Expanding slab gate valve and single slab gate valve

In our production scope, API 6A gate valve is popular used on pipeline, wellhead, flowhead, choke manifold, and etc.

Our gate valves are divided into two kinds of structure. One is expanding slab gate valve, the other is single slab gate valve. The important difference is on the gate. For expanding gate valve, the gate is composed by two split gates; one is bigger, and the other is smaller. And the gates connect by special spring.

The difference on gate also reflects to operation. For expanding gate valve, when the operator feels gate contact the bottom flat, he should use more power to close tight. But for single slab gate valve, when the operator feel the gate contact bottom flat he should turn back handwheel 1/4 circle.

Let’s explain why there is different operation. For expanding gate valve, stem is connected with bigger gate. If need to close the valve, force is transferred from handwheel to stem, and then to bigger gate. When bigger gate contact to the bottom plat, the spring will deform, and push smaller gate to attach to seat seal. In order to realize double front face seal, the workman should roll handwheel very tight. For single slab gate valve, the seal theory is back seat seal. The fluid pressure can help to seal. So there should be tiny movable space for slab gate.

But for low pressure gate valve, there is still expanding gate valve. This kind of expanding gate valve is popular used on thermal well head. But the bore size reaches 8” to 10”. Below form is used to show some difference.