As with screws and barrels, choosing the right metallurgy selection and thermal treatment are equally essential with non-return valves. Good geometric design is very important for fast and accurate valve operation, but we also want long valve lifespan.
Selection of the type of non-return valve depends on a number of factors. These include the plastic type to be processed, as well as the desired dosing accuracy and wear resistance. And, last but not least, we must not forget the price. Ball valves are much more accurate than every other type but they also require more manufacturing processes, which makes them more expensive. We categorize non-return valves into four different types*.
(*Of course, there are still many variants in each of these four types)
1. Three-piece non-return valve with separate ring
The three-piece non-return valve is the most common type. The valve consists of a winged centre, a ring and a seat. The manufacturing process for this type of valve is relatively simple, which means that the price is also relatively low. The use of armoured coating and proper thermal treatments make our valves extremely wear resistant.
2. Ball valve
Ball valves are known for their very accurate shot precision and capacity for repetition. This accuracy is due to the high level of pressure sensitivity and reaction speed of the ball in the valve. Our valves are both internally and externally armoured with special steel alloys and then thermally treated. But ball valves cannot be used for all materials. In addition, a number of rules must be observed when using this type of valve.
3. Three-piece non-return valve with rotating ring
This type of valve is easier to manufacture and has a relatively good characteristics for injection moulding. In view of the ring turning with the screw, a number of important rules must be observed when using this type of valve. Good warm-up conditions and good barrel condition are important for preventing this valve’s ring getting broken.
4. Special valves for exceptional applications and valves with mixing action
Euro-Stair also supplies a number of special valves for processing materials such as thin liquids, highly-transparent PC, fibreglass-filled PA, etc. And we also supply valves with a special mixing action. These valves are specially designed to suit the plastic that will be processed and to achieve the intended result.
Reconditioned non-return valves
Non-return valves are very susceptible to wear due to the high pressure in the metering area and the axial movement of the screw. We recommend having non-return valve repairs done in good time, because correct operation of an injection moulding machine depends to a large extent on this vital component operating properly.
In the case of ring valves, the non-return ring and the seat must always be replaced with new parts; the tip and mixing ring can usually be reconditioned. On ball valves, the inner seat is re-worked and possibly the outer diameter too, depending on the extent of wear. The ball valve is polished and a new ball is fitted. Valves are always manufactured according to the customer’s model (according to installation dimensions). But the version we supply meets the Euro-Stel standard, with improved operation and a longer service life.
A good thing to know: Each reconditioning task requires thorough analysis of the worn parts by an experienced Euro-Stel expert, so that we can propose the most appropriate method (economically and technically).