The present invention relates to a pressure valve for a compressor, particularly for a hermetically sealed refrig¬ erator whose valve plate has a longitudinal recess contain- ing a valve seat, a flat valve spring, and a retainer bridge.

From DE 33 05 791 C2, among others, it is commonly known to place pressure valves in recesses in the valve plate. From Danfoss compressors type NL it is known to have notches guide the flat valve spring and the booster plate. The retainer bridge is pressed firmly into the recess, holding the elements below in position.

From DE-OS 2 215 974, DE-OS 2 842 611 and DE 39 09 176 Al long flat valve springs are known, which are held on both sides of the valve ports. The flat valve springs and the retainer bridges are fastened to the surface of the valve plates with screws or pins.

The object of the present invention is to provide a pressure valve that increases the efficiency of the com¬ pressor by opening and closing quickly, where the pressure valve has a long life, and which has low production costs.

With a pressure valve as the one described in the introduc¬ tion, the set problem is solved by making the effective length of the flat valve spring greater when the valve is closed than when it is open.

In this manner a soft valve is obtained when it is near its closed position, and a stiff valve when it is open. This ensures quick emptying of the cylinder with a minimum pressure drop across the pressure valve. Hereby the effi- ciency of the compressor is increased. The pressure valve has low production costs because a booster plate is not used.

The flat valve spring can be guided at both ends of the recess. This makes it possible to ensure effectively the position of the flat valve spring in relation to known valves, which are guided at one end of the flat valve spring only. Also, the resistance to wear of the valve is improved by the fact that the edge of the recess surrounds the flat valve spring on all sides.

The flat valve spring may advantageously lie loose, but it may be secured at both ends by means of a superjacent retainer bridge. Hereby both ends of the flat valve spring are kept near the bottom of the recess by the ends of the retainer bridge, whereas the centre section of the flat valve spring can be moved up to touch the retainer bridge.

The flat valve spring may advantageously be pre-tensioned in the opening direction. This reduces the force to be overcome by the gas pressure for opening the valve, and at equal pressure across the valve it will be open.

The valve may have a soft opening characteristic at incipi¬ ent opening, whereas the opening characteristic at increas¬ ing opening is increased stepwise. Hereby the impact against the retainer bridge is damped, and the impact against the valve seat is also reduced.

At full opening the flat valve spring may have return spring action, ensuring quick closing of the valve.

The recess in the valve plate may have a first depth for receiving the retainer bridge, and it may have another, greater depth for receiving the flat valve spring. Thereby the flat valve spring may lie safe under the retainer bridge without being fastened, and guided by the second recess.

The flat valve spring may rest on several points against the bottom of the recess and against the retainer bridge, where the contact points change and/or shift during the opening/closing cycle of the valve. Thereby the active spring length of the flat valve spring will change from a long and thus soft spring when the valve is close to the valve seat, to a shorter and stiffer spring when the valve is open.

The flat valve spring can be retained by projections in the sides of the recess, hereby further ensuring its proper position under the retainer bridge.

The flat valve spring has advantageously large width at the ends and large width above the valve seat, whereas it is narrower between valve seat and ends. This ensures good outward flow when the valve is open. The compressed gas is pressed up from the recess where the flat valve spring is narrow. The narrow areas of the flat valve spring also contribute towards making the valve softer.

The flat valve spring may have a first bend upwards at a distance from the left edge amounting to 15-30 per cent of the length of the flat valve spring. Hereby the flat valve spring is pre-tensioned in the opening direction.

The flat valve spring may also have a second bend upwards at a distance from the right edge amounting to 1 to 5 per cent of the length of the flat valve spring. At incipient opening the bent-up edge is in contact with the retainer bridge, and it contributes to the pre-tensioning of the flat valve spring.

When the valve is closed, the flat valve spring may have a first contact point at the left edge at the retainer bridge, and the flat valve spring may rest against the valve plate to the left of the valve seat at a second

contact point, and the flat valve spring may also rest at the right edge against the valve plate at a third contact point. This results in a soft spring, and a minimum pres¬ sure is required for opening the valve.

When the valve is in neutral position, the flat valve spring may still have the first contact point at the left edge at the retainer bridge, and the flat valve spring may still rest against the valve plate to the left of the second contact point, while at the right edge the flat valve spring rests against the retainer bridge at a fourth contact point. Thus the valve is open at pressure equality, and the pressure loss across the valve is considerably reduced.

At incipient opening the flat valve spring may still have the first contact point at the left edge at the retainer bridge, and at the opposite side of the valve seat the flat valve spring may press against the retainer bridge at a fifth contact point, and the flat valve spring may rest with the second bend against the valve plate. Hereby the flat valve spring is fixed at its right end, and the valve is stiffened.

At full opening the flat valve spring may have a contact surface at the left edge at the retaining bridge, and on the opposite side of the valve seat the flat valve spring may rest against the retainer bridge at a sixth contact point, and the flat valve spring presses with the second bend against the valve plate. Hereby the valve becomes very stiff, and the effective length of the flat valve spring is reduced. The stiff valve will have a spring action back towards the valve seat, hereby ensuring quick closing. The pretensioning of the flat valve spring brakes the flat valve spring before contact, and wear of the valve seat and valve noise are reduced.

In the following the invention is explained by means of the drawings, showing:

Fig. 1 A possible embodiment of a flat valve spring seen from above.

Fig. 2 A possible embodiment of a flat valve spring seen from one side.

Fig. 3 A possible embodiment of the invention, where the valve is closed due to counter-pressure.

Fig. 4 The same embodiment, but with a slightly open valve - here shown where the pressure is equalised.

Fig. 5 The same embodiment as Fig. 4, but with the valve with incipient opening.

Fig. 6 The same embodiment as Fig. 5, with the valve fully open.

Fig. 1 shows a possible embodiment of the flat valve spring seen from above. The width of the flat valve spring is largest at the ends 15 and 17, and in the middle at 13 above the valve seat 11. There are waists 18 and 19 between the ends and the valve seat. These waists ensure good passage of the gas when is flows up from below around the flat valve spring 12. Similarly, the waists 18 and 19 con¬ tribute towards softening the valve.

Fig. 2 shows a possible embodiment of the flat valve spring seen from one side, showing the first bend 14 and the second bend 16.

Fig. 3 shows a valve plate 1, typically from a hermetic

refrigerator compressor, where the valve plate lies on top of a cylinder, forming the upper delimitation of the cylin¬ der. Valve plate 1 has a pressure valve port 10, and on the upper side of the valve plate 1 the valve seat 11 is situ- ated. Above the valve port 10 and the valve seat 11 lies the flat valve spring 12, and it is secured in position by the overlying retainer bridge 4.

The retainer bridge 4 and the flat valve spring 12 are placed in the recesses 2 and 3. The recess 2 prevents the flat valve spring 12 from sliding sideways and lengthways, while recess 3 fixes the retainer bridge 7, where the retainer bridge is possibly pressed into recess 3. The flat valve spring 12 has a contact point 20 at the left edge 5 at the retainer bridge 4. Also, there is a contact point

21, where bend 14 (Fig. 2) on the flat valve spring 12 has contact with the valve plate 1. At the right side the flat valve spring 12 is in contact with the valve plate 1 at a contact point 2211. Because the pressure is higher above the flat valve spring 12 than under it, the valve is closed.

Fig. 4 shows the valve at pressure equalisation, where the pre-tensioning of the valve causes it to be open. The flat valve spring 12 has still contact at the points 20 and 21 to the left of the valve seat, but to the right of the valve seat the flat valve spring has lifted from the point

22, now forming contact with the bent-up edge 17 at the contact point 23. Owing to the fact that the flat valve spring 12 is pre-tensioned in the opening direction, a minimum pressure drop is ensured across the valve when it is about to open. This means that this valve opens earlier than known pressure valves.

Fig. 5 shows the valve when there is an incipient outward flow. Fig. 5 differs from Fig. 4 by the fact that there is no longer contact at point 21. The flat valve spring 12 has

been lifted from contact with the valve plate 1. At the opposite end the bent-up end of flat valve spring 12 has caused contact at contact point 24, while at the same time there is now contact at bend 16 of the flat valve spring (Fig. 2) and the valve plate with contact point 25.

Hereby the flat valve spring has been fixed, and the valve becomes stiffer. Only small pressure forces are required to move the flat valve spring from the position shown in Fig. 4 to the position shown in Fig. 5. This means that a very small differential pressure suffices to open the valve and ensure a relatively high outflow rate.

Fig. 6 shows the valve fully open. At the left end of the flat valve spring the latter has now been lifted so high that there is contact with the retainer bridge at the contact surface 27. Immediately above the valve port 10 there is also contact with the retainer bridge at point 26, and at the right hand end of the flat valve spring there is now contact with the retainer bridge at contact point 27. A comparison between Fig. 3 and Fig. 4 shows that the contact point 24 has shifted to having contact now at point 27. Similarly, contact point 25 has also moved to the left. This means that the active length of the flat valve spring has been reduced, resulting in a very stiff valve. When the valve begins to close, a strong return spring action of the flat valve spring takes place. This ensures quick closing, but the quick downward movement is braked before contact at the valve seat 11 owing to the fact that flat valve spring 12 is pre-tensioned in the opening direction. This ensures soft closing against the valve seat, reducing wear and valve noise.