or left at a fixed level which at any time ensures sufficient draining of oil. With this mode of setting, a problem arises when only

a little or intermittent oil separation is needed, since an unnecessary large amount of cooling medium is thus returned, whereby the efficiency of the system is reduced. This type of purger is therefore not optimal as discharge/return is performed continuously, irrespectively whether there is oil to be purged or whether only cooling medium gas is flowing through the purger valve. In such a case, if manual regulation is not performed on the purger, a loss in efficiency and capacity of e. g. the magnitude 20% may easily arise.

It is the purpose of the invention to indicate a liquid purger ensuring a sufficient purg- ing of collected liquid and which at the same time maintains a high efficiency on the system, where the purger is very compact and in very simple form, thus taking up little space, and where the liquid purging is effected automatically and therefore does not need manual monitoring and setting.

The invention is based on the view that by establishing a weak fluid flow from the bot- tom of the pressurised vessel in which purged liquid may occur, it is possible to lead this flow through a narrow passage in a pressure loaded valve piston in such a way that this through-flow may occur without any tangible influence on the position of the valve piston as long as only gas is present, whereas an increased pressure is built up against the valve piston at the appearance of liquid in the flow due to the higher density and viscosity of the liquid, whereby the piston is pushed back against the pressure load and thereby opens a wide return duct for the supplied fluid so that this is returned to its area of application. The conditions may be adapted so that a totally demand controlled and dynamic liquid discharging may thereby be effected, which may occur with consid- erable capacity in actual cases, whereas by pure gas through-flow there will only be so small volume flow that this will be without any appreciable operative significance as short-circuit source between the pressure side and suction side of the system.

A liquid purger and a liquid purger system according to the invention allows separation of a liquid medium, preferably oil, where the occurrence of a liquid causes a pressure loaded valve piston to be displaced, thereby opening a return duct when a continuous flow of a gas medium is interrupted, preferably a cooling medium, where the liquid purger has a valve block that may be held in closed position by a adjusted pressing

force, and where a suitably adapted boring through the valve piston is provided in lon- gitudinal direction of the valve piston for through-flow of a gas, that the gas may be led away through a nozzle, and that a liquid may press the valve piston against the pressing force by its presence and thereby open a return duct for the liquid and the gas.

When the gas flows through the valve piston, a pressure loss over the valve piston greater than the pressing force retaining the valve piston in the valve seat does not oc- cur, so that the valve piston is still retained in the seat. However, when liquid, prefera- bly oil, appears, there is formed such a large pressure loss over the valve piston that the pressing force on the valve piston is overcome, and thereby the valve piston is forced back, opening for a return duct. This return duct has a markedly greater cross-sectional area than the boring through the valve piston. When the valve piston is pressed back and the return duct is open, the liquid collected at the valve piston is removed quickly, whereafter the gas medium flows through both return duct and valve piston. This flow implies that the valve piston is brought back to its seat, thereby closing the return duct, and the flow through the valve is reduced to a minimum. This liquid purger system ensures that the amount of collected oil to be purged is always at minimum, and thereby the capacity and efficiency of the system are maintained. Due to the continuous flow through the nozzle, the valve block may be placed higher than the liquid collecting place, which may be an advantage for space reasons.

In a preferred embodiment, the liquid purger is made with an adjustable pressing load, e. g. with an adjustable helical spring. Hereby is achieved possibility of adapting the liquid purger to different types of medias with different temperatures or viscosities.

In a further, preferred embodiment, the liquid purger is made with a valve piston where the cross-section of the boring in the valve piston is adjustable, preferably with ex- changeable discs with different hole size. This property provides an additional possibil- ity of adapting the liquid purger to different medias.

The invention will be described in more detail below with reference to the drawing, which is not to be construed as limiting for the scope of the invention, showing a pre- ferred embodiment of a liquid purger according to the invention, wherein :

Fig. 1 is a part diagram of a cooling system incorporating a liquid purger according to the invention, and Fig. 2 is a cross-section of a purger unit.

In Fig. 1 is seen a diagram of a cooling circuit 2, where a purger according to the in- vention may typically find application. A compressor 4 communicates with a pressure vessel 6 containing an oil reservoir 8, from which lubricating oil 12 may be led to the compressor 4 via an oil conduit 10. The cooling medium 14 which is conducted under pressure down into the pressure vessel 6 and through a separating filter 16 contains an amount of oil 12. The oil 12 in the gaseous cooling medium 14 is purged in the sepa- rating filter 16 and collected in an oil sump 18 from which the oil is led to a purger unit 20. The purger unit 20 has a valve piston 22, which is provided with a suitably adapted boring 24 in its longitudinal direction, and which is held in place in its seat 28 by a spring force 26. Through the adapted boring 24, a small amount of cooling medium 24 may flow, continuing further into a return duct 30 through a nozzle 32. In this version of the system, there is connection to the suction side of the compressor from the return duct 30 via a return conduit 34.

In Fig. 2 is clearly seen an embodiment of the valve block 20 where the valve piston 22 with its adapted boring 24 is held in place in its seat 28 by the helical spring 26. The helical spring 26 is placed in a boring 38, and kept in place by a stopper or adjusting screw 40 allowing variation of the spring force 26. From the boring 38 where the heli- cal spring 26 is acting, there is connection to the return duct 30 via the nozzle 32 and further on via return conduit 34 to the compressor 4 or to an oil reservoir. The trans- verse boring 36, which is opened when the valve piston 22 is displaced, is blocked with a stopper at the outer edge 20 of the valve block, just as is the case with the return duct 30 at the end of the valve block 20. These stoppers 42 may be removed, and the apertures may be used as alternative connecting points, though they are only present for manufacturing reasons. The nozzle 32 is exchangeable and may have different sizes for different applications. The same is the case with respect to the boring 24 of the valve piston 22. The valve piston 22 may also be provided with an exchangeable noz- zle.

When no oil 12 has been collected in the system, a small and insignificant amount of cooling medium gas 14 flows through valve piston 22 and nozzle 32 and further on into the cooling system 2. When oil 12 has been collected in the system, it is led straight into the valve block 20, and due to the greater viscosity of the oil 12 compared with that of the cooling medium 14, an increased pressure loss arises over the piston 22. The reason is that the oil 14 is then not flowing so easily through the piston 22 as the cooling medium 14. This change in pressure conditions causes the pressure on the valve piston end to grow and to exceed the spring force 26, thereby moving the valve piston 22 and exposing the transverse boring 36, and oil 12 is consequently conducted to the return duct 30. When the oil 12 has been discharged, and only cooling medium 14 is flowing, the spring force 26 is again the greater and forces the valve piston 22 back against its seat 28. Then the system again functions with a small and controlled through-flow of cooling medium 14.